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1
Silva, Pedro Manuel Ribeiro. "Langmuir Films of Perfluoroalkylalkanes : Multiscale Insights on Molecular Structure, Mixing, and Subphase Deformability Effects". Electronic Thesis or Diss., Sorbonne université, 2024. http://www.theses.fr/2024SORUS215.
Testo completoAbstract (sommario):
Les perfluoroalkylalcanes (PFAA ; CnF2n+1CmH2m+1 ; FnHm) sont des molécules diblocs formées par des blocs hydrogénés (CH) et perfluorés (CF). Les deux sont hydrophobes et mutuellement phobiques. Bien qu'ils ne possèdent pas de groupe polaire, ces tensioactifs primitifs forment des films de Langmuir sur l'eau ou des substrats hydrophiles. Les films comprennent des hémimicelles monodispersées bien définies, ordonnées de manière hexagonale, comme le montrent les expériences de microscopie à force atomique (AFM) et de diffraction des rayons X à incidence rasante. Il a été observé que le diamètre de ces hémimicelles est lié à la structure moléculaire. Cependant, les effets de la structure moléculaire variable (n et/ou m), du mélange dans des films binaires et des propriétés physicochimiques de la sous-phase liquide sur la structure et l'ordre des films de Langmuir restent encore inexploités.Des études numériques préalables (simulation de dynamique moléculaire (MD)) ont élucidé la structure interne des hémimicelles F8H16 pures. Ici, les hémimicelles FnHm ont également été étudiées par MD en fonction de n et m. Il a été constaté que la disposition en éventail des molécules au sein des hémimicelles explique la variation du diamètre de l'hémimicelle avec l'architecture moléculaire, en particulier l'inadéquation des sections transversales des chaînes CH et CF et les longueurs relatives des chaînes CH. et chaînes CF. Un modèle basé sur des arguments géométriques est proposé. En outre, il a été constaté que la fosse centrale des hémimicelles mise en évidence par les mesures AFM résulte à la fois de l'interaction intermoléculaire des dipôles CH2-CF2 et de la capacité à déformer le substrat liquide. Enfin, il a été constaté que la formation d'hémimicelles ordonnées de FnHm est possible sur d'autres sous-phases liquides telles que les alcools CH et CF à chaîne courte.En outre, la structure et l'ordre des films de Langmuir mixtes F8H14: F8H20 ont été sondés par des isothermes de pression de surface et de surface moléculaire, la diffusion des rayons X aux petits angles à incidence rasante (GISAXS) et la diffraction des rayons X à incidence rasante (GIXD). Il a été constaté que le paramètre de réseau du réseau d'hémimicelles se situe entre celui des cas purs. Ceci indique soit un mélange au niveau moléculaire (formation d'hémimicelles monodispersées mixtes) soit un mélange de deux types d'hémimicelles FnHm pures.Ces résultats sont prometteurs et mettent en lumière les principes fondamentaux qui régissent l'auto-assemblage et, à terme, la prédiction et le contrôle de la morphologie des films de Langmuir nanostructurés des PFAA, envisageant leur utilisation comme modèles pour les applications de nanostructuration de surface et de nanotechnologie. Les travaux futurs devraient se concentrer sur une caractérisation plus approfondie des films binaires mixtes, y compris avec différents n et m, afin de discerner les scénarios proposés. De plus, en s'appuyant sur les connaissances accumulées, les études devraient progresser vers l'étude de films et d'émulsions mixtes de PFAA avec des biomolécules pertinentes (par exemple les phospholipides)Perfluoroalkylalkanes (PFAAs; CnF2n+1CmH2m+1; FnHm) are diblock molecules formed by a hydrogenated (CH) and a perfluorinated (CF) blocks. Both are hydrophobic and mutually phobic. Despite lacking a polar group, these primitive surfactants form Langmuir films on water or hydrophilic substrates. The films comprise well-defined, hexagonally ordered, monodispersed hemimicelles as shown by Atomic Force Microscopy (AFM) and Grazing Incidence X-rays Diffraction experiments. It has been observed that the diameter of these hemimicelles is linked to the molecular structure. However, the effects of varying molecular structure (n and/or m), mixing in binary films and the physicochemical properties of the liquid subphase on the structure and ordering of the Langmuir films are still left untapped.Computational (Molecular Dynamics (MD) simulation) studies have elucidated the internal structure of pure F8H16 hemimicelles. Herein, FnHm hemimicelles were also studied by MD as functions of n and m. It was found that the fan-like arrangement of the molecules within the hemimicelles explains the variation of the diameter of the hemimicelle with the molecular architecture, specifically the mismatch of the CH and CF chains' cross-sectional areas and the relative lengths of the CH and CF chains. A model based on geometrical arguments is proposed. Furthermore, it was found that the central pit of the hemimicelles evidenced by AFM measurements results from both the CH2-CF2 dipoles intermolecular interaction and the ability to deform the liquid substrate. Finally, it was found that the formation of ordered hemimicelles of FnHm is possible on other liquid subphases such as short-chain CH and CF alcohols.Further, the structure and order of mixed F8H14:F8H20 Langmuir films were probed by surface pressure-molecular area isotherms, Grazing Incidence Small Angle X-Ray Scattering (GISAXS) and Grazing Incidence X-Ray Diffraction (GIXD). It was found that the lattice parameter of the network of hemimicelles is between the ones of the pure cases. This indicates either a mixing at the molecular level (formation of mixed monodisperse hemimicelles) or a mixture of two types of pure FnHm hemimicelles.These results are promising and shed light on the fundamental principles driving the self-assembling and, ultimately, the prediction and control of the morphology of the nanostructured Langmuir films of PFAAs, envisaging their use as templates for surface nanopatterning and nanotechnology applications. Future work should focus on further characterising the mixed binary films, including with different n and m, to discern between the proposed scenarios. Moreover, drawing on the accumulated knowledge, the studies should advance towards studying mixed films and emulsions of PFAAs with relevant biomolecules (e.g. phospholipids)
2
Colbrook, Richard. "Pyroelectric Langmuir-Blodgett films". Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257662.
Testo completo
3
Ou, Shih-hong. "Non-centrosymmetric Langmuir films". Case Western Reserve University School of Graduate Studies / OhioLINK, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1060358516.
Testo completo
4
Yu, Lisha. "Vibrational spectroscopy of diamond films, Langmuir and Langmuir-Blodgett films and aromatic polyethers". Case Western Reserve University School of Graduate Studies / OhioLINK, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=case1056553553.
Testo completo
5
Romualdo, Torres Gemma. "Systèmes hybrides en films de Langmuir et Langmuir-Blodgett". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2002. http://tel.archives-ouvertes.fr/tel-00815388.
Testo completoAbstract (sommario):
Ce travail porte sur la formation et la caractérisation de nouveaux systèmes organiques-inorganiques par l'utilisation de films de Langmuir et de la technique de Langmuir-Blodgett. Plusieurs voies ont ainsi été explorées afin d'obtenir des films minces hybrides aux propriétés multiples, en particulier magnétiques. L'utilisation de l'interaction entre monocouches cationiques et des anions présents en sous-phase a ainsi permis l'organisation de différents polyanions inorganiques en structure lamellaire. Cette stratégie a ensuite été généralisée au cas de colloïdes de Bleu de Prusse, composés bimétalliques étendus. Une large étude (de la préparation à la caractérisation) a été consacrée à ces matériaux mixtes Bleu de Prusse-dérivé amphiphile de Ru(bpy)3 2+. Il a été également montré que la cristallisation du Bleu de Prusse et de ses analogues est favorisée en-dessous des films de Langmuir. Finalement, la coordination d'ions dissous en sous-phase avec des molécules amphiphiles à l'interface permet d'élaborer de nouveaux systèmes pouvant former des films LB, ce qui est notamment le cas d'agencements à base de cyanures métalliques.
6
Jones, Carole A. "Pyroelectricity in Langmuir-Blodgett films". Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6784/.
Testo completoAbstract (sommario):
The fabrication of pyroelectric devices using the Langmuir-Blodgett (LB) technique is described. Studies of a wide range of materials are reported; however, the thesis concentrates on electrical and structural investigations of two specific alternate layer films: 22-tricosenoic acid/l-docosylamine and 22-tricosenoic acid/4-octadecylaniline. The latter system possesses a pyroelectric coefficient of 0.65 nCcm(^-2)K(^-1), representing the largest reported value, to date, for an LB film. The pyroelectric figure of merit (p/e(^1)(_T)) of such films is approximately 0.22 nCcm(^-2)K(^-1), which is comparable with the values for commercially available materials. The difference in pyroelectric coefficient of the two types of alternate layer film is attributed to differences in inter-layer bonding, as revealed by infrared spectroscopy. The dependence of the pyroelectric coefficients on parameters such as film thickness, substrate thickness and temperature is investigated. Structural studies, performed using electron and X-ray diffraction techniques, are also described. These provide information on the orientation of the molecules relative to the substrate and on the d-spacing of the LB films. It is shown that the substrate has a deleterious effect on the responsivity of LB film devices, and studies of films deposited onto different substrate materials indicate that there is a significant piezoelectric ally induced secondary effect contributing to the overall pyroelectric coefficient. This secondary effect is small at low temperatures, but becomes dominant at around 250 K. The results of thermally stimulated discharge experiments indicate that both free charges and dipolar groups are incorporated in the films during deposition, and become tightly bound within the polar structure.
7
Amiri, M. A. "Optically nonlinear Langmuir Blodgett films". Thesis, Cranfield University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273468.
Testo completo
8
Oliveira, Junior Osvaldo Novais de. "Electrical properties of Langmuir monolayers and deposited Langmuir-Blodgett films". Thesis, Bangor University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236716.
Testo completo
9
Wang, Ji. "LANGMUIR LAYERS AND LANGMUIR/SCHAEFER FILMS OF BENT-CORE MOLECULES". Kent State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=kent1194385768.
Testo completo
10
Constantino, Carlos José Leopoldo. "Filmes de Langmuir e Langmuir-Blodgett de ligninas". Universidade de São Paulo, 1995. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-18062008-083333/.
Testo completoAbstract (sommario):
Filmes de Langmuir e Langmuir-Blodgett (LB) foram fabricados a partir de ligninas de bagaço de cana-de-açúcar e da Pinus caribaea hondurensis, extraídas via processo organossolve. Obteve-se nove tipos de lignina de pinus, sendo que cada uma foi extraída com um sol vente diferente, e seis tipos de lignina de cana, as quais passaram por um fracionamento, diminuindo sua polidispersividade. Os filmes de Langmuir foram fabricados sobre subfases de água ultrapura e caracterizados por medidas de pressão e potencial de superfície. Em todos os casos constatou-se a formação de agregados não monomoleculares quando o filme é comprimido além do ponto de colapso, o que é notado pela grande histerese na isoterma pressãoárea. Para ligninas de baixa massa molecular, estruturas estáveis não monomoleculares são formadas antes do colapso. No caso das ligninas menos polidispersas (cana), a massa molecular aumenta linearmente com a área molecular média da lignina. Monocamadas das ligninas de pinus e cana puderam ser transferidas para substratos de vidro, constituindo-se nos primeiros filmes de Langmuir-Blodgett destes materiais. Através do monitoramento da velocidade de imersão e retirada do substrato da subfase pode-se fabricar diferentes tipos de filmes LB, os quais podem ser do tipo Y com a deposição ocorrendo na imersão e retirada do substrato e também dos tipos X e Z se a deposição ocorre preferencialmente na imersão ou retirada do substrato, respectivamente. Os filmes LB foram caracterizados por medidas do potencial de superfície e elipsometria. O potencial de superfície para os filmes de pinus são positivos, enquanto que para os filmes de cana são negativos. Esta inversão de sinal foi surpreendente, pois para as monocamadas os valores de potencial são sempre positivos, tanto para as ligninas de cana como para as de pinus, embora sejam maiores no caso da pinus. A razão para esta inversão é uma contribuição negativa da interface filme/substrato que suplanta a contribuição positiva dos dipolos do filme de lignina de cana. Os dados elipsométricos revelaram que a lignina apresenta um arranjo tridimensional, com muitos espaços vazios e uma espessura em torno de 60 \'angstrom\' por camada.Langmuir monolayers and Langmuir-Blodgett (LB) films were fabricated from lignins extracted from Pinus caribaea hondurensis and sugar cane bagasse using the organosolv processo Nine types of pinus lignins were obtained by employing different solvents. The lignins of sugar cane bagasse were extracted using only one solvent but the material was fractioned into six fractions according to the molecular sizes. The resulting lignins were then less polydisperse than the pinus lignins. Langmuir monolayers were spread onto ultrapure water subphases and characterized by surface pressure and surface potential measurements. In all cases, non-monomolecular aggregates are formed when the monolayer is compressed beyond the collapse pressure, which is denoted by large hysteresis in pressurearea isotherms. For the low molecular weight lignins, stable multilayer structures are formed even before collapse. In the less polydisperse bagasse lignins, the average area per molecule increases linearly with the molecular weight. Monolayers from both pinus and bagasse lignins could be transferred onto glass substrates, thus forming the first ever reported Langmuir-Blodgett (LB) films of these materials. By controlling the dipping speed one can build-up different types of LB film which can be y-type with deposition occurring in both upstrokes and downstrokes and also Z or x-type if transfer occurs only in the upstrokes or downstrokes, respectively. The deposited LB films were characterized by surface potential and ellipsometric measurements. The surface potential of pinus films is positive whereas that of bagasse lignins is negative. This sign inversion was surprising since the monolayer surface potentials were always positive for all materials, even though they were higher for the Pinus lignins. The reason for the inversion is the negative contribution of the film/substrate interface which surpass the small, positive contribution from the dipole moments in the bagasse lignins. The ellipsometric data showed that the lignin molecules assume a three-dimensional arrangement, even within a single layer. The LB film appears to be a highly porous structure, with a thickness of 60 Á per layer.
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Constantino, Carlos José Leopoldo. "Filmes de Langmuir e Langmuir-Blodgett (LB) de ligninas". Universidade de São Paulo, 1999. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-18112014-162235/.
Testo completoAbstract (sommario):
Filmes de Langmuir e Langmuir-Blodgett (LB) de ligninas extraídas do bagaço de cana-de-açúcar, via processo organossolve, foram fabricados. As isotermas de pressão revelaram uma área para a seção média da lignina em torno de 100 Å para a monocamada condensada, enquanto a modelagem a partir dos espectros elipsométricos indicou uma espessura por camada de cerca 60 Å para os filmes LB. Porém a deposição não se mostrou homogênea sobre toda a superfície do substrato como observado pelas medidas de microscopia de força atômica (AFM), de forma que filmes mais homogêneos foram obtidos a partir de uma solução mista de Iignina com estearato de cádmio. A área por molécula, calculada com base no número de moléculas de ácido esteárico sobre a subfase, aumenta com a quantidade de lignina na solução mista, indicando a presença de ambos os componentes também na monocamada. Os espectros de infravermelho com transformada de Fourier (FTIR) mostraram que tanto a lignina quanto o estearato de cádmio são transferidos e os espectros de ultravioleta visível (UV-vis) indicaram que esta deposição é homogênea até a 20ª camada. Os difratogramas de raios-X e as medidas de AFM mostram que a deposição de lignina e estearato de cádmio ocorre em domínios separados. As medidas de AFM revelaram ainda um aumento da rugosidade do filme com o aumento do número de camadas depositadas e com a maior irregularidade do substrato utilizado. Vale destacar que os filmes de lignina pura mostraram-se mais homogêneos que os filmes mistos, apesar da maior estabilidade destes sobre a subfase. A uniformidade macroscópica dos filmes LB foram confirmadas por medidas de potencial de superfície. Um estudo comparativo de filmes de Langmuir de ligninas extraídas por diferentes processos e de diferentes fontes (madeira mole, madeira dura e cana-de- açúcar) foi realizado. Destacou-se a importância dos grupos funcionais nas medidas de pressão e potencial de superfície, sendo que a área molecular média mostrou-se aumentar com a massa molar das ligninas em questão. A observação de uma inversão nos valores do potencial de superfície para filmes LB de lignina de cana e de pinus abriu caminho para uma investigação mais detalhada dos fatores que contribuem para o potencial de superfície dos filmes LB. Além da Iignina, filmes LB de polianilina e estearato de cádmio também foram estudados. Os resultados revelaram que os valores do potencial de superfície para estes filmes podem ser melhor compreendidos levando-se em consideração modelos teóricos que tratam tanto da contribuição dipolar das moléculas que constituem o filme como da contribuição da interface filme/substrato, a qual geralmente é negativa e se dá pela injeção de cargas. No caso dos filmes LB de estearato de cádmio o potencial é positivo para um número ímpar de camadas e negativo para um número parLangmuir monolayers and Langmuir-Blodgett (LB) films were produced from lignins extracted from sugar cane bagasse, via the organosolv process The surface pressure isotherms revealed an area per molecule of 100 Å for a condensed monolayer, and the modelling of ellipsometric data led to a thickness of 60 Å per layer for the LB films. The latter were not homogeneous, as demonstrated by atomic force microscopy (AFM) studies, and therefore mixed monolayers of Iignin and cadmium stearate were transferred with the aim of achieving more homogeneous films. The area per molecule, based on the number of stearic acid molecules on the airlwater interface, increased with the lignin contents in the mixed monolayers, thus confirming the presence of both components in the Langmuir monolayer. Fourier transform infra-red (FTIR) spectroscopy of LB films indicated that cadmium stearate as well as lignin were transferred onto the substrate. An equal amount of material was transferred in each deposition step, as demonstrated by the linear increase in UV-vis absorbance with the number of deposited layers up to the 20ª layer. Lignin and cadmium stearate are transferred in separate domains, which was indicated in X-ray diffraction measurements and AFM images. The latter also reveal that the roughness increases with the number of layers and may depend upon the substrate. Interestingly, films of pure lignin were more homogeneous than mixed films with cadmium searate, in spite of the higher stability and transterability of the mixed monolayers. Surface potential measurements showed a unitorm profile when the probe was scanned across an LB film, which may be taken as demonstration of uniformity at least at the macroscopic levei, though the film comprises domains and is usually rough for a molecular film. A comparative study was made ot monolayer characteristics for lignins obtained trom different sources and using different extracting procedures. The importance of functional groups was highlighted in these measurements, in which the area per molecule increased with the molecular weight ot the material. The observation that LB films from pinus and sugar cane bagasse exhibit surface potentials ot inverted sign has prompted us to investigate the possible contributions to such surface potentials. In addition to Iignins, in this study cadmium stearate and polyaniline LB films were also used. The overall conclusion was that the surface potential depends on the dipole moment of the monolayer-torming molecules, but is also affected substantially by the contribution from the substrate/film interface. The latter arises from charge injection from the electrode and is generally negative. For simple cadmium stearate LB films, the surface potential is positive for an odd number of layers, but negative for even numbers, since the dipole contribution is cancelled out
12
Davis, Frank. "Langmuir-Blodgett films of preformed copolymers". Thesis, Lancaster University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306423.
Testo completo
13
Burrows, P. E. "Electron Transport in Langmuir-Blodgett films". Thesis, Queen Mary, University of London, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531005.
Testo completo
14
Cresswell, J. P. "Waveguiding in electrooptic Langmuir-Blodgett films". Thesis, Durham University, 1992. http://etheses.dur.ac.uk/6142/.
Testo completoAbstract (sommario):
This thesis describes work on the waveguiding and second-order nonlinear optics of Langmuir-Blodgett (LB) films. A number of new monomeric materials are assessed for their LB deposition and their second-order nonlinear properties. Both the Pockels effect and second harmonic generation are studied. One new chromophore, diphenyl butadiyne is shown to possess exceptional nonlinear effects in monolayer form with x((^2))(-w; w, 0) = 2.7 x 10(^-10) mV(^-1) A novel aminonitrostilbene carboxylic acid with x((^2))(-w;w,0) = 1.43 x 10(^-10) m V(^-1) is also described. Polymeric LB materials have been found to possess greater stability than monomers but the deposition properties are often poor. Two oligomers are investigated, these both form high-quality LB layers and one gave X((^2))(-w;w,0) = (3.4-1-1.0j) x 10(^-11) m V(^-1). Two alternate-layer systems are considered. The first, of an amidonitrostilbene and a novel functionalised diarylalkyne deposits to 150 bilayers, but the nonlinear coefficients are shown to diminish after fewer than ten layers. X-ray diffraction, waveguiding and Fourier transform infra-red measurements are also performed. The second system alternates the two oligomers; only films of fewer than seven layer are studied due to the low value of Pockels effect and second-harmonic generation detected. A novel method of waveguide fabrication combining solution dipped polymer layers with LB films is introduced. This technique allows the rapid fabrication of waveguides with nonlinear properties. Monomode waveguides are produced and their electrooptic properties measured. These are the first such measurements on an LB film waveguide. It is shown theoretically that such waveguides could be used to produce modulators of similar figures of merit to those made from poled-polymers but that an order of magnitude improvement in X((^2))(-w; w, 0) is needed to match lithium niobate systems.
15
Green, Christopher A. "Covalent immobilisation of Langmuir-Blodgett films". Thesis, University of Salford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386420.
Testo completo
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Fernandes, Anwesha Nahavita. "Langmuir-Blodgett films of functional nanomaterials". Thesis, University of Sheffield, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442969.
Testo completo
17
Kim, Kwang Soo. "Computer simulation of Langmuir-Blodgett films". Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358629.
Testo completo
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Cruz, Cláudia Bonardi Kniphoff da. "Potencial de superfície de filmes de Langmuir e Langmuir-Blodgett". Universidade de São Paulo, 1995. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-15052009-120635/.
Testo completoAbstract (sommario):
Resultados antigos de potencial de superfície de filmes de Langmuir não eram reprodutíveis, devido B presença de impurezas na subfase aquosa sobre a qual os filmes se formavam. Dados recentes para o ácido esteárico, no entanto, mostram um comportamento reprodutível Neste trabalho, foi promovida com sucesso uma recaracterização através de medidas de pressão de superfície (II) e potencial de superfície (ΔV) de compostos alifáticos simples (álcoois, ésteres, ácido e amina), obtidos sobre subfases devidamente purificadas. Os resultados obtidos são inéditos e mostram que o potencial de superfície desses filmes é nulo para grandes valores de área molecular média (A), aumentando a partir de um valor de área crítico, Acr, até atingir um valor máximo, ΔVmax. Modelos para o potencial de superfície de filmes de Langmuir mostram boa concordância com os resultados obtidos. As curvas de pressão e potencial de superfície para os álcoois e ésteres praticamente não se modificam pela alteração do pH da subfase na faixa de 1 a 13. Porém para a amina e ácido há grandes alterações, principalmente nas curvas de potencial de superfície, em virtude da contribuição da dupla camada elétrica. Foram produzidos, também, filmes de Langmuir-Blodgett (LB) a partir de monocamadas de ácido esteárico que foram caracterizados através de medidas de potencial de superfície, com o objetivo de comprovar a importância da contribuição dipolar para o potencial desses filmes. Os resultados indicam que além da contribuição dipolar, há uma contribuição negativa (em tomo de -200 mV) da interface substrato/filme. O potencial de superfície se confirma como uma técnica de caracterização bastante sensível, tanto para filmes de Langmuir como para filmes LB.Old surface potential data in the literature were not reproducible, because of impurities in the aqueous subphase where the monolayers were formed. Recent data for stearic acid, however, show a reproducible behavior. In this work, a recharacterization of surface presssure (II) and surface potential (ΔV) for Langmuir monolayers of simple aliphatic compounds (alcohols, esters, acid and amine), fabricated over conveniently pure subphases, were successfully carried out. These new results show that the surface potential is zero for large areas per molecule and only increased below a critical area per molecule, Acr. Surface potential models for Langmuir films are in good agreement with the data obtained. There is almost no change in the surface pressure and surface potential for alcohols and esters for a subphase pH range of 1 to 13. However, for amine and acid large changes are observed, mainly in the surface potential curves, because of the electric double layer contribution Langmuir-Blodgett (LB) films were deposited from stearic acid monolayers. They were characterized by surface potential measurements in order to confirm the importance of the contribution from dipole moments of the film-forming molecules. The results also point towards a negative contribution (around - 200 mV) due to the film/substrate interface. The surface potential technique has been demonstrated to be a very sensitive characterization technique for Langmuir monolayers as well as for LB films.
19
Tanazefti, Kaïs. "Caractérisation de films de Langmuir et de Langmuir-Blodgett de molécules mésogènes". Paris 5, 1998. http://www.theses.fr/1998PA055020.
Testo completoAbstract (sommario):
Notre travail concerne l'étude des modes d'organisation de molécules mésogenes de conformation bolique ayant un cœur central hydrophobe, forme de trois ou quatre noyaux phenyls, auquel sont attachées de longues chaines hydrocarbonées. La flexibilité du cœur des molécules et la longueur des chaines peuvent être modifiées. L'objectif de notre étude est de comparer l'arrangement moléculaire entre les phases à deux dimensions et les phases trois dimensions. Les composes mésogenes étudiés s'étalent spontanément a la surface de l'eau sous forme de films appelés films de langmuir. La première partie de ce travail est relative à l'analyse des différents modes d'organisation de films de langmuir de ces composes. Plusieurs techniques ont été utilisées pour caractériser leur structure. Les différents états du film ont d'abord été étudiés par une méthode thermique (balance de langmuir). Différentes transitions de phases du premier ordre ont été ainsi mises en évidence. La structure du film, à l'échelle macroscopique a été ensuite déterminée par un dispositif d'imagerie de fluorescence. L'orientation des molécules à l'interface air-eau, a été déterminée par la mesure de courant de déplacement sensible à l'orientation des moments dipolaires permanents des molécules. La structure du film, a la fin de la transition principale, a ensuite été déterminée par diffraction des rayons x (rx) en incidence rasante, au lure, a Orsay. Nous avons ainsi interprété l'ordre observe, comme un arrangement rectangulaire des chaines latérales, les paramètres de la maille étant a = 5,32 a et b = 4,72 a. La seconde partie de notre travail concerne l'étude des mêmes composes bolique déposés sur un substrat solide sous forme de monocouches appelées films de langmuir-blodgett. Le dépôt de ces films sur un verre amorphe, par la technique de langmuir-blodgett (lb), a été réalisé avec succès. Le taux de transfert, voisin de l'unité, montre que l'arrangement moléculaire dans la monocouche déposée sur substrat solide est le même qu'à la surface de l'eau. L'analyse de la topographie de la monocouche de langmuir-blodgett a été effectuée par microscopie a force atomique (afm) au laboratoire dibe (université de Gènes, Italie). L'étude de la monocouche a été réalisée de l'échelle du micron à l'échelle du nanomètre. Les images obtenues confirment les résultats déduits des autres méthodes. Elles mettent en évidence l'arrangement colonnaire du cœur des molécules boliques, l'orientation vers l'air des chaines latérales et leur arrangement dans un réseau rectangulaire régulier.
20
Júnior, Antonio Riul. "Filmes de Langmuir e Langmuir-Blodgett de polianilina processada com ácidos funcionalizados". Universidade de São Paulo, 1995. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-08112013-151141/.
Testo completoAbstract (sommario):
Filmes de Langmuir e Langmuir-Blodgett (LB) foram produzidos a partir da polianilina não substituída, que se tornou processável e solúvel em clorofórmio apos ser dopada com ácidos funcionalizados. Para atingir condições otimizadas de formação e deposição dos filmes, foi realizado um estudo criterioso empregando vários ácidos funcionalizados: canfor sulfônico (CSA), dodecilbenzeno sulfônico (DBSA) e tolueno sulfônico (TSA); e também os solventes e plastificantes N-metilpirrolidinona (NMP) e m-cresol. Soluções de polianilina de alta massa molar processada com estes ácidos foram depositadas sobre subfases aquosas ácidas (pH = 2), formando os chamados filmes monomoleculares de Langmuir. Através de um estudo dos parâmetros que influenciam a formação dos filmes de Langmuir conseguimos obter monocamadas estáveis. Desta forma os filmes puderam ser transferidos para substratos sólidos (vidro bk7), usando a técnica de Langmuir-Blodgett. Os filmes LB produzidos são do tipo Z, ou seja, a deposição só é bem sucedida na retirada do substrato, o que significa que mesmo no filme de Langmuir alguns grupos hidrofílicos se encontravam na interface filme/ar. Os filmes LB foram caracterizados por espectroscopia de UV-vis., medidas de condutividade usando o método de quatro pontas, voltametria cíclica e medidas do potencial de superfície. Os filmes LB apresentam propriedades óticas e eletroativas semelhantes as dos filmes de polianilina fabricados por centrifugação. A absorbância da banda polarônica aumenta linearmente com o número de camadas depositadas, o que demonstra que cada camada contribui com a mesma quantidade de material para o filme. A condutividade dos filmes e da ordem de 10-4 S/cm, inferior aos valores medidos para filmes obtidos por centrifugação de soluções de polianilina com CSA e DBSA, mas é maior do que a de alguns outros filmes LB de polianilina relatados na literaturaLangmuir-Blodgett (LB) films were fabricated from parent polyaniline (PANI), which was made soluble in chloroform by being doped with functionalized acids. Optimized conditions for LB film deposition were only reached after a systematic processability study in which use was made of camphor sulfonic acid (CSA), dodecylbenzene sulfonic acid (DBSA), toluene sulfonic acid (TSA) and of N-methyl pyrrolidinone (NMP) and m-cresol as plasticizers. Solutions of high molecular weight PANI were spread on acidic, aqueous subphases (pH = 2), thus forming the so-called Langmuir monolayer. These monolayer were transferred onto solid substrates (bk7 glass) in the form of Z-type films, i.e. deposition was successful only in the upstrokes. This means that hydrophilic groups must protrude from the water surface in the Langmuir film. The LB films were characterized using UV-vis spectroscopy, cyclic voltammeter, surface potential and conductivity measurements. The optical and electroactive properties of the deposited LB films were essentially the same as those obtained with spin-coated PANI films. The absorbance of the polaronic peak increases linearly with the number of deposited layers, demonstrating that each layer contributed an equal amount of material to the LB film. The films conductivity was of the order of 10-4 S/cm, which is below the values of spin coated PANI films processed with CSA or DBSA, but higher than some published values for LB films from polyaniline
21
ZANONI, RAYMOND. "BRILLOUIN SPECTROSCOPY OF LANGMUIR-BLODGETT FILMS (THIN FILMS, ELASTIC CONSTANTS)". Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183852.
Testo completoAbstract (sommario):
The goal of this dissertation has been to develop techniques in order to use Brillouin spectroscopy as a tool for studying the elastic properties of thin films on a scale of ≃100 Å. In order to develop that capability we have built a tandem multi-pass Fabry-Perot interferometer, and that interferometer was used to study the elastic properties of Langmuir-Blodgett films. These films were chosen because they can be deposited one molecular layer at a time. As a result of these investigations we have measured the density and elastic constants of the Langmuir-Blodgett film cadmium arachidate. Samples of cadmium arachidate were prepared on molybdenum and BK-7 glass substrates. Data were accumulated for a range of thicknesses and for different scattering geometries. These data will be used to argue that guided acoustic waves were observed in a highly anisotropic film. The observed guided acoustic waves will be identified as a Rayleigh wave and a tight band of Sezawa modes. No Love modes were detected in these experiments; however, evidence for reorientational modes typical of anisotropic liquids was detected. The dispersion of the Rayleigh wave as a function of thickness together with thick film scattering data were used to estimate the elastic constants in cadmium arachidate. In particular the shear elastic constant c₄₄ was found to be a small value: c₄₄ < 4.0x10⁸ N/m². The remaining elastic constants were estimated, assuming hexagonal film symmetry, to be c₆₆ < 4.5x10⁹ N/m², C₁₁ ≃ 1.1x10¹⁰ N/m², c₃₃ ≃ 2.1x10¹⁰ N/m², c₁₃ ≃ 1.0x10¹⁰ N/m², and c₁₂ > 3.x10¹⁰ N/m². It is interesting to note that the acoustical behavior of cadmium arachidate is quite similar to the smectic phase liquid crystals (c₄₄ = 0).
22
Portus, Dan. "Langmuir-Blodgett films of porphyrins and phthalocyanines". Thesis, Cranfield University, 2002. http://hdl.handle.net/1826/3372.
Testo completoAbstract (sommario):
Phthalocyanines and porphyrins have been studied for many years as bulk, thick
and thin films. Their use in Langmuir and Langmuir-Blodgett films is governed their peripheral substituents. These can enhance or reduce their ability to form "quality"
ultra-thin films.
There are a number of potential and current applications for thin films porphyrins and phthalocyanines, which include CD-R discs and gas-sensors. It is latter that this PhD has focussed on.
Ultra-thin films of phthalocyanines, porphyrins and a porphyrin/phthalocyanine
hybrid dye were deposited onto glass microscope slides, gold-coated glass microscope
slides and quartz crystals. These assemblies were then characterised using Ultraviolet-
Visible spectroscopy, pressure-area isotherms, surface plasmon resonance and a quartz
crystal microbalance to try and determine the nature of the molecules on the surface the substrate. The thin films were exposed to chlorine gas and the change in their
absorption spectrum and (in some cases) their surface plasmon resonance curve monitored.
A short series of phthalocyanines showed that the central metal atom can play important role in the orientation of the macrocycles - with copper adopting an edge-configuration, zinc, face-down and metal-free, random. This in turn affected sensitivity of the gas-sensor with the facedown orientation offering a significantly
greater response than the other two.
A series of substituted tetraphenylporphyrins also illustrated that the sensitivity of the dye molecules is dependent on the orientation and spacing of molecules in the film. Generally the response to the chlorine was quite low, but porphyrin (stearamido) demonstrated a 2"d order decay in the absorbance due to oxidation of the macrocycle, the time constants being 31 and 425 seconds for surface and bulk diffusion responses respectively.
The use of differentiation on the Pressure-Area Isotherms of the deposited
Langmuir-Blodgett films is a new concept developed in this thesis. It proved a useful
tool for looking at the effect of the quality of the film on the gas sensitivity.
23
Travers, Paul James. "Langmuir-blodgett films for second harmonic generation". Thesis, Coventry University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254209.
Testo completo
24
Holcroft, B. "Novel electronic devices incorporating Langmuir-Blodgett films". Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235171.
Testo completo
25
Kalita, N. "The Pockels' effect in Langmuir-Blodgett films". Thesis, Durham University, 1991. http://etheses.dur.ac.uk/6072/.
Testo completoAbstract (sommario):
Simple, compact and inexpensive automated apparatus for recording surface plasmon resonance and the Pockels (or linear electro-optic) effect in Langmuir-Blodgett films has been used to estimate the thickness, permittivity and second order non linear susceptibility X(^(2))(_xxx)(-w;w,0) of several novel Langmuir-Blodgett film-forming materials. The results agree with estimates of nonlinear susceptibility obtained by second-harmonic generation. The materials synthesised at Durham were all functionalised diaryl alkynes of the general formula CH(_3)(CH(_2))(_n)(Py(^+))C=C(Ph-R), wherein n =17 or 21 and R=H or OCH(_3). Of these, that with n =21 and R=OCH(_3) showed particularly promising Langmuir-Blodgett film-forming properties; its nonlinear susceptibility per mono layer, however, was approximately one hundredth that of a hemicyanine monolayer. The nonlinear susceptibility per monolayer, as measured by the Pockels effect and second harmonic generation, was inversely proportional to the square root of the film thickness. This indicated rapid deterioration of in-plane order with increasing film thickness. Several novel polymeric materials synthesised at Hull and examined at Durham consisted of a siloxane spine of approximately 16 Si atoms, with randomly substituted bipolar chromophoric sidegroups. All were highly stable in floating film form. Of them, one known as AMCR23 showed promising optical nonlinearity when deposited on silver: a nonlinear susceptibility of-15+9.6i pm V(^-1) was recorded for a monolayer (cf. 94.5+49.9i pm V(^-1) for a hemicyanine monolayer).
26
Neal, D. B. "Langmuir-Blodgett films for non-linear optics". Thesis, Durham University, 1987. http://etheses.dur.ac.uk/9527/.
Testo completoAbstract (sommario):
In recent years there has been considerable interest in media which display significant non-linear optical properties; the telecommunications industry may exploit chin films of such materials for signal processing applications. The Langmuir-Blodgett (LB) technique provides a means of depositing organic layers of a precisely defined thickness. Moreover, by alternating layers of different materials, supermolecular arrays may be fabricated in which there is no centrosymmetry, and therefore the second-order non-linearity of the constituent molecules may be exploited. An investigation of the properties of water-surface monolayers of a number of novel materials with potentially large non-linearities is described. Several of these compounds are shown to form high quality homogeneous or heterogeneous LB films. The optical and electrical properties of the layers are characterized by optical absorption spectroscopy, surface plasmon resonance, and measurements of capacitance, whilst their structure is examined by electron diffraction. Monolayers of a nitrostilbene dye are shown to exhibit: on exceptionally high degree of crystalline order. Data are also given for theoretical calculations of non-linear coefficients and for the relative efficiency of second harmonic generation from bulk samples of various materials. Studies of second harmonic generation from monolayer and alternate multilayer films are reported. Optical non-linearity in an alternating donor-acceptor: inverted donor-acceptor dye system is demonstrated for the first time; the results are analysed in terms of second harmonic surface susceptibilities, and the value of the second-order hyperpolarizability determined for the first bilayer is found to be much superior to that expected by the simple addition of the hyperpolarizabilities of the separate layers. Monolayers containing a mixture of hemicyanine and cadmium arachldate are found to give rise to second harmonic generation which is enhanced relative to that obtained from a pure monolayer of the dye. Corresponding changes in the absorption spectra of the layers can be observed. These findings may have important implications for improving the efficiencies of any non-linear optical device which utilises IB films.
27
Simmons, John M. "Langmuir-Blodgett films of some novel phthalocyanines". Thesis, University of East Anglia, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280973.
Testo completo
28
Darby, John Edward. "Semiconducting Langmuir-Blodgett films as gas sensors". Thesis, University of Kent, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293551.
Testo completo
29
Hao, Shuang. "Josephson tunnel junctions using Langmuir-Blodgett films". Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252717.
Testo completo
30
Leeson, Paul. "Langmuir-Blodgett films for second harmonic generation". Thesis, Cranfield University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323931.
Testo completo
31
Barrell, K. J. "The Langmuir-Blodgett films of conjugated pigments". Thesis, University of the West of England, Bristol, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234286.
Testo completo
32
Das, Abhijna [Verfasser], Günter [Akademischer Betreuer] Reiter e Renate [Akademischer Betreuer] Reiter. "Controlling phase transitions in Langmuir polymer films". Freiburg : Universität, 2020. http://d-nb.info/1218464011/34.
Testo completo
33
Tucker, George. "Formation of Labyrinth Patterns in Langmuir Films". Scholarship @ Claremont, 2008. https://scholarship.claremont.edu/hmc_theses/215.
Testo completoAbstract (sommario):
A Langmuir film is a molecularly thin fluid layer on the surface of a subfluid. When dipole dipole forces are negligible, bounded films relax to energy minimizing circular domains. We investigate numerically the case where dipole dipole interactions are strong enough to deform the domain into highly distorted labyrinth type patterns. Our numerical method is designed to achieve higher accuracy and better stability than previous work and exploits an analytic formulation that removes a singularity in the dipole dipole forces without resorting to a small cutoff parameter. We calculate the relaxation rates for a linearly perturbed circular domain, and we verify them numerically. We are also able to numerically reproduce experimentally observed circle to dogbone transitions with minimal area loss.
34
Júnior, Antonio Riul. "Filmes de Langmuir e Langmuir-Blodgett de Polianilinas". Universidade de São Paulo, 1998. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-03052010-171319/.
Testo completoAbstract (sommario):
Explorou-se a caracterização de monocamadas e filmes LB de polianilina (PANi), e um oligômero de polianilina, chamado aqui de 16-mero, com estearato de cádmio (CdSt). A análise dos filmes de Langmuir indicou que possivelmente não há mistura em nível molecular da PANi e do 16-mero com CdSt, ainda que a quantidade adicionada em solução de polímero ou oligômero influencie a estabilidade das monocamadas. Utilizou-se UV-vis, FTIR, difração de raios-X, condutividade elétrica, elipsometria, microscopia óptica e potencial de superficie para caracterização dos filmes LB. Os resultados de UV-vis indicaram uma transferência uniforme e ainda que os filmes recém depositados encontram-se desdopados. A análise de FTIR confirma a presença de CdSt nos filmes LB, e o efeito de desdopagem em subfases neutras, corroborando os resultados de UV-vis. A difração de raios-X indica a presença de domínios separados de PANi (e 16-mero) com CdSt nos filmes LB. Resultados elipsométricos indicaram uma espessura por camada em tomo de 25 Å. A excelente uniformidade obtida nos filmes LB mistos foi comprovada pelos resultados de microscopia óptica e potencial de superficie. Esses filmes mistos apresentaram valores de condutividade elétrica em tomo de 10-4 a 10-5 S.cm-1 (van der Pauw), tanto para a PANi quanto para o 16-mero. Investigou-se também o efeito da exposição dos filmes mistos PANi/CdSt aos raios-X. Nota-se um deslocamento para a região do vermelho, na região do visível, nos espectros de UVvis, similar à observada pela dopagem através de ácidos inorgânicos. Verificou-se que os efeitos de umidade da atmosfera de medida são predominantes nesse processo de dopagem. É feita uma análise dos resultados de condutividade elétrica, comparando-os com os encontrados na literatura.A study has been made of composite Langmuir and Langmuir-Blodgett (LB) films of polyaniline (PANi), and a polyaniline oligomer (l6-mer polyaniline), with cadmium stearate (CdSt). The monolayers studies pointed to a phase separated system containing the polymer (or the 16-mer) and CdSt, with no mixing at the molecular leveI, although the relative contents of PANi and 16-mer in the solution have a strong influence on the monolayer stability. UV-vis, FTIR, X-ray difIraction (XRD), electrical conductivity, ellipsometry, optical microscopy and surface potential measurements were used in the LB film characterization. UV-vis results have shown a uniform transfer, with the as deposited films in the undoped state. FTIR results confirmed the presence of CdSt and undoped polyaniline (and 16-mer) in the transferred LB films, corroborating the UV-vis results. XRD has shown separated domains of CdSt and PANi (l6-mer also) in the LB films. Ellipsometry data indicated a thickness of 25 Å per deposited layer. The high uniformity in these mixed LB films was confirmed by optical microscopy and surface potential measurements. The electrical conductivity was approximately 10-4 to 10-5 S.cm-1 for both PANi and 16-mer. Mixed PANi/CdSt films were also exposed to X-ray irradiation. After a given dose rate there is a red shift in the UV-vis spectra from the 600 nm region to the 800 nm region, similar to the usual acid doping process observed in polyaniline. Humidity effects have a strong influence on the doping process. A comparison is made of the conductivity measurements made here with those reported in the literature.
35
Embs, Frank, Dirk Funhoff, André Laschewsky, Ulrike Licht, Holger Ohst, Werner Prass, Helmut Ringsdorf, Gerhard Wegner e Rolf Wehrmann. "Preformed polymers for Langmuir-Blodgett films- molecular concepts". Universität Potsdam, 1991. http://opus.kobv.de/ubp/volltexte/2008/1719/.
Testo completoAbstract (sommario):
The use of preformed polymers for the preparation of Langmuir-Blodgett (LB) multilayers is reviewed. Principles for polymer self-organization are outlined and the appropriate molecular designs are discussed. Recent developments in the different classes of polymers for LB multilayers are presented, and their outstanding properties highlighted.
36
Young, C. J. "Gas sensitivity of Langmuir-Blodgett films of porphyrins". Thesis, Lancaster University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371069.
Testo completo
37
Parry, David A. "Optical gas sensing using Langmuir-Blodgett thin films". Thesis, Coventry University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241840.
Testo completo
38
Stone, Peter Jeffrey William. "Langmuir-Blodgett films for non-linear optical applications". Thesis, Coventry University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259613.
Testo completo
39
Howarth, Vaughan Antony. "A study of Langmuir-Blodgett films of valinomycin". Thesis, Durham University, 1989. http://etheses.dur.ac.uk/6518/.
Testo completoAbstract (sommario):
The deposition and characterisation of Langmuir-Blodgett (LB) films containing the ionophore valinomycin are described. In particular, the thesis concentrates on two specific mixed LB systems incorporating the ionophore, namely, arachidic acid/valinomycin and L-a-phosphatidic acid dipalmitoyl (DPPA)/valinomycin. The extremely sensitive spectroscopic technique of attenuated total reflection (ATR) Fourier transform infrared (FTRIR) spectroscopy is used to investigate the interaction of these ultra-thin LB structures with aqueous solutions containing potassium ions. It is shown that LB layers of pure valinomycin do not complex with potassium ions and that, in order for complexation to occur, the ionophore must be mixed with a secondary component. The formation of the valinomycin-potassium (VM/K(^+)) complex in the arachidic acid/vahnomycin system is demonstrated and the effects of the mole-fraction of arachidic acid, and of the potassium ion concentration upon complexation are described. The IR studies also reveal profound structural changes in the fatty acid matrix upon complexation, and the important result that dissociation of the VM/K(^+) complex does not occur in this mixed system. However, it is shown that if the fatty acid molecule is replaced by the phosphohpid molecule, DPPA, then both formation and dissociation of the complex occur. The results, however, indicate that this system is unstable with loss of the LB film into the aqueous solution during immersion. A number of attempts to eliminate this problem are described. The fabrication and characterisation of ion-selective-field-effect transistors (IS-FETs) are also reported. One of the aims of the research is to develop a potassium- ion sensor, and with this in mind, the deposition of LB films onto the gate surface of the ISFET is demonstrated. The K(^+)-response of the LB film coated devices is described and the results interpreted in terms of the IR evidence.
40
Fowler, M. T. "Optical and photoelectrical applications of Langmuir Blodgett films". Thesis, Durham University, 1985. http://etheses.dur.ac.uk/7116/.
Testo completoAbstract (sommario):
The Langmuir-Blodgett (LB) technique is well known for the deposition of thin, uniform films of precisely defined thickness. These films can he used in electronic devices as an active layer, or in a passive role as insulators. Results are presented of investigations using films of both types. Novel LB films of a merocyanine dye have been developed for use as a spectral sensitiser, and films of phthalocyanine used as insulators for the enhancement of the electroluminescent (EL) properties of a metal-semiconductor structure. The merocyanine dye used has none of the clear amphiphilic molecular substitutions associated with classical LB film materials, but behaves well as a Langmuir film. Incorporated into a matrix of cadmium arachidate the dye can be deposited onto various substrates using the LB technique. The optical properties of such deposited films are characterised and coipared with those of a merocyanine dye featuring anphiphilic substitutions. For both dyes these properties indicate that good quality LB films have been deposited, and that some dimeric structure is present in these films. The feasibility of using these films for the spectral sensitisation of semiconductors is demonstrated by their modifying effect on the photoconductive response of polycrystalline zinc sulphide. The incorporation of LB films of phthalocyanine into the gold/ZnSeS system enables low voltage forward bias d.c EL to be observed with a threshold ~1V. Measurement of the increase in intensity of emitted EL with bias suggests that the presence of the insulating layer increases the minority current available for radiative recombination by supporting realignment of energy bands in the metal and semiconductor. EL efficiency of devices is shown to increase with insulator thickness up to ten deposited layers of phthalocyanine a thickness of ~23nm. A simple energy band model for the system is proposed which takes into account series resistance effects.
41
Baker, S. "Phthalocyanine Langmuir-Blodgett films and their associated devices". Thesis, Durham University, 1985. http://etheses.dur.ac.uk/7589/.
Testo completoAbstract (sommario):
Interest in the Langmuir-Blodgett (LB) technique has led to a number of investigations into different types of materials that can be deposited in the form of monolayers. For example, as well as the classic long Cham fatty acids and alcohols, materials such as polymerisable molecules, aromatic hydrocarbons and dye substances can now all be produced in monomolecular form. Unfortunately, few of these materials yet fulfil the requirements of mechanical and thermal stability that will be necessary if LB films are to be used commercially. This work has dealt with the use of phthalocyanine, a substance well known for its thermal and chemical stability, in the production of LB films. Initially two compounds were investigated, dilithlum phthalocyanine and tetra-tert-butyl phthalocyanine. Although it was found that both materials produced layers of reproducible quality which adhered tenaciously to various substrates and to each other, single monolayers were not obtained. More success has been achieved using an asymmetrically substituted phthalocyanine molecule. Electron microscopy studies have shown that the majority of films are polycrystalline. However, a substitute CuPc proved to be a valuable exception. Multilayer films of this molecule were found to have domains of the order of 3 mm in size showing a preferred orientation. Even so, it has to be accepted that the phthalocyanine films produced to date are not as structurally perfect as for example, multilayers of lo-tricosenoic acid. Our ability to produce monomolecular layers of phthalocyanine now extends the range of possible applications for this material. For instance it is known that the fine control of insulator thickness is crucial in the optimisation of photovoltaic and electroluminescent metal-lnsulator-semlconductor devices. Examples of both types of device have been demonstrated using our phthalocyaine films. For the bistable switch, a gallium arsenide substrate was used; both gallium phosphide and zinc selenlde have been utilized in the electroluminescent structures. Moreover, In the case of phthalocyanine another possibility presents Itself. It has long been known that the conductivities of this material and its derivatives are very sensitive to the presence of certain gases, particularly the oxides of nitrogen. The increased conductivity of such materials has been demonstrated to be confined to the surface of the crystal. Hence many phthalocyanine gas detector systems have been based on thin films. Unfortunately because phthalocyanine exhibits polymorphism, the exact structure of such films can be complicated. making interpretation of results and subsequent device optimisation difficult. Also the response and recovery times of these thin film devices can also be excessively long. It is possible that monomolecular LB films of phthalocyanine could well overcome some or all of these problems. Our experiments have concentrated on asymmetrically substituted copper phthalocyanine and its usefulness to detect nitrogen dioxide. Preliminary results show the response and recovery times for the simple gas structures to be faster than those previously reported for other thin film phthalocyanine devices. It is suggested that this is due to the more ordered structure of the LB film, which enables the gas to adsorb on, or desorb from the molecular sites more readily.
42
Pearson, C. "Langmuir-Blodgett films of organic charge-transfer complexes". Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5390/.
Testo completoAbstract (sommario):
This thesis is concerned with the preparation of floating films of electrically conductive organic charge-transfer complexes and their subsequent transfer to solid substrates by the Langmuir-Blodgett (LB) technique. Characterisation of the morphology (using ellipsometry, surface profiling, optical and scanning electron microscopy, energy dispersive spectroscopy and optical absorption spectroscopy) and electrical properties (at room temperature and low temperature) of the resulting multilayer structures is discussed. Three different systems were investigated: (i) mixed films containing the long chain tetrathiafulvalene (TTF) derivative octadecanoyl-TTF (ODTTF) and either octadecanoic acid (OA) or pentacosa-10,12-diynoic acid (PA); (ii) pure films of the charge-transfer complex Ν-octadecylpyridiniura-bis-(4,5-dimercapto-1,3-dithiole-2- thione) palladium (Ci8Py-Pd(dmit)2); and (iii) pure films of the charge-transfer complex N-octadecylpyridinium-bis-(4,5-dimercapto-1,3-dithiole-2-thione) nickel (CigPy- Ni(dmit)2). Some interesting electrical properties were observed in these films. Also, Ci8Py-Ni(dmit)2 has been incorporated as the active layer in a thin film field effect transistor structure. Carrier mobility values of 1.9 ± 0.5 x l0(^-5) cm(^2) V(^-1) S(^-1) and 0.3 ± 0.1 cm(^2) V(^-1) s-(^-1) were calculated from the device characteristics, before and after doping with iodine, respectively In the case of films containing ODTTF, a maximum room temperature in-plane dc conductivity after iodine doping of 2±lxl0(^-2) S cm(^-1) was recorded. This conductivity was found to be strongly dependent on the molar ratio of the two components present in the film. The behaviour has been explained using two-site percolation models. For C(_18)Py-Pd(dmit)(_2) and C(_18)Py-Ni(dmit)(_2), the properties of the floating layers and transferred films were found to be influenced by the exact experimental conditions. Ci8Py-Pd(dmit)(_2) films were conductive as deposited, with a stable maximum room temperature in-plane dc conductivity value of 1.5±1.0xl0(^-l) S cm(^-1). C(_18)Py-Ni(dmit)(_2) samples became conductive after exposure to iodine vapour, with a stable peak conductivity value of 1.3±0.8 x10(^-1)S cm(^-1).
43
ROMERO, WENNDY STEFFANNÍA PANTOJA. "LANGMUIR FILMS OF FATTY ACID MONOESTERS OF GLYCEROL". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36991@1.
Testo completoAbstract (sommario):
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
Ésteres de glicerol derivados de ácidos graxos são surfactantes não iônicos com aplicação como lubrificantes, agentes anti-estáticos, auxiliares de processamento, plastificantes, anti-espumas, agentes de dispersão e de outras aplicações que requerem atividade bifuncional. Os monoésteres de glicerol derivados de ácidos graxos naturais, tais como ácido octanóico (C menos 8), decanóico (C menos 10) e octadecanóico (C menos 18), foram sintetizados e caracterizados por técnicas de infravermelho e ressonância magnética nuclear de hidrogênio e carbono 13. Eles foram espalhados sobre uma subfase aquosa formando filmes de Langmuir em uma cuba de teflon. As propriedades interfaciais destes surfactantes foram investigadas na interface ar-água. Desta forma, foi também possível avaliar a isoterma de Langmuir Pi-A e as propriedades mecânicas das monocamadas através do módulo de compressão (Cs elevado a potencia negativa 1). As monocamadas mostraram um comportamento na fase de líquido expandido confirmado pelo módulo de compressão de 10 a 70 mN/m e na fase de líquido condensado confirmado pelo módulo de compressão de 70 a 175 mN/m. Por meio da espectroscopia de reflexão-absorção de infravermelho com fotomodulação (PM-IRRAS) e a microscopia no ângulo de Brewster (BAM) foi avaliada a organização dos filmes de Langmuir dos surfactantes. A elasticidade superficial dilatacional (E) dos filmes adsorvidos foram analisadas pelo método da gota pendente em um goniômetro.
Fatty acid glycerol esters are non-ionic surfactants with application as lubricants, antistatic agents, processing aids, plasticizers, defoamers, dispersion aids and other applications requiring bifunctional activities. Monoesters of glycerol based on natural fatty acids such as octanoic acid (C less 8), decanoic acid (C less 10) and octadecanoic acid (C less 18), were synthesized and characterized by infrared and hydrogen nuclear magnetic resonance and carbon 13 nuclear magnetic resonance techniques. They were spread over the water subphase forming Langmuir films in a Teflon trough. The interfacial properties of these surfactants at the air/water interface have been investigated. Thus it was also possible to evaluate the Langmuir Pi-A isotherm and mechanical properties of the monolayers by calculating the compression modulus (Cs elevated to negative power 1). The monolayers showed a behavior in the expanded liquid phase, confirmed by the compression modulus between 10 and 70 mN/m and a behavior in the condensed liquid phase confirmed by the compression modulus between 70 and 175 mN/m. Through photomodulated-infrared reflection-absorption spectroscopy (PM-IRRAS) and Brewster angle microscopy (BAM) was evaluated organization of Langmuir films of surfactants. The surface dilatational elasticity (E) of the adsorbed films were analyzed by the pendant drop method with a goniometer apparatus.
44
NASSOY, PIERRE. "Effets de segregation dans les films de langmuir". Paris 6, 1996. http://www.theses.fr/1996PA066307.
Testo completoAbstract (sommario):
Les effets de segregation a deux dimensions dans les films monomoleculaires d'amphiphiles etales a l'interface eau/air ont ete abordes sous trois angles differents. Dans une premiere partie, nous avons considere des monocouches de langmuir d'amphiphiles fluores, assimilables a des batonnets rigides. Leur diagramme de phase a des caracteristiques inhabituelles par rapport a celui des tensio-actifs a chaine hydrocarbonee. Une compression mecanique conduit a une seule transition de phase du premier ordre de type gaz/solide. La phase solide, dont la structure est deduite d'experiences de diffraction de rayons x en incidence rasante, est caracterisee par son monomorphisme sur toute la gamme de pressions de surface et de temperatures accessibles. La phase gazeuse, determinee par son equation d'etat -a, existe jusqu'a des densites surfaciques aussi elevees que 0,5 fois la densite de la phase solide. La seconde partie concerne l'etude d'une monocouche mixte formee d'un melange de molecules chirales. Nous avons choisi un melange racemique de myristoyl-alanine (chaine aliphatique+tete polaire derivee de l'alanine). En volume, l'etat thermodynamiquement stable est le compose racemique, tandis qu'en surface, nous avons observe une segregation spontanee entre molecules droites et gauches. Cela a ete mis en evidence par la combinaison de mesures de pression de surface, microscopie de fluorescence, et diffraction de rayons x. Le mecanisme suggere demande encore a etre etendu a d'autres systemes. Enfin, dans une troisieme partie, nous avons propose une methode, n'utilisant pas d'electrode, pour mesurer les champs electriques generes par des heterogeneites de densite de surface dans les films de langmuir. Il s'agit d'une methode hydrodynamique utilisant des micro-billes de latex comme sonde du champ electrique. L'interaction entre une bille et un ilot condense par exemple est de nature dipole-dipole. La vitesse de deplacement de la bille est proportionnelle au gradient de champ electrique cree par le domaine. Nous avons montre que ces champs atteignent plusieurs dizaines de volt/centimetre a courte distance, et s'etendent sur plusieurs dizaines de microns. Ces resultats sont en bon accord avec les calculs theoriques
45
Antoine, Claire. "Composés d'insertion inorganiques en films de Langmuir-Blodgett". Paris 11, 1989. http://www.theses.fr/1989PA112328.
Testo completoAbstract (sommario):
L'étude des composés organiques ou minéraux en films minces a montré qu'ils présentaient des propriétés tout à fait originales par rapport aux composés massifs. Le présent travail vise à l'obtention de semi-conducteurs minéraux en films ultraminces, en particulier des sulfures métalliques de mercure et de cadmium. La synthèse est réalisée dans des conditions douces au sein d'une matrice organique réalisée grâce à la technique de Langmuir-Blodgett, par diffusions successives des réactifs minéraux. La formation des sels, contrôlée géométriquement par la matrice d'accueil, est suivie par spectroscopie IR. Les propriétés physiques de ces composés ont été étudiées par différentes techniques : spectroscopies U. V. Visible et I. R. , dichroïsme linéaire, diffraction des RX, X. P. S. , conduction, etc. . . Les propriétés structurales et électroniques de ces films ultraminces ces confirment que les sulfures métalliques adoptent une géométrie lamellaire d'épaisseur moléculaire. La conductivité et la photoconductivité sont interprétées par un diagramme de bande classique et confirment l'existence d'un plan continu. Cette méthode de synthèse ouvre la voie vers une nouvelle famille de matériaux ultrafins aux propriétés électroniques originales. Ce travail a fait l'objet de deux publications, et d'un dépôt de brevet.
46
Ouattara, Mariane. "Polymères amphiphiles : des films Langmuir-Blodgett au transistor". Doctoral thesis, Université Laval, 2016. http://hdl.handle.net/20.500.11794/26569.
Testo completoAbstract (sommario):
Au cours des 25 dernières années, l’intérêt pour l’utilisation de semi-conducteurs organiques comme couche active dans les transistors à effet de champ (TOECs), à la place du silicium, a crû spectaculairement. L’utilisation de polymères π-conjugués dans ce domaine a grandement entraîné cet essor. Au fil du temps, on observe une amélioration des performances atteintes contribuant à l’émergence de nouveaux matériaux. Par contre, différents paramètres tels que la mobilité et la stabilité demeurent moins impressionnants que ceux des semi-conducteurs à base de matériaux inorganiques. De meilleurs résultats pourraient être obtenus si le transport de charges se faisait sans entraves. Ainsi, une très bonne organisation au sein des matériaux utilisés est nécessaire. Dans cette optique, des polymères conjugués amphiphiles constitués d’unités thiéno [3,4-c] pyrrole-4,6-dione (TPD) ont été synthétisés. En se servant de la technique Langmuir-Blodgett (LB) pour optimiser l’organisation des molécules au sein des films, il a été possible de réaliser des films stables avec des pressions de collapse de 60 mN/m. Les microscopies à angle de Brewster (BAM) et à force atomique (AFM) nous ont démontré l’homogénéité des films à l’interface air-eau (BAM) et une fois transférés sur un substrat solide (AFM). L’orientation a été étudiée principalement par spectroscopie infrarouge à réflexion totale atténuée (ATR). D’autres techniques spectroscopiques comme l’UV-visible, la spectroscopie infrarouge de réflexion absorption par modulation de polarisation (PM-IRRAS) et l’ellipsométrie ont permis de corroborer les résultats obtenus via l’ATR. Les mesures ont permis de confirmer l’obtention de l’orientation préférentielle hors du plan. Pour compléter ce projet, des tests ont été effectués avec des transistors organiques. Des valeurs de mobilité intéressantes de 1,2 × 10-3 cm2/(V.s) ont été enregistrées pour des transistors obtenus à partir de films LB.Over the past 25 years, interest in the use of organic semiconductors as active layers in field effect transistors (TFTs) instead of silicon has grown dramatically. The use of π-conjugated polymers in this area has greatly driven this growth. Over time, there has been an improvement in performance achieved contributing to the emergence of new materials. However, the performances of organic semiconductors remains inferior that of their inorganic counterpart regarding parameters such as the mobility and stability. Better results could be achieved if the charge transport was done without hindrance. Thus, a very good organiza- tion within the material is needed. In this regard, amphiphilic polymers based on thieno [3,4-c] pyrrole-4,6-dione (TPD) units were synthesized. By using the Langmuir-Blodgett technique (LB) to optimize the organization of the molecules within the films, it was possible to achieve stable films with a collapse pressure of 60 mN/m. Brewster angle (BAM) and atomic force (AFM) microscopies have demonstrated that homogeneous films are obtained at the air-water interface (BAM) and remain so once transferred onto a solid substrate (AFM). Orientation has been studied mainly by attenuated total reflection infrared spectroscopy (ATR). Other spectroscopic techniques such as UV-visible, absorption polarization modulation infrared reflection spectroscopy (PM-IRRAS) and ellipsometry have confirmed the ATR results. Measurements show that molecules adopted an edge-on orientation in the polymer films. To complete this project, organic transistors were fabricated. Interesting mobility values of 1.2 × 10-3 cm2/(V.s) were recorded for organic LB film transistors.
47
L'HEVEDER, CLARISSE. "Etude dynamique et rheologique des films de langmuir". Paris 6, 1999. http://www.theses.fr/1999PA066308.
Testo completoAbstract (sommario):
Cette these presente, en premiere partie, un nouveau type de microscope a angle de brewster. Le principe de cet instrument est base sur les proprietes de reflectivite des interfaces. C'est une technique tres performante pour l'etude des films de langmuir : elle permet une visualisation directe des coexistences de phases dans les films. Cet instrument permet egalement d'observer l'anisotropie optique des films. Le nouveau microscope ouvre la voie a l'exploration d'un nouveau domaine de recherche. En effet, il autorise la realisation d'etudes dynamiques sur les films de langmuir. La seconde partie de cette these est une application de cette technique a l'etude de films monomoleculaires d'acides gras (acide palmitique) a l'interface eau-air. Nous nous sommes interesses a la transition de phase entre le gaz et la phase l2. Sous certaines conditions, la phase l2 se presente sous la forme de domaines ronds ayant une structure interne particuliere et appeles boojums. L'observation de ces domaines, entre polariseur et analyseur croises, permet de determiner l'orientation moleculaire moyenne du domaine dans le plan de la surface. Nous avons realise plusieurs etudes statistiques sur les directions d'orientation de domaines voisins. Nous avons determine l'origine de l'orientation collective des domaines de phase condensee l2 dans une meme direction d'orientation azimutale.
48
Lecourt, Boris. "Ellipsométrie spectroscopique conventionnelle et généralisée de films moléculaires ultraminces : bases théoriques et instrumentales, application à l'étude de films Langmuir-Blodgett et de films autosupportés". Bordeaux 1, 1998. http://www.theses.fr/1998BOR10580.
Testo completoAbstract (sommario):
Cette these est consacree au developpement et a l'application de methodes d'ellipsometrie conventionnelle et generalisee pour l'etude de films moleculaires ultraminces. Dans la premiere partie sont exposes les bases de l'ellipsometrie et en particulier les problemes de modelisation et d'inversion des donnees experimentales. La deuxieme partie est dediee aux techniques instrumentales de mesures realisees sur un ellipsometre a polariseur tournant (gesp5) de la societe sopra. La troisieme partie est consacree a la determination des constantes optiques de films autosupportes ultraminces de surfactant et de cristaux liquides par ellipsometrie en transmission et reflectometrie autour de l'angle de brewster. Enfin, les deux derniers chapitres decrivent une methode specifique d'ellipsometrie generalisee pour la determination de faibles anisotropies dans le plan et l'application de cette methode a l'etude de films langmuir-blodgett.
49
Romualdo, Torres Gemma. "Sistemas híbridos orgánicos-inorgánicos en films de Langmuir-Blodgett". Doctoral thesis, Universitat de València, 2002. http://hdl.handle.net/10803/10274.
Testo completoAbstract (sommario):
ÉCe travail porte sur la formation et la caractérisation de nouveaux systèmes organiques-inorganiques par l'utilisation de films de Langmuir et de la technique de Langmuir-Blodgett. Plusieurs voies ont ainsi été explorées afin d'obtenir des films minces hybrides aux propriétés multiples, en particulier magnétiques. L'utilisation de l'interaction entre monocouches cationiques et des anions présents en sous-phase a ainsi permis l'organisation de différents polyanions inorganiques en structure lamellaire. Cette stratégie a ensuite été généralisée au cas de colloïdes de Bleu de Prusse, composés bimétalliques étendus. Une large étude (de la préparation à la caractérisation) a été consacrée à ces matériaux mixtes Bleu de Prusse-dérivé amphiphile de Ru(bpy)32+. Il a été également montré que la cristallisation du Bleu de Prusse et de ses analogues est favorisée en-dessous des films de Langmuir. Finalement, la coordination d'ions dissous en sous-phase avec des molécules amphiphiles à l'interface permet d'élaborer de nouveaux systèmes pouvant former des films LB, ce qui est notamment le cas d'agencements à base de cyanures métalliques.El trabajo presentado como Tesis Doctoral trata sobre la formación y la caracterización de nuevos sistemas orgánicos-inorgánicos en películas de Langmuir y Langmuir-Blodgett. El método semi-anfifílico ha sido utilizado para obtener películas delgadas donde las dos entidades pueden participar en las propiedades del material híbrido. Así, un amplio estudio (desde la preparación hasta la caracterización) ha sido dedicado a las películas moleculares de Azul de Prusia y un derivado anfifílico de Ru(bpy)32+. Además, otras estrategias han sido desarrolladas para obtener sistemas extendidos. La coordinación de iones disueltos en la subfase con las moléculas anfifílicas en la interfase permite elaborar nuevos sistemas que pueden formar posteriormente multicapas, como es el caso de los compuestos a base de cianuros. Se ha demostrado también que la cristalización del Azul de Prusia y sus análogos a partir de sus iones precursores está favorecida en la interfase bajo las películas de Langmuir. Las películas de Langmuir han sido estudiadas a partir de las isotermas de compresión y de la difracción de rayos X a ángulos rasantes y las películas de Langmuir-Blodgett han sido caracterizadas por espectroscopías infrarroja y UV-visible, difracción de rayos X a ángulos pequeños, magnetismo, electroquímica y Microscopía Electrónica a Transmisión.
50
Wilde, Jason N. "Optical sensing of organic vapours using Langmuir-Blodgett films". Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4763/.
Testo completoAbstract (sommario):
This thesis describes hydrocarbon vapour sensing using Langmuir-Blodgett films prepared from: a co-ordination polymer; substituted phthalocyanines containing copper and zinc as the central metal ions; and a polysiloxane. The physical and chemical properties of the co-ordination polymer, 5,5'-methylenebis (N- hexadecylsalicylidenamine), at the air water interface were investigated using Brewster angle microscopy and surface pressure versus area measurements. Langmuir-Blodgett films were built-up on a variety of substrates. The addition of copper acetate to the subphase caused a change in both the physical and optical properties of the Langmuir- Blodgett layers. Film thickness data suggest that a true monolayer (thickness ca 2 nm) is only formed under these conditions. The multilayer films were studied using X-ray diffraction, UV/Visible spectroscopy, ellipsometry, surface plasmon resonance, surface profiling and electron spin resonance. The response of each film when exposed to, benzene, toluene, ethanol and water vapours were recorded. Two optical systems were used, both based on surface plasmon resonance. The first incorporated a silicon photodiode to record the intensity of the reflected light. The second was similar to that of surface plasmon microscopy, using a charge coupled device camera to monitor the reflected light intensity from the Langmuir-Blodgett film/metal interface. The co-ordination polymer was found to be most sensitive to benzene and could reliably detect concentrations of this vapour down to 100 vapour parts per million. Data obtained when the co-ordination polymer was exposed to benzene and water vapour (using the latter system) were presented to a neural network for recognition.