Academic literature on the topic 'Langmuir-Blodgett Techniques'

Structural and electronic properties of pentacene/pentacenequinone thin films prepared on various solid-state substrates by the Langmuir–Blodgett technique are reported. Amorphous structure of the prepared films has been proved by XRD measurements. Oxygen-related defects have been identified in the Langmuir–Blodgett films as a consequence of the exposure of pentacene Langmuir layer to air. Crystallization induced by thermal treatment of the prepared amorphous thin films has been observed. Electronic properties of pentacene/ pentacenequinone Langmuir–Blodgett films have been investigated in the contact-less architecture using electrochemical techniques. The energy band diagram of the amorphous pentacene/pentacenequinone Langmuir–Blodgett film on a metallic surface was constructed from the obtained electrochemical data.

Because of their applications in the areas of non-linear optics, molecular electronics, and biosensors, Langmuir-Blodgett (LB) films have been extensively studied by a wide variety of scattering and spectroscopic techniques. The atomic force microscope has emerged as an important tool for studying LB films because of its unprecedented ability to quantitatively measure films with high resolution.The unique abilities of quantitative AFM imaging motivated us to investigate the effect of incorporating different divalent metal cations and fatty acids of different chain length into films deposited on both amorphous and ordered substrates. Once substrate effects have been accounted for, multilayer Langmuir-Blodgett films of palmitic, stearic and arachidic acid salts show that the area per molecule is primarily controlled by the detailed interactions of the counterion with the carboxylic acid group. However, the lattice dimensions and symmetry are dictated by the close packing of the alkane chains, given the constraint of area per molecule set by the counterion.

Phospholipid monolayers and bilayers prepared by the Langmuir-Blodgett technique are simplified model systems of biological membranes. The molecular organization of these monolayers and bilayers has been intensely studied as they are excellent tools for understanding biological processes such as adhesion, fusion, protein structure and organization, etc. Recent structural studies have included electron diffraction of monolayers deposited on substrates and X-ray diffraction of monolayers at the air-water interface. Both diffraction techniques suggest that in the gel phase, the lipid hydrocarbon chains possess long range orientational order, but relatively short range positional order. As a result, L-B films in the gel state closely resemble the “hexatic” phases better known in thermotropic liquid crystals. However, both shortrange and long-range order have not yet been studied in a single Langmuir-Blodgett film.

Studies of excited singlet and triplet states of porphyrins and phthalocyanines in organized media of reverse micelles, vesicles, monolayers, and Langmuir-Blodgett films along with more complex supramolecular organizates with proteins and dendrimers, are reported. Self-assembly in these systems was followed by imaging and temporal fluorescence techniques.

The characterization of Langmuir–Blodgett thin films of 10,12-pentacosadiynoic acid (PDA) and their use in metal–insulator–metal (MIM) devices were studied. The Langmuir monolayer behavior of the PDA film was studied at the air/water interface using surface tension–area isotherms of polymeric and monomeric PDA. Langmuir–Blodgett (LB, vertical deposition) and Langmuir–Schaefer (LS, horizontal deposition) techniques were used to deposit the PDA film on various substrates (glass, quartz, silicon, and nickel-coated film on glass). The electrochemical, electrical and optical properties of the LB and LS PDA films were studied using cyclic voltammetry, current–voltage characteristics (I–V), and UV–vis and FTIR spectroscopies. Atomic force microscopy measurements were performed in order to analyze the surface morphology and roughness of the films. A MIM tunnel diode was fabricated using a PDA monolayer assembly as the insulating barrier, which was sandwiched between two nickel layers. The precise control of the thickness of the insulating monolayers proved critical for electron tunneling to take place in the MIM structure. The current–voltage characteristics of the MIM diode revealed tunneling behavior in the fabricated Ni–PDA LB film–Ni structures.

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.

Cette étude porte sur l'organisation en films ultraminces de protéines fortement tensioactives et sur leurs interactions avec des lipides. Elle a été réalisée principalement par microspectroscopie Raman confocale associée à d'autres méthodes complémentaires telles que des mesures de tension superficielle, la microscopie à l'angle de Brewster et la spectroscopie infrarouge PM-IRRAS. Le signal Raman de tels systèmes étant très faible, la première étage de ce travail a consisté à mener des tests comparatifs entre différents types de caméra CCD de technologies récentes afin d'optimiser la détection du montage. L'optimisation de notre instrumentation a permis l'étude de différents films protéiques. D'une part, des films de Langmuir constitués de protéines du surfactant pulmonaire SP-B ou SP-C ont été étudiés, les protéines étant pures ou en interaction avec deux phospholipides, le DPPC et le DPPG, présents majoritairement dans le système in-vivo. Ensuite, la puroindoline-a, protéine végétale dont les fortes propriétés tensioactives permettent la réalisation et la caractérisation de films noirs protéiques, a aussi été étudiée. Nous avons en particulier montré que cette protéine subit des changements importants de structure secondaire selon la nature du système étudié (poudre, solution aqueuse ou film noir). Des changements ont également été constatés en présence du lyso-palmitoylphosphatidylcholine (LPC), phospholipide à une seule chaîne aliphatique.

DE LA TESIS EN CASTELLANO

Antecedentes

Un avance importante en el campo de química analítica se hizo por Clark y Lyons en los años setenta. Ellos propusieron acoplar la especificidad de la enzima glucosa oxidasa con la transducción electroquímica de la señal en "biosensores". En general, los biosensores son artefactos integrados autocontenidos, capazes de proporcionar información analítica, cuantitativa utilizando un elemento biológico de reconocimiento (receptor bioquímico) que se retiene en contacto espacial directo con un elemento de transducción. Posteriormente, los primeros biosensores de glucosa, basados en la detección amperométrica de peróxido de hidrógeno generado por glucosa oxidasa en la presencia de oxígeno fueron introducidos en el mercado por la empresa estadounidense Yellow Spring Instrument Co. (Ohio, EE. UU.) en 1975.
La respuesta de biosensores electroquímicos basados en el uso de oxígeno como cosustrato para oxidasas se ve desviada por la presencia de interferencias que pueden contribuir a la corriente. Por lo tanto la superficie de electrodo debe estar protegida por una membrana no permeable por sustancias que pueden interferir con la señal. Para evitar corrientes que perjudican la selectividad de los biosensores, el potencial aplicado puede ser aminorado usando electrocatalizadores difusionales ("mediadores") en lugar de oxígeno, con un potencial redox controlable. Pero la respuesta de estos sensores también depende de la concentración de oxígeno porque este compite con los mediadores, para la reoxidación de las oxidasas. Un inconveniente adicional del uso de mediadores diffusionales artificiales en biosensores es la baja estabilidad de los mismos debida al escape de mediadores desde la superficie del electrodo cuando esto se usa en linea. Se puede aliviar este problema creando enlaces covalentes entre los mediadores y la superficie del electrodo o usando polímeros redox que se adsorben fućrtemente en la superficie del electrodo.
Una de las posibles maneras para disminuir la influencia del oxígeno a la corriente de la respuesta de biosensores es el uso de las deshidrogenasas dependientes de la pareja redox NAD+/NADH. El potencial estándar redox de esta pareja es -0.56 V vs. SCE pero para conseguir la oxidación de NADH en la superficie de electrodos de carbono un sobrepotencial de +0.5 V vs. SCE debe aplicarse. Bajo estas condiciones los electrodos tienen tiempo de vida corto debido a la adsorción de los productos de oxidación en su superficie ya que la oxidación de NADH no es reversible químicamente. Por otro lado estos electrodos sufren por la oxidación no especifica de interferencias a estos potenciales de operación. Los electrodos modificados químicamente por mediadores pueden oxidar NADH a potenciales más bajos. Sin embargo, muchos de los mediadores mencionados en la bibliografía no son estables o/y no forman NAD+ enzimaticamente activo. Un problema adicional de los sistemas analíticos basados en deshidrogenasas dependientes de NAD+ es la necesidad de añadir este cofactór, que tiene alto coste y es inestable, en las muestras. Se puede inmovilizar NAD+ en la superficie de electrodos para producir biosensores capaces de funcionar en muestras que no contienen NAD+, biosensores reagentless (sin necesidad de adición de reactivos). Los métodos descritos en la bibliografía para la fabricación de biosensores reagentless se basan en cinco estrategias: (1) la inmovilización en hidrogeles formados in situ; (2) la inmovilización por una membrana; (3) la inmovilización en películas preparadas por electropolimerización; (4) la inmovilización en una pasta de carbono; (5) la inmovilización en monocapas auto ensambladas. Sólo los electrodos preparados con la estrategia (4) son biosensores reagentless con estabilidad operacional relativamente alta. Las demás estrategias no resultan en biosensores con suficiente estabilidad operacional por culpa de la perdida del mediador, de NAD+ o de la deshidrogenasa. Sin embargo la estrategia basada en electrodos de pasta de carbono no permite su aplicación a la producción de microsensores (electrodos con diámetro de menos de 10 m) para su uso in vivo.

Metodología

El objetivo principal de esta tesis es el desarrollo de nuevas estrategias para la fabricación de biosensores reagentless basados en deshidrogenasas dependientes de NAD+ con características mejoradas respecto a la densidad de la corriente, de la estabilidad operacional y de almacenamiento.
Para cumplir el objetivo se han sintetizado dos nuevos mediadores para la oxidación de NADH: un polímero insoluble en agua [Os(1,10-fenantrolina-5,6-diona)2(PVP)4Cl]Cl, (Os-fendiona-PVP) y un complejo amfifílico [Os(1,10-fenantrolina-5,6-diona)24,4'-(n-C18H37NHCO)2bpi)](PF6)2 (Os-fendiona-surfactante). El polímero Os-fendiona-PVP fue producido vía la derivatización de poli(vinilpiridina) (peso molecular 50000) con [Os(1,10-fenantrolina-5,6-diona)2Cl2]. El estudio electroquímico de este polímero redox adsorbido en electrodos de grafito se realizó por voltametría cíclica a distintas velocidades de barrido para evaluar el número de protones y electrones que participan en la reacción redox, la influencia del pH a su potencial estándar formal, y la constante de la transferencia heterogénea del electrónes kS. Bajo bien definidas condiciones hidrodinámicas se realizaron estudios para encontrar la constante de la interacción con NADH k[NADH]=0. Os-fendiona-surfactante fue producido por la complejacion de [Os(1,10-fenantrolina-5,6-diona)2]Cl2 con el ligando hidrófobo octadodecilamida del acido 2,2'-Bipiridina-4,4'-dicarboxilico. Las monocapas de Langmuir-Blorgett de Os-fendiona-surfactante y las de su análogo [Os(bpi)24,4'-(n-C18H37NHCO)2bpi)](PF6)2 fueron estudiados en un equipo de Langmuir-Blodgett.
Os-fendiona-surfactante fue aplicado a la construcción de biosensores reagentless del glutamato vía la inmovilización de glucosa deshidrogenasa y de NAD+ entre las bicapas en la fase lamelar formada por Os-fendiona-surfactante y el lípido 1,2-dioleoilo-sn-glicero-3-fosfatidilcolina. Dos métodos adicionales para la fabricación de los biosensores reagentless de glutamato y glucosa basados en deshidrogenasas fueron desarrollados. Los electrodos del grafito fueron modificados con Os-fendiona-PVP y utilizados para (a) la inmovilización de deshidrogenasa y de NAD+ en un hidrogel formado por entercruzamiento de poli(vinilpiridina) modificado por grupos amino con el éter diglicidil de poli(etilenglicol); (b) la inmovilización por adsorción de la deshidrogenasa y del ácido algínico modificado por NAD+. Se ha hecho un estudio de los biosensores reagentless para calcular sus constantes de Michaelis, el efecto del pH y de la temperatura en su respuesta y su estabilidad operacional. Además se ha comparado la estabilidad operacional a temperaturas elevadas de biosensores de la configuración (a) usando glutamato, glucosa y glucosa-6-fosfato deshidrogenasas termófilas y mesófilas. Por otro lado se han estudiado métodos nuevos para mejorar le estabilidad durante el almacenamiento de sensores de glutamato. Con este fin, se han preparado electrodos utilizando glutamato deshidrogenasa mesófila y termófila con varios estabilizadores.

Conclusiones

1. El polímero [Os(1,10-fenantrolina-5,6-diona)2(PVP)4Cl]Cl, (Os-fendiona-PVP) para la oxidación de NADH se puede sintetizar por la complejación de [Os(1,10-fenantrolina-5,6-diona)2Cl2] con poli(vinilpiridina). La adsorción física de este polímero sobre los electrodos de grafito desde su solución en etilenglicol resulta en la formación de una monocapa de este polimero redox en la superficie del electrodo.

2. El proceso redox de este mediador es casi-reversible e implica 4 electrones y 4 protones dentro del rango del pH de 3-6.5. El mediador pierde su estabilidad química en valores de pH más altos que 6.5. Tres ramas lineales en el diagrama de E0' frente a pH con diversas pendientes se observan.

3. La constante heterogénea de la velocidad de transferencia de electrones (kS) de Os-fendiona-PVP es del mismo orden de magnitud que la de otros mediadores capaces de oxidar NADH mencionados en la bibliografía (kS= 18±2 s-1) .

4. Os-fendiona-PVP es un electrocatalizador eficiente para la oxidación del NADH. La modificación de los electrodos del grafito con Os-fendiona-PVP conduce a la disminución del sobrepotential para la oxidación electroquímica del NADH desde +0.33 V vs. Ag/AgCl/KClsat para los electrodos no modificados hasta +0.11 V vs. Ag/AgCl/KClsat. La constante cinética para la interacción del polímero redox con el NADH (k1,[NADH]=0 = (1.9±0.2)x103 s-1 M-1) coincide prácticamente con la de Os-fendiona que sugiere que el número de los ligandos de fendiona en los complejos del osmio es proporcional a la corriente de la respuesta al NADH pero no afecta a las constantes cinéticas electroquímicas.
The objective of this work was the development of new configurations of reagentless biosensors based on NAD+ dependent dehydrogenases. These configurations are based on the immobilisation of enzyme, cofactor and the electrochemical catalyst used for its regeneration. In addition to being reagentless these configurations yielded biosensors with improved current density and operational stability compared to the state of the art.
To achieve the objective two new NADH oxidising mediators were synthesised: a water insoluble polymer [Os(1,10-phenanthroline-5,6-dione)2(PVP)4Cl]Cl (Os-phendione-PVP) and an amphiphilic complex [Os(1,10-phenanthroline-5,6-dione)24,4'-(n-C18H37NHCO)2bpy)](PF6)2 (Os-phendione-surfactant). The electrochemical study of Os-phendione-PVP has revealed a rate constant for the heterogeneous electron transfer of the phendione redox couple ks = 252 s-1, and a second order rate constant for NADH oxidation k[NADH]=0=(1.10.1)x103 M-1 s-1. These constants are higher or of the same order of magnitude as those of previously described NADH oxidising mediators. The tensoactive mediators Os-phendione-surfactant and its analogue [Os(bpy)24,4'-(n-C18H37NHCO)2bpy)](PF6)2 (Os-bpy-surfactant) form very stable monolayers at the air-water interface collapsing at the surface pressure 60-65 mN m-1.
The Os-phendione-surfactant was used for the construction of reagentless glutamate biosensors via the immobilisation of dehydrogenase and NAD+ between bilayers in lamellar phase formed by Os-phendione-surfactant and the lipid 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine. The resulting glutamate biosensors demonstrated maximum current density of 3.5 A cm-2 (RSD=25%), apparent Michaelis constant of 47 mM, and operational half life of 0.5 h. In addition graphite electrodes were modified by Os-phendione-PVP and utilised for (a) immobilisation of dehydrogenase and NAD+ in a hydrogel formed by crosslinking of poly(vinylpyridine) carrying amino groups with polyethylene glycol diglycidyl ether and (b) immobilisation of dehydrogenase and an NAD+-alginic acid derivative by adsorption. The configuration (a) yielded glutamate sensors with maximum current density of 8.7 A cm-2 (RSD=5%), apparent Michaelis constant of 9.1 mM, operational half life of 12 h and glucose sensors with maximum current density of 37 A cm-2 (RSD=14%), apparent Michaelis constant of 4.2 mM, the operational half life of 1 h. The glutamate sensors based on the configuration (b) showed maximum current density of 15.8 A/cm2 (RSD=21%), apparent Michaelis constant of 17.6 mM and operational half life of 1.5 h.
Glucose, glucose-6-phosphate, and glutamate biosensors were prepared and characterised. The employment of the thermophilic enzymes helps to dramatically increase the operational stability of biosensors at elevated temperatures higher than 60oC. The shelf life of glutamate electrodes built with the use of thermophilic dehydrogenase was eleven times longer than this of electrodes modified with the mesophilic enzyme. The addition of the copolymer of vinyl-pyrrolidone and dimethylamino ethyl methacrylate termed as Gafquat HS100 to the enzyme also significantly improved shelf life

In the work 9,10-diphenyl anthracene and rubrene were used to decorate an amphiphilic polymer matrix polymethylmethacrylate (PMMA) lm. ITO electrodes equipped with LB lm were used in ECL experiment with tripropylamine co-reactant. Obtained ECL response satis es expectation in looking for a new technology for ECL sensor fabrication.

In this project, the formation and characterisation of CdS nanoparticles embedded within Langmuir-Blodgett (LB) films have been studied systematically. CdS nanoparticles were formed within calix[8]arene (CA) and stearic acid (SA) Cd-salt LB films by exposure to H[2]S gas at room temperature. The AFM images of the treated SA and CA bilayers show CdS clusters with lateral dimensions in the range of 20-30 nm and 10-15 nm, respectively. These particles are pseudo two-dimensional and have a shape of hexagonal platelets which is most likely consequence of their wurtzite structure. Calculations of the cluster thickness Lz yield the value of 2 nm (Photoluminescence excitation-PLE) and 1.9 nm (UV-visible) for CdS clusters in SA matrix and two values of 1.2 nm and 1.6 nm (PLE) and 1.08 nm and 1.42 nm (UV-visible) for CA LB films. The PL spectra demonstrate a large Stokes shift, indicating the formation of "dark excitons" in the platelet CdS clusters. The transformations of the absorption spectra caused by ageing yield a monotonic increase in CdS cluster size with the tendency of saturation. This behaviour can be explained by the model of two dimensional (2D) diffusion. According to this model, CdS molecules in the SA films, initially evenly distributed within each LB bilayer, aggregate and form "large" particles with an average size of 1.9 nm and smaller particles with their size distributed over a wide range down to single molecules. The Surface Plasmon Resonance (SPR) and ellipsometry measurements confirmed that the H2S treatment to the LB films results both in the increase in thickness and refractive index of the LB films due to formation of CdS nanoparticles inside. SPR kinetics measurements during H[2]S treatment show that the formation of CdS clusters happened very fast and almost reached the saturation in about 30 minutes. The I-V characteristics of the sandwich structures of Aluminium/LB films/ Aluminium show exponential behaviour and weak temperature dependence, indicating a combination of electron-tunnelling and hopping mechanism. The formation of CdS clusters in the film matrix did not result in either an enhancement of the electron transfer or an additional polarisation at a small (50 mV) AC signal. Most likely, the observed changes in DC conductivity and AC impedance are caused by the film disorder introduced by CdS nanoparticles.

Nous presentons ici le developpement d'un biocapteur de glucose base sur la technique de langmuir-blodgett. Cette approche consiste en l'elaboration de structures organisees dans lesquelles est immobilisee une enzyme (la glucose oxydase). Une couche monomoleculaire mixte acide gras/enzyme formee a la surface d'une solution aqueuse dans une cuve de langmuir est transferee sur un support solide recouvert d'or. Nous nous sommes attaches a definir les proprietes physico-chimiques des films deposes. Par spectroscopies (ir et uv) nous avons pu correler la quantite d'acide behenique et de glucose oxydase en fonction du nombre de couches deposees. Par microscopie a force atomique et microscopie electronique a balayage, nous avons observe des structures dont les dimensions sont en accord avec les donnees de la litterature. La technique de langmuir-blodgett est adaptee a l'immobilisation d'enzyme et permet d'elaborer des echantillons pouvant servir d'electrode specifique du glucose. Cette electrode permet de detecter le courant d'oxydation de l'eau oxygenee, produit issu de la reaction enzymatique. Par chronoamperometrie, on mesure le courant d'oxydation a potentiel constant; la reponse du biocapteur est rapide (quelques secondes) et le signal obtenu presente une quasi-linearite en fonction de la concentration en glucose. Neanmoins, la faible reproductibilite des resultats nous a conduits a l'emploi d'un mediateur electrochimique qui permet d'abaisser le potentiel de travail

The piezoelectric and pyroelectric properties of oriented films possessing dipole moments are increasingly being used in pressure, acoustic, thermal and optical devices. The performance of these devices in many applications may be enhanced by thin-film technology.The developing Langmuir-Blodgett thin-film deposition technique offers the opportunity to obtain highly oriented and uniform organic-based films in the 10–5000 nm thickness range. Special techniques must be used, however, to assemble these molecules in such a way as to result in polar multilayer films. Several possible deposition techniques are investigated, with one resulting in a polar and pyroelectric film about 50 nm thick.

Various technologies depend on interfacial events that are influenced by various molecular interactions at a solid-liquid interface. The functionality of a surface plays an important role in many applications such as catalysis, sensing, and bio-compatibility, which can benefit from distinctive chemical and physical surface properties. To create tailor-made functional surfaces, surface host-guest assemblies based on Langmuir-Blodgett and self-assembly technique have been employed as a model system as they may offer the potential ability to regenerate surface properties via intercalation of various functional guest molecules. This thesis ranges over the development and characterization of host-guest assemblies and their feasibilities for the regeneration of surface properties via intercalation of functional guests. In our work, 3-dimensional host structures with cavities are constructed on a targeted solid substrate using Langmuir-Blodgett and self-assembly techniques. In particular, by adopting the fundamental concept of host-guest interaction in supramolecular chemistry, we expect that structurally homologous guest molecules where functional groups are anchored can be intercalated into the cavities between hydrophobe arrays at the liquid-solid interface from solution under well-controlled conditions. This approach offers the potential of separating the functional of the monolayer from the inherent structure of the host. The first part of this thesis details two-dimensional host-guest assemblies consisting of guanidinium (G), octadecylsulfonate (S) and various functional alkane guests at the air-aqueous interface and following deposition onto solid substrates via the Langmuir-Blodgett technique. In particular, we evaluated the stability of the host-guest assemblies and the feasibility of exchanging molecular guests under exposure to various organic solvent environments. Analysis of X-ray reflectivity measurements of the thin films showed that good stability of the host-guest assembly could not be achieved due to weak interactions between the host monoalyer and the solid surface. In addition, no evidence of intercalation of guest molecules into guest-free host-cavities was observed. The second part of this thesis discusses the effective methodologies to prepare low-density self-assembled monolayers (LDSAMs) with cavities on silicon substrates. We employed a step-wise reaction based on hydrolytic or silane chemistry: integral spacer molecules such as anthracene-derivatives were anchored to the Si substrate and then long alkane chains were appended to the spacer molecules. The results showed that LDSAMs using an anthryl spacer are attached at the SAM/Si interface via a Si-O-C linkage, and the films do not exhibit a densely packed monolayer quality as would be expected for a non-sterically hindered alkyltrichlorosilane on Si. Thus, the resulting LDSAMs (with cavities) may be capable of accommodating other guest molecules with hydrocarbon chains through intercalation in order to form host-guest assemblies. The third part of this thesis demonstrates the ability of LDSAMs to produce functional surfaces via the intercalation of various functional guest molecules. Self-assembled monolayers of (10-octadecyl)-9-anthracenethiol (host-SAMs) on Au substrates were prepared. Quartz crystal microbalance with dissipation (QCM-D) measurements was used to demonstrate the capacity of LDSAMs to confine guest molecules in the cavities and to probe the structural changes of the host-guest assembly during guest intercalation from ethanol solution. X-ray photoelectron spectroscopy (XPS) measurements were then used to probe host-guest monolayers formed by immersing the host monolayer in solutions in a variety of other solvents. A combined study of QCM-D and XPS showed that guest molecules were intercalated into host-cavities. The reversibility of the intercalation process allows a guest already situated in a host-cavity to be replaced with second guest under well-regulated solvent conditions.
Ph. D.

Le present travail concerne la realisation d'edifices supramoleculaires organises en film langmuir-blodgett (lb). Les molecules utilisees appartiennent a la famille des porphyrines. Elles sont tetrafonctionnalisees et peuvent etre transferees suivant une methode semi-amphiphile. La premiere voie abordee concerne la realisation de divers edifices moleculaires par la methode amphiphile. Elle est basee sur une reconnaissance moleculaire a l'interface air-eau, faisant appel aux forces de coulomb, entre deux macrocycles differemment tetrafonctionnalises. Le simple melange equimolaire d'un macrocycle a caractere basique conduit a la formation d'heterodimeres en film b. La caracterisation precise des heterodimeres porphyrine-porphyrine et porphyrine-phtalocyanine a ete mise en evidence par diverses techniques convergentes (isothermes de compression, spectroscopie ir, rpe et uv-visible). L'utilisation de macrocycles axialement encombres (ferriporphyrines dimerisees par un lien oxo, porphyrines de cobalt axialement complexees par un derive amphiphile de l'imidazole) permet l'elaboration, suivant le meme principe, d'un reseau ionique en film lb. La seconde voie abordee utilise une methode semi-amphiphile et concerne l'etablissement de liaisons covalentes entre macrocycles identiques et tetrafonctionnalises. La formation d'un polymere bidimensionnel par une reaction de polycondensation a l'interieur des films lb ou a l'interface air-eau est mise en evidence. Les macrocycles porphyriniques utilises dans cette etude sont substitues par quatre fonctions alcynes vraies. Ils sont relies les uns-aux-autres par couplage oxydant des triples liaisons. Le polymere obtenu est hautement insoluble et peut former des membranes autosustentees

This article describes three-dimensional open architectures with free-standing grid-like nanostructure arrays as photocatalytic electrodes for a new type of dye-sensitized solar cell. It introduces a novel technique for fabricating a series of semiconducting oxides with grid-like nanostructures replicated from the biotemplates. These semiconducting oxides, including n-type titanium dioxide or p-type nickel oxide nanogrids, were sensitized with the dye molecules, then assembled into 3D stacked-grid arrays on a flexible substrate by means of the Langmuir–Blodgett method or the ink-jet printing technique for the photocatalytic electrodes. The article first considers the fabrication of photoelectrodes with 2D grid-like nanostructures by means of the biotemplating approach before discussing the assembly and photophysicsof grid-like nanostructures into 3D open architectures for the photocatalytic electrodes.

There has been an increasing interest in polydiacetylenes as nonlinear waveguide materials. Although a number of crystal growth techniques can be used to process the polydiacetylene polymers into a planar waveguide form (e.g., the Langmuir-Blodgett multilayer deposition technique and shear growth technique1), there is a lack of fabrication methods to create optical components in these guides. We report the successful fabrication of optical grating structures by direct electron-beam writing on the polymer. The technique can also be used for microfabrication of other integrated optics components, e.g., channel waveguides.

Formation and characterization of organic thin film assemblies intended for use in biomolecular devices, such as biosensors, is currently a very active area of research. We have been investigating techniques for creating macroscopically ordered protein films formed by covalent bonding between a unique site on the protein and an appropriately derivatized substrate surface. Assemblies consisting of heme proteins immobilized on substrates coated with self-assembled monolayers and Langmuir-Blodgett are being examined. Macroscopic film order is probed using a combination of total internal reflectance fluorescence and planar integrated optical waveguide-attenuated total reflection spectroscopies, from which the orientation distribution of heme tilt angles in the protein film is determined.

Abstract Nanofluid flooding is an emerging enhanced oil recovery (EOR) technique whereby injection fluids containing nanoparticles or nanocomposites are utilized for the oil displacement or injectivity improvement in oil reservoirs. However, current nanofluids with conventional nanoparticles have relatively low efficiency for EOR at simulated reservoir conditions, especially at low concentrations of nanoparticles. This research reported a new cost-effective method for scale-up synthesis of Janus graphene nanosheets and demonstrated a new type of nanomaterials, Janus nanofluids, as highly effective alternative nano-agents for EOR applications. A lyotropic liquid crystal phase as a novel "interfacial nano-reactor" system has been developed for fabricating Janus nanomaterials at nano-scaled liquid-liquid interfaces. Compared to interfacial reaction in a conventional bi-phase system, the new "interfacial nano-reactors" could tremendously enlarge the interfacial area by more than million times for chemical reactions at the interface, and thus allow production of Janus nanomaterials in mass quantity economically for industrial applications. Janus graphene nanosheets synthesized via this method have been characterized and confirmed by multiple techniques including scanning electron microscopy (SEM), Langmuir-Blodgett (LB) isotherm, contact angle, and interfacial tension (IFT) measurements. Interfacial tension measurements have shown that the Janus graphene nanosheets could significantly lower the IFTs between brine and crude oil at simulated reservoir conditions. With low concentration of Janus graphene nanosheets in nanofluid formula, microfluidic flooding experiments have been performed to evaluate the efficiency of the nanofluids for oil displacement in carbonate reservoirs. The results have demonstrated improved efficiency of oil recovery by the novel Janus graphene nanofluids at ultra-low concentration (0.01 wt%).

Lipid oxidation is a common phenomenon in emulsions that can be controlled by different techniques. Since proteins are beneficial emulsifiers but with low antioxidant ability, they are used in combination with an antioxidant compound such as polyphenols. Strong interaction between the protein and the polyphenol makes this combination more effective. In this study, soluble fraction of faba protein concentrate (FPC) was conjugated with tannic acid via the free radical grafting, and the structural and functional characteristics of the conjugates were determined in comparison with the mixture of the protein and tannic acid, and the pure protein. After dialysis, the amount of protein and polyphenol from the conjugated materials was significantly reduced, indicating that the unreacted peptides and polyphenol left the solutions. The reduction of the free amino and thiol groups in the protein specified the establishment of a strong interaction between the protein and tannic acid remaining in the solution. Moreover, the conjugate showed high ABTS, hydroxyl radical scavenging activity and ferric reducing power than the protein alone. As the purpose of making the conjugate was to be used as a multilayer film around the oil droplets, the film formation ability of the conjugates was investigated using Langmuir-Blodgett technique. Depending on the size of the trough and the nature of the compounds being used, the concentration and surface pressure required to form a strong film will vary. All samples showed an extended gas state of the film that changed abruptly and directly into a solid state below a critical surface area. Such LB film of the protein-tannic acid conjugate will be used to test its free radical scavenging ability so that its ability to prevent lipid oxidation in emulsions can be predicted.

The Brillouin spectra of thin films of cadmium arachidate have been measured. These films are multiple layers of ordered monolayers (26.8 Å thick) of the cadmium salt of arachidic acid deposited one monolayer at a time onto aluminum and glass substrates by the Langmuir-Blodgett technique.1 The elastic properties of these films can be determined from these Brillouin scattering spectra. Light from a single-mode argon-ion laser at 0.5145 m was scattered by multiple, high frequency, surface acoustic waves guided by LB films of thickness 100, 35, and 11 monolayers. The scattered light was collected and spectrum analyzed with a 9-pass tandem Fabry-Perot interferometer to obtain the velocities of the surface acoustic waves. The use of the tandem interferometer provided the high contrast needed to detect the weak Brillouin signals in the presence of the intense elastically scattered light. The Brillouin spectra are now being analyzed to determine the elastic properties of the Langmuir-Blodgett films.

Processing polymers near room temperature to produce all-polymeric nonlinear optical films has important advantages [1]. For example, the Langmuir-Blodgett-Kuhn (LBK) technique offers control over final film thickness to within one monolayer. Also, materials may be precisely located within the film to control properties for purposes such as phase matching of the fundamental and second harmonic waveguide modes [2].