Rozprawy doktorskie na temat „Nanoparticle- polymer Blend”

In this thesis, atomic force microscopy (AFM), transmission electron microscopy (TEM) and optical microscopy techniques were used to investigate systematically the self-assembled nanostructure behaviour of two different types of spin-cast polymer thin films: poly(isoprene-b-ethylene oxide), PI-b-PEO diblock copolymers and [poly(9,9-dioctylfluorene-co-benzothiadiazole)]:poly[9,9- dioctyfluorene-co-N-(4-butylphenyl)-diphenylamine], F8BT:TFB conjugated polymer blends. In the particular case of the polymer blend thin films, the morphology of their composites with cadmium selenide (CdSe) quantum dot (QD) nanoparticles was also investigated. For the diblock copolymer thin films, the behaviour of the nanostructures formed and the wetting behaviour on mica, varying the volume fraction of the PEO block (fPEO) and the average film thickness was explored. For the polymer blend films, the effect of the F8BT/TFB blend ratio (per weight), spin-coating parameters and solution concentration on the phase-separated nanodomains was investigated. The influence of the quantum dots on the phase separation when these were embedded in the F8BT:TFB thin films was also examined. It was found that in the case of PI-b-PEO copolymer thin films, robust nanostructures, which remained unchanged after heating/annealing and/or ageing, were obtained immediately after spin coating on hydrophilic mica substrates from aqueous solutions. The competition and coupling of the PEO crystallisation and the phase separation between the PEO and PI blocks determined the ultimate morphology of the thin films. Due to the great biocompatible properties of the PEO block (protein resistance), robust PEO-based nanostructures find important applications in the development of micro/nano patterns for biological and biomedical applications. It was also found that sub-micrometre length-scale phase-separated domains were formed in F8BT:TFB spin cast thin films. The nanophase-separated domains of F8BT-rich and TFB-rich areas were close to one order of magnitude smaller (in the lateral direction) than those reported in the literature. When the quantum dot nanoparticles were added to the blend thin films, it was found that the QDs prefer to lie in the F8BT areas alone. Furthermore, adding quantum dots to the system, purer F8BT and TFB nano-phase separated domains were obtained. Conjugated polymer blend thin films are excellent candidates for alternatives to the inorganic semiconductor materials for use in applications such as light emitting diodes and photovoltaic cells, mainly due to the ease of processing, low-cost fabrication and mechanical flexibility. The rather limited optoelectronic efficiency of the organic thin films can be significantly improved by adding inorganic semiconducting nanoparticles.

A variety of factors make semiconducting polymers a fascinating alternative for both device development and new areas of fundamental research. Among these are solution processability, low cost, flexibility, and the strong dependence of conduction on the presence of charge compensating ions. With the lack of a complete fundamental understanding of the materials, and the growing demand for novel solutions to semiconductor device design, research in the field can take many, often multifaceted, routes. Due to ion-mediated conduction and versatility of fabrication, conducting polymers can provide a route to the study of neural signaling. In the first of three research topics presented, junctions of polypyrrole electropolymerized on microelectrode arrays are demonstrated. Individual junctions, when synthesized in a three-electrode configuration, exhibit current switching behavior analogous to neural weighting. Junctions copolymerized with thiophene exhibit current rectification and the nonlinear current-voltage behavior requisite for complex neural systems. Applications to larger networks, and eventual use in analysis of signaling, are discussed. In the second research topic, nonvolatile resistive memory consisting of gold nanoparticles embedded in a polymer film is examined using admittance spectroscopy. The frequency dependence of the devices indicates space-charge-limited transport in the high-conductivity "on" state, and similar transport in the lower-conductivity "off" state. Furthermore, a larger dc capacitance of the on state indicates that a greater amount of filling of midgap trap levels introduced by the nanoparticles increases conductivity, leading to the memory effect. Implications on the question as to whether or not the on state is the result of percolation pathways is discussed. The third and final research topic is a presentation of enhanced efficiency of polymer light-emitting electrochemical cells (LECs) by means of forming a doping self-assembled monolayer (SAM) at the cathode-polymer interface. The addition of the SAM causes a twofold increase in quantum efficiency. Photovoltaic analysis indicates that the SAM increases both open-circuit voltage and short-circuit current. Current versus voltage data are presented which indicate that the SAM does not simply introduce an interfacial dipole layer, but rather provides a fixed doping region, and thus a more stable p-i-n structure.

The incorporation of nanoparticles into polydimethylsiloxane polymers either in the form of physical blending or chemical crosslinking has long been studied as it can improve the properties of composite materials. Interactions between the host polymer and the filler particle, filler concentration and conformation of each component are the key factors that influence these properties. Understanding the effect of these factors is of fundamental importance in all practical applications of composite materials. This thesis describes the study of a range of PDMS composites by using a variety of experimental techniques. The main techniques used were spin-spin (T2) relaxation and diffusion NMR spectroscopy, rheology and small-angle neutron scattering (SANS). The molecular mobility of a series of PDMS melts has been studied for both unentangled and entangled molecular weight regimes separated by the critical entanglement molecular weight (Mc) of the polymer. The experimental results revealed the effect of molecular weight and polydispersity of the polymers on their segmental mobility. The dramatic decrease of chain mobility observed at molecular weight above Mc was attributed to the effect of chain entanglements. The effect of nano-sized trimethylsilylated polysilicate resin (R2) on the chain mobility of PDMS in the form of physically blended was also examined. Two different concentrations (17 and 30 vol%) of R2 were incorporated into a wide range molecular weight of PDMS melts. Below Mc, the R2 particle was found to reinforce the PDMS at all particle loadings, whereas a plasticisation effect was observed for high molecular weight PDMS above Mc. This was attributed to a reduction of the degree of the entanglements when polymer chains adsorbed on particles. Chemically bonded composites of PDMS and polyhedral oligomeric silsesquioxane (POSS) were successfully synthesised via hydrosilylation. The length of the PDMS central block was found to affect both the size and the molecular mobility of the triblock polymers. The weight fraction of POSS and substituted groups on POSS were also seen to affect the molecular mobility. Finally, a series ofrandom crosslink polymer films ofPDMS and phenylsilsesquioxane (TPh) was studied by AFM, TEM, SAXS and SANS techniques to investigate the factors influencing the optical clarity of the samples. The degree of swelling and the segmental mobility of the sample films swollen in good and poor solvents were also studied.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico
Researches based on the mixture of synthetic with natural polymers have intensified in recent times. The idea of using polysaccharides nano or micro level with polyolefins is the new of this work. Three compositions of polypropylene and commercial citrus pectin was prepared in proportions of 1, 3 and 5%. A coupling agent was used, the graphitized polypropylene with maleic anhydride to advance interaction between natural and synthetic particles. The obtaining of particles in nanometric scale pectin was made from colloid mill grinding. Some particles arrived near 100nm and majority the particles reached scales around 300nm. The structural analysis by X-ray diffraction and Fourier transform infrared spectroscopy demonstrated an interaction between maleic anhydride and pectin despite clusters of hydrophilic particles that were seen by scanning electron microscopy In the X-ray diffraction, the presence of crystals of sugars were detected. These crystals may have caramelized because processing temperatures are close to 200 C and were detected by colorimetry. Based on the mechanical data, it is possible realize that pectin had a plasticizing effect on the synthetic polymer, corroborating the rheological data and thermogravimetric tests, considering that the addition of higher amount of particles produces more thermal stability of the synthetic polymer.
Os estudos baseados na mistura de polímeros sintéticos com polímeros naturais têm se intensificado nos últimos tempos. A ideia de usar polissacarídeos em nano ou micro escala junto com poliolefinas é a novidade deste trabalho. Foram preparadas três composições de polipropileno e pectina cítrica comercial em proporções de 1, 3 e 5%. Foi utilizado um agente compatibilizante, o polipropileno grafitizado com anidrido maleico para favorecer a interação entre partículas naturais e as sintéticas. A obtenção de partículas em escala nanométricas de pectina foi feita partir de moagem em moinho coloidal e chegou próxima da faixa de 100nm, pois as partículas atingiram escalas em torno de 300nm. A análise estrutural feita por infravermelho e difração de raios-X demonstrou que houve interação entre o anidrido maleico e a pectina apesar dos aglomerados de partículas hidrofílicas que foram percebidos através da microscopia eletrônica de varredura. Também a partir dos dados de difração de raios-X, a presença de cristais de açúcares foram detectados, que por colorimetria podem ter se caralemizado devido temperaturas de processamento estarem próximas de 200ºC. A partir dos dados mecânicos, é possível perceber que a pectina teve um efeito plastificante no polímero sintético, corroborando com dados reológicos e com os testes termogravimétricos, considerando que quanto maior adição de partículas, maior a estabilidade térmica do polímero sintético.

Composites based on binary polymer blends of polystyrene (PS)/poly(ethylene-co-vinyl alcohol) (EVOH) (70/30 wt%) containing natural Montmorillonite, Na-MMTs (Nanomer PGW or Cloisite Na+) and organically modified Montmorillonite clays, OMMTs (Nanomer I.30T, Cloisite 30B or Cloisite 10A) were prepared via melt compounding. The interactions between the polymers and clays were studied using flow micro-calorimetry (FMC). Data obtained from FMC indicated that the probe molecule mimicking EVOH (butan-2-ol) interacted with the MMTs and OMMTs much more strongly than PS. Scanning electron microscopy (SEM) revealed that composites based on binary blends had dispersed/continuous morphologies, in which EVOH was dispersed in a PS matrix. The size of the EVOH droplets in the PS matrix increased with increasing clay loading. Transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD) were used to determine the extent of dispersion and location of clay in the PS/EVOH/clay composites. These techniques confirmed the formation of intercalated clay structures. As predicted by FMC, the clay platelets were selectively located in the EVOH phase, independent of the blending sequence and the type of organic modifier in the OMMT. Composites containing OMMTs showed better dispersion of platelets within the EVOH phase than those containing Na-MMTs. Differential scanning calorimetry (DSC); showed the crystallisation behaviour of EVOH to depend on the clay loading and the nature of the organic modifier in the OMMT. Nanomer PGW, Cloisite Na+ and Cloisite 30B acted as weak nucleating agents. In contrast, Nanomer I.30T and Cloisite 10A significantly hindered the crystallisation of EVOH in the blends due to the restriction of chain segment mobility. Dynamic mechanical thermal analysis (DMTA) confirmed that the presence of clay increases the storage modulus of the composites compared to an unfilled blend. In addition, the improvement in storage modulus reflected the dispersion state of the different clays and their interaction with the polymers of the blend. Ternary-blend based composites were formed by adding poly(styrene-co-acrylonitrile) (SAN) to the composites based on binary PS/EVOH blends. This resulted in a finer dispersion of the EVOH phase and the development of a core-shell morphology, in which SAN encapsulated and formed shells around EVOH droplets. In contrast to binary blend composites, the clay platelets were found at the interface between SAN and EVOH in the ternary blends.

Thin film bilayers and blends composed of polymers and nanoparticles are increasingly important for technological applications that range from space survivable coatings to novel drug delivery systems. Dewetting or spontaneous hole formation in amorphous polymer films and phase separation in multicomponent polymer films can hinder the stability of these systems at elevated temperatures. Hence, fundamental understanding of dewetting and phase separation in polymer/nanoparticle bilayer and blend films is crucial for controlling transport and thermomechanical properties and surface morphologies of these systems. This dissertation provides studies on morphological evolution driven by phase separation and/or dewetting in model polymer/nanoparticle thin film bilayers and blends at elevated temperatures. Morphological evolution in dewetting bilayers of poly(t-butyl acrylate) (PtBA) or polystyrene (PS) and a polyhedral oligomeric silsesquioxane (POSS), trisilanolphenyl-POSS (TPP) is explored at elevated temperatures. The results demonstrate unique dewetting morphologies in both PtBA/TPP and PS/TPP bilayers that are significantly different from those typically observed in dewetting polymer/polymer bilayers. Upon annealing the PtBA/TPP bilayers at 95°C, a two-step dewetting process is observed. PtBA immediately diffuses into the upper TPP layer leading to hole formation and subsequently the holes merge to form interconnected rim structures in the upper TPP layer. Dewetting of both the TPP and PtBA layers at longer annealing times leads to the evolution of scattered holes containing TPP-rich, fractal aggregates. The fractal dimensions of the TPP-rich, fractal aggregates are ~2.2 suggesting fractal pattern formation via cluster-cluster aggregation. Dewetting in PS/TPP bilayers also proceeds via a two-step process; however, the observed dewetting morphologies are dramatically different from those observed in PtBA/TPP bilayers. Cracks immediately form in the upper TPP layer during annealing of PS/TPP bilayers at 200°C. With increasing annealing times, the cracks in the TPP layer act as nucleation sites for dewetting and aggregation of the TPP layer and subsequent dewetting of the underlying PS layer. Complete dewetting of both the TPP and PS layers results in the formation of TPP encapsulated PS droplets. Phase separation in PtBA/TPP thin film blends is investigated as functions of annealing temperature and time. The PtBA/TPP thin film blend system exhibits an upper critical solution temperature (LCST) phase diagram with a critical composition and temperature of 60 wt% PtBA and ~70°C, respectively. Spinodal decomposition (SD) is observed for 60 wt% PtBA blend films and off-critical SD is seen for 58 and 62 wt% PtBA blend films. The temporal evolution of SD in 60 wt% PtBA blend films is also explored. Power law scaling for the characteristic wavevector with time (q ~ t^n with n = -1/4 to -1/3) during the early stages of phase separation yields to domain pinning at the later stages for films annealed at 75, 85, and 95°C. In contrast, domain growth is instantly pinned for films annealed at 105°C. Our work provides an important first step towards understanding how nanoparticles affect polymer thin film stability and this knowledge may be utilized to fabricate surfaces with tunable morphologies via controlled dewetting and/or phase separation.
Ph. D.

Les matériaux polymères appelés communément "Plastiques" sont très présents dans notre vie quotidienne. Leurs propriétés intrinsèques nécessitent souvent d'être améliorées pour répondre aux normes et autres cahiers des charges régissant leur utilisation. Ainsi, deux grandes stratégies sont aujourd'hui utilisées. La première consiste à incorporer des renforts (exemple de la fibre de verre) pour augmenter certaines propriétés mécaniques. La seconde consiste à mélanger deux polymères distincts possédant chacun des caractéristiques spécifiques pour obtenir un matériau combinant les propriétés des deux polymères de base, Il s'agit alors de "compatibilisation". L'objectif de ce travail de thèse est de fabriquer des nanoparticules capables de combiner les notions de renfort et de compatibilisation précédemment évoquées. Pour ce faire, une stratégie de synthèse en miniémulsion reposant sur un phénomène de séparation interne de phase a permis de produire des nanoparticules hybrides asymétriques. Ces dernières sont formées d'un cœur de silice d'environ 50 nanomètres de diamètre dont l'un des hémisphères seulement a été greffé par des chaînes de polystyrène (PS) formant un nodule d'environ 80 nanomètres de diamètre. Ces nanoparticules asymétriques silice/PS ont ensuite été introduites dans un mélange de polystyrène et de polyamide-6 (PS/PA6). La migration des nanoparticules silice/PS à l'interface de ce mélange a été vérifiée par microscopie électronique à balayage (MEB). Les phénomènes mis en jeu dans cette migration ont été étudiés de façon approfondie via une étude modèle. Des nanocomposites PS/PA6 comportant différents taux de charges de nanoparticules asymétriques ont été réalisés pour vérifier l'effet compatibilisant de ces dernières. Ainsi, une nette diminution des tailles des phases dispersées de PA6 a pu être mise en évidence par MEB et par granulométrie à diffraction laser correspondant à un effet émulsifiant. Enfin, des essais rhéologiques à l'état fondu qui finalisent cette étude et ont permis de montrer via l'utilisation d'un modèle de Palierne ajusté, une diminution de la tension interfaciale apparente du mélange liée au taux de charges en nanoparticules silice/PS
Polymers materials usually named « plastics » are widely present in our daily life. Their intrinsic properties often need to be improved in order to respect regulations, standards and others specifications governing their commercial use. Thus, two main strategies are used. The first one consists in incorporating solid fillers to improve some mechanical properties. The second one is based on the mixing of two polymers with specific characteristics to obtain a new material combining the properties of the two initial polymers used. The main goal of this work is to synthesize nanoparticles able to combine the both strategies presented before. To do this, a protocol of synthesis by miniemulsion based on an intern phase separation process was employed and hybrid asymmetric nanoparticles were obtained. These hybrid asymmetric nanoparticles correspond to a silica core (around 50 nanometers diameter) with only one hemisphere grafted by polystyrene (PS) chains resulting in a PS nodule (around 80 nanometers diameter). Then, these asymmetric silica/PS nanoparticles were incorporated into a polystyrene/polyamide-6 (PS/PA6) blend and their migration to the matrix/nodule interface was highlighted by scanning electron microscope (SEM). Experimental and theoretical investigations were focus on the phenomena involved in this migration. To evaluate the compatibilizing effect of silica/PS nanoparticles, several PS/PA6 nanocomposites with various contents of nanoparticles were prepared. A significant decrease of PA6 nodules size as function of nanoparticles concentration was observed by SEM and diffraction particle size analyzer which prove an emulsifying effect for silica/PS nanoparticles. Finally, the rheological tests at the melted state combined with an adjusted Palierne model method, show a decrease of the apparent interfacial tension of the blend as function of the silica/PS nanoparticles content

In this thesis we developed three copper-containing systems. Copper shows intriguing abilities in photocatalysis, however, one of the major limitations of many copper complexes is that photochemical properties might be quenched in solution caused by π-interactions between solvent and solute, due to Jahn-Teller distortion in the excited state. As such, we herein seek to synthesise copper heteroleptic complexes that will subsequently be nanoprecipitated with a polymer. This will allow the polymer to encase the complex and prevent the solvent-induced quenching. Subsequently, the preparation of blends of polymer with the aforementioned copper complexes, at different weight ratios is sought. The preparation of the blend is particularly interesting as the catalytic properties are anticipated to be inferior on account of the low surface area. However, owing to the polymer matrix better, mechanical properties are anticipated. The blends can combine the mechanical properties of the polymer and the luminescence of the complex, with the advantage that the polymer matrix can also prevent quenching from oxygen. As final task, we developed a copper-containing monomer. The synthesis of a monomer that contains copper and can be excited under ultraviolet (UV) light is particularly interesting.

For over a century, Langmuir films have served as excellent two-dimensional model systems for studying the conformation and ordering of amphiphilic molecules at the air/water (A/W) interface. With the equipment of Wilhelmy plate technique, Brewster angle microscopy (BAM), and surface light scattering (SLS), the interfacial phase and rheological behavior of Langmuir films can be investigated. In this dissertation, these techniques are employed to examine Langmuir films of polyhedral oligomeric silsesquioxane (POSS), polymer blends, and magnetic nanoparticles (MNPs). In a first time, SLS is employed to study POSS molecules. The interfacial rheological properties of trisilanolisobutyl-POSS (TiBuP) indicate that TiBuP forms a viscoelastic Langmuir film that is almost perfectly elastic in the monolayer state with a maximum dynamic dilational elasticity of around 50 mNâ m-1 prior to film collapse. This result suggests that TiBuP can serve as model nanofiller with polymers. As an interesting next step, blends of TiBuP and polydimethylsiloxane (PDMS) with different compositions are examined via surface pressure (surface pressureâ surface area occupied per molecule (A) isotherms and SLS. The results show that TiBuP, with its attendant water, serves as a plasticizer and lowers the dilational modulus of the films at low surface pressure. As surface pressure increases, composition dependent behavior occurs. Around the collapse pressure of PDMS, the TiBuP component is able to form networks at the A/W interface as PDMS collapse into the upper layer. Blends of non-amphiphilic octaisobutyl-POSS (OiBuP) and PDMS are also studied as an interesting comparison to TiBuP/PDMS blends. In these blends, OiBuP serves as a filler and reinforces the blends prior to the collapse of PDMS by forming â bridgeâ structure on top of PDMS monolayer. However, OiBuP is non-amphiphilic and fails to anchor PDMS chains to the A/W interface. Hence, OiBuP/PDMS blends exhibit negligible dilational viscoelasticity after the collapse of PDMS. Furthermore, the phase behavior of PDMS blended with a trisilanol-POSS derivative containing different substituents, trisilanolcyclopentyl-POSS (TCpP), is also investigated via the Wilhelmy plate technique and BAM. These TCpP/PDMS blends exhibit dramatically different phase behavior and morphological features from previously studied POSS/PDMS blends, showing that the organic substituents on trisilanol-POSS have considerable impact on the phase behavior of POSS/PDMS blends. The interfacial rheological behavior of tricarboxylic acid terminated PDMS (PDMS-Stabilizer) and PDMS stabilized MNPs are investigated and compared with â regularâ PDMS containing non-polar end groups. The tricarboxylic acid end group of the PDMS-Stabilizer leads to a different collapse mechanism. The PDMS stabilized MNPs exhibit viscoelastic behavior that is similar to PDMS showing all the tricarboxylic acid end groups are bound to the magnetite cores. Studying the interfacial behavior of different Langmuir films at the A/W interface provides us insight into the impact of molecule-molecule and molecule-subphase interactions on film morphology and rheology. These results are able to serve as important guides for designing surface films with preferred morphological and mechanical properties.
Ph. D.

L'objectif est 1/ de contribuer à une meilleure caractérisation de l'interphase, de ses propriétés et de son influence sur la structure et le comportement rhéologique de mélanges polyéthylène/polyamide comptabilisés de manière organique ou par ajout de nano-argiles, 2/ de comparer les propriétés et les effets d'interphase des systèmes comptabilisés de manière organique à ceux des systèmes chargés de nanoparticules argileuses. Ces travaux ont été menés sur quatre couples de mélanges polyéthylène/polyamide, de rapport de viscosités différents, comptabilisés soit par un polyéthylène greffé anhydride maléique, soit chargés de nanoparticules d'argile. L'étude des propriétés d'interphase révèle que, pour les deux types de mélanges ternaires étudiés, les caractéristiques à l'échelle moléculaire du polyéthylène et du polyamide influencent significativement les propriétés viscoélastiques de l'interphase. Un des quatre couples polyéthylène/polyamide conduit à des systèmes ternaires chargés de nanoparticules d'argiles ou comptabilisés par voie chimique présentant des morphologies nodulaires identiques et un effet émulsifiant, autorisant la comparaison des deux types d'interphase. Les résultats montrent que l'interphase argile/polyamide intercalé a des propriétés dissipatives plus marquées que l'interphase obtenue à partir d'une comptabilisation organique. La modélisation des propriétés viscoélastiques des deux types de systèmes ternaires par le modèle de Palierne suggère l'existence de mécanismes de relaxation complexes au sein de ces interphases, impliquant des interactions spécifiques entre les trois composants de ces mélanges
The objective is 1/ to contribute to a better characterization of the interphase, of its properties and of its influence on the structure and rheological behaviour of polyethylene/polyamide blends compatibilized either chemically or physically by addition of nanoclays, 2/ to compare the properties and interphase effects of systems chemically compatibilized with those of systems filled with clay nanoparticles. These works have been performed on four different polyethylene-polyamyde blends, with various viscosity ratio, compatibilized either with a maleic anhydride grafted polyethylene or filled with clay nanoparticules. The study of interphase properties shows that, for the two types of ternary blends studied, the molecular characteristics of polyethylene and polyamide significantly influence the interphase viscoelastic properties. One of the four polyethylene/polyamide couples leads to ternary systems, filled with claynanoparticles or chemically compatibilized, which ewhibit both identical nodular morphology and emulsifying effect, allowing the comparison of the two types of interphase. The results show that the clay/intercalated polyamide interphase has dissipative properties which are more marked than the interphase obtained from a chemical compatibilization. The modeling of the viscoelastic properties of both types of ternary systems, using the Palierne model, suggests the existence of complex relaxation mechanisms within these interphases, involving specific interactions between the three componenets of these blends

博士
國立臺灣大學
化學工程學研究所
105
Thin films of polymer-polymer blend or polymer-nanoparticle blend (PNB) have been utilized in many applications for last few decades. However, the uniformity control of both materials is still difficult to achieve. In this study, we adopt dissipative particle dynamics to investigate the factors affecting the phase behaviors of such materials. By understanding the mechanisms of surface segregation and bulk aggregation, it is achievable to control the distribution of target species (polymers or nanoparticles). This thesis is organized into three major parts. First, surface segregation of binary athermal polymer blends confined in a nanoscale thin film has been investigated. The polymer blend includes linear/linear, star/linear, bottlebrush/linear, and rod-like/linear polymer systems. The segregation is driven by purely entropic effects and two mechanisms are found. For linear/linear and star/linear polymer blends, the polymers of smaller size are preferentially segregated to the boundary because their excluded volumes are smaller than those of matrix polymers. For bottlebrush/linear and rod-like/linear polymer blends, the polymers with larger persistent length are preferentially segregated to the boundary because they favor to stay in the depletion zone by the alignment with the wall. These consequences are of great importance to the control of the homogeneity as well as the surface properties of polymer blend thin film. Secondly, surface segregation and bulk aggregation in a thin film of athermal PNB have been explored. The thin film is confined between two athermal walls and the shape of the nanoparticles is spherical or cubic. Both phases are driven purely by the entropic effect, i.e. depletion attraction, which depends significantly on the nanoparticle size. At a specified particle volume fraction, surface segregation dominates for small nanoparticles but bulk aggregation emerges for large ones. The crossover between the two phases is a result of the competition between particle-wall and particle-particle depletion attractions. The dominance of the former leads to surface segregation while the control of the latter results in bulk aggregation. Since nanocubes possess more contact areas and thus exhibit stronger depletion attractions than nanospheres do, the crossover from surface segregation to bulk aggregation occurs at smaller particle size for nanocubes. Last, the phase behavior of an athermal film of PNB driven by depletion attraction is studied for nanospheres and nanocubes. Surface segregation is observed at low nanoparticle concentrations while bulk aggregation is seen at high concentrations. Surface excess and the aggregation number can be controlled by tuning the nanoparticle concentration. As surface-roughened or polymer-grafted nanoparticles are used, uniform PNBs are acquired due to the lack of depletion. Thus, the addition of surface-roughened nanoparticles into polymer-smooth nanoparticle blend can be employed to tune the phase characteristics. It is found that bulk aggregation is suppressed for both polymer-nanosphere and polymer-nanocube blends. However, surface segregation is impeded for polymer-nanosphere blend but enhanced for polymer-nanocube blend owing to the distinct influence of the nanoparticle shape on depletion.

Introducing nanoscale fillers into polymer matrices can serve as a means to compatibilize polymer blends and represents a clever way to manipulate their morphology at the micro-scale. Such a novel “compatibilization” strategy represents a viable route for optimizing the performance of polymer systems, which are ubiquitous in the modern society. The effects of nanoparticles on the micrometer-sized arrangement of the polymer phases, however, are difficult to predict, and most of the recent literature on this topic lack in terms of generality. Many issues remain unclear, and even well-established phenomena are actually far from being fully understood. Is the origin of the uneven distribution of the filler in a multiphase host matrix merely dictated by thermodynamic arguments? Is it possible to drive the systems towards desired non-equilibrium configurations? How the filler affects the blend microstructure? And how the fluids in turn affect the nanoparticle assembly? This dissertation addresses these matters from both a theoretical and a practical point of view, shedding light on the sequence of events which determine the final morphology of nanoparticle-containing polymer blends through a combination of morphological and rheological analyses. In the first experimental part of this study, the physical mechanisms that govern the melt-state microstructural evolutions of polymer blends in the presence of nanoparticles are elucidated through a combination of several analyses and measurements. Using ternary blends of polystyrene (PS), poly(methyl methacrylate) (PMMA), and clay nanoplatelets we prove the generality of the mechanism of morphology stabilization by interfacial crowding of the nanoparticles, which keeps working in spite of the high viscosity of the liquid phases and the plate-like shape of the nanoparticles. The effect of the co-continuous morphology of the host matrix is highlighted through a comparative analysis with systems based on the same polymers and nanoparticles, but in which the matrix is either a single polymer or a drop-in-matrix blend. This allows us to emphasize the role of the multiphase nature of the host medium in driving the nanoparticle assembly. In particular, the elasticity and structure of the three-dimensional filler network which forms above Φc were studied in detail by resorting to the percolation theory. As regards the second part of the study the attention was paid to systems in which the filler gathers inside either of the polymer phases. Nanoclays with different hydrophobicity were selected to evaluate their localizations and consequently their effect on the blend. According to the research findings, it was emerged that the refinement ability of the filler was slightly better in the case of bulk localization, but interfacial nanoplatelets were more effective in stabilizing co-continuous morphologies against phase coarsening in the melt state. Foreground arising from the work carried out, regarding the nanoparticle-induced morphological modifications in multiphase systems, preliminary analyses were exploited for assessing the effect of nanoparticle morphology on the beginning systems.

The steep rise in the contamination of natural water sources, has led to an increasing demand for alternate solutions to cater safe drinking water to mankind. Water treatment by separation technology utilizes semipermeable membranes to filter the contaminants commonly present in potable water. In this context, the current work focuses on the development of membranes that are affordable, exhibit chemical resistance and can be developed at industrial scale. By blending two immiscible polymers like polyethylene (PE) and polyethylene oxide (PEO), different morphologies can be generated and porous structures can be developed by selectively etching the water soluble phase (PEO). Microorganisms in the feed stream often tend to foul the membrane by forming biofilms on the surface that tends to increase the resistance offered by the membrane. Therefore, preventing this biofilm is a key challenge in this field and can be overcome by use of functional group or materials that prevent the attachment or growth of microorganisms on the surface, while maintaining a good permeation rate of water. This thesis entitled “Porous Antibacterial Membranes Derived from Polyethylene (PE)/Polyethylene oxide (PEO) Blends and Engineered Nanoparticles” systematically studies the various morphologies generated by melt blending polyethylene (PE)/polyethylene oxide (PEO) in presence and absence of a compatibilizer (maleated PE). Porous structures are developed by selectively etching PEO from the blends and the nature of the pores, which is dependent on the blend composition, is assessed by tomography. The potential of these membranes are discussed for water purification application. Further, various modifications either on the surface or in the bulk have been systematically studied. For instance, incorporation of biocidal agents like graphene oxide (GO) and modified GO in the matrix and coating/grafting of membrane surface with biocidal agents like silver (Ag), GO for preventing the biofouling and to meet the specific requirements for safe drinking water. The thesis consists of ten chapters. Chapter 1 is a review on polymer blends for membrane applications. This chapter covers the fundamentals of polymer blends in transport processes and compares the merits and demerits of the conventional methods. This chapter mainly covers the melting blending technique and the optimizing parameters for obtaining a desired morphology. Further, the various methodologies for stabilization of the morphology against post processing operation have been discussed. The various methodologies for designing membranes (for water purification) that suppress or inhibit the bacterial activity on the membrane surfaces have been discussed elaborately. Chapter 2 outlines the materials, experimental set-up and procedures employed. Chapter 3 focuses on the morphologies that are developed during the blending of PE/PEO with varying weight ratios. The morphologies developed are supported by SEM analysis. The factors governing the localization of particles in PE/PEO blends are discussed in detail. The gradient in morphology obtained during post processing operations is highlighted. Based on the type of morphologies obtained, the thesis is divided into two parts as (I) membranes designed using matrix droplet type of morphology and (II) membranes designed using co-continuous morphology. Part I consists of four chapters that involves the development of membranes utilizing matrix droplet morphology. Chapter 4 focuses on the development of morphology, the length scales of which are smaller than a bacterial cell. This ensures sieving of the contaminants that are commonly present in the drinking water though the surface of the membranes may not be antibiofouling. Thus a passive strategy of antibiofouling has been employed by blending biocidal agents like GO and amine modified GO during melt mixing. The antibacterial mechanism and its effect on bacterial activity have been thoroughly studied. Chapter 5 focuses on modification of membrane by incorporating silver decorated GO in the bulk. The effect of incorporation of these particles and their effect on bacterial activity have been discussed systematically. Chapter 6 emphasizes on the surface coating of membrane with chitosan to enhance the antibacterial activity and antibiofouling. Chapter 7 focuses on the development of membrane with pore sizes that are larger than a bacterial cell. These membranes are grafted with antibacterial polymers like polyethylene imine (PEI) and Ag to achieve antibacterial and antibiofouling surface. The possible mechanism of bacterial inactivity is described and the leaching of Ag from the membranes has been discussed. Part II of the thesis focuses on the development of co-continuous morphology in PE/PEO blends and has been assessed using 3D tomography. Chapter 8 describes the development of co-continuous morphology in PE/PEO blend. 2D and 3D micrographs have been corroborated for understanding the morphology evolution during post processing operation like remelting or hot-pressing. The blend has been strategically compatibilized to arrest the morphology and retain the co-continuity in the blends. GO was anchored onto the surface of the membrane by rendering suitable surface active groups. The antibiofouling and bacterial inhibition was studied in detail. The effect of anchoring GO on the membrane surface has been discussed with respect to their membrane performance and its antibacterial activity. Chapter 9 discusses the development of membranes using PE based Ionomer (Surlyn) and PEO. The Ionomer provided active sites for reducing silver nitrate directly onto the surface of PE to render antibacterial surface which otherwise requires a two-step protocol in the case of inert PE. The effect of coating Ag on the membrane performance and its antibacterial activity is elaborated. Chapter 10 sums up the major conclusions from each chapter and highlights the outcome of the work.

M. Tech. Polymer Technology.
This study was undertaken to investigate the effect of the addition of boehmite alumina (AlO(OH)) nanoparticles in polypropylene grafted maleic anhydride (PP-g-MA) compatibilized polypropylene (PP)/polyamide 12 (PA12) blend.

In recent years, increased use of electronic devices and wireless operations resulted in unavoidable electromagnetic (EM) pollution which has a significant impact on civil and military sectors. Considering the foremost requirement, huge efforts were invested in the development of electromagnetic interference (EMI) shielding materials. In this context, metals are usually preferred but design complexities like high density and susceptibility towards corrosion are limiting factors; additionally, the reflection of microwaves from the surface fails to serve as EM absorbers. The concern here is to minimize the reflection of the high frequency electromagnetic wave from the surface and to enhance the microwave absorption in GHz frequencies. In this thesis, we have made an attempt to design EMI shielding materials with exceptional absorption ability derived from Polycarbonate (PC)/ Poly styrene-co-acrylonitrile (SAN) based polymer blends. Herein, unique co-continuous micro-phase separated blend structures with selective localization of microwave active nanoparticles in one of the phases were realized to be most effective for microwave attenuation over just dispersing it in one polymer matrix (i.e. PC and SAN composites). The synergistic attenuation of electric and magnetic field associated with EM radiation was achieved through incorporation of various magnetic nanoparticles, however, dispersion of magnetic nanoparticles was a challenging task. Therefore, in order to localize magnetic nanoparticles in PC phase of the blends and to enhance the dispersion state, various modification strategies have been designed. In summary, we have developed a library of engineered nanoparticles to achieve synergistic attenuation of EM radiation mostly through absorption. For instance, the PC/SAN blends containing MWNTs and rGO-Fe3O4 nanoparticles manifested in exceptional EMI shielding, well above required shielding effectiveness value for most of the commercial applications, essentially through absorption. Taken together, the finding suggests that immiscible blends containing MWNTs and the decoration of magnetic nanoparticles (rGO-Fe3O4) on the surface of reduced graphene oxide sheets can be utilized to engineer high-performance EMI shielding materials with exceptional absorption ability.

The overall aim of the research activity has been identifying bio-based and eco-sustainable polymeric formulations potentially suitable for applications of technological interest. Together with the typically high costs, the major technical challenge to widespread acceptance of bio-polymers is the difficulty in achieving physical and mechanical properties comparable with those of conventional petroleum-based polymers. Among bio-polymers, poly lactic acid (PLA) is one of the most promising candidate for the substitution, totally or partially, of many petroleum-based polymers. In fact, PLA exhibits the best compromise among eco-sustainability, physical and mechanical features and industrial development prospect. However, the low mechanical resistance at high temperature (Heat Deflection Temperature = 50÷60°C) has prevented its complete access to relevant industrial sectors. In the present work, the poor mechanical properties of the amorphous PLA above its glass transition are corrected by blending it with Polyamide 11 (PA11), a semicrystalline bio-based polymer, and promoting the continuity of the latter phase through the addition of nanoparticles. Specifically, three different kinds of nanoparticles, inclined to enrich PA11 phase, have been used: an organo-modified montmorillonite (OMMT), an organo-modified sepiolite (MS) and carbon nanotubes (CNTs). The preferential positioning of the three fillers inside the PA11 minor phase of PLA/PA11 blends has resulted effective in inducing its phase continuity. In particular, provided a critical nanoparticles loading is exceeded, the drops-matrix morphology of a blend at 70% wt of PLA converts in a co-continuous one. In such a way, remarkable improvements of the high temperature mechanical performances are achieved owing to the filled PA11 framework, which interpenetrates the PLA major phase and contributes to bear stress up to ~160°C, i.e. ~100°C above the PLA glass transition. Nanoparticles-induced co-continuity in immiscible polymer blends has been previously observed in many systems, but the underlying mechanism is still unclear. An additional goal of this work is to better clarify the mechanism behind the co-continuity development observed in our bio-based nanocomposite polymer blend. In particular, we focus on the roles played by (i) bulk rheology of filled phase, (ii) self-networking propensity of nanoparticles, and (iii) properties of the blend interface. The latter are differently affected by changing chemistry and geometrical features of the nanoparticles. Among others, two issues are examined more in depth: how effective it is to promote co-continuity by kinetically arresting the relaxation dynamics of the bulk polymer phases by means of nanoparticles? And, if so, is the self-networking ability of the particles the only relevant parameter? The cross-check of the experimental data obtained from morphological, dynamical-mechanical and rheological analyses reveals that simply slowing down the melt state relaxation dynamics of the minor phase through the aggregation of nanoparticles in a space-spanning elastic network may be not sufficient to promote co-continuity. The effect of the geometrical features of the particles is discussed, as well as their ability to affect interfacial tension. In particular, the lowering of the latter seems to play a crucial role, stabilizing irregularly-shaped domains whose merging eventually results into co-continuity. Concluding, the results obtained in the present thesis provide the experimental evidence that a judicial selection of the blend constituents, combined with a clever manipulation of the blend microstructure through the addition of nanoparticles, may effectively result in ‘‘engineered’’ materials with enhanced properties. Applying such an approach to bio-based polymers represents a viable route to expand and diversify the field of possible applications of such promising materials.