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Nanoscale colloidal particles display fascinating electronic, optical and reinforcement properties as a consequence of their dimensions. Stable dispersions of nanoscale colloids find applications in drug delivery, biodiagnostics, photonic and electronic devices, and polymer nanocomposites. Most nanoparticles are unstable in dispersions and polymeric surfactants are added generally to improve dispersability and control self-assembly. However, the effect of polymeric modifiers on nanocolloid properties is poorly understood and design of modifiers is guided usually by empirical approaches. Monte Carlo simulations are used to gain a fundamental molecular-level understanding of the effect of modifiers properties on the thermodynamics and interaction forces of nanoscale colloidal particles. A novel method based on the expanded ensemble Monte Carlo technique has been developed for calculation of the chemical potential of colloidal particles in colloid-polymer mixtures (CPM). Using this method, the effect of molecular parameters like colloid diameter, polymer chain length, colloid-polymer interaction strength, and colloid and polymer concentrations, on the colloid chemical potential is investigated for both hard-sphere and attractive Lennard-Jones CPM. The presence of short-chain polymeric modifiers reduces the colloid chemical potential in attractive as well as athermal systems. In attractive CPM, there is a strong correlation between polymer adsorption and colloid chemical potential, as both show a similar dependence on the polymer molecular weight. Based on the simulation results, simple scaling relationships are proposed that capture the functional dependence of the thermodynamic properties on the molecular parameters. The polymer-induced interaction forces between the nanoparticles have been calculated as a function of the above parameters for freely-adsorbing and end-grafted homopolymer modifiers. The polymer-induced force profiles are used to identify design criteria for effective modifiers. Adsorbing modifiers give rise to attractive interactions between the nanoparticles over the whole parameter range explored in this study. Grafted surface modifiers lead to attraction or repulsion based on the polymer chain length and grafting density. The polymer-induced attraction in both adsorbing and grafted modifiers is attributed primarily to polymer intersegmental interactions and bridging. The location of the thermodynamic minimum corresponding to the equilibrium particle spacing in nanoparticle-polymer mixtures can be controlled by tuning the modifier properties.

Non-conventional techniques for polymerization and depolymerization were investigated. The rates of polymerization were enhanced higher in ultrasonic, supercritical fluids and microwaves. However in these system under certain conditions, simultaneous degradation also occurred. Depolymerization was studied by various methods like thermal degradation in supercritical fluids and in presence of oxidizers, Lewis acid and other organic acids. Degradation by ultrasound and thermal degradation of polymer mixtures were also investigated. The scission of the polymer backbone is random for thermal degradation while the scission occurs at the midpoint for ultrasonic degradation. The degradation rates in all the investigated techniques were higher than the degradation rates observed for pyrolysis. Degradation was possible at low temperature (< 50°C) for oxidative and ultrasound degradation while the degradation rates were two orders of magnitude higher in supercritical conditions. The molecular weight distribution was obtained by GPC analysis and the continuous distribution models were used to obtain the rate coefficients. The activation energies were calculated from the temperature dependence of the rate coefficients.

Interfacial instabilities and wetting phenomena of phase separated colloid-polymer mixtures are addressed in this study. Colloidal particles offer certain advantages over molecular systems, due to their larger lengthscales and slower timescales. Moreover, the phenomena can be directly visualised using laser scanning confocal microscopy, and a perfect match with soft-lithography fabrication techniques can be exploited. In particular, we study the viscous fingering instability in three dimensions, focusing on the role of wetting conditions and of thermal fluctuations. Combined with results obtained by lattice Boltzmann simulations, we reveal that the cross-over of the meniscus in the direction across the channel thickness is controlled by the capillary and Peclet numbers, and viscosity contrast of the system. The curvature of the meniscus has a pronounced effect on the onset of the Saffman-Taylor instability, in which the formation of the viscous fingers is suppressed up to a certain threshold. Furthermore, we investigate a related contact line instability, which leads to entrainment and subsequent droplet pinch-off. A theoretical prediction for the onset of the instability is developed, which shows a good agreement with the experimental observations and yields a method to directly measure the slip length of the interface. The large thermal fluctuations of our interface play an important role in pinch-off events, leading to periodic emission of droplets of similar sizes. Finally, we study wetting phenomena at geometrically sculpted walls. We focus on the shape, the thickness and the radius of curvature of the adsorbed liquid film, and find good agreement with theory. Changing the curvature of the wedge from a flat surface to a capil- lary slit furthermore smoothly connects wetting behaviour and capillary condensation, again in qualitative agreement with theory. Non-equilibrium effects may interfere with the data and are difficult to rule out. We end with recommendations for future work.

Изучена равновесная сорбция паров воды образцами линейных ПДАДМАХ, ПАА и их смесей разного состава, а также сетчатых сополимеров ДАДМАХ/АА. Измерены теплоты растворения образцов в воде. Рассчитаны величины разностей химических потенциалов воды 1, полимерного компонента 2, средние удельные энергии Гиббса набухания сополимеров и растворения смесей в воде gm. С помощью термодинамического цикла рассчитаны средняя удельная энергия Гиббса смешения gx, средняя удельная энтальпия смешения hx и энтропийный вклад в смешение ПДАДМАХ с ПАА Tsx. Показано, что как для смесей ПДАДМАХ и ПАА, так и для сополимеров ДАДМАХ/АА с увеличением содержания акриламидного компонента существенно уменьшается водопоглощение. При этом меняется вид изотерм с S–образной на вогнутую, что свидетельствует об увеличении плотности упаковки полимеров. Установлено, что энергии Гиббса набухания сополимеров ДАДМАХ/АА, и растворения ПДАДМАХ и ПАА в воде отрицательны во всей исследованной области составов. С увеличением содержания АА термодинамическое сродство к воде закономерно понижается. Установлено, что смешение с водой ПДАДМАХ, ПАА и их смесей происходит с экзотермическим тепловым эффектом. При этом наблюдаются положительные отклонения от аддитивности во всей области составов, что свидетельствует о лучшем взаимодействии полимеров друг с другом, чем с водой. Обнаружено, что энергии Гиббса взаимодействия ПДАДМАХ с ПАА отрицательны во всей области составов смесей, но кривизна зависимости разная. Когда в составе один из компонентов преобладает, вторая производная энергии Гиббса положительна (∂2g/∂ω22> 0), т.е. полимеры термодинамически совместимы. В случае, если содержание компонентов близко друг к другу, (∂2g/∂ω22 <0). Это означает, что компоненты термодинамически не совместимы и образуют двухфазную коллоидную систему. При этом ПДАДМАХ с ПАА смешивается экзотермически во всей области составов, а энтропия меняет свой знак. / The equilibrium sorption of water vapor by samples of linear PDADMAC, PAA and their mixtures of different compositions, as well as cross-linked copolymers DADMAC/AA, has been studied. The heats of dissolution of samples in water were measured. The values of the differences in the chemical potentials of water 1, polymer component 2, and the average specific Gibbs energies of swelling of copolymers and dissolution of mixtures in water gm are calculated. Using the thermodynamic cycle, the average specific Gibbs energy of mixing gx, the average specific enthalpy of mixing hx, and the entropy contribution to mixing of PDADMAC with PAA Tsx were calculated. It was shown that both for mixtures of PDADMAC and PAA and for copolymers DADMAC/AA with an increase in the content of the acrylamide component, water absorption significantly decreases. In this case, the form of isotherms changes from S-shaped to concave, which indicates an increase in the packing density. It was found that the Gibbs energies of swelling of the DADMAC / AA copolymers and the dissolution of PDADMAC and PAA in water are negative in the entire studied range of compositions. With an increase in AA content, the thermodynamic affinity for water naturally decreases. It has been established that the mixing of PDADMAC, PAA and their mixtures with water occurs with an exothermic thermal effect. In this case, positive deviations from additivity are observed in the entire range of compositions, which indicates a better interaction of polymers with each other than with water. It was found that the Gibbs energies of the interaction of PDADMAC with PAA are negative in the entire range of mixture compositions, but the curvature of the dependence is different. When one of the components prevails in the composition, the second derivative of the Gibbs energy is positive (∂2g/ ∂ω22> 0), i.e. polymers are thermodynamically compatible. If the content of the components is close to each other, (∂2g/∂ω22 <0). This means that the components are thermodynamically incompatible and form a two-phase colloidal system. In this case, PDADMAC with PAA mixes exothermically in the entire range of compositions, and the entropy changes its sign.

Binary mixtures of polymers and soft nanocolloids, also called as polymer nanocomposites are well known and studied for their enormous potentials on various technological fronts. In this thesis blends of polystyrene grafted gold nanoparticles (PGNPs) and polystyrene (PS) are studied experimentally, both in bulk and in thin films. This thesis comprises three parts; 1) evolution of microscopic dynamics in the bulk(chapter-3),2) dispersion behavior of PGNPs in thin and ultra thin polymer matrices (chapter-4) 3) effect of dispersion on the glass transition behavior (chapter-5). In first part, the state of art technique, x-ray photon correlation spectroscopy is used to study the temperature and wave vector dependent microscopic dy¬namics of PGNPs and PGNP-PS mixtures. Structural similarities between PGNPs and star polymers (SPs) are shown using small angle x-ray scatter¬ing and scaling relations. We find unexpected (when compared with SPs) non-monotonic dependence of the structural relaxation time of the nanoparticles with functionality (number of arms attached to the surface). Role of core-core attractions in PGNPs is shown and discussed to be the cause of anomalous behavior in dynamics. In PGNP-PS mixtures, we find evidence of melting of the dynamically arrested state of the PGNPs with addition of PS followed by a reentrant slowing down of the dynamics with further increase in polymer frac¬tion, depending on the size ratio(δ)of PS and PGNPs. For higher δ the reen¬trant behavior is not observed with polymer densities explored here. Possible explanation of the observed dynamics in terms of the presence of double-glass phase is provided. The correlation between structure and reentrant vitrifica¬tion in both pristine PGNPs and blends are derived rather qualitatively. In the second part, the focus is shifted to miscibility between PGNPs and polymers under confinement i.e., in thin films. This chapter provide a compre¬hensive study on the different parameters affecting dispersion viz., annealing conditions, fraction of the added particles, polymer-particle interface and more importantly the thickness of the films. Changes in the dispersion behavior with annealing is shown and the need for annealing the films at temperatures higher than the glass transition temperature of the matrix polymers is clearly elucidated. Irrespective of the thickness of the films( 20 and 65 nm) studied, immiscible particle-polymer blends unequivocally prove the presence of gradi¬ent in dynamics along the depth of the films. To our knowledge for the first time, we report results on confinement induced enhancement in the dispersion of the nanoparticles in thin polymer films. The enhanced dispersion is argued to be facilitated by the increased free volume in the polymer due to confinement as shown by others. Based on these results we have proposed a phase diagram for dispersibility of the nanoparticles in polymer films. The phase diagram for ultra thin films highlights an important point: In ultra thin films the particles are dispersed even with grafting molecular weight less than matrix molecular weight. In the third part, we have studied the glass transition of the thin films whose structure has been studied earlier in the earlier part. Non-monotonic variation in glass transition with the fraction of particles in thin films has increased our belief on the gradient in the dynamics of thin polymer films. En¬hanced dispersion with confinement is captured with the enhanced deviation in glass transition temperature of ultra thin films. Effect of miscibility param¬eter on Tgis studied and the results are explained with the subtle interplay of polymer-particle interface and confinement.