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After the advent of nanotechnology, self-assembly has become an active area of research, as it being one of the few efficient methods to generate ensembles of nanostructures. In this thesis, we present studies on two dimensional self-assembly of polymer grafted nanoparticle (PGNPs) and thin film modelling approach to understand the physics involved in the self-assembly mechanism of polymeric nanoparticles. The two dimensional, hierarchical assemblies of PGNPs are created from evaporating solution films spread at the air-water interface using Langmuir-Blodgett technique. A transition in the patterns is observed with increase in concentration which is followed by a remarkable re-entrance of initial patterns with further concentration increment. The pattern is long length scale network type at low and high concentrations whereas it is short length scale distribution of clusters at intermediate concentrations. Clusters are composed of lateral arrangement of individual PGNPs. The characteristics of clusters are tailored by changing various experimental conditions such as molecular weight of the grafted chains, concentration, temperature and evaporation rate. The patterns are unaffected by the transfer surface pressure, suggesting that the self-assembly occurs in the presence of solvent via solution thin film instabilities and the resulting structures of PGNPs are frozen upon complete evaporation. Films of neat polystyrene also exhibit similar morphology and transitions in pattern length scales with initial solution concentration as observed in PGNP films. This confirms that the self-assembly of PGNPs is driven by the intrinsic nature of the grafted polymer chains. Gradient dynamics model is employed to study the stability and dynamics of polymer solution thin films by incorporating Flory Huggins free energy and concentration dependent Hamaker constant. Dispersion curves obtained from linear stability analysis of thin film equations show existence of bimodal instability in the film that corresponds to dewetting and decomposition. Phase diagram spanned by concentration and Flory parameter indicate that the thin film instability transits from dewetting to decomposition and then re-enters to dewetting with increase in concentration of the solution. Using the material parameters of the PGNP thin films for linear stability analysis, experimental observations of bimodal length scale of patterns and re-entrant nature are well explained. Nonlinear simulations which are performed to capture the evolution of patterns in the film show that the decomposition progresses through different pathways depending upon the concentration of the solution. This is explained by analyzing the local variation of spinodal parameter (curvature of the free energy per unit area) in the film. The gradient dynamics model is extended to study the stability and dynamics of evaporating solution thin films. Nonlinear simulations demonstrate that the film undergoes evaporative thinning without any significant growth of dewetting or decomposition instability initially and becomes unstable at a certain intermediate thickness where the spinodal parameter of dewetting or decomposition changes the sign. The rupture of the film (dewetting) or the phase segregation (decomposition) occurs explosively and subsequently evaporation progresses till the film attains chemical equilibrium with the ambient vapour phase. Rate of evaporation significantly affect the intermediate thickness at which the patterns emerge and thereby determines the length scale of initial patterns and instability growth rate. Quasi-steady analysis and nonlinear simulations show that the length scales of patterns of dewetting and decomposition decrease with evaporation rate and exhibit a power law behaviour. Thin films in which the solvent quality drops down with confinement due to evaporation are modelled by assuming a simple functional dependence of Flory parameter on mean film thickness. Quasi-steady analysis demonstrates that the dominating instability of such films switches from dewetting to decomposition and then returns to dewetting with increase in the initial concentration of the solution. We note that even though the functional form of Flory parameter with confinement is not exact, it represents the essential nature of the expected variation. We presume that the phenomenon discussed above is quite generic and may manifest itself in many situations where thin films of colloidal solutions undergo a decrease in the solvent quality due to confinement effects resulting in a competition between spinodal dewetting and decomposition instabilities. This will result in a competition and interplay of the different instability scales and by choosing appropriate control parameters novel self-assembled patterns can be created.

The thesis describes the study of slow dynamics of confined polymers and soft colloids. We study the finite size effect on the dynamics of glassy polymers using newly developed interfacial microrheology technique. Systematic measurement have been performed to address the issue of reduction of glass transition under confinements. Slow and heterogeneous dynamics are the underlined observed behavior for dynamics in confined glassy polymers. The slow relaxation dynamics and dynamical heterogeneity in polymer grafted nanoparticles (PGNPs) systems were studied using advanced X - ray photon correlation spectroscopy (XPCS) techniques. Our studies presented in this thesis on dynamics of polymer grafted nanoparticle systems in melts and solution are the first attempt to study them experimentally. Thus our work shed the light about new technique to study confined system more accurately and explore new soft colloidal system to study fascinating dynamics and interesting phase behavior. In Chapter 1, we provide the theoretical background along with brief review of the literature for understanding the results presented in this thesis. The details of the experimental set up and their operating principle along with the details of the experimental conditions are provided in Chapter 2. In Chapter 3 we present our newly developed technique (interfacial microrhelogy) and its consequences to study the complex fluids at interface. Chapter 4 discusses the concentration and temperature dependent glassy dynamics in confined glassy polymers. In Chapter 5 we provide the structural and dynamical study of polymer grafted nanoparticles in melts and solutions. We provide the summary of our result and the future prospective of the work in Chapter 6. Chapter-1 provides the ground work and theoretical aspects for understanding the results presented in this thesis. It starts with the discussion about the slow dynamics of complex fluids and transit to dynamic behavior of polymer in confinement, glassy dynamics in confinements . This also discusses the basic aspects of studying viscoelastic properties using rheology, interface rheology, microrheology, interface microrheology techinques. In continuation it discusses structure and dynamics of different soft colloids investigated for last decade and then theoretical aspects of XPCS is discussed. Towards the end of this Chapter, we discuss the procedure to explain and understand systems dynamical heterogeneity near glass like phase transition. Chapter-2 contains the details of the experimental techniques which has been used for the study of confined polymers and soft colloids. Brief introduction to basic principles of the measurements followed by details of the material and methods have been provided. Chapter-3 we discuss the interafacial microrheology of different complex fluids and advantages of the techniques is discussed in Chapter 3. This includes discussion about the technique sensitivity at the surface using quantum dots (QDs) as a probe and about the configuration of the QDs at/on monolayer. Later on establishment of the technique has been demonstrated through easurements on arachidic acid, poly(methylmethacrylate) (PMMA), poly(vinylacetate) (PVAc), poly(methylacrylate) (PMA) monolayers. The extracted subdiffusive nature of QDs in on monolayers through mean square displacement has been explained using fractional Brownian motion model. Towards the end of the chapter we discuss about the extraction of real and imaginary elastic modulus from mean square displacement data using generalized Stokes-Einstein relation for the quasi two dimensional systems and explains about the possible viscoelastic transition in the different monolayers. The concentration and temperature dependent glassy dynamics of confined polymers (PMMA) are discussed in Chapter-4. We demonstrate the microscopic nature of spatio-temporal variation of dynamics of glassy polymers confined to a monolayer of 2 3 nm thickness as a function of surface density and temperature. It illustrates the systems dynamical heterogeneity and explain the observed large reduction of glass transition temperature in confined system through finite size effect. In Chapter 5 we discuss the result based on systematic studies of dynamics of PGNPs in melts and solutions. In addition it also illustrates the structural anisotropy and anomalous dynamical transitions in binary mixture of PGNPs and homopolymers in good solvent condition. It provides temperature and wave vector dependent XPCS measurements on polymer grafted nanoparticles with the variation of functionality. The functionality ( f ) dependent nonmonotonic relaxation in melts of PGNPs and solvent quality dependent non monotonic relaxation of PGNPs system have been elaborated in the continuation. We present possible phase behavior of PGNPs system in good solvent with addition of homopolymer of two different molecular weight. Chapter 6 contains the summary and the future perspective of the work presented.

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.