The kinetics of phase separation of sodium Poly(styrene sulfonate) (NaPSS) in water with barium chloride (BaCl2) was studied by static and dynamic light scattering. This polyelectrolyte system shows an upper critical solution temperature behavior, such that the solutions are homogeneious at temperatures above the phase boundary. Using dynamic light scattering, two diffusive modes were detected, and unaggregated polyelectrolyte chains and aggregates coexist in the homogeneous phase. The hydrodynamic radius (RH) of the unaggregated chains is of the order of 1 to 10 nm depending on the molecular weight of NaPSS, while RH of aggregates is of the order of 100 nm independent of the molecular weight of NaPSS. Unaggregated chains follow good solution behavior with a fractal dimension of 5/3. On the other hand, the fractal dimension of aggregates is larger than 3.5. The value of the fractal dimension suggests that the structure of aggregate is similar to branched polymers, such as star polymers. Upon rapidly cooling the NaPSS sample below the phase boundary, phase separation takes place. During the initial stage, unaggregated chains were converted to aggregates. Newly generated aggregates have a similar fractal dimension and size to aggregates found above the phase boundary. The size of aggregates remained constant while the number of aggregates increased. During the initial stage, nucleation time is sensitive to quench depth and salt concentration. Either deepening a quench depth or increasing BaCl 2 concentration shortened the nucleation time. After the nucleation time, the size of aggregates grew linearly with time. This marks the growth period, at which time the growth rate is higher for deeper quench depths and higher BaCl2 concentrations. The mechanism of phase separation of NaPSS in water and BaCl2 is similar to the nucleation and growth mechanism where the aggregate serves as a nucleus. However, it is different from conventional nucleation and growth theory in that the nucleus already exists above the phase boundary.

The use of electric fields to control the orientation of copolymer microstructures in a thin film geometry is demonstrated. Copolymers of polystyrene-block-poly(methyl methacrylate), P(S-b-MMA), and polystyrene-block polyisoprene, P(S-b-I), were prepared by living anionic techniques for use in this study. An emphasis was given on scattering and reflectivity techniques to elucidate information regarding the mechanism of alignment. Alignment is understood, for all copolymer systems, in terms of a simple dielectric body argument whose energy is dependent on a dielectric mismatch parameter. The observed pathway along which the alignment is realized depends on the initial state of the sample. Vastly different behavior is observed for thick films, where the effect of the substrate can be effectively ignored, and thin films, where the surface interactions dominate. In thick films, the alignment mechanism was followed via in-situ small angle scattering (SAXS) experiments and proceeds via disruption of the grains of the copolymer microdomains with a subsequent rotation of the grains along the field direction. Observed similarities in alignment of diblock and triblock copolymers, further strengthen the grain rotation argument. If alignment occurred by an enhancement of interfacial fluctuations or a mechanism requiring a molecular response, distinct differences in the alignment mechanism between the di- and triblock copolymers would be evident. Additionally, it was observed that if a copolymer system is allowed to relax between applied fields, the resulting final alignment was found to be better than the alignment achieved under a constant applied field. This indicates that, under a constant applied field, the copolymer is trapped in a non-equilibrium state that can be overcome by allowing a partial relaxation of the system. In thin films, a direct competition between the interfacial interactions and the electric field force is observed. Complete reorientation occurs only when the applied field overcomes the interfacial interactions. This occurred at a well-defined threshold electric field strength, Et, and was observed to be independent of the film thickness over a range of thicknesses. In these thin films, the mechanism of alignment must proceed through a fluctuation pathway where the applied electric field amplifies the fluctuations until alignment is achieved. Preliminary neutron reflectivity data shows a large disruption of the surface-induced parallel orientation by the electric field that is directly related to the electric field strength, the interfacial interactions, as well as the copolymer initial state. This is consistent with an electric-field induced fluctuation disrupting the surface-induced lamellar stacking.

The effect of hydrostatic pressure on the lower disorder-to-order transition (LDOT) in poly(d-styrene-block-n-butyl methacrylate) having symmetric and asymmetric block lengths was investigated by in situ small-angle neutron scattering (SANS). Currently, linear diblock copolymers having styrenic and methacrylic monomers are the only systems that display a thermally accessible phase transition from the disordered homogeneous melt to the ordered microphase-separated state upon heating. The location of this phase transition was mapped as a function of temperature and pressure by analyzing one dimensional SANS intensities, where discontinuities in the width and height of the scattering peak indicated the traversal of the transition isothermally or isobarically. The T-P phase diagram of p(d-S-b-nBMA) built using this method shows an expansion of the disordered, homogenous region with increasing pressure. For the diblock copolymer with a lamellar morphology and Mw = 8.5 × 104, the slope of the phase transition line was ∼150 K/kbar, and was approximately linear over a range of 1 kbar. Increasing the molecular weight of p(d-S- b-nBMA) resulted in a vertical shift of the phase transition line in the phase diagram and no detectable change in slope. Similar effects were observed for diblock copolymers with a cylindrical morphology. The bulk enthalpy and volume changes at the phase transition, which dictate the pressure coefficient for a one component system, were either at the limit of experimental resolution or unobservable due to kinetic factors. In-situ X-ray reflectivity experiments, however, showed a significantly reduced thermal expansion coefficient in the disordered phase and a discontinuous increase in film thickness as a function of temperature at the bulk LDOT. The pressure coefficient, dTLDOT/dP, for these materials is greater by a factor of five than currently observed in diblock copolymers with conventional UODT phase behavior, i.e. ordering upon cooling . This dramatic phase behavior allows rapid and convenient access to the order-disorder phase transition, isothermally, and suggests that LDOT block copolymers could be employed in blend and multi-component systems as minor components to impart pressure-induced compatibilization, surface activity, or flow properties.

The effects of molecular architecture and block conformational asymmetry on the equilibrium bulk morphological behavior of strongly phase-separated, amorphous block copolymers have been studied. Transmission electron microscopy techniques and small angle x-ray scattering, as well as small angle neutron scattering, were primarily utilized to characterize the block copolymer morphologies. Both architecture and block conformational characteristics are found to be molecular parameters, in addition to the relative volume fractions of the constituent blocks, with which one can controllably manipulate the bulk morphological behavior. The effects of novel molecular architecture were discerned via a systematic morphological study of a series of simple graft A$\sb2$B, or "Y", block copolymers where A=polyisoprene (PI) and B=polystyrene (PS). In the microphase separated state a 2:1 A to B arm number asymmetry is introduced across the AB interface due to the simple graft architecture. This arm number asymmetry causes significant deviations in the volume fraction dependence of the morphologies formed by the A$\sb2$B series as compared to the volume fraction dependence of linear diblock morphology. In addition, at a unique volume fraction in the A$\sb2$B series where the two PI arms per molecule are first forced to the concave side of the interface, a new morphology in neat block copolymers is observed which has not been predicted by theory. The bulk morphological behavior of a series of poly(isoprene-block-tert-butylmethacrylate) linear block copolymers was characterized. The larger unperturbed dimension of PtBMA, due to its larger statistical segment length relative to PI, provides for a lower PtBMA entropic chain stretching penalty in the microphase separated state. This also causes the relative volume fraction windows in which morphologies are observed to shift to higher relative volume fractions of the more easily stretched PtBMA block than found in conformationally symmetric AB linear diblocks. In addition, initial morphology studies on more complicated graft architectures and linear diblocks with tunable conformational asymmetry are presented.

In this thesis, the crystallization and melting of blends of high and low density homogeneous ethylene-1-octene copolymers with appended long chain branches have been investigated in real time by means of time-resolved SALS under cross-polarized and parallel-polarized optical alignments using a charge-coupled device camera (CCD) system, simultaneous small angle-X-ray and wide angle X-ray measurements using synchrotron radiation and differential scanning calorimetry (DSC). For the highest density material studied, our data show that in the case of crystallization at low supercooling, spherulitic growth (primary crystallization) occurs first while the apparent degree of crystallinity is less than 2%. Over 90% of the crystallinity develops after the primary crystallization process. When the average branch content of the blend is 14 branches per 1000 carbons complete spherulites are observed. The internal spherulite disorder is unchanged relative to that obtained for the high density component. When the average branch content of the blend is increased to 58 branches per 1000 carbons, the crystallization rate is faster than that of the moderate increase but the morphology suggested from SALS is consistent with incomplete spherulites. For this case, our data suggest that the domain sizes resulting from the incipient melt phase separation is the likely cause of the accelerated crystal growth. We propose that the incomplete spherulites formed may be a consequence of the competition between amorphous phase separation in the residual melt and crystallization. The results of a numerical study investigating the dynamics of spinodal decomposition in blends of linear Gaussian chains in three dimensions were used to evaluate the effect of branch content on the phase separation kinetics for mixtures of linear Gaussian chains and branched chains. The phase separation kinetics in the branched systems are identical to that of linear mixtures with larger domain sizes. Hence, it may not be possible to detect differences in the time dependence of the structure factor and domain size from scattering measurements if one varies the branch content of the blend. Blends of linear and branched polymers can be treated as blends of linear Gaussian chains even when the branch content is very high.

This dissertation describes computer simulations and theoretical analyses of ordering processes in liquid crystals and polymers. One ordering process in liquid crystals occurs during the isotropic to nematic transition in which point and line defects form and annihilate. Monte Carlo simulations support the newly-derived scaling of the defect density, which was found to scale with time as $-$6/7 in both two and three dimensions, contrary to the mean-field result of $-$1. Frustration was determined to be a key factor in this difference. Another ordering process in liquid crystals is the evolution of inversion walls and loops. Analogous to the model of a shrinking elastic loop in a viscous medium which has been theoretically investigated by deGennes and Brochard, our lattice Monte Carlo simulations of inversion walls and loops show the same scaling behavior with time and the same predicted dependence of shrinkage rate on the orientational diffusion coefficient. Polymer crystallization constitutes the other major topic of this dissertation. The initial stages of crystallization are difficult to study experimentally but by using the united-atom Langevin dynamics method, single and multi-chain crystallization can be simulated. The simulations show that random fluctuations nucleate regions of higher order which in turn can induce further crystallization. Lamellar thicknesses obtained from simulations at various undercoolings showed the same scaling behavior as experimental data from literature. Besides homogeneous nucleation, secondary nucleation was also observed, with the newly-attached chains continuing to undergo conformational changes on the crystal surface. Finally, the phenomenon of lamellar thickening was investigated. Lamellar thickening was observed to occur cooperatively in a stepwise, quantized manner.

The utilization of poly(styrene-random-methyl methacrylate), P(S-r-MMA), random copolymer brush surfaces to control the structure of polymer films is demonstrated. Random copolymer brush layers were generated by end anchoring the copolymers onto silicon substrates. By dictating the chemical composition of the random copolymer, the resultant brush layer could be precisely tuned to have properties ranging from pure PS to pure PMMA. This was determined by experiments where PS and PMMA homopolymer films showed dewetting behavior characteristic of the interactions between the homopolymer film and the underlying brush layer. Brushes having a styrene fraction of 0.58 have balanced interactions with PS and PMMA and constitute surfaces that are nonpreferential or neutral to PS and PMMA. The influence of interactions between polymer films and random copolymer brush layers is addressed for three systems. First, the interfacial structures of dPS and dPMMA homopolymer films with the brush layer were examined with neutron reflectivity (NR). The interfacial width between the two layers strongly depended upon the interactions between them. Furthermore, it is observed that penetration of dPMMA to the silicon substrate can occur for cases where the brush layer does not provide a sufficient enthalpic or entropic barrier. Second, atomic force microscopy studies (AFM) show that PS/PMMA demixed films had morphologies that varied greatly with substrate interactions. With annealing, some of these structures rearranged significantly while others remained relatively unchanged. The third type of polymer film examined in this study, diblock copolymers constitutes the main focus of this work. Normally, preferential interactions of one block at an interface induce a parallel orientation of the block copolymer domains. By utilizing neutral random copolymers, preferential segregation of each block is eliminated resulting in a perpendicular orientation of block copolymer domains. This was shown for poly(styrene-block-methyl methacrylate), P(S-b-MMA), block copolymers having lamellar and cylindrical morphologies. Using a wide variety of techniques the structural dependence of these films with annealing time and the effects of commensurability were examined. By controlling the growth of these domains, the generation of novel film structures comprised of perpendicular lamellar and cylindrical domains was achieved.

Diblock copolymers are a class of polymers where two dissimilar polymer blocks are joined together at a common end. The dissimilarity of the blocks causes a phase separation to take place, however the connectivity of the blocks keeps the length scale of this phase separation on the order of the radius of gyration of each of the blocks. Throughout this thesis, the synthesis and morphology of diblock copolymers that have a specific, UV cleavable chemical moiety located at the junction point between the two blocks is investigated. The two junction points targeted to this end are the [4π + 4π] photodimer of anthracene and the 2-nitrobenzyl ester. The diblock copolymer containing the [4π + 4π] photodimer of anthracene exhibits thermal as well as UV lability upon heating above ∼130°C, or UV irradiation at 280 nm. Thin films of this polymer on neutrally-interacting substrates were annealed at 80°C under the presence of supercritical carbon dioxide to avoid thermal degradation that would occur if films were annealed above the glass transition temperature of both blocks (>110°C). The transition from microphase-separated to macrophase-separated morphology is thoroughly investigated by AFM upon thermal and UV cleavage to create blends of diblock and homopolymer in situ. In addition, the selective removal of each polymer block after cleavage by washing with selective solvents is demonstrated. The diblock copolymer containing the 2-nirobenzyl ester moiety is also synthesized and its morphology in thin films is investigated. This diblock, upon cleavage, leaves behind more useful functionality than the diblock with the [4π + 4π] photodimer of anthracene as junction point, as well as being thermally stable at temperatures that allows thermal annealing of thin films. The UV cleavage characteristics of this copolymer in solution are investigated by SEC. Also, irradiation of thin films at a wavelength that does not degrade or cross-link either polymer block causes selective junction point cleavage, as expected. The morphology of UV cleaved thin films on neutrally-interacting substrates is investigated by AFM.

Hierarchical assembly of materials has attracted significant interest, since it provides opportunities to fabricate novel materials. In this thesis, we investigated three different systems where polymer chains organize hierarchically. First, a semicrystalline triblock copolymer, poly(L-lactic acid- b-ethylene oxide-b-L-lactic acid) (PLLA- b-PEO-b-PLLA), was prepared and the effect of the block-wise construction on the sequential crystallization was investigated by comparison to the corresponding homopolymer blend. In the resultant spherulitic morphology, the crystallization of PEO occurred within the framework established by the PLLA crystals. The preformed PLLA crystals biased the PEO chain orientation and the effect was more significant in the block copolymer system, where PEO chains were covalently anchored to PLLA. Secondly, the influence of the microenvironment of multifunctional chains on their organization was studied. For this investigation, styrene-based linear polymers having two different pendant groups, a carboxylic acid and a neutral group, on every repeat unit were prepared. With alkyl (n-C 10H21-) groups as the neutral pendant, the linear macromolecules assembled into thermally reversible globular aggregates through non-covalent interaction with multifunctional tertiary amines. The aggregates had a structural hierarchy and remained stable without inter-particle crosslinking. In the absence of the alkyl pendant groups, control over the structure and properties of the aggregates was lost. In a third system, the coupled self-assembly of bionanoparticles and block copolymers was investigated. A simple way to incorporate bionanoparticles into a thin film of water-insoluble block copolymer was developed by combining the bionanoparticle adsorption on a polymer film and subsequent annealing under solvent vapor. Through the use of a block copolymer having a positively charged component, the loading of bionanoparticles increased significantly. When highly loaded, a hierarchical co-assembly of the block copolymer and the bionanoparticle was observed where the microphase separation of the block copolymer forced a segregation of bionanoparticles to the grain boundaries, forming a much larger scale structure.

Herein we establish a relationship between controlled nanoscale surface interactions and subsequent macromolecular ordering. Chemically heterogeneous striped surfaces of polar silicon oxide and non polar gold are generated over large areas, via glancing angle evaporation on facetted silicon substrates. The processing conditions required for generation of stripe widths comparable to the size of a polymer molecule are outlined. Substrates with 20–30 nm metal linewidths and 40–60 rim stripe periods are prepared. Spin and solution casting of incompatible polymer mixtures of polystyrene (PS) and polymethylmethacrylate (PMMA) on heterogeneous surfaces are found to generate films with unique, substrate directed morphologies dependant on the kinetics of the casting process. Spin cast films posses a surface adsorbed layer of blended composition due to rapid polymer adsorption from solution, while solution cast films phase separate at the substrate/polymer interface on a molecular level. Preferential adsorption of PS to the non polar gold stripes and PMMA to polar silicon oxide stripes is observed at the substrate beneath the macroscopically phase separated domains of the blend components. Preferential adsorption occurs over a large molecular weight range, with a molecular weight dependence on the morphology of the adsorbed polymer lines found. Solution cast films of the symmetric copolymer poly(styrene-block-methylmethacrylate), P(S-b-MMA), on heterogeneous surfaces show lamellar microdomain orientations perpendicular to the substrate plane, parallel to the striping. Commensurability of the block copolymer and substrate stripe periods is found to be essential for producing such a surface directed morphology. The commensurability window depends inversely on the degree of confinement of the morphology, with unconfined films requiring more stringent conditions for surface directed morphology reorientation. The distance over which the orientation of the microdomains persists in thick films is found to depend on the ordering kinetics, scaling with copolymer molecular weight. Confinement effects such as tension and compression and defects in the lateral long range orientation of surface directed lamellar morphologies are observed for slightly incommensurate morphologies, with the amount of strain and defect concentration found to increase with the loss of commensurability.