Kinetics of Preferential Adsorption and Equilibrium Properties of Interfacial Layers Formed from Polymer Chains That Tether by Multiple Ends

Due to their ability to straddle phase boundaries, polymer brushes represent a model system for studies of polymer-modified surfaces. The research presented in this dissertation focuses on understanding a special type of polymer brushes formed at the solid-fluid interface by self-assembly of block copolymer chains that have the ability to tether by multiple ends, thus creating loops on the surface. Specifically, I study the self-assembly of a series of poly(2-vinylpyridine)-polystyrene-poly(2-vinylpyridine) (PVP-b-PS-b-PVP) triblock copolymers and PVP-b-PS star block copolymers adsorbed from the selective solvent toluene onto silicon and mica surfaces. The triblock and star copolymers have different molecular weights and PS/PVP ratios systematically varying from asymmetric to symmetric compositions. In the case of the stars, the number of arms is also varied. The self-assembly processes and structure are studied mostly in a solvent that is selective for the PS block. I focus on understanding how having multiple tethering points and how composition parameters (molecular weight, PS/PVP ratios, and number of arms) affect the kinetics of preferential adsorption and layer structure of the resulting brushes. The triblock copolymers form a looped polymer layer with average properties that can be described by considering the brush as made of equivalent diblocks of half the molecular weight of the triblock copolymer. The kinetics of preferential adsorption displays the two regimes expected for adsorption of diblock copolymers--there is rapid adsorption at early times followed by a transition to a slower regime. However, there are characteristic differences for the triblock materials: they adsorb faster than an analogous diblock copolymer of similar (total) molecular weight, and form a brush with approximately one-half the thickness of the brush made from the analogous diblock copolymer. Both characteristics are a direct result of the looped conformation adopted by the preferentially adsorbed triblocks, and this looping also results in the structure that displays a polydispersity-like effect introduced by the layer having a distribution of distances between tethering points of the brush chains. The kinetics of preferential adsorption and the force profiles for the adsorbed star copolymers are shown to be affected by star parameters such as total molecular weight, PS/PVP ratio, and number of arms. However, the dependence on these parameters is more complex in this case and there is no obvious trend evident in the data. The results reported in this dissertation show that by manipulating copolymer architecture, looped polymer brushes can be created, and their layer structure, interactions, and therefore properties, can be manipulated by chain parameters such as: molecular weight, asymmetry of chains, and degree of branching. Also, the detailed knowledge of the kinetics of preferential adsorption presented in this dissertation opens the possibility of manipulating brush structure by controlling, for example, chain grafting densities or creating mixed polymer brushes.