Section A (1) AN EXPERIMENTAL AND SIMULATION STUDY OF THE EFFECTS OF SOLVENT QUALITY ON THE RHEOLOGY OF POLYMER BRUSHES

The rheology of confined polymer layers is of great fundamental importance because of its numerous industrial applications, e.g. the use of polymer as an additive to enhance the lubrication effect of two shearing surfaces separated by a very small distance. In the present study, we focus on one specific type of confined polymer system, the so-called polymer brush. A brush consists of many polymer chains with one end permanently anchored onto an interface while the rest of the chain dangles freely in solution. When the density of the chains on the surface becomes sufficiently high, interchain excluded volume effects cause the segments of the polymer to stretch away from the interface thereby forming a brush structure. While the equilibrium brush structure and behavior have been extensively studied both experimentally and theoretically, the rheology of these layers remains relatively not well understood. Through the use of the surface forces apparatus and Brownian dynamics simulations, we present experimental and simulation results on the differences in the rheological responses of polymer brushes in good and theta solvents. Besides the force vs. distance relationship, we also examine the change in the friction force between the layers due to varying shear velocities and degree of confinement.