Concentration dependence of the global and anisotropic dimensions of confined macromolecules

Abstract

The chain dimension of nondilute polymer solutions confined to a slit of the width D were studied using lattice simulations. It was found that the chain compression induced in good solvents by the concentration O in confined and unconfined theta solutions. At intermediate slit widths, a region was noted where coils are squeezed along all three axes. This region is manifested as a channel on a three-dimensional surface (D,O) in both good and theta solvents. The coil anisotropy, given by the ratio of the parallel and perpendicular components of the chain dimensions R / , reaches high values at strong confinements, where coils form quasi-two-dimensional pancakes. The concentration-induced reduction of the global chain dimensions in good solvents is almost fully transmitted the parallel component . The computed effects of concentration and confinement were compared with the predictions of mean-field and scaling theories, and implications of the results to ultrathin films and layered nanocomposites were discussed. In addition, the distribution functions of the components of the end-to-end distance R perpendicular and parallel to the plates, W(R x ) and W(R y ), were calculated. The function W(R x ) combined with the concentration profile O(x) along the pore provided details of the chain structure close to walls. A marked difference in the pace of the filling up of the depletion layer was noticed between chains in theta and good solvents. From the distribution function W(R x ) and W(r y ), the highly anisotropic force-elongation relations imply the deformation of chains in confined solutions and ultrathin bulk films.