Concentration dependence of the global and anisotropic dimensions of confined macromolecules

The chain dimensions [R-2] of nondilute polymer solutions confined to a sli t of the width D were studied using lattice simulations. It was found that the chain compression induced in good solvents by the concentration phi is enhanced in a slit relative to the bulk. The global dimensions of chains al so change with phi in confined and unconfined theta solutions. At intermedi ate slit widths, a region was noted where coils are squeezed along all thre e axes. This region is manifested as a channel on the three-dimensional sur face [R2](D,phi) in both good and theta solvents. The coil anisotropy, give n by the ration of the parallel and perpendicular components of the chain d imensions [R-y(2)]/[R-x(2)], reaches high values at strong confinements whe re coils form quasi-two-dimensional pancakes. The concentration-induced red uction of the global chain dimensions in good solvents is almost fully tran smitted to the parallel component [Ry2]. The computed effects of concentrat ion and confinement were compared with the predictions of mean-field and sc aling theories, and implications of the results to ultrathin films and laye red nanocomposites were discussed. In addition, the distribution functions of the components of the end-to-end distance R perpendicular and parallel t o the plates. W(R-x) combined with the concentration profile phi (x) along the pore provided details of the chain structure close to walls. A marked d ifference in the pace of the filling up of the depletion layer was noticed between chains in theta and good solvents. From the distribution functions W(Rx) and W(R-y), the highly anisotropic force-elongation relations imply t he deformations of chains in confined solutions and ultrathin bulk films.