New statistical mechanical treatment of systems near surfaces. IV. Surfaceand surface-induced capillary transitions in polymer solutions

We apply a recently developed analytic but approximate method to study surf ace and surface-induced capillary transitions in a solution of polydisperse linear and/or branched polymers confined between two infinite but identica l surfaces. We use an equilibrium polymerization model where various densit ies in the system are controlled by the corresponding activities. The bulk region, i.e., the central region between the surfaces may or may not be in the bulk equilibrium state (see the text). We find a line of first-order tr ansitions, commonly known as a prewetting transition line, passing through the phase separation point in the bulk equilibrium state, at which the surf ace undergoes a first-order transition. For a certain range around the bulk equilibrium transition point, the bulk region undergoes a stable-metastabl e transition. This presents us with the possibility of being able to prepar e the system in a bulk metastable state, no matter how far apart the two su rfaces are. This range is found to be identical to the range of metastabili ty for the bulk equilibrium state. Outside of this range, the transition li ne behaves like a prewetting transition line and, as usual, terminates at s urface critical points, one on each side of the above range. (C) 1998 Ameri can Institute of Physics. [S0021-9606(98)51048-3].