Signatures of a Concentration Dependent Flory chi Parameter: Swelling and Collapse of Coils and Brushes
arXiv:cond-mat/0206458 · doi:10.1002/mats.200350014
Abstract
The quality of solvents of polymers is often described in terms of the Flory chi parameter typically assumed to depend only on the temperature, T. In certain polymer-solvent systems fitting the experimental data enforces the replacement of chi(T) by a concentration dependent chieff. In turn, this modifies the swelling and collapse behavior. These effects are studied, in the framework of a mean-field theory, for isolated coils and for planar brushes. The phi dependence of chieff gives rise to three main consequences: (i) Shift in the cross-over between Gaussian and self-avoidance regimes; (ii) A possibility of first-order collapse transition for isolated flexible coils; (iii) The possibility of a first-order phase transition leading to a vertical phase separation within the brush. The discussion relates these effects directly to thermodynamic measurements and does not involve a specific microscopic model. The implementation for the case of Poly(N-isopropylacrylamide) (PNIPAM) is discussed.
12 pages, 9 figures