BOND FLUCTUATION MODEL OF POLYMERS IN RANDOM-MEDIA

Conventional descriptions of polymers in random media often characteri ze the disorder by way of a spatially random potential. When averaged, the potential produces an effective attractive interaction between ch ain segments that can lead to chain collapse. As an alternative to thi s approach, we consider here a model in which the effects of disorder are manifested as a random alternation of the Kuhn length of the polym er between two average values. A path integral formulation of this mod el gene:rates an effective Hamiltonian whose interaction term (represe nting the disorder in the medium) is quadratic and nonlocal in the spa tial coordinates of the monomers. The average end-to-end distance of t he chain is computed exactly as a function of the ratio of the two Kuh n lengths for different values of the frequency of alternation. For ce rtain parameter values, chain contraction is found to occur to a state that is chain length dependent. In both the expanded and compact conf igurations, the scaling exponent that characterizes this dependence is found to be the same. (C) 1998 American Institute of Physics. [S0021- 9606(98)50539-9].