SINGLE-CHAIN COLLAPSE AS A FIRST-ORDER TRANSITION - MODEL FOR PEO IN WATER

A simple model for polyethyleneoxide (PEG) is introduced and analyzed by Monte Carlo simulation. The occurrence of a solvation shell of PEO in water is modeled by two internal states of the monomers with an ene rgy difference epsilon(P). In the solvated state the monomer excluded volume increases due to the bound water and prevents the collapse of t he poor-solvent backbone. As a function of epsilon(P), which can be po sitive or negative, we find for epsilon(P) less than or similar to 0.7 k(B)T a first-order collapse transition, while for epsilon(P) greater than or similar to 0.7k(B)T the standard theta-point is recovered. Thu s, if the solvation shell is accompanied by a lower internal energy (e psilon(P) < 0 as for PEG), the transition is always of first order.