CRITICAL-POINT WETTING FOR BINARY 2-PHASE POLYMER-SOLVENT MIXTURES ONSOLID INTERFACES

Cahn argued that the wetting temperature, T-W is always below the crit ical temperature, T-C, of a binary solvent mixture. A self-consistent field theory is used to show that this phenomenon is expected to be be st observable for low molecular weight compounds. In polymer-solvent m ixtures in contact with a rigid surface made of the same material as t he polymer units, the difference T-W - T-C becomes minimal for an inte rmediate degree of polymerization N = N* (similar to 65). The polymer wets the surface for N < N*, whereas for larger N the solvent is at the wall. Critical wetting is the rule; first-order wetting is only fo und for relatively short chains, 2 less than or equal to N less than o r equal to 16.