CAPILLARY WAVE STUDIES OF MULTIBLOCK POLYPEPTIDE COPOLYMERS AT THE AIR WATER INTERFACE/

To observe the changes in the mechanical properties of copolymer inter facial films when controlled changes are imposed on molecular architec ture, we have studied capillary waves in spread monolayers of triblock and pentablock copolymers of gamma-benzyl-L-glutamate and D,L-glutami c acid having similar molecular weights and hence different block size s. Using the mechanically generated capillary wave method and the capi llary wave dispersion relation, we have extracted the values of viscoe lastic parameters including surface pressure, transverse viscosity, lo ngitudinal elasticity, and longitudinal viscosity of copolymer monolay ers at the air-water interface, as a function of the interfacial numbe r density of molecules of the triblocks and the pentablocks. The surfa ce pressure, pi, shows a clear saturation as a function of the number density for both copolymers. The saturation surface pressure of the pe ntablocks is not dramatically larger than that of the triblocks, in co ntradiction to expectations from a steric blocking argument. The longi tudinal elasticity increases at a larger rate as the function of the i nterfacial number density for the pentablocks as compared to the tribl ocks. We observe negligibly small values of the transverse and the lon gitudinal viscosity at all number densities of the two copolymers.