ADSORPTION OF WATER-VAPOR ON BLOCK COPOLYMERS

Adsorption isotherms of water vapor on bis(A-polycarbonate)-polydimethyl siloxane of various siloxane contents and of polycarbonate (Lexan) have been measured at -10, 0, 10, and 20°C. Isosteric heats and differential molar entropies have been evaluated. The data show increasing water adsorption with decreasing siloxane content. Highest isosteric heats before completion of a monolayer were observed with samples of small and intermediate siloxane contents; the entropies indicate a structure of the adsorbate of greater order than that of ice. The sample with highest siloxane content shows isosteric heats smaller than that for liquefaction of water. The entropies indicate that the adsorbate behaves in this case like a two-dimensional, mobile gas. The data for polycarbonate (Lexan) lies between those for the block copolymer samples. Ice-releasing adhesive strength values-coatings were made of the block copolymers-correlate well with the data obtained in the present study. The copolymer with the largest polysiloxane content yielded the lowest adhesive strength values. © 1979.