Surface Pressure from Block Copolymers with One Block Forming a Monolayer and the Other Block Dangling in Solution+

Surface pressure has been measured as a function of surface concentration for monolayers of poly(dimethylsi1oxane)-polystyrene (PDMS-PS) diblock copolymers, PDMS-poly(wmethy1styrene) (PDMS-PaMS) multiblock copolymers, and the respective homopolymers, spread on the surface against air of tricresyl phosphate a t 26 “C. A sparingly soluble monolayer was formed by PDMS homopolymer. No surface pressure was associated with either PS or PaMS homopolymer; these appeared to pass into bulk solution. For the block copolymers, a t low surface concentrations the surface pressure was indistinguishable from that for PDMS homopolymer at the same concentration of PDMS. At higher concentrations the surface pressure exceeded this value, to an extent which increased with increasing surface concentration of PS or PaMS. The supplemental surface pressure from dangling chains was calculated by subtraction. The findings are in qualitative agreement with theoretical predictions by de Gennes, Alexander, and Cantor that osmotic interactions between polymer chains dangling into a liquid from an interface contribute substantially to the reduction of surface tension. Idealizations in the theoretical models are noted.