INTERFACIAL-TENSION OF A POLYSTYRENE-POLY(ETHYLENE OXIDE) DIBLOCK COPOLYMER AT THE WATER-TOLUENE INTERFACE

This paper investigates the interfacial properties of a polystyrene-po ly(ethylene oxide) (PS-PEO) diblock copolymer adsorbed at the water-to luene interface using axisymmetric drop shape analysis profile (ADSA-P ). The molecular weight of the PS block was 231 400 while the PEO bloc k had a molecular weight of 20 670. The diblock copolymer was dissolve d in toluene to form a 0.131 mg/mL solution and was allowed to adsorb onto a pendant drop of water at 20 degrees C. The variation in interfa cial tension with time during the equilibration process was similar to that of a surfactant, beginning at the water-toluene interfacial tens ion and decreasing to an equilibrium value of 27.8 mJ/m(2) after a per iod of 2 h. The interface was then compressed by decreasing the volume of the drop in a linear manner. The shape of the resulting interfacia l tension-area isotherm can be rationalized by a schematic model of th e interfacial molecular conformation. According to the proposed model, the average molecular spacing is determined by the PS block at the st art of compression and by a combination of the PEO block and the PS br ush at the end of compression. These results show that the use of ADSA -P to measure interfacial tensions is a useful way to obtain indirect evidence of the interfacial molecular conformation.