DYNAMIC INTERFACIAL PROPERTIES OF POLY(ETHYLENE OXIDE) AND POLYSTYRENE AT TOLUENE WATER INTERFACE

An experimental technique called electrocapillary waves diffraction has been implemented to investigate viscous polymeric liquid-liquid interfaces. The instrument constructed recently in our laboratory has been calibrated with several standards, the static surface tensions and interfacial tensions of air/water, air/ hydrocarbon, and hydrocarbon/water. The results on surface tensions and interfacial tensions are in good agreement with the literature values in the static limit, and they are confirmed to remain the same over a wide range of frequencies (0.1-5 kHz). Next, we have examined the solutions of poly (ethylene oxide) (PEO) and polystyrene (PS) in various interfacial configurations: (1) toluene/PEO in water, (2) PEO in toluene/water, (3) spread films of PEO at toluene/water, (4) PS in toluene/water, (5) PS and PEO in toluene/water, and finally (6) PS in toluene/PEO in water. The interfacial tensions at the surface saturation limit are found to be the same at 19 mN/m in the first three cases, indicating that PEO is highly interface active and its adsorbed state is independent of the path by which it reaches the interface of toluene and water. In the fourth case, PS in toluene/water, the static limit of the interfacial tension is shown to be the same as that for pure toluene/water(without any polymer in either phase) at 36 mN/m, which may be taken as evidence for a depletion layer of PS at the interface. Further, the interfacial tension a is shown to be insensitive to frequency if the PS concentration is less than or equal to 2% in toluene whereas it is sensitive to frequency if the concentration is at about 8%. In the fifth case of PS and PEO in toluene/water, σ decreases from 36 to 19 mN/m while its frequency dependence is somewhat similar to the fourth case. In the last case of PS in toluene/PEO in water, σ is found to remain constant at 19 mN/m regardless of PS concentration up to 14% in toluene. These results are used to surmise that the interfacial properties of toluene/water are predominantly controlled by PEO while being somehow affected by the viscoelastic properties of the toluene phase if the PS concentration exceeds a certain threshold. © 1990, American Chemical Society. All rights reserved.