Colloidal Studies on Surface Active Agents. XXII.

Abstract

The velocity gradient dependence of flow birefringence has been investigated on highly concentrated aqueous solutions (10-25%) of polyoxyethylene dodecyl ether sodium sulfate (C12H25 (OCH2CH2) nOSO3Na, n=6 and 13) (I) and sodium dodecyl sulfate (II).In the concentration and temperature range experimented, every solution showed positive birefringence. This suggests that the solution structure mainly consists of lamellar micelle. In addition, in the solutions of I a network is likely to be formed by the interlinking of the polyoxyethylene chains situated outside the micelle. The solution of II showed larger velocity gradient dependency in flow birefringence than the solutions of I. This would be due to absence of the network formation.Flow birefringence was measured twice at every velocity gradient, in the course of raising the velocity gradient and in the returning course. In the case of 6 OE dodecyl ether sulfate, bire-fringence curves obtained on lowering the velocity gradient laid above those on raising, that is, hysteresis in velocity gradient dependence of the birefringence is present. Elevation of temperature and addition of electrolyte reduced the hysteresis. This supports the inference that in the case of 6 OE dodecyl ether sulfate the formation of the network, which is hindered, because of the relatively short chain length, by electrostatic effect of the ion group at the end of the polyoxyethylene chain, is promoted by the increase of the velocity gradient.