EFFECT OF SURFACTANTS ON THE KINETICS OF AN IMMISCIBLE DISPLACEMENT IN VERY THIN CAPILLARIES

Rates v of mutual spontaneous and forced displacement of aqueous surfa ctant solutions (CTAB, EO(10)) by oils in thin quartz capillaries are measured, The capillaries were initially equilibrated with surfactant solutions under investigation for preventing adsorption in the course of displacement, In the region of flow rates 10(-4) to 2 x 10(-2) cm/s , dynamic capillary pressures, both advancing and receding, are consta nt, The dynamic interface tension of the receding menisci may markedly exceed the bulk value, The concentration of surfactant molecules near to receding menisci decreases due to exchange with the remaining wett ing film, Receding contact angles are close to 0, while advancing ones pass through a maximum CTAB concentration near to 10(-5) M. To unders tand the dynamic effects, experiments were continued in the region of v from 10(-4) to 10(-6) cm/s. In this region of v capillary pressures and interface tensions become rate dependent as a result of mass excha nge processes between a moving meniscus and a wetting film on capillar y walls, On the basis of this phenomenon, a theoretical approach was d eveloped, The results of calculations are in a qualitative agreement w ith the experimental data. (C) 1996 Academic Press, Inc.