THE USE OF RAMAN-SCATTERING TO STUDY WETTING AND FLUID-FLOW OF BINARY LIQUIDS IN POROUS-MEDIA

We describe the use of Raman scattering as a technique for measuring the concentration of binary liquid mixtures inside a porous medium. The technique is demonstrated by measuring the concentration of mixtures of 2,6-lutidine and water inside the porous glass Vycor. These measurements reveal a large increase in the lutidine concentration inside the Vycor relative to that in a reservoir in contact with the Vycor. This shift is a strong function of concentration and temperature. We formulate a theory for the shift based on a Flory-Huggins model for the concentration dependence of the free energy of the liquid mixture which fits the data well. The measurements allow us to deduce the strength of the surface field h1 exerted by the internal glass surfaces on the imbibed liquid. Finally, we show that fluid flow in porous media can be effectively studied with Raman scattering by studying the diffusion of concentration gradients within the Vycor. © 1990 American Institute of Physics.