Abstract

The study of fluids in porous media has clearly demonstrated that their fundamental properties are strongly influenced by confinement in small structures. Previous microscopic studies of the molecular reorientation time of liquid oxygen filling porous glasses¹ has given clear proof that the freezing point of a confined fluid in a pore of radius R may be depressed by an amount ΔT which is inversely proportional to the pore radius. A phenomenological model based only on the effects of geometrical constraint was consistent with the observed supercooling and picosecond molecular realxation. In contrast to a rapidly developing microscopic picture, little is known about confined fluids over longer length scales where the interconnecting network of pores allows collective fluid excitations. To study possible collective behavior over macroscopic length scales, we have conducted an ultrasonic investigation of supercooled ethanol in porous glass for sound wavelengths much larger than the size of the confining pores.

© 1988 Optical Society of America