CAPILLARY-RISE STUDY OF NONEQUILIBRIUM WETTING BY A BINARY-LIQUID CAUSED BY TEMPERATURE RAMPS

A phase-separated mixture of cyclohexane and acetic anhydride was subj ected to positive linear temperature ramps while the capillary rise of the acetic anhydride-rich phase against a glass substrate was measure d. The ramps, which drove the system out of thermal equilibrium, had t he effect of producing large nonlinear changes in capillary rise with respect to ramp rate. These changes may be explained in terms of the n onequilibrium behavior of the wetting-layer thickness, and depended on ly weakly on the size of the ramps. The deviation of the capillary ris e from its equilibrium value was found to attain a steady state after the temperature had been raised by almost-equal-to 0.6 K from the star ting temperature of T(c) - T = 5.9 K, independent of the ramp rate. Th is steady state may be indicative of the virtual disappearance of the wetting layer. Unlike recent direct observations of wetting-layer thic kness [Dean Ripple and Carl Franck, Phys. Rev. A 44, 8289 (1991)], our results could not be simply described as the ''equilibrium'' wetting behavior of a bulk nonequilibrium experiencing linear response to a we ak temperature ramp.