SPECIFIC-HEAT OF A LIQUID-MIXTURE NEAR THE CONSOLUTE POINT IN THE BULK PHASE AND IN A POROUS-MEDIUM

The critical behavior of the specific heat of the mixture 2.6-lutidine + water near the consolute point was investigated in the bulk phase and in a porous medium. The measurements of the bulk specific heat yield a critical exponent alpha = 0.111 +/- 0.018 and a universal amplitude ratio A-/A+ = 1.77, in good agreement with theoretical predictions. Using previous experimental data for nitroethane + isooctane, we also determined the two-scale-factor ratio X+ = 0.271 between the critical amplitude of the specific heat and of the correlation length in agreement with the results reported for other fluid systems. The specific heat in the porous medium with a pore size of about 100 nm was measured. The behavior of the specific heat differs from that of the bulk specific heat. This may be the result of finite size effects, of a wetting layer in the pores, and of a distortion of the coexistence curve.