Critical exponent of the heat of transport of water– isobutyric acid mixtures

The Dufour effect (diffusion thermoeffect) has been used to obtain the critical exponent of the heat of transport in binary mixtures of isobutyric acid and water near the liquid–liquid critical point. As the critical temperature is approached experimentally, the heat of transport vanishes with a critical exponent of about 2/3. The i critical exponent for the Onsager coefficient Ω01 is zero. This value is consistent with the semidefinite positive entropy production r requirement and is identical to the best literature value for the critical exponent of the reciprocal Onsager coefficient Ω10. In order to explain the observed critical behavior of the heat of transport a new molecular interpretation based on the random thermal motion model for diffusion is suggested.