Soret-decoupled thermoelectric potential in binary highly ionized liquids

A self-consistent theory of the Seebeck effect in highly ionized fluids is developed using nonequilibrium thermodynamics. The relationship between Onsager kinetic coefficients is derived from material transport equations based on thermodynamic fluxes, in order to obtain single-valued component concentration profiles. The model determines the heat of transport as a thermodynamic quasi-equilibrium parameter equal to the respective electrochemical potential with the opposite sign to express the Seebeck coefficient through component molecular entropies in the absence of a Soret effect and without employing kinetic quantities such as activation energy, ratcheting, and transference numbers. The model explains the large Seebeck coefficients measured in (poly)ethylene glycol (PEG) solutions modified with NaOH as a result of the increased entropy of small ions when complexed with large polar molecules. In order to test the model, empirical values of the Seebeck coefficient for NaOH-modified PEG liquids are incorporated into the model to calculate molecular entropy; the calculated values are consistent with those independently measured in the literature.