TABLE OF CONTENTS To permeate an electrolyte or solvent through an ion exchange membrane, other driving forces such as a thermal gradient (thermo-osmosis) can be used. Because heat transfer is higher than the transport of ions and solvent in the ion exchange membrane, the transport of ions and solvents through the membrane is difficult to measure accurately. Therefore, various improvements have been made in measuring apparatus and methods. [207]
The thermal membrane potential of the cation exchange membrane is positive at the hot side [208] and that of an anion exchange membrane is negative at the hot side [209] in potassium chloride solution. In general, ions permeate through the ion exchange membranes from the cold to the hot side. However, the cation exchange membrane HCl solution system shows that the thermal membrane potential is positive on the hot side at low concentrations and that the potential is reversed at high concentrations. [208] It has also been reported that thermal transport of various salts, KCl, LiCl, NH 4Cl, KIO 3, K 2SO 4, etc. through anion exchange membranes occurs from the cold to the hot side. [210] For KlO 3, the absolute value of thermo-osmosis is larger than that of other electrolytes because the pore volume fraction of the membrane for KIO 3 is larger than that for the other electrolytes. Though the thermo-osmosis volume flux (solvent transport) is generally from the cold towards the hot side,...
