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The expansibility of a nonionic water soluble polymer, a propylene oxide-ethylene oxide copolymer, in aqueous solution, was measured as a function of temperature between 2 and 80 °C. Volume changes were measured, with a dilatometer of novel design, to an accuracy of 0.1 pL. Values for the apparent molar volume, , and apparent molar expansibility, , of the polymer were obtained. A sharp transition with change in apparent molar volume was found to occur, indicating cooperativity. The value of this change increased with increasing propylene to ethylene ratio, at constant molar mass of the polymer. Typical values obtained for the increment in apparent molar volume and expansibility, per mole of monomer residue, were = 0.60 X 10"6 m3 mol"1, = 0.11 X 10"6 m3 mol"1 K"1, at propylene to ethylene ratio of 0.29:1, and = 3.82 X 10"6 m3 mol"1, = 0.42 X 10"6 m3 mol"1 K"1, at a propylene to ethylene ratio of 6.78:1. The increase in transition volume with increase in propylene to ethylene ratio was also associated with a decrease in the cloud point, which indicated an increase in hydrophobic interaction.

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A differential heat capacity flow microcalorimeter is used to monitor in a continuous mode the thermal expansion of a sample during a programmed temperature scan. The sample may consist of liquids, suspensions, or bulk solids in a confining liquid and the typical temperature scanning rate is of the order of 1 K/min. The technique has a precision better than 1% and a detection limit of 10(-6) ml s(-1). In contrast to conventional dilatometers, this technique offers variable sensitivity and is not limited by the magnitude of the total volume change during the experiment. Various expansibility data obtained in the temperature range 10-55 degrees C are reported for several systems, namely water, benzene, carbon tetrachloride, and aqueous solutions of sodium chloride. The volume changes for the thermal transition of Teflon and the phase separation of 2-butoxyethanol/water mixtures further illustrate the possibilities of this new technique.

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