Partial molal volumes of some non-ionic detergents in monomeric and micellar form.

Abstract

Abstract Partial molal volumes of five synthetic non-ionic detergents have been measured above and below their critical micellar concentrations. The increases in volume on micellisation are discussed in terms of changes in hydration and hydrophobic bonding. The change in partial molal volume at the critical micellar concentration decreased with temperature. At 20° increases of 5, 9 and 17 ml mole−1 were obtained for the n-butyl, n-hexyl and n-octyl hexaoxyethylene glycol ethers respectively. For comparison with the alkyl ethers, the partial molal volume of hexaoxyethylene glycol was determined at four temperatures. The utility of density measurements for the determination of the critical micelle concentration of these non-ionic detergents depended on the temperature of the system; at higher temperatures the change in slope of density-concentration plots at the critical micelle concentration decreases and sometimes is not detectable.