AGGREGATION OF POLYOXYETHYLENE GLYCOL MONODECYL ETHER IN NONPOLAR-SOLVENTS AND THE EFFECT OF WATER .2. APPARENT MOLAR VOLUMES AND HEAT-CAPACITIES IN CYCLOHEXANE AND DECANE AT 298.15-K

The apparent molar volumes Vφ and the apparent molar heat capacities Cp,φ of the amphiphiles polyoxyethylene glycol monodecyl ether C10En for n = 1 to 8 and decanol were determined in cyclohexane and decane up to 0.8 mole kg-1 at 298.15 K. Those properties of C10E8 in heptane were also measured to complete the series of systems, C10En + heptane, investigated previously. The process of forming aggregates depends on the length of polar chain of the amphiphiles and solvents. Although their aggregations proceed, in general, gradually with increase in the molality the amphiphile C10E8 aggregates as sharply as alkanol in alkane. An abnormal increase in Cp,φ at the dilute region due to intramolecular association was observed for C10En of {A figure is presented} 4 in all of the investigated solvents. By adding a small amount of water the aggregation is enhanced and swollen micelles are formed passing through a sharp transition. The molality where this transition occurs shifts to a smaller value when the polar-chain of the amphiphiles is longer and/or the solvent molecule is a hydrocarbon of a longer straight-chain. © 1990.