Aggregation of polyoxyethylene glycol monodecyl ether in heptane and the effect of water: Apparent molar volumes and heat capacities at 298.15 K

Abstract

The apparent molar volumes V φ and the apparent molar heat capacities C φ,p of polyoxyethylene glycol monodecyl ether C 10E n for n = 1 to 7 were determined in heptane solution at 298.15 K. The aggregates of these amphiphiles are formed gradualy with an increase in molality m without passing through sharp CMC. An intramolecular association is found for the amphiphiles with n larger than 4 in the extremely dilute region. In the ternary systems formed by adding a relatively small amount of water to C 10E 3 a very sharp peak appears in C φ,p at m = 0.20 mole kg −1 when the addition of water is increased to a ratio of more than 0.25 mole per each mole of C 10E 3. This will be assigned to the criical concentration at which a pseudo-phase transition of first-order type occurs in the aggregates consisting of water and amphiphile molecules: the macroemulsion changes the microemulsion or the swollen micellar solution.