Effects of temperature and chain length on the properties of long chain polyoxyethylene dodecyl ethers in aqueous solution

The micelle formation and adsorption phenomena at the air-water interface of four long-chain polyosyethylene dodecyl ethers, C12H25O(C2H5O)(m) H abbreviated as C12En (n = 6, 7: 10, 20, 30, and 40), which have newly been synthesized to have more narrow polyoxyethylene chain-length distribution than previously used, have been investigated in aqueous solution by surface tension measurements over a concentration rang of the surfactants(10(-5)-10(-3) m) at different temperatures (25, 35, 40, and 45 degrees C. The critical micelle concentration (CMC), the area (A) per surfactant molecule. and the standard Gibbs free-energy change of micellization (Delta G(m)) were determined from the surface-tension data of the solutions and the Gibbs adsorption equation at the various temperatures. It has been Found that the CMC values of C12En increase with increasing chain length oi polyoxyethylene but decrease with increasing temperature. The area per molecule A increases with elevating temperature, their increment from 25 degrees C to 45 degrees C being 3.3, 12.2, 20.5, and 36.9 Angstrom(2) for the C12En ill = 10, 20, 30, and 40), respectively. application of a scaling rule in polymer science to parameters A and Delta G(m) has suggested that a coil-globule transition takes place between 35 and 45 I;C both at the micellar surface and at the air-water interface for the C12E40 and C12E40 around 40 degrees C.