Solution Behavior of Nonionic Surfactants with Multi-hydrophobic Chaifis in Water

Abstract

The solution behavior of poly (oxyethylene) hydrogenated castor oils (EC) and poly (oxyethy-lene) sorbitol tetroleates (ESTO) with different oxyethylene chain length in water was investigated and discussed in comparison with that of poly (oxyethylene) nonylphenyl ether (NP). Their binary phase diagrams were obtained by a polarizing microscopic technique and differential seanninig calorimetry. With an increase of the oxyethylene chain length, the dissolved states of these surfactants in water changed from dispersion of concentric lamella liquid crystal to micellar solution at low concentrations. At relatively high concentrations however, it changed from neat phase to middle phase liquid crystal and further to micellar solution. These observations can be attributable to the decrease of the aggregation number of the aggregates. The aggregation number increased with a multiplication of the hydrophobic chain. When the dissolved states of NP, EC and ESTO each having the same clouding point were compared in the same constitution, EC formed the middle phase and ESTO formed the neat phase at low concentrations where NP formed the micellar solution. Furthermore EC and ESTO formed the neat phase at high concentrations where NP formed the middle phase liquid crystal. This study indicated that a surfactant with multi-hydrophobic chains acts more hydrophobically than an ordinary single-chain surfactant having the same H/L balance. © 1981, The Chemical Society of Japan. All rights reserved.