The formation of liquid ordered (Lo) phase-like structures in stearyltrimethylammonium chloride/cholesterol/1,3-butanediol/water and hepta(oxyethylen) octadecyl ether/cholesterol/1,3-butanediol/water systems was investigated. Differential scanning calorimetry and X-ray scattering measurements confirmed that Lo phase-like structures were formed in both surfactant/cholesterol systems, similar to the lysophospholipid/cholesterol system. It was revealed that the concentration of cholesterol at which only Lo phase-like structures are formed increases in the order stearyltrimethylammonium chloride < lysophospholipid < hepta(oxyethylen) octadecyl ether. In addition, for both surfactants, the interlayer spacing, d, was larger for Lo phase-like structures than for α-gel structures. These results suggest that the ionicity and structure of the hydrophilic group of each surfactant play important roles.
Keywords: cholesterol-induced structure; gel; liquid ordered phase–like structure; phase transition.