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j. Soc. Cosmet. Chem., 33, 131-140 (May/June) Influence of bubble size on rheological properties of soap foam H. YAMADA, H. KOMATSU AND M. TANAKA, Shiseido Laboratories, 1050 Nippa-cho, Kohoku-ku Yokohama, Japan 223 Received September 21, 1981. Presented at 28th Meeting, Society of Rheology October I980, Sendai, Miyagi, Japan. Synopsis The viscoelasticity of soap foam and the bubble size were measured. They were influenced by the dissolved state of the soap and/or the viscosity of the solution. The elasticity of the foam and the reciprocal of the bubble size decreased with increasing viscosity of the solution. The correlation between the elasticity of the foam and the reciprocal of the bubble size was a linear relation having a minus coefficient. INTRODUCTION Foam characteristics is one of the dominant factors that determine the commercial value of such cosmetic products as soap, shampoo, shaving foam, cleansing foam, tooth paste, etc. Among the various properties of foam such as foaminess, foaming capacity, stability and mechanical property, the mechanical property has been rarely studied (t•5) by the lack of appropriate measuring instruments. The review in this area is given by Bikerman (6). An apparatus was devised to measure the mechanical property of foam, details of which were described previously (7). The principle of the measurement is based on the analysis of the oscillation of a coil spring dampened by foam. The effect of adding super-fatting agents to a soap on the physicochemical properties of the soap has been recently studied. The results of the study were presented elsewhere (8). This paper reports the relationship between the mechanical property of foam and bubble size. MATERIALS AND METHODS MATERIALS All compounds except water-soluble thickening agents were reagent-grade and were used without further purification. The water used was distilled after deionization. 131