j. Cosmet. Sci., 50, 351-362 (November/December 1999) Rheological properties of aerosol foams containing aqueous cationic polymer and anionic surfactant YOSHIFUMI YAMAGATA, Material Science Research Center, Lion Corporation, 7-13-12 Hirai, Edogawa-ku, Tokyo 132-0035, Japan. Accepted for publication September 30, 1999. Synopsis Aerosol foams containing cationic cellulose of different molecular weights and an anionic surfactant were studied by using the cyclic shearing tests. The yield value, xn, of the aerosol foams increased with the apparent viscosity of the concentrate, qqc- However, the apparent viscosity of the foam, qqf, showed a maximum value when plotted against qqc, at the charge ratio between the cationic cellulose and the anionic surfactant, R .... between 2.0 and 4.0. From these results, we presume that the dissolved states for the polymer and the surfactant in the liquid film of the foam are different below and above INTRODUCTION Foam can be produced by various methods. By an air injection method, air is blown into the vessel containing a surfactant solution. Shaking, rotating, and stirring methods are also applicable (1). In other methods, liquefied hydrocarbon gases are allowed to evapo- rate and serve as foaming agents or as a propellant. The foam generated by this method is called aerosol foam, and is used as shaving and styling foams in the field of cosmetics. The above-mentioned foams were so unstable hitherto that it was difficult to study them experimentally. There are several factors associated with foam instability, i.e., drainage rupture of the liquid films followed by coalescence, and change in bubble size (2). To improve stability, multiple surfactants (2,3) or water-soluble polymers (4) are added. It is known that foam properties are considerably affected by complexes formed by the addition of long-chain alcohols to ionic surfactants in an aqueous solution, as a result of being adsorbed at the air/liquid interface (2,3,5). Another complex has been investigated for the system using water-soluble polymers with ionic surfactants (6-11). For example, Goddard and co-workers (6-8,12-19) and Ohbu eta/. (20,21) studied complex formation between water-soluble cationic cellulose polymers and anionic or amphoteric surfactants. It is generally accepted that the for- mation and precipitation of the complex formed between polyelectrolytes and oppositely charged surfactants and the resolubilization by excess surfactants are due to the simul- taneous electrostatic and hydrophobic interactions between them. 351

352 JOURNAL OF COSMETIC SCIENCE However, few foam systems have been reported in which the complex between a water- soluble cationic polymer and an anionic surfactant were combined. In the present paper, we examine systematically the rheological properties of the foams prepared from a glycidyl trimethylammonium chloride, adduct to hydroxyethylcellulose and an anionic acyl glutamate. We discuss the dissolved states of the components in foams on the basis of macroscopic flow behavior, together with direct microscopic observation of the foam. EXPERIMENTAL MATERIALS Cationic celluloses of different molecular weights (cationic cellulose, Leogard ©, Lion Corp.), were used as water-soluble cationic polymers. Figure 1 shows the structural formula of the cationic celluloses of molecular weight 50,000, 150,000, or 500,000, identified as L-type, M-type, and H-type, respectively. The average degree of cationic substitution was about 0.3-0.4 per anhydroglucose unit. A surfactant used was trieth- anolamine cocoyl-l-glutamate (Amisoft © CT-12, Ajinomoto Corp.). The nonionic sur- factant nonoxynol-15 (Liponox © NC-150, Lion Corp.) was also used in the solubilized system. All compounds were used without further purification. Aqueous solutions, described as concentrates, were prepared by adding 0.1 wt% anionic surfactant, 0.5 wt% nonionic surfactant, and various amounts of the cationic celluloses to deionized water, and mixing and stirring with a rod with four paddles at room temperature. The prepared concentrates (94 parts and six parts of a propellant [w/w]) were confined in a pressure-proof aluminum container (35-mm diameter). The propel- lant used was liquefied petroleum gas consisting of propane, n-butane, and isopentane with an equilibrium vapor pressure of 4.4 x 105 Pa at 20øC. MEASUREMENT All experiments were carried out at 25øC. When the aluminum container was allowed to stand, the contents were separated into two layers, i.e., concentrate and propellant phases. In such a condition, uniform foam cannot be obtained even if the contents are _ CH20(CH2CH20)n•SCH2Ci HCH2N+(CH3)3Cl')p \• H/H O•[N OH OX\OH H )1 N •=18 N N• /I•i' N •=013-0.4 H OH Figure 1. Structural formula of cationic cellulose.