AEROSOL FOAMS 359 10 4 103 - 10 2 _ 10 10 -2 ! ! A ß H-Type _ ß ' M-Type 0 ' L-Type ' I .... I ' ' ' I .... I ' ' ' I I I I .... I , , , I .... I I I , 10 4 10 ø apparent viscosity rlc (poise) Figure 8. Relationship between Bingham yield value ('rB) and apparent viscosity of the concentrate 0qc). degree of cationic substitution was about 0.3-0.4 per anhydro-glucose unit, one anionic surfactant molecule can be combined ionically to six glucose units on average. The weight ratio of the cationic cellulose to the anionic surfactant falls into 7/1, when they are at balance of the charge. The concentration of the anionic surfactant is 0.1 wt% in this study. We define the charge ratio of the cationic cellulose to the anionic surfactant as R. When R is unity, the concentration of cationic cellulose should be to 0.7 wt%. Figure 10 expresses the results in Figure 9 in a different manner because the x-axis represents R instead of the cationic cellulose concentration. The maximum point on is observed at a ratio, R, of ca. 2.0 between the cationic cellulose and the anionic surfactant for the M-type and the H-type, and ca. 4.0 for the L-type. Thus, Xlf changed remarkably below and above R ..... i.e., between 2.0 and 4.0. Leung and Goddard (16) considered that the behavior of a solution comprising a cationic polymer (Polymer JR ©) and sodium dodecyl sulfate was different as a function of the charge ratio between them. Maximal complex formation (precipitation) was observed near R of unity. As a consequence, the viscosity increases. Although the precipitation of the complex is low, a similar complex formation was recognized in a ternary component system with an additional nonionic surfactant (24,25).

360 JOURNAL OF COSMETIC SCIENCE 10 ø 'H-type O ß M-type 0 ß L-type I I I 10 -1 I I 10 -z 1 O-• 10 ø A -$ oo I 10 • apparent viscosity of the concentrate tic (poise) Figure 9. Relationship between apparent viscosity (qq•) and apparent viscosity of the concentrate (qqc)- From the foregoing we consider the dissolved state for the polymer and the surfactant in a liquid film of a foam as follows: When R is below Rm•x, there exists the excess anionic surfactant, and the complex formation is increasing with the cationic cellulose concen- tration to Rm• , i.e., 2.0-4.0. Consequently, the thixotropic behavior is enhanced. Furthermore, T B and thixotropy increase continuously, even when R exceeds Rma x. This could be explained by assuming increasing levels of entangled free cationic cellulose. When the shear rate is increased, however, the degree of entanglement among the charged cellulose chains decreases so that the desorption of the complexes at the air/ liquid interface might occur. The interface between air and liquid then becomes un- stable, resulting in the coalescence and the breakdown of the foams. CONCLUSIONS The yield value, TB, of the aerosol foams increases with the apparent viscosity of the concentrate, qqc. However, the apparent viscosity of the foams, qqo shows a maximum value when plotted against qqc. The charge ratio between the cationic cellulose and the anionic surfactant, R, is 2.0-4.0 at the maximum qqf. From these results, we presume