FIXED AND BULK EMULSION WATER 51 AG 2,5, 1.5 1.0 AG I I I I I I I I 20 30 40 50 60 70 80 90 loci 0.00 [mg/s] 0.02 0.04 Figure 5. TG-curve (AG-curve) and DTG-curve (AG/dt - curve) of a two-phase emulsion (Skin Life Emulsion ©, Helena Rubinstein, FRG). Total water content: 80%. With pure water the same shapes of the two curves are obtained. semihydrate water from cetostearyl alcohol and by the evaporation of water, which is entrapped mechanically in the cetostearyl alcohol gel-network. After melting of the hydrophilic gel phase at 72øC, the weight loss is governed by the evaporation of the interlamellarly fixed water. In the temperature interval of 84-97øC the interlamellarly fixed hydration water is released. All results for the water-containing hydrophilic ointment are summarized in Figure 7. The total water contents of the different creams are plotted against the interlamellarly inserted water. At a total water amount of 10 percent, the whole amount of water is interlamellarly fixed. At a total water amount of 70 percent, more than 40 percent is interlamellarly fixed in the hydrophilic gel phase. If the total water amount exceeds 80 percent, the hydrophilic gel phase has reached a saturation state in which the water molecules in the middle of the water layer between the bilayers have the same free energy in comparison with that of the bulk water molecules at the same temperature. This saturated state of the hydrophilic gel phase represents the transition point from cream to a liquid emulsion. Simultaneously the fraction of interlamellarly fixed water markedly decreases in favor of the fraction of the bulk water phase (Figure 7). Various pharmacopoeias and formularia have taken up formulations for O/W creams with non-ionic surfactants because these systems do not show most of the disadvan- tages of the O/W creams with ionic surfactants. The formula of the Deutscher

52 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS - 5.$ - 4.5 -4 -:3.5 -:3 -2.5 ling/s] -0.00 0.04 0.08 zXG I I I I I I I i I 30 40 50 õO 70 80 90 1OO [øC] Figure 6. TG-curve (AG-curve) and DTG-curve (AG/dt - curve) of water-containing hydrophilic ointment DAB 8 (for further explanation see text). Arzneimittelcodex (DAC) (12) for an O/W cream with non-ionic surfactants is as follows: (Poly)oxyethylated glycerolmonostearate (Tagat S 2*) Cetyl alcohol Stearyl alcohol Paraffinurn perliquidum 5 parts 5 parts 5 parts 7.5 parts *Theo Goldschmidt, Essen, FRG