DEAD SEA SALTS IN COSMETIC EMULSION 13 Comparison of Figures 9 and 10 reveals that the decrease in conductivity of the salt-free sample with storage time is more pronounced than that of the salted sample. This supports our previous results, that the rate of water evaporation in the salt-free sample is greater than that in the samples with added salt. This result is confirmed by the results of weight measurement, where the weight loss in the salted sample is less than the weight loss in the salt-free sample (see, for example, Figure 5 ). CONCLUSIONS The addition of Dead Sea salt to a cosmetic emulsion has a large impact on viscosity even at low concentrations. The obtained two maxima in viscosity are due to the presence of different monovalent and divalent ions in the DS salt. The resulting increase in viscosity was due to flocculation that led to an increase in the apparent dispersed-phase volume. The cream samples containing more than 0.25 wt% of DS salt showed phase separation. Emulsion samples containing 0.15% of DS salt exhibited the maximum viscosity under all test conditions, and therefore, were considered the optimal sample. The evaporation of water from the emulsion samples led to increased viscosity with storage time and storage temperature. In addition, the presence of DS salt in the cosmetic emulsion significantly reduced the rate of water evaporation. It was also found that the conduc­ tivity of the emulsion decreased with storage time, reflecting the decrease in free water. However, the presence of DS salt reduced the rate of conductivity decrease. ACKNOWLEDGMENTS This work was supported by the Deanship of Scientific Research at Jordan University of Science and Technology under grant 61/2003. The authors are grateful to Dr. Hussam El-Haffar and Mrs. Aida Frehatt from Ammon Co. for their kind cooperation and supply of materials. REFERENCES (1) R. Brummer and S. Godersky, Rheological studies to objectify sensations occurring when cosmetic emulsions are applied to the skin, Colloids Surf A: Physicochem. Eng. Aspects, 152, 89-94 (1999). (2) M. M. Jimenez Soriano, M. J. Frenso Contreras, and E. S. Selles Flores, Development of a cream from a self-emulsifying base and moisturizing actives, Il Farmaco, 56, 513-522 (2001). (3) M. Korhonen, L. Hellen, J. Hirvonen, and J. Yliruusi, Rheological properties of creams with four different surfactant combinations-Effect of storage time and conditions, Int.]. Pharmaceut., 221, 187-196 (2001). (4) H. Szelag and B. Pauzder, Rheological properties of emulsions stabilized by acylglycerol emulsifiers modified with sodium carboxylates, Colloids Surf A: Physicochem. Eng. AJpects, 219, 87-95 (2003). (5) L. R. Gaspar and P. M. B. G. Maia Campos, Rheological behavior and the SPF of sunscreens, Int.]. Pharmaceut., 250, 35--44 (2003). (6) M. L. Yao and]. C. Patel, Rheological characterization of body lotions, Appl. Rheol. 11, 83-88 (2001). (7) Z. Maor, S. Magadassi, D. Efron, and S. Yehuda, Dead Sea mineral-based cosmetics-Facts and illusion, Isr.]. Med. Sci., 32, S28-S35 (1996). (8) B. Abu-Jdayil, H. Mohameed, M. Sa'id, and T. Snobar, Rheological characterization of hair shampoo in the presence of Dead Sea salt, Int.]. Cosmet. Sci., 26, 19-29 (2004).

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