Influence of the emollient structure on the properties of cosmetic emulsion containing lamellar liquid crystals

Abstract

In the present study the effect of cosmetic emollients (oils and esters) varying from their chemical structure on the lamellar liquid crystals organization has been investigated. The cetearyl alcohol/cetearyl glucoside emulsifier, known for its ability to form lamellar phases was used at a level of 10% in emulsions. At this high concentration a strong lamellar network is formed. Also, each of the seven selected emollients was incorporated at level of 20%, as for a classical cosmetic emulsion. These quantities were necessary in order to assure the presence of lamellar phases in all the samples and to amplify the impact of the emollient on the structural organization of the surfactant. Additionally, a control sample was formulated, containing only emulsifier and water. Emollients were divided as a function of their chemical structure in group A (without heteroatom) and B (with heteroatom). They were first described as a function of the interfacial tension against water, in order to classify them according to their hydrophobicity.The presence of the lamellar phases in all samples was confirmed by means of optical microscopy under polarized light, and then the differences between emulsions physical properties were evidenced by static light scattering and rheological measurements. It was shown that use of A group emollients induces larger droplets size and, respectively, more elastic behavior to the emulsions. This phenomenon is related to the lamellar organization, which is dominated by α-gel for A group oils and by lamellar liquid crystals combined to α-gel for B group emollients, as showed through wide angle X-ray diffraction technique. Moreover, the influence of such structures on usage properties of emulsions was characterized via thermal analyses and spreadability tests.