The Influence of Various Silicones on the Rheological Parameters of AZG Containing Silicone-Based Gels

Aluminium zirconium tetrachlorohydrex glycine (AZG) is a popular antiperspirant/deodorant agent, formulated in various forms including the clear gels. Silicones are used for the preparation of these gels, giving them desirable characteristics. The aim of this study was to investigate the influence of various silicones, when used in combination, on the rheological properties of the resulting AZG gels prepared. Based on preliminary studies, various AZG containing silicone-based gel formulations were prepared. Silicones used (as ternary mixtures) included ABIL^® EM 97, ABIL^® 8839 and ABIL^® 8852. Formulations prepared were then examined rheologically and their plastic viscosity and yield values determined. Results showed that the amount of ABIL^® EM 97 (used as an emulsifier) present within the gel formulation is critical. An increase in the amount of this silicone, corresponding to a small decrease in the amount of the hydrophobic structure building (gelling agent) ABIL^® B8839, increased the plastic viscosity and yield values of the gel. On the other hand, an excess amount of ABIL^® B8852, as a hydrophilic co-surfactant, reduced the viscosity and yield values of the resulting gel. Eventually, among the formulations prepared, formulation F5 with suitable aesthetic and skin feel properties, spreadability and rheological behaviors, was selected for further studies. By constructing the up-curve and down-curve of this formulation, presence of a plastic thixotropic behavior was confirmed. Inclusion of various amounts of the hydrophobic silicone-based agent, dimethicone, within formulation F5 showed that by increasing the amount of dimethicone present, the plastic viscosity and yield values of the gel would be reduced. This reduction was significant at dimethicone concentrations above 0.5%. Furthermore, by increasing the amount of dimethicone present, the calculated "percentage of reduction in plastic viscosity" also increased. This means that the extent of thixotropicity of the gel formulation increases by the addition of dimethicone. This finding was also backed up by the resulting rheograms constructed. Overall, addition of 0.75% dimethicone produced the most acceptable product in terms of an appropriate viscosity, yield value and extent of thixotropicity. In conclusion, this study shows that in-depth rheological assessment of AZG gels prepared from silicones could be used as an important tool during their formulation and characterization in order to obtain an effective formulation with desirable properties.