Optimization of optical transparency of personal care products using the refractive index matching method

Many toothpastes and personal care products consist of suspensions of silica particles in aqueous gels of humectants and other soluble constituents. It is highly desirable to develop new formulations that retain the desired characteristics of the original products but also have high optical transparency. Here, we used the refractive index matching method to manufacture highly transparent toothpastes. Accordingly, we determined the refractive indexes of different liquid gels, each containing a different humectant concentration, and measured the light transmittance and turbidity of formulations containing those gels and the silica. By fine tuning the humectant fraction in the gel, we obtained toothpastes with optimal transparency and also determined the effective refractive indexes of different commercial silica. All silica had similar indexes irrespective of their supplier, particle size distribution, and morphology. We believe that this approach could be extended to other commercial products and therefore contribute to the development of new advanced formulations.