Measuring Viscosity of Cosmetics with microVISC
Key Words: Face lotion, hand lotion, cream, viscosity, shear thinning, cleaning, high shear, non-Newtonian fluid, protocol, thixotropy
Goal: Cosmetic lotions are often non-Newtonian fluids with yield stresses and thixotropic structure. These properties are vital for their function as self-care products, but also make their rheological properties difficult to characterize. In particular, data collection can be time consuming and instrument cleaning can be challenging. This application note will share an easy-to-implement protocol to precisely measure complex cosmetic formulations using VROC technology.
Skin care is an important part of personal healthcare. The epidermis is one of the body’s largest organs and is the first line of defense against pathogens, so maintaining and promoting healthy skin is vital for healthy life. Skincare products, specifically lotions, have been used for decades to promote skin health. When developing these products, manufacturers must carefully choose ingredients that must meet both consumer tastes and regulatory standards. These constraints make it vital to characterize lotion formulations, but also these criteria make consistent and fast measurements more challenging. Lotions are comprised of multiple materials including polymers, oils, waxes, gels, and silicones (Sharma et al. 2018). These ingredients can dramatically alter the viscosity of the lotion, but also make measuring viscosity difficult, messy, and variable. The combination of these ingredients can even cause lotions to behave as thixotropic materials.
Thixotropy is the time dependent shear thinning property of non-Newtonian fluids (Mewis 1979). Thixotropic materials will slowly return to their high viscosity state once shearing has ceased. The thixotropic behavior of lotions can result in inconsistent data. The same shear force and/or shear rate can be applied to a material multiple times in quick succession and the measured viscosity will vary after each measurement because the microstructure (one of the driving forces of thixotropy) of the material has not recovered to its original state.
Here we present a ten-step protocol to measure high viscosity, complex lotion samples using Viscometer-Rheometer-on-a-chip (VROC®) technology. This protocol will describe the steps to prime the VROC chip with glycerol, run a lotion sample, and clean the VROC chip with glycerol, using minimal material, quickly and efficiently, resulting in repeatable data. The lotion tested in this protocol had an average viscosity of 424.40 mPa-s, a standard deviation of 1.68 mPa-s, and a %RSD (relative standard deviation) of 0.40%. Download below!