PHYSICO-CHEMICAL STUDY OF THIN FILMS FORMED IN COSMETIC APPLICATIONS

In partnership with Croda do Brasil, this project studies the proprieties of thin films formed by sunscreen (W/O and O/W emulsions), evaluating the drying process, water resistance, and rheological proprieties of the formulations.
The drying process analysis was carried out using the Time Domain Nuclear Magnetic Resonance (TD-NMR) technique to evaluate the changes in the microstructure of the formulations with the variations in the distribution of hydrogen relaxation times (T2); A methodology for film forming with reproducibility and the appropriated thickness¬1 value of 2 mg/cm² was developed using Spin Coating and the water resistance was evaluated with submersions, abrasions and contact angle2 tests with different types of water (ultrapure, tap, and seawater).
The TD-NMR analysis was efficient to demonstrate changes in the microstructure of the formation after several hours Submersion and contact angle tests demonstrate that the ionic strength of water may affect the interaction between sunscreen film and water, a factor that may be important in sunscreen formulation development.

1. COLIPA. Guidelines for Evaluating Sun Product Water Resistance. The European Cosmetic Toiletry and Perfumery Association, Brussels (2005)
2. HAGENS, R. et al. Contact angle measurement–a reliable supportive method for screening water‐resistance of ultraviolet‐protecting products in vivo. International Journal of Cosmetic Science, v. 29, n. 4, p. 283-291, 2007.