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Evaporation of particle-stabilised emulsion sunscreen films

Binks, Bernard P.; Fletcher, Paul D.I.; Johnson, Andrew J.; Marinopoulos, Ioannis; Crowther, Jonathan M.; Thompson, Michael A.

Authors

Paul D.I. Fletcher

Andrew J. Johnson

Ioannis Marinopoulos

Jonathan M. Crowther

Michael A. Thompson

Abstract

We recently showed (Binks et al., ACS Appl. Mater. Interfaces, 2016, DOI: 10.1021/acsami.6b02696) how evaporation of sunscreen films consisting of solutions of molecular UV filters leads to loss of UV light absorption and derived sun protection factor (SPF). In the present work, we investigate evaporation-induced effects for sunscreen films consisting of particle-stabilized emulsions containing a dissolved UV filter. The emulsions contained either droplets of propylene glycol (PG) in squalane (SQ), droplets of SQ in PG or droplets of decane in PG. In these different emulsion types, the SQ is involatile and shows no evaporation, the PG is volatile and evaporates relatively slowly, whereas the decane is relatively very volatile and evaporates quickly. We have measured the film mass and area, optical micrographs of the film structure, and the UV absorbance spectra during evaporation. For emulsion films containing the involatile SQ, evaporation of the PG causes collapse of the emulsion structure with some loss of specular UV absorbance due to light scattering. However, for these emulsions with droplets much larger than the wavelength of light, the light is scattered only at small forward angles so does not contribute to the diffuse absorbance and the film SPF. The UV filter remains soluble throughout the evaporation and thus the UV absorption by the filter and the SPF remain approximately constant. Both PG-in-SQ and SQ-in-PG films behave similarly and do not show area shrinkage by dewetting. In contrast, the decane-in-PG film shows rapid evaporative loss of the decane, followed by slower loss of the PG resulting in precipitation of the UV filter and film area shrinkage by dewetting which cause the UV absorbance and derived SPF to decrease. Measured UV spectra during evaporation are in reasonable agreement with spectra calculated using models discussed here.

Publication Date Aug 24, 2016
Journal ACS applied materials & interfaces
Print ISSN 1944-8244
Electronic ISSN 1944-8252
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 8
Issue 33
Pages 21201-21213
Institution Citation Binks, B. P., Fletcher, P. D., Johnson, A. J., Marinopoulos, I., Crowther, J. M., & Thompson, M. A. (2016). Evaporation of particle-stabilised emulsion sunscreen films. ACS applied materials & interfaces, 8(33), 21201-21213. https://doi.org/10.1021/acsami.6b06310
DOI https://doi.org/10.1021/acsami.6b06310
Keywords Sunscreen, Evaporation, Emulsion, Spectrophotometry, Precipitation, SPF
Publisher URL http://pubs.acs.org/doi/abs/10.1021/acsami.6b06310
Copyright Statement ©2017 University of Hull
Additional Information This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS applied materials & interfaces, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acsami.6b06310

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