title: Evaporation of Sunscreen Films: How the UV Protection Properties Change.
abstract: We have investigated the evaporation of thin sunscreen films and how the light absorption and the derived sun protection factor (SPF) change. For films consisting of solutions of common UV filters in propylene glycol (PG) as solvent, we show how evaporation generally causes three effects. First, the film area can decrease by dewetting leading to a transient increase in the average film thickness. Second, the film thins by evaporative loss of the solvent. Third, precipitation of the UV filter occurs when solvent loss causes the solubility limit to be reached. These evaporation-induced changes cause the UV absorbance of the film to decrease with resultant loss of SPF over the time scale of the evaporation. We derive an approximate model which accounts semiquantitatively for the variation of SPF with evaporation. Experimental results for solutions of different UV filters on quartz, different skin mimicking substrates, films with added nanoparticles, films with an added polymer and films with fast-evaporating decane as solvent (instead of slow evaporating PG) are discussed and compared with model calculations. Addition of either nanoparticles or polymer suppress film dewetting. Overall, it is hoped that the understanding gained about the mechanisms whereby film evaporation affects the SPF will provide useful guidance for the formulation of more effective sunscreens.
authors.affiliation: Department of Chemistry, University of Hull , Hull HU6 7RX, United Kingdom.
authors.forename: Bernard P
authors.initials: BP
authors.lastname: Binks
authors.forename: Jonathan
authors.initials: J
authors.lastname: Brown
authors.affiliation: Department of Chemistry, University of Hull , Hull HU6 7RX, United Kingdom.
authors.forename: Paul D I
authors.initials: PD
authors.lastname: Fletcher
authors.affiliation: Department of Chemistry, University of Hull , Hull HU6 7RX, United Kingdom.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Johnson
authors.affiliation: Department of Chemistry, University of Hull , Hull HU6 7RX, United Kingdom.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Marinopoulos
authors.affiliation: GSK Consumer Healthcare (U.K.) Ltd. , 980 Great West Road, Brentford, Middlesex TW8 9GS, United Kingdom.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Crowther
authors.affiliation: GSK Consumer Healthcare , STF 1N-45, 20 TW Alexander Drive, Research Triangle Park, North Carolina 27709-3398, United States.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Thompson
mesh_terms: D003890:Desiccation; D011108:Polymers / Q000737:chemistry; D012867:Skin / Q000187:drug effects* / Q000528:radiation effects; D059405:Sun Protection Factor / Q000592:standards*; D013473:Sunscreening Agents / Q000737:chemistry* / Q000494:pharmacology*; D014466:Ultraviolet Rays
chemical_list: D011108:Polymers; D013473:Sunscreening Agents
keywords: evaporation; precipitation; spectrophotometry; sun protection factor; sunscreen; wetting