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Wilmington, DE, United States

Davies M.A.,Ashland Specialty Ingredients
International Journal of Cosmetic Science | Year: 2015

Objective: Salicylic acid (SA) is a widely used active in anti-acne face wash products. Only about 1-2% of the total dose is actually deposited on skin during washing, and more efficient deposition systems are sought. The objective of this work was to develop an improved method, including data analysis, to measure deposition of SA from wash-off formulae. Methods: Full fluorescence excitation-emission matrices (EEMs) were acquired for non-invasive measurement of deposition of SA from wash-off products. Multivariate data analysis methods - parallel factor analysis and N-way partial least-squares regression - were used to develop and compare deposition models on human volunteers and porcine skin. Results: Although both models are useful, there are differences between them. First, the range of linear response to dosages of SA was 60 μg cm-2 in vivo compared to 25 μg cm-2 on porcine skin. Second, the actual shape of the SA band was different between substrates. Conclusion: The methods employed in this work highlight the utility of the use of EEMs, in conjunction with multivariate analysis tools such as parallel factor analysis and multiway partial least-squares calibration, in determining sources of spectral variability in skin and quantification of exogenous species deposited on skin. The human model exhibited the widest range of linearity, but porcine model is still useful up to deposition levels of 25 μg cm-2 or used with nonlinear calibration models. © 2015 Society of Cosmetic Scientists. Source

Cunningham V.J.,University of Sheffield | Alswieleh A.M.,University of Sheffield | Thompson K.L.,University of Sheffield | Williams M.,University of Sheffield | And 3 more authors.
Macromolecules | Year: 2014

A poly(glycerol monomethacrylate) (PGMA) macromolecular chain transfer agent has been utilized to polymerize benzyl methacrylate (BzMA) via reversible addition-fragmentation chain transfer (RAFT)-mediated aqueous emulsion polymerization. This formulation leads to the efficient formation of spherical diblock copolymer nanoparticles at up to 50% solids. The degree of polymerization (DP) of the core-forming PBzMA block has been systematically varied to control the mean particle diameter from 20 to 193 nm. Conversions of more than 99% were achieved for PGMA51-PBzMA250 within 6 h at 70 °C using macro-CTA/initiator molar ratios ranging from 3.0 to 10.0. DMF GPC analyses confirmed that relatively low polydispersities (M w/Mn < 1.30) and high blocking efficiencies could be achieved. These spherical nanoparticles are stable to both freeze-thaw cycles and the presence of added salt (up to 0.25 M MgSO4). Three sets of PGMA51-PBzMAx spherical nanoparticles have been used to prepare stable Pickering emulsions at various copolymer concentrations in four model oils: sunflower oil, n-dodecane, n-hexane, and isopropyl myristate. A reduction in mean droplet diameter was observed via laser diffraction on increasing the nanoparticle concentration. Finally, the cis diol functionality on the PGMA stabilizer chains has been exploited to demonstrate the selective adsorption of PGMA51-PBzMA100 nanoparticles onto a micropatterned phenylboronic acid-functionalized planar surface. Formation of a cyclic boronate ester at pH 10 causes strong selective binding of the nanoparticles via the cis-diol groups in the PGMA stabilizer chains, as judged by AFM studies. Control experiments confirmed that minimal selective nanoparticle binding occurred at pH 4, or if the PGMA51 stabilizer block was replaced with a poly(ethylene glycol) PEG113 stabilizer block. © 2014 American Chemical Society. Source

The aim of this study was to investigate the mechanism by which a VA/butyl maleate/isobornyl acrylate copolymer increases the SPF and water resistance of sunscreen formulations. Anhydrous sunscreen formulations with and without polymer were applied on polymethyl methacrylate (PMMA) plates and absorbance spectra were generated. Before immersion, the areas under the curve for the control and test samples were 98.49 and 117.09, respectively, and were 94.63 and 118.22, after immersion. Static and after-immersion, in vivo SPF values confirmed a boost in SPF and an increase in water resistance for the formulation containing the polymer (VA/butyl maleate/isobornyl acrylate copolymer). Digital imaging of sunscreen films combined with image analysis and contact angle measurements suggest that the polymer conformation changes upon exposure to water. The polymer forms a protective barrier over the sunscreen film upon exposure to water, which explains the enhancement in water resistance. The polymeric film formed has a different refractive index than the sunscreen film. The change in refractive indices causes diffraction of incident light, thus increasing its pathlength, leading to an increase in SPF. Source

Cunningham V.J.,University of Sheffield | Armes S.P.,University of Sheffield | Musa O.M.,Ashland Specialty Ingredients
Polymer Chemistry | Year: 2016

A near-monodisperse poly(stearyl methacrylate) macromolecular chain transfer agent (PSMA macro-CTA) was prepared via reversible addition-fragmentation chain transfer (RAFT) solution polymerisation in toluene. This PSMA macro-CTA was then utilised as a stabiliser block for the RAFT dispersion polymerisation of a highly polar monomer, N-2-(methacryloyloxy)ethyl pyrrolidone (NMEP), in n-dodecane at 90 °C. 1H NMR studies confirmed that the rate of NMEP polymerisation was significantly faster than that of a non-polar monomer (benzyl methacrylate, BzMA) under the same conditions. For example, when targeting a PSMA14-PNMEP100 diblock copolymer, more than 99% NMEP conversion was achieved within 30 min, whereas only 19% BzMA conversion was obtained on the same time scale for the corresponding PSMA14-PBzMA100 synthesis. The resulting PSMA-PNMEP diblock copolymer chains underwent polymerisation-induced self-assembly (PISA) during growth of the insoluble PNMEP block to form either spherical micelles, highly anisotropic worms or polydisperse vesicles, depending on the target DP of the PNMEP chains. Systematic variation of this latter parameter, along with the solids content, allowed the construction of a phase diagram which enabled pure morphologies to be reproducibly targeted. Syntheses conducted at 10% w/w solids led to the formation of kinetically-trapped spheres. A monotonic increase in particle diameter with PNMEP DP was observed for such PISA syntheses, with particle diameters of up to 462 nm being obtained for PSMA14-PNMEP960. Increasing the copolymer concentration to 15% w/w solids led to worm-like micelles, while vesicles were obtained at 27.5% w/w solids. High (≥95%) NMEP conversions were achieved in all cases and 3:1 chloroform/methanol GPC analysis indicated relatively high blocking efficiencies. However, relatively broad molecular weight distributions (Mw/Mn > 1.50) were observed when targeting PNMEP DPs greater than 150. This indicates light branching caused by the presence of a low level of dimethacrylate impurity. Finally, PSMA14-PNMEP49 spheres were evaluated as Pickering emulsifiers. Unexpectedly, it was found that either water-in-oil or oil-in-water Pickering emulsions could be obtained depending on the shear rate employed for homogenisation. Further investigation suggested that high shear rates lead to in situ inversion of the initial hydrophobic PSMA14-PNMEP49 spheres to form hydrophilic PNMEP49-PSMA14 spheres. © 2016 The Royal Society of Chemistry. Source

Synopsis Objectives The water resistance of sunscreen products has taken more importance for the UV protection of consumers involved in water activities and sports. The present work introduces a new in vivo approach to measure the water resistance of sunscreens on the actual skin of subjects, which can be easily applied to salt, chlorine and tap waters. The stress sources of sunscreen films on skin originate from two phenomena: high surface tension stress as the skin transits through the air/water interface and water diffusion into the film immersed in bulk water. Methods The water resistance of sunscreen products is measured on the forearms of subjects by means of a new layered water bath approach that physically separates both stresses. Tape strips are subsequently taken and analysed for UV-A and UV-B optical densities via (1) imaging for remaining filters and (2) in vitro SPF absorption spectra. Results Water-resistant sunscreens generally perform well when immersed in bulk water even subjected to agitation, but they show a wide range of performances when considering their behaviour at the air/water interface. The differences are more pronounced in salt water than tap water. Conclusions The results confirm 2 stress origins in sunscreen exposure to water: interfacial surface tension and bulk water diffusion. Polymers bring improvements to the resistance of sunscreens to bulk water but show wide latitude in performances when subject to the water surface tension stress. Globally, a higher loss of filters is observed in the UV-A than in the UV-B, which is attributed to more UV-A filter loss or degradation and thus resulting in a decreased protection in the UV-A. Source

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