New formulation technology to boost sun protection.

OBJECTIVE: As every skin type worldwide is concerned by photoprotection, with consumers preferring cosmetic elegant and efficient sunscreen products, we aim at developing the most performant and desirable sun care products. METHODS: We selected an interesting polymer, abbreviated AAHCP and designed scanning electron cryomicroscopy (cryoSEM), small angle and wide angle X-ray scattering and confocal laser scanning microscopy studies to understand its behaviour in solution and in simplex sun care formulations. This allowed us to develop innovative sunscreen formulation technology that was demonstrated by in vitro and in vivo photoprotection methods. Comprehensive photoprotection evaluations were made on the fully developed sun protection product. RESULTS: We observed the polymer oil structuring properties as well as its ability to form small and stable droplets in simplex emulsions. In vitro and in vivo sun protection factor (SPF) measurements demonstrated the sun protection boosting efficacy of AAHCP polymer in several emulsions or as a stand-alone emulsifier. This formulation technology also allowed to filtering system concentration optimization. Use-test performed on a fully developed AAHCP-based sunscreen validated its optimal performances as well as its ideal cosmetic features, with non-sticky, non-greasy perception and invisible skin result. CONCLUSION: For the first time, thanks to a new specific polymer creating a new type of emulsion, we succeed in reconciliate in a single sun care product maximal SPF efficacy, resistance to numerous stresses and optimal sensoriality.

OBJECTIF: Tous les types de peau du monde étant concernés par la photoprotection, avec des consommateurs qui préfèrent des produits solaires élégants et efficaces, nous nous sommes donné pour mission de développer les produits de protection solaire les plus performants et les plus agréables. MÉTHODES: Nous avons sélectionné un polymère intéressant, l'« AAHCP ¼ dans sa forme abrégée, et avons conçu les études de cryomicroscopie électronique à balayage (CryoSEM), de diffusion des rayons X et de microscopie confocale à balayage laser (Confocal Laser Scanning Microscopy) pour comprendre son comportement en solution et dans des formulations de protection solaire simples. Cela nous a permis de développer une technologie innovante de formulation de protection solaire, qui a été démontrée par des méthodes de photoprotection in vitro et in vivo. Le produit de protection solaire a fait l'objet d'évaluations exhaustives de la photoprotection à la fin de sa phase de développement. RÉSULTATS: Nous avons observé les propriétés de structuration de l'huile polymère, ainsi que sa capacité à former de petites gouttelettes stables dans les émulsions de simplex. Les mesures du facteur de protection solaire (sun protection factor, SPF) in vitro et in vivo ont montré que la présence du polymère AAHCP dans plusieurs émulsions ou comme émulsifiant autonome optimise le niveau de protection solaire obtenu. Cette technologie de formulation a également permis d'ajuster la concentration du système de filtration. Le test en conditions réelles d'utilisation effectué sur une protection solaire à base d'AAHCP à la fin de la phase de développement a permis de valider ses performances optimales, ainsi que ses caractéristiques cosmétiques idéales, avec une sensation non collante et non grasse, et un résultat invisible sur la peau. CONCLUSION: Pour la première fois, grâce à un nouveau polymère spécifique créant un nouveau type d'émulsion, nous avons réussi à développer un produit de protection solaire simple à l'efficacité SPF maximale, qui résiste à de nombreuses contraintes et possède une sensibilité optimale.

Spinodal stratification in micellar films between oil and silica.

We report on the thinning mechanisms of supported films of surfactant (nTAB) solutions above the critical micellar concentration. The films are formed by pressing an oil drop immersed in an aqueous surfactant solution on a silica surface. Depending on the length of the carbon chain of the surfactant and its concentration, two modes of destabilization of the stratified films are observed. The first one proceeds by heterogeneous nucleation, characterized by the lateral expansion of the domain of lower thickness as evidenced long ago in suspended micellar films. In addition, the simultaneous stepwise thinning of several domains, called spinodal stratification, is observed here in supported films. We measure the time evolution of the thickness of the films, and we discuss the selection mechanism of each destabilization mode.

Dramatic Slowing Down of Oil/Water/Silica Contact Line Dynamics Driven by Cationic Surfactant Adsorption on the Solid.

We report on the contact line dynamics of a triple-phase system silica/oil/water. When oil advances onto silica within a water film squeezed between oil and silica, a rim forms in water and recedes at constant velocity. We evidence a sharp (three orders of magnitude) decrease of the contact line velocity upon the addition of cationic surfactants above a threshold concentration, which is slightly smaller than the critical micellar concentration. We show that, with or without surfactant, and within the range of small capillary numbers investigated, the contact line dynamics can be described by a friction term that does not reduce to pure hydrodynamical effects. In addition, we derive a model that successfully accounts for the selected contact line velocity of the rim. We further demonstrate the strong increase of the friction coefficient with surfactant bulk concentration results from the strongly nonlinear adsorption isotherm of surfactants on silica. From the variations of the friction coefficient and spreading parameter with surface concentration, we suggest a picture in which the part of the adsorbed surfactants that are strongly bound to the silica interface is trapped under the oil droplet and is responsible for the large increase in line friction.