Insights into the structure of sunscreen lotions: a small-angle neutron scattering study

Sunscreen lotions and creams are arguably the most popular products used to protect the skin against harmful UV radiation. Several studies have been conducted to untangle the internal microstructure of creams and lotions. However, the effect of UV filters and other materials such as preservatives, on the internal microstructure and the aesthetics of these products is not yet fully understood. Using small-angle neutron scattering (SANS), we were able to investigate the effect of adding the commonly used organic UV filters (avobenzone (AVB), ethylhexyl methoxycinnamate (EMC), ethylhexyl triazone (EHT) and bemotrizinol (BMT)) and the water soluble preservatives (1,5-pentanediol (1,5-PD) and 1,2-hexanediol (1,2-HD)), on the internal architecture and microstructure of an oil-in-water (o/w) based sunscreen lotion. Our findings highlight the complexities of these formulations, and how the introduction of different additives could influence their structure and possibly their performance.

Sunscreen lotions and creams are arguably the most popular products used to protect the skin against harmful UV radiation.

3D printed spherical environmental chamber for neutron reflectometry and grazing-incidence small-angle neutron scattering experiments

In neutron scattering on soft matter, an important concern is the control and stability of environmental conditions surrounding the sample. Complex sample environment setups are often expensive to fabricate or simply not achievable by conventional workshop manufacturing. We make use of state-of-the-art 3D metal-printing technology to realize a sample environment for large sample sizes, optimized for investigations on thin film samples with neutron reflectometry (NR) and grazing-incidence small-angle neutron scattering (GISANS). With the flexibility and freedom of design given by 3D metal-printing, a spherical chamber with fluidic channels inside its walls is printed from an AlSi10Mg powder via selective laser melting (SLM). The thin channels ensure a homogeneous heating of the sample environment from all directions and allow for quick temperature switches in well-equilibrated atmospheres. In order to optimize the channel layout, flow simulations were carried out and verified in temperature switching tests. The spherical, edgeless design aids the prevention of condensation inside the chamber in case of high humidity conditions. The large volume of the sample chamber allows for high flexibility in sample size and geometry. While a small-angle neutron scattering (SANS) measurement through the chamber walls reveals a strong isotropic scattering signal resulting from the evenly orientated granular structure introduced by SLM, a second SANS measurement through the windows shows no additional background originating from the chamber. Exemplary GISANS and NR measurements in time-of-flight mode are shown to prove that the chamber provides a stable, background free sample environment for the investigation of thin films.

Neutron Reflectometry of an Anionic Surfactant at the Solid-Liquid Interface under Shear

Neutron reflectometry with in situ rheology is used to measure the shear response of an adsorbed anionic surfactant (sodium bis(2-ethylhexyl) sulfosuccinate, AOT) at the alumina-water interface. A low surfactant concentration is measured where a single bilayer adsorbs at the interface as well as a higher concentration where a multilamellar structure forms. The low concentration structure does not change with the imposed shear (oscillatory or steady). However, the lamellar phase shows a loss of structure under both steady and oscillatory shear. There are differences between the steady and oscillatory cases, which are discussed, with both showing a strong dependence on the strain amplitude.