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This paper describes an experimental setup that combines friction measurements with in situ confocal Raman microscopy on a lubricating fluid film. The setup allows the determination of film thickness and shear-rate profiles, the position-dependent lubricant composition within the rubbing contact, as well as optical imaging of the contact and its surroundings. The tribological contact can be investigated at continuous rubbing conditions over a range of sliding speeds from 1×10−3to2m∕s. The setup’s capabilities are demonstrated for a soft poly(dimethylsiloxane) sphere pressed and rotated against a quartz flat. Friction forces are presented in the boundary, mixed, and elastohydrodynamic lubrication (EHL) regimes for both a hydrophilic and a hydrophobic flat surface. Optical images of the contact show that, for single-phase aqueous Newtonian lubricants in the EHL regime, starvation of the contact occurs above a critical value of the product of the entrainment speed and the lubricant viscosity. Starvation results in a lower film thickness and lower friction values than predicted by numerical calculations that do not take starvation into account. The capability to determine, using Raman spectroscopy, the composition of the lubricant within the contact is demonstrated for oil-in-water emulsions, stabilized by a nonionic surfactant (Tween 60). The oil concentration was found to depend on both the sliding speed and the position within the rubbing contact. For the investigated tribological conditions, the oil content within the contact was lower than that of the bulk emulsion. This is attributed to the fact that the aqueous matrix phase preferentially wets the hydrophilic quartz slide, which prevents oil droplets from entering the contact if the film thickness is of the order of the droplet size. The ability to determine friction forces, lubricant composition and film thickness, and shear-rate profiles will provide invaluable information in the pursuit of a better understanding of lubrication of soft and hard contacts by multiphase complex fluids.

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To cite this article: M. Heppenstall-Butler , A.-M. Williamson & E. M. Terentjev Corresponding author (2005) Selection of droplet size and the stability of nematic emulsions, Liquid Crystals, 32:1, 77-84,The topological stability of emulsions of thermotropic nematic liquid crystal dispersed in water is examined for a wide range of materials and concentrations. There is a characteristic size of emulsion droplets, R*5K/W, determined by the ratio of Frank elastic, K, and surface anchoring, W, energies of the liquid crystal. Nematic droplets below this size are not topologically charged and coalesce freely. Droplets with R.R* possess a topological charge +1 and present a high elastic energy barrier for coalescence. We studied the evolution of droplet size distribution with time, illustrating their accumulation in the narrow region around R*, and the dependence of the droplet size distribution on temperature and type of surfactant that controls the director anchoring on droplet inner surfaces.

It is well known that perceived taste intensity varies greatly among individuals, and that several factors including taste phenotypes (PROP Taster Status (PTS), Sweet Liking Status (SLS), Thermal Taster Status (TTS)), ethnicity and gender, contribute to variation in taste responsiveness, although such factors are usually investigated in isolation. This study aimed to investigate the association between different taste pheno/genotypes, explore whether these taste phenotypes associated with ethnicity (Caucasian vs Asian) and gender, and determine the relative effects of the different factors on perceived taste intensity. As analysis of this type of data with ANOVA can be difficult due to confounding factors, interactions, and small sample sizes in subcategories, the use of regression tree analysis as an alternative approach was investigated. To that end, two-hundred and twenty-three volunteers were phenotyped for their PTS, SLS and TTS and genotyped for TAS2R38 -rs713598 and gustin -rs2274333. They also rated their perceived intensity of five basic taste and metallic solutions on a gLMS scale. No significant association between the three taste phenotypes were found indicating PTS, SLS and TTS are independent taste phenotypes. However, the results indicated that Asians were not only more likely to be PROP supertasters, but also more likely to be thermal tasters or Low Sweet Likers, compared to Caucasians. Gender was also significantly associated with SLS, where males were more likely to be High Sweet Likers. For perceived taste intensity, traditional ANOVA analysis proved to be challenging. The alternative approach, using regression trees, was shown to be an effective tool to provide a visualised framework to demonstrate the multiple interactions in this dataset. For example, ethnicity was the most influencing factor for perceived sour and metallic taste intensity, where Asians had heightened response compared to Caucasians. The regression tree analysis also highlighted that the PTS effect was dependent on ethnicity for sour taste, and PTS and TTS effect was dependent on ethnicity for metallic taste. This study is the first study to use regression tree analysis to explore variation in taste intensity ratings, and demonstrated it can be an effective tool to handle and interpret complex sensory datasets.

We describe the development of in vivo one-dimensional MRI (profiling) using a GARField (Gradient At Right angles to Field) magnet for the characterisation of side-of-hand human skin. For the first time and in vivo, we report measurements of the NMR longitudinal and transverse relaxation parameters and self-diffusivity of the upper layers of human skin with a nominal spatial resolution better than 10 µm. The results are correlated with in vivo confocal Raman spectroscopy measurements of water concentration and natural moisturiser factors, and discussed in terms of known skin biology and microstructure of the stratum corneum and viable epidermis. The application of model moisturiser solutions to the skin is followed and their dynamics of ingress are characterised using the MRI methodology developed. Selected hydrophilic and lipophilic formulations are studied. The results are corroborated by standard in vivo measurements of transepidermal water loss and hydration status. A further insight into moisturisation mechanisms is gained. The effect of two different penetration enhancers on a commonly used skin care oil is also discussed, and different timescales of oil penetration into the skin are reported depending on the type of enhancer.