Dielectric spectroscopy of concentrated cosmetic W/O-emulsions: possibilities to distinguish product changes caused by coalescence, sedimentation and variation of ingredients.

A quick result whether a newly developed cosmetic water-in-oil (W/O)-emulsion shows constant sensory behavior (stable) or whether it changes its behavior over time (instable) is an important aspect in cosmetic research. In order to observe changes as quickly as possible, analytic methods are used. An established method is rheology, a sensitive method that gives direct information on sensory aspects. Additional information concerning the kind of instability allows a more focused improvement of formulation in the case of instabilities. In order to gain this information, an additional analytic method with a more ingredient specific focus is needed. In this article, the possibilities of using dielectric spectroscopy in order to get additional information are discussed. For concentrated W/O-emulsions a dependence of emulsion behavior from volume median droplet diameter d(v50) is visible by both methods: rheology and dielectric spectroscopy. A variation of droplet size distribution at constant volume median droplet diameter d(v50) does not change the results for the examined emulsions. Quantitative information about mean droplet size is possible with calibration. Because of their different physical forci, rheology and dielectric spectroscopy complement each other in high-sensitive detection of coalescence. In contrast to the mechanical properties of W/O-emulsion, dielectric spectroscopy gives additional information concerning some reasons of change in emulsion structure. Mechanism like sedimentation and coalescence can be distinguished and the phase where changes take place (oil phase or water phase) can be located. The latter is possible by a new parameter - the correlation between maximum of dielectric loss epsilon''(f(R)) and the relaxation frequency f(R). Their correlation can be described by a simple power law. By coupling rheology and dielectric spectroscopy, an improvement in fast emulsion development and production control may be achieved without losing the advantage of a quick and easy measurement procedure.

Osteoarthritis of the metacarpophalangeal joints: the relation between ray prevalence, trauma, and utilisation.

The gradient in prevalence of idiopathic osteoarthritis of the metacarpophalangeal (MCP) joints from the index to the little finger was used to test three theories. Trauma was correlated by analysis of fracture incidence in the four rays in 142 patients. Correlation with utilisation of arc was assessed by goniometric measurement of mean MCP flexion in five hand positions in a sample of 200 activities, and recording utilisation of these positions by behavioural observation techniques in the course of 2831 actions, 2746 domestic and 85 nondomestic. Both correlations were negative. The hypotheses of excessive loading and incomplete use were compared and tested against external evidence. It is suggested that the gradient in MCP prevalence of osteoarthritis is consistent with a bifactorial aetiology, with site and incidence determined by incomplete use, and with the rate of progress by cartilage loading.