The importance of transepidermal water loss (TEWL) as a measure of the skin barrier is well recognized. Currently, the open-chamber method is dominant, but it is increasingly challenged by newer closed-chamber technologies. Whilst there is familiarity with open-chamber characteristics, there is uncertainty about the capabilities of the challengers. The main issues are related to how microclimate affects TEWL measurements. The aim of this paper is to provide a framework for understanding the effects of microclimate on TEWL measurement. Part of the problem is that TEWL measurement is indirect. TEWL is the diffusion of condensed water through the stratum corneum (SC), whereas TEWL methods measure water vapour flux in the air above the SC. This vapour flux depends on (i) the rate of supply of water to the skin surface and (ii) the rate of evaporation of water from the skin surface. Rate (i) is a skin property (TEWL), rate (ii) is a microclimate property. The controlling rate for the combined process is the lower of the above two rates. Therefore, TEWL instruments measure TEWL only when TEWL is the rate-limiting process. Another problem is that SC barrier property and SC hydration are affected by the microclimate adjacent to the skin surface. This is discussed insofar as it affects the measurement of TEWL. The conclusion is that such changes occur on a timescale that is long compared with TEWL measurement times. An important aspect of TEWL measurement is calibration. We present an analysis of the traditional wet-cup method and a new droplet method that is traceable and has been independently verified by a standards laboratory. Finally, we review performance indicators of commercial closed-chamber instruments with reference to open-chamber instruments. The main findings are that TEWL readings correlate well, but there are significant differences in the other aspects of performance.

No abstract

The segmental relaxation of poly(acrylic acid), PAA, and poly(methacrylic acid), PMAA, in dilute methanolic solutions has been studied using time-resolved fluorescence anisotropy. The anisotropy data, as analyzed by a variety of data retrieval procedures, indicate that a single exponential function is sufficient in description of the relaxational behavior of these systems. The segmental motions of PAA and PMAA in methanol are characterized by rotational correlation times of ca. 1.3 and 4.2 ns, respectively.

No abstract

We present a new technique, thermal emission decay Fourier transform infrared spectroscopy, designed to perform noninvasive, noncontacting absorption spectrum measurements on unprepared, arbitrary surfaces. It uses pulsed optical heating of the near-surface region of the sample to produce transient thermal emission spectra in'the midinfrared spectral region for room temperature samples. The raw data of intensity versus path difference versus time after excitation can be processed in two ways; (1) to yield time-resolved spectra for depth profiling of layered samples: and (2) to yield decay-associated spectra for absolute absorbance measurements of homogeneous samples. 0 199.5