a b s t r a c tMechanochromic polymers display detectable changes in their fluorescence emission upon deformation of their macromolecular structure. Here, we study reversible mechanochromism of pyrene functionalized nanocomposite hydrogels. Highly stretchable nanocomposite hydrogels are prepared by free radical polymerization of poly(N-isopropylacrylamide) and pyrene terminated poly(ethylene) glycol methacrylate copolymers in the presence of nanoclay, acting as the physical crosslinker. Mechanochromic behavior is characterized through uniaxial tensile experiments, where force, deformation, and fluorescence emission are simultaneously measured. To demonstrate the application of mechanochromic nanocomposite hydrogels in pressure sensing, membranes are used to detect differential pressures on the order of 10 2 Pa. We envision the integration of these mechanochromic hydrogels in the design of novel force and pressure sensors with application to mechanics, fluid dynamics, and biophysics.

Management of the public health aspects of generalized environmental contamination by 1131 requires that estimates be made of the mean thyroid dose received by a given segment of the population. Some measure of the distribution of doses around the mean is also desirable.It is possible to estimate the absorbed dose to the thyroid gland by analysis of post-mortem material, by in viuo measurements of a sample of the exposed population, or by calculations based on environmental data. When the exposed population is so small that meaningful data can be obtained on a sample of manageable proportions, in vivo measurements are highly useful. However, when the exposed population is a substantial part of the country, as in the case of fallout associated with the testing of nuclear weapons, it is impractical to obtain reliable estimates of the distribution of thyroid dose because of difficulties of obtaining a representative sample and because of the logistic problems associated with this type of measurement.The problem of calculating the distribution of doses based upon knowledge of environmental factors is simplified by the fact that fresh cow's milk is known to be the principal route by which 1131 is absorbed. This paper discusses the mathematical relationships that determine the distribution of thyroid doses in the exposed population and discusses the feasibility of undertaking such calculations based on both existing data and data yet to be obtained.

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