The application of dynamic mechanical analysis (DMA) for quantifying interfacial interactions in composites is briefly reviewed. Carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument. The dependencies of dynamic mechanical properties of the composites on experimental parameters such as oscillation mode, amplitude, frequency, and temperature were investigated. As opposed to the storage modulus, the loss modulus is found to be sensitive to all parameters. In a fixed multiple frequency mode, the loss modulus of the composites increases with oscillation amplitude and decreases with frequency and the number of tests. The information produced in the resonant mode is more reproducible. An additional damping at the interfaces, apart from those of the constituents, suggests a poor interface adhesion in these composites. A linear relationship between the excess damping at the interfaces and the fiber volume fraction shows a similar interface quality for these composites having different fiber volume fractions. The detection of interfacial properities was found to be more sensitive in the flexural deformation mode than in the torsional mode. At temperatures higher than the glass transition temperature of the matrix, the effective volume fraction of the matrix is reduced. Such a reduction can be interpreted from the mismatch of thermal expansion of the matrix and the fibers.
Desert beetles and cactus plants collect water from fog in arid regions. The desert beetle uses heterogeneous wettability to transport water to its mouth. A cactus uses conical spines which provide Laplace pressure gradient to transport water to its base. In this study, bioinspired triangular patterns with various wettability and different from the surrounding regions were investigated to transport condensed water from ambient air. A low temperature of 5°C was used to decrease saturated vapour pressure to promote water condensation. Results from this study can be used to enhance the performance of water collection systems.This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology'.
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