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Modelling the mechanical properties of an auxetic molecular network

A novel molecular network structure that has the unusual property of a negative Poisson's ratio has been modelled. This network is a combination of acetylene bonds and benzene rings that can be designed to have a range of different elastic constants and anisotropy. Molecular modelling techniques have been used to predict the elastic constants. The Young's moduli range between 20 and 117 GPa and Poisson's ratios between -0.94 and 1.4 are predicted, depending on the exact details of the network geometry. These values are within the limits for an orthotropic elastic material. Alternative analytical and finite-element models have also been used to try to simplify the calculations needed to predict the properties of the network. It is shown that considerable reductions in computational complexity, without an undue loss of accuracy, can be achieved. This method represents a new approach that is of use where complex network structures are built up from relatively simple, predictable sub-units.