A sorption study of auxetic materials : a preliminary study

Abstract

The sorption properties of several nano-scale auxetic frameworks were investigated. The previously reported sorption simulations of the loading of C60 and C70 Buckminister fullerenes into 2,8-re:flexyne were re-investigated. The results reported by Alderson et al. in 2005 were reproduced, even though a very large dispersion of the data points was observed. The procedure used was improved upon by increasing the cut-off distance, by applying charges during structure minimisation, and by increasing the fineness by which the free volume within the framework was calculated. These modifications allowed for the production of results with a much lower dispersion than previously reported. A previously unobserved linear trend in the data became apparent, which led to the formulation of a simpler hypothesis than that proposed by Alderson et al. to explain how the increase in applied external stress translates into an increase in the loading of the framework. The number of sorbate molecules loaded into the framework also coincided very closely with that expected theoretically. The sorption of H2O molecules into meta-NAT, minimised at 573K, was also investigated. After having determined by experiment the ideal setting for two of the more important user-selected variables (that is, the interaction cut-off and the number of iterations to be carried out), preliminary sorption simulations showed that loading of these sorbate molecules also increased with increasing applied stress. Even though the results could not have been interpreted further, they clearly demonstrated that sorption simulations are force-field dependent.