On the effect of solvent molecules on the structure and mechanical properties of organic polyphenylacetylene auxetic re-entrant network polymers

Auxetics exhibit the unusual property of a negative Poisson's ratio, meaning they get wider rather than thinner when stretched. This work employs force-field based simulations to study the effect of solvent molecules on the structure and mechanical properties of porous polyphenylacetylene auxetic organic networked polymers. In particular, nano-level re-entrant honeycombs 1,4- and 2,8-reflexyne were exposed to three types of solvent molecules (ethanol, propanol and benzene) at different concentrations by performing Monte-Carlo based sorption simulations in two scenarios, one where the solvent was permitted into the pores of the system upon exposure, and one were the solvent could also enter in between the layers of the polymer. Results indicate that the presence of solvent molecules within the molecular framework of the networked polymers has a significant effect on their density and stiffness but does not influence the Poisson's ratio of the material. The effect on the stiffness was found to be highly dependent on various factors, including the properties of the network and the type and amount of solvent adsorbed. These results have important implications in future case scenarios which may involve the synthesis of such systems, and it throws light on how the mechanical properties could be affected due to contamination, while also identifying new methods on how to tailor such properties by exposing the material to specific solvents.