Thermal Stability of Two-Dimensional Crystals with Extended OH Hydrogen-Bonded Chains

Abstract

Numerical simulations of the dynamics of monolayer structures of molecules deposited on a sheet of hexagonal boron nitride (h-BN) have been performed. It is shown that molecules containing benzene rings and hydroxyl groups in their structure can form stable two-dimensional crystals with linear chains of hydrogen bonds OH$\cdots$OH$\cdots$OH$\cdots$ Such structures are formed by the following molecules: phenol (C$_6$H$_5$OH), hydroquinone (C$_6$H$_4$(OH)$_2$), 4-phenylphenol (C$_6$H$_5$--C$_6$H$_4$OH), 4-(4-phenylphenyl)phenol (C$_6$H$_5$--C$_6$H$_4$--C$_6$H$_4$OH), paracetamol (CH$_3$C(O)NHC$_6$H$_4$OH), 4-hydroxybenzanilide (C$_6$H$_5$C(O)NHC$_6$H$_4$OH) and 4,4-dihydroxybenzanilide (C$_6$H$_4$OHC(O)NHC$_6$H$_4$OH). On the one hand, the benzene rings in these molecules ensure their strong interaction with the flat substrate; on the other hand, they do not hinder the formation of extended hydrogen-bonded chains. The monolayer structures of these molecules exhibit high thermal stability: the onset melting temperatures of their 2D crystals are 47, 187, 127, 247, 167, 307, and 377 $^\circ$C, respectively. The simulations allow us to conclude that multilayer structures composed of h-BN sheets and molecules of hydroquinone, paracetamol, and 4-hydroxybenzanilide can be used for the development of novel proton-exchange membranes capable of operating at elevated temperatures.