Ionic interactions to tune mechanical and electrical properties of hydrated liquid crystal graphene oxide films

Abstract

Considerable improvements have been obtained in physical and mechanical properties of free standing liquid crystal graphene oxide (LCGO) films in their hydrated state, by modification of LCGO dispersions with a low quantity of chloride salts. Addition of salts to LCGO dispersions result in an increase of the storage and loss moduli and viscosity through the interaction between cations and functional groups of LCGO, with the magnitude of increase being dependent upon the concentration of the salt added. A viscosity increase of between 30× and 300× (depending on the salt type) is recorded when salt is added at a concentration as low as 80 mM while storage and loss moduli increase up to 23× and 29×, respectively. Free standing films made from the salt treated LCGO dispersions contained up to 26% water in their structure and were observed to have significantly improved mechanical (2× to 5× increase) and electrical properties (decreased surface resistance up to approximately 670×) compared to free standing films prepared without chloride salts. The influence of the salts on properties of LCGO dispersions and their hydrated free standing films is postulated as a complex interplay of many factors such as the size of cations, the valency of positive charge of the cations, ratio of charge and cations size, as well as the hygroscopic nature of the salts.