Deterioration and recovery of electro-optical performance of aqueous graphene-oxide liquid-crystal cells after prolonged storage

Electro-optical switching of graphene oxide (GO) liquid crystals is of great interest owing to its potential applications. However, a GO dispersion undergoes vinylogous carboxylic acidic reaction with time, accompanied by a decrease in pH, which deteriorates the electro-optical performance of a GO cell. We find that the vinylogous carboxylic reaction is hindered in high concentration GO dispersions, and also demonstrate that the deteriorating electro-optical performance can be recovered either by re-cleaning or by ionic neutralization treatment. The electro-optical performance is systematically analyzed in terms of the acidity of the neutralizing solvent, GO dispersion, and supernatant liquid. The best performance is obtained in a GO dispersion with a pH-7 supernatant liquid after neutralization by weakly alkaline water. The neutralization process decreases the bulk conductivity, and also improves the surface conductivity on GO. Approximately 56% of newly generated H+ ions reside near the GO surface, and the rest diffuse away into the bulk solvent. These findings may provide better understanding for the electro-optical switching phenomenon and its applicability. (C) 2016 Elsevier Ltd. All rights reserved.