Tuning the structure of graphene oxide and the properties of poly(vinyl alcohol)/graphene oxide nanocomposites by ultrasonication

The structure of graphene oxide (GO) was tuned by controlled ultrasonication (40 kHz, 400 W). It was found that one hour of sonication was the critical point. Under ultrasonication, GO was exfoliated gradually in one hour and further treatment led to a reverse trend. The size of GO sheets decreased sharply in the first hour and then remained almost unchanged with the extension of sonication. In other words, once the GO sheets were cut into pieces small enough, they tended to restack together. Defects on the surface of GO were easily generated even within a short period of ultrasonication and the chemical structure was also changed. GO treated with different sonication times was incorporated into poly(vinyl alcohol) (PVA), and the structure and properties of PVA/GO nanocomposites were also discussed. The hydrogen bonding between the GO and PVA matrix increased before the critical point and then decreased, which was the key factor influencing the glass transition temperature. Meanwhile, the mechanical strength of the nanocomposites was improved before the critical point. The reinforcing mechanism is believed to be the effective load transfer between the PVA matrix and GO via strong hydrogen bonding interactions caused by the exfoliation effect.