Investigation Of Dispersion Behavior And Mechanism Of GNP In Liquid Medium

Graphite nanoplatelets(GNPs) have been paid much attention recent years as promising and inexpensive fillers in composite materials substituting expensive carbon nanotubes due to excellent thermal and electrical properties,unique two dimensional nanostructure.However,the strong intersheet van der walls force (over 2ev·nm^<sup>-2) makes the resultant GNPs or graphene-like sheets easily aggregate and difficult to be dispersed in matrix,especially in liquid medium.In this paper,stable GNP dispersion in liquid medium was prepared from expounded graphite(EG) via ultrasonic treatment or ball milling technology in the presence of high molecular dispersant and/or resin.The dispersion behavior of GNPs in liquid medium as well as the effects of dispersant and/or resin,dispersion method, and surface modification on the dispersion of GNPs were also investigated.On the basis of this,the mechanism of GNP dispersion in liquid medium was also proposed.At first,stable GNP dispersion in organic solvent was prepared by ultrasonic treatment of EG in solvent(ethylene glycol butyl ether acetate) with addition of both high molecular weight dispersant Disperbyk-163 and Vinyl resin VYHH. The maximum concentration of stable GNP dispersion obtained is 0.67 mg·mL^-1. This dispersion is very stable and dose not deposit even after being laid for six months.For stable dispersion of GNP in organic solvent,both high molecular weight dispersant and resin are of great importance.In this paper,the dispersant acts mainly as a wetting agent and form a close and thin layer by anchoring on GNPs via hydrogen bond to promote the foliation of GNPs,whereas a loosely adsorbed resin forms a thick solvent-swollen polymer layer to provide an effective steric hindrance for the stabilization of foliated GNPs. Secondly,stable GNP dispersion in water system was prepared by ball milling of EG in water with addition of high molecular weight ionic polymer dispersant J-68.The maximum concentration of stable GNP dispersion in water obtained is 2.5 mg·mL^-1.It is investigated that both steric and electric hindrance are of great importance for the stable dispersion of GNP in water.Therefore,we can adjust the pH value of the system to increase theζpotential of GNP,and consequently promote the dispersion ability of GNP.In addition,more acidic groups can be introduced on the surface of GNPs by surface modification,which can not only increase the wetting ability of GNPs,but also provide more electric hindrance after dissociation,and consequently promote the dispersion of GNPs in water.