Linear relationship between lateral size of reduced graphene oxide (RGO) and water vapor barrier property in RGO/PEI composite membrane

Abstract

The wide distribution of the lateral size of lab-prepared graphene oxide (GO) sheets often complicates the measurement of accurate average size. Herein, a series of reduced-GO/polyethyleneimine (RGO/PEI) composite membranes with compact brick-wall structures were successfully prepared. The large lateral size of RGO sheets in the membrane benefited gas barrier properties, including oxygen, nitrogen, and water vapor. The RGO sheets acted as impermeable inorganic filler to prolong the diffusion path, forcing gas molecules to wiggle through the permeable and tortuous channels of the PEI/water mixture. The water vapor transmission rate of RGO/PEI composite membranes was relatively high, and a linear correlation was established between the length of PEI/water channels and the water vapor barrier property. The length of PEI/water channels under the same membrane thickness was determined by the lateral size of RGO sheets. Therefore, the statistic averages of lateral size of RGO sheets (from 2.48μm to 44.35μm) showed a linear correlation with the water vapor barrier property, as confirmed by the positron annihilation technique and molecular dynamics simulations. In sum, the linear correlation could be used to practicably measure the statistic averages of lateral size of GO sheets according to water vapor permeability measurements.