Mid Sweden University

Graphene has generated a great deal of interest all over the world in the last decade, mainly as a result of its unique properties such as high con-ductance and strength, which is of potential benefit for many electronic applications. One common strategy for producing increased quantities of few-layer graphene includes liquid-based methods, where graphite is peeled off or exfoliated. Ultraviolet-Visible (UV-Vis) spectrophotometry can be used for measuring the degree of exfoliation since the optical ab-sorbance at a given amount of graphite increases with the degree of exfo-liation. In this work, a UV-Vis method was tested where the exfoliated samples were stabilized with glycerol. This enabled measurements of both polydisperse samples directly after the exfoliation and also top-phase samples collected after gravitational sedimentation. Beer-Lam-bert’s law could be applied for quantifying the amount of exfoliated graphite in the samples. The samples were analyzed by focusing on the connection between absorbance, extinction and light scattering. It was found that the particle size and the contribution from light scattering de-creased at the presence of smaller particle sizes. It was also evident that the absorbance peak of graphite was shifted toward higher wavelengths as the exfoliation was progressed by repeated shearing. These are intri-guing results that warrant further studies as well as verification by alter-native spectroscopic analysis.In order to investigate the change in absorbance with different chemical and mechanical exfoliation conditions, studies were performed using a high-pressure capillary viscometer, ACAV A2. It was clear that an addi-tion of 2% polyacrylic acid (PAA) facilitated mixing and also increased the amount of dispersed graphite by more than six times. The mechanical treatment showed that both high-pressure shearing and sonication gave higher concentrations of nanographite compared to mechanical disper-sion by a rotary disperser. The overall conclusion of this study is that a combination of analysis is required for characterizing the particles. In or-der to quantify graphene, the analysis of chemical structure, inter-particle stability and flake cleanliness is very important.