Raman Spectroscopic Studies Of Graphene-Epoxy Composites

Graphene is a new two-dimensional carbon material which is one-atom-thickness. Since first discovered in 2004, it has caused widespread concern of the scientific community for the distinctive two-dimensional structure and excellent mechanical, electrical, thermal, optical properties and so on. Not only has the potential application in the fields of electrophotonic detector, gas detector, solar cell, super capacitor, graphene is also an effective nanofiller to strengthen the properties of polymer composites. In this thesis, graphene oxide （GO） and reduced graphene oxide （rGO） were prepared by modified Hummers method and thermal treatment, and high conductve few layers graphene （FLG） was obtained using intercalation-exfoliation method, respectively. The corresponding epoxy resin composites were also fabricated, then we studied the dispersion of graphene in the epoxy composites using Raman imaging and revealed the influence for electrical and mechanical properties. The main content are listed as below:First, FeCl₃ was used as the intercalator to fabricate FeCl3-graphite intercalation compounds （FeCl3--GICs） and then FeCl3-GICs were exfoliated to form FLG after ultrasonic treatment with H2O2.It is proved that FLG has less defect and high intrinsic conductivity comparing to rGO fabricated by oxidation and thermal annealing. Then, different loadings FLG/rGO-epoxy composites were prepared, and FLG-epoxy displays the better electrical conductivity at lower loading. Thus, FLG exfoliated by FeCl3-GICs is a more promising filler for conductive polymer composites.Furthermore, we investigated as-prepared composites by Raman imaging and observed that a conductive network is gradually formed with the adding of graphene. What’s more, the electrical conductivity of composites is directly related to the area of graphene in the epoxy matrix. We found that graphene area fraction could be used as an alternative for volume fraction to fit the percolation mode, and the area threshold is around 25%. Besides, the stirring temperature during the mixture of graphene and epoxy is also an important factor to influence the dispersion of graphene in the polymer matrix. When stirring temperature exceed 18℃, graphene could not diffuse in the epoxy matrix timely, resulting in the decrease of electrical conductivity.For improving the mechanical property of composites, GO was fabricated using modified Hummers method, and we applied thermal annealing treatment to fabricate rGO. The results confirm that the process of thermal annealing could remove oxygen-containing groups and restore the structure of graphene effectively. As the rich oxygen functional groups on the surface of GO could improve the interfacial binding energy, the mechanical property of GO-epoxy composites was enhanced obviously. However, owing to the lack of oxygen-containing groups on the surface, rGO-epoxy composites show less reinforcement of mechanical property. The tensile strengths of both GO and rGO epoxy composites show a trend of rise first then fall with the increase of graphene weight fraction. Raman imaging shows that the relative area density of graphene gradually incrases with the increasing of graphene weight fraction, due to the aggragation of graphene in polymer matrix, which explains the variation trend of mechanical properites.