Effects of Dispersion and Ultraviolet/Ozonolysis Functionalization of Graphite Nanoplatelets on the Electrical Properties of Epoxy Nanocomposites

The influence of liquid dispersive mediums used in the fabrication of graphite nanoplatelets (GNPs) on their morphology as well as the surface state and electrical conductivity of GNPs/epoxy nanocomposites (NCs) was studied in detail. Ultrasonic dispersion of thermally expanded graphite (TEG) in alcohol medium has been found to be the most effective by the time parameter and allows fabrication of GNPs with rather high aspect ratio (102) and low level of defects. Ultrasonic dispersion of TEG in water medium requires a long time (up to 20 h) of ultrasonic action, but the resulting GNPs are characterized by large lateral size and, therefore, a higher aspect ratio (104). The effects of different ultraviolet (UV)/ozone treatment time on GNPs/epoxy NCs morphology and electrical properties were investigated by optical microscopy, scanning electron microscopy (SEM), infrared (IR) spectrometry, and Raman spectroscopy. The NCs with GNPs subjected to UV/ozone treatment have shown the increase of electrical conductivity with the increase of UV/ozone treatment time, which can be associated with the improved dispersion and distribution of GNPs within the epoxy matrix as well as decreased contact resistance between individual GNPs in conductive network due to chemical functionalization of GNPs during UV/ozone treatment.