Preparation And Electrical Properties Of Polymer/Graphite Nanosheets Composites

Graphite nanosheets (GNSs) were prepared from expandable graphite by microwavefast expansion plus supersonic treatment, then Epoxy resin/GNSs (ER/GNSs) bulkcomposites and Silicone rubber/GNSs (SR/GNSs) film composites were obtained resortto solution mixing. XRD and SEM techniques were applied to probe the phases andmicrostructure of GNSs and their composites, the electrical properties were measuredand analyzed with respect to several ambience parameters, such as pressure,temperature and time.The tests show both ER/GNSs and SR/GNSs systems exhibit percolation conductionwith a relative low threshold of6wt%and6.5wt%, respectively. This is ascribed to thespecial shape and good connectivity for GNSs. Data fitting shows the conductionbehavior in both composite systems obeys Stauffer’s percolation theory, from which ascaling factor t=1.6-2.0was obtained. Besides, the in-plane resistance for SR/GNSssystem was found more than off-plane resistance, indicting GNSs is oriented to in film-plane during spinning preparation.In the temperature range of30℃to140℃, the resistance of ER/GNSs systemexhibits good negative temperature coefficient (NTC) effect, which is correlated withthe enhanced thermal activation of electrons transporting across tunnel junctionconsisting of two adjacent separate GNSs. On the other hand, that of SR/GNSs systemis of positive temperature coefficient (PTC) effect, which implying polymer expansionplays a more role on the increase in tunnel gap than thermal activated electrons.Also, the resistance of ER/GNSs system exhibits negative pressure coefficient (NPC)effect, contrary to it, a positive pressure coefficient (PPC) effect of in-plane resistancewas found in SR/GNSs system. Cycle tests show the Piezoresistance effects were ratherstable, especially for the latter, the drift error is little in100-run tests. The correlationsof resistance to pressure can be explained from Simmons-Ruschau model, according towhich the conducting network through polymer is equivalent somewhat to series andparallel connection network consisting of lots of tunnel-junction resistors, and thetunnel gaps so resulting resistance can be controlled by the linear strain of polymer frommacro-pressure loaded in sample surfaces.