Structure-reinforcement correlation and chain dynamics in graphene oxide and Laponite-filled epoxy nanocomposites

The present work attempts at a relative deduction of correlations between structure-reinforcement and chain dynamics in Laponite- and graphene oxide (GO)-dispersed epoxy nanocomposites. The fillers were reasonably well dispersed in the epoxy matrix as revealed by wide-angle X-ray diffraction, transmission electron microscopy and small-angle X-ray scattering studies. The scattering from the nanocomposites exhibited power-law behaviour at low q region with fractal dimensions, implying presence of platelets and tactoids of varying thicknesses. A comprehensive study on the thermomechanical properties of the nanocomposites was made in terms of tensile, dynamic mechanical analysis and flexural and fracture toughness measurements. The studies revealed simultaneous reinforcement as well as toughening effects in the nanocomposites; similar to 42 and similar to 34 % increases in flexural strength and mode I fracture toughness (K (IC)), respectively, with 0.1 wt% GO; and similar to 25 and similar to 20 % enhancements in flexural modulus and K (IC) with 0.1 and 0.3 wt% Laponite, respectively. A unique phenomenon of bimodal distribution of glass transition temperatures was observed as two overlapped peaks in terms of Gaussian contributions in the tan delta versus temperature profiles of the nanocomposites (from dynamic mechanical analysis) and derivative of reversible heat capacity with respect to temperature, dC (p,rev)/dT versus temperature profiles (from modulated differential scanning calorimetric measurements); as against a single symmetric profile for the unfilled matrix. We attempt to understand the nanofiller-induced alteration in the primary relaxation mechanisms as well as notable reinforcement and toughening effects by invoking the filler/polymer interactions, filler dispersion and fractographic investigations.