Modulus Determination of Polymer Matrix Composites: Comparison of Nanoindentation and Dynamic Mechanical Analysis

ABSTRACTThe results of modulus measurements, on carbon black-filled poly(N-vinylpyrrolidone), using dynamic mechanical analysis and nanoindentation were compared. It was shown that beyond the critical pigment volume concentration for this composite system (∼ 25 vol% carbon black), the storage modulus, obtained with dynamic mechanical analysis, decreased with increasing filler concentration. This dropping modulus was due to porosity that developed in the composite films when the critical pigment volume concentration had been exceeded. Elastic modulus obtained with nanoindentation showed the opposite trend, with modulus increasing with additional carbon black loading. An analysis of the method used to calculate modulus based upon indentation data was performed and a mechanism was proposed to explain the disparity between the moduli obtained using these two different methods of measurement.