Carbon Based Dimensional Composites

J. Loomis, B. King, B. Panchapakesan
University of Louisville, US

Keywords: carbon nanostructure, composite, photomechanical, actuation

Summary:

Dimensional dependence of mechanical response in carbon nanostructure composites to near-infrared (NIR) light are reported. Using polydimethylsiloxane, composites were fabricated with one-dimensional multi-wall carbon nanotubes (MWCNTs), two dimensional single-layer graphene, two and a half-dimensional graphene nanoplatelets, and three dimensional highly ordered pyrolytic graphite. An evaporative mixing technique was utilized to achieve homogeneous dispersions of carbon in the polymer composites, and their photomechanical responses to NIR illumination were studied. For a given carbon concentration, both steady-state photomechanical stress response and energy conversion efficiency were found to be directly related to dimensional state of carbon nanostructure additive. A maximum observed stress change of ~60 kPa and ~5 × 10-3% efficiency were obtained with just 1 wt% MWCNT loading. Actuation and relaxation kinetic responses were found to be related not to dimensionality, but to the percolation threshold of carbon nanostructure additive in the polymer. Establishing a connective network of carbon nanostructure additive allowed for energy transduction responsible for photomechanical effect to activate carbon beyond the NIR illumination point, resulting in enhanced actuation. For samples greater than percolation threshold, photoconductivity of the nanocomposite structure as a function of applied pre-strain was measured. Photoconductive response was found to be inversely proportional to applied pre-strain.