Thermal Conductivity, Heat Capacity, and Cross-Linking of Polyisoprene/Single-Wall Carbon Nanotube Composites under High Pressure

Abstract

Polyisoprene (PI)/single-wall carbon nanotube (SWCNT) composites and pure PI have been cross-linked by high-pressure treatment to yield densified elastomeric states. Simultaneously, the SWCNT and cross-linked-induced changes of the thermal conductivity, heat capacity per unit volume, and glass transition were investigated by in situ measurements. The thermal conductivity of both the elastomeric and liquid PI improves ∼120% by the addition of 5 wt % SWCNT filler. The SWCNT filler (5 wt %) increases the glass-transition temperature of liquid PI by ∼7 K and that of the elastomeric state by as much as 12 K, which is due to a filler-induced increase in the cross-link density. Moreover, the 5 wt % filler yields a heat capacity decrease by ∼30% in both the glassy and liquid/elastomeric states, which indicates that SWCNTs cause a remarkably large reduction of both the vibrational and configurational heat capacity of PI. Finally, the consequences of high-pressure densification and the possibilities this provides to help elucidating the nature of the heat conduction in polymer/carbon nanotube composites are discussed.