Glass Transition Behavior of Single-Walled Carbon Nanotube−Polystyrene Composites

Abstract

A variety of measurements using a differential scanning calorimeter were used to probe how single-walled carbon nanotubes (SWCNTs) affect polymer dynamics associated with the glass transition. Tubes were dispersed in N,N-dimethylformamide containing dissolved polystyrene, and precipitation was quickly forced by the addition to large amounts of water. The percolation threshold was found to be less than 0.5 wt %, indicating good dispersion of the tubes. The glass transition temperature (T g ) increased at low nanotube fractions to a constant value about 6-7°C higher than the T g of pure polystyrene, and did not change further as the nanotube amount changed from 1 to 30 wt %. The heat capacity change at the glass transition decreased with increasing nanotube concentration, except at very high SWCNT contents (>10 wt %), where the heat capacity change began to increase. The decrease of heat capacity at low nanotube contents indicates that a fraction of the polymer is made immobile via the addition of SWCNTs; while the large increase at high contents suggests that nanotubes are participating in the molecular motion that is the glass transition. The relaxation rate as determined by the change in limiting fictive temperature with annealing time showed the same qualitative behavior as the glass transition, a decrease in polymer mobility at very low nanotube fractions followed by a constant value. Surprisingly, one measure of the activation energy increased at low nanotube contents (<0.5 wt %) and dropped at high nanotube contents to an energy that looks to be slightly higher than that for pure polystyrene. In other words, in the region where the formation of a continuous network occurs the activation energy is highest.

Effects of carbon nanotubes on polymer physics

“…Even the fully-loaded sample had a T g that was less than the T g of the polymer. 96 This reduction is in direct contrast to normally dispersed polystyrene which has universally always caused an increase 49,71,97,98 (or no change in one case 49 ) in the glass transition temperature with added nanotubes. The difference is likely caused by wetting differences the infusion process is done at atmospheric pressure, while melt mixing is not; and in solvent-mixing processes the solvent plays a significant role in promoting wetting of the nanotubes by the polymer.…”

Thermal properties and transition studies of multi-wall carbon nanotube/nylon-6 composites

“…When CNTs are added to a polymer, T g typically increases a few degrees [30,31] but may also increase a few tenth of degrees [32]. Because of its nano- After HP&HT treatment at 1 GPa and 530 K (see experimental), the T g features of the Pcomposite and nylon-6 vanished.…”

The effect of carbon nanotubes on epoxy matrix nanocomposites

“…On the other hand, some results indicate that the addition of carbon nanotubes may deteriorate thermal stability of the epoxy matrix [5,6]. It has been also reported that modification with nanotubes changes glass transition temperature, T g [7], which in the case of the CNTs functionalised with amino groups considerably increases [8]. In this context, the aim of this work was to investigate the thermal properties of epoxy-nanotube composites with CNTs of different lengths and subjected to different surface functionalization.…”