On the Crucial Role of Wetting in the Preparation of Conductive Polystyrene−Carbon Nanotube Composites

Abstract

Polystyrene−single-wall carbon nanotube (PS−SWNT) nanocomposites were prepared by directly mixing aqueous suspensions of exfoliated SWNTs and PS latex particles. After freeze-drying and compression molding, homogeneous polymer films were obtained with well-dispersed carbon nanotubes, as evidenced by scanning electron microscopy imaging. The nanocomposite films display a low percolation threshold and high levels of electrical conductivity. Simultaneously, a considerable increase in the glass-transition temperature of PS is achieved, provided that a sufficient amount of low-molar-mass PS is present in the matrix material. It is suggested that a certain extent of molar mass segregation occurs in the samples, with shorter PS chains preferentially adsorbed onto the nanotube surface. The latter wetting mechanism is indispensable for obtaining favorable electrical and thermal properties.

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.…”

“…47 However, changing the amount of hydroxyl functionality on the surface of a nanotube made no appreciable change in the T g for a polyurethane-MWCNT composite. 48 Although the surface energy of the nanotubes or the polymer can be altered to change the interaction between the polymer and the nanotube, another mechanism is available as described in a unique study by Koning et al 49 For a low molecular weight polystyrene having a very low T g of 90 C (about 10 C below that of a polystyrene sample with a more typical molecular weight), there is an increase in T g of about 8 C/wt % nanotube with added nanotubes until a plateau is reached at a nanotube content of 2 wt %. For a material of more typical molecular weight, there is essentially no change in the glass transition temperature with added nanotubes after the effect of surfactant is accounted for (surfactant is used to disperse the tubes).…”

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

“…In this case, 5 wt% SWCNTs caused a 30% decrease of the heat capacity. Moreover, one DSC study indicates a similar decrease for polystyrene with 5 wt% SWCNTs [40], but another reports essentially no change for a 2.5 wt% SWCNT/polystyrene composite [41]. A DSC study of 1 wt% SWCNTs in poly(methylmethacrylate) [42] also shows essentially the same heat capacity as the neat polymer.…”

Enhancing the mechanical performance of polymer based nanocomposites by plasma-modification of nanoparticles

“…In fact, one of the main goals in the preparation of nano-scaled composites is to prevent the nanoparticles from agglomerating in clusters or bundles. This can be achieved by introducing specific surfactants or functional groups on the nanofiller surface in order to improve compatibility with the host polymer [2,4,5].…”