Mc Marie Claire Hermant

Controlling electrical percolation in multicomponent carbon nanotube dispersions

Carbon nanotube reinforced polymeric composites can have favourable electrical properties, which make them useful for applications such as flat-panel displays and photovoltaic devices. However, using aqueous dispersions to fabricate composites with specific physical properties requires that the processing of the nanotube dispersion be understood and controlled while in the liquid phase. Here, using a combination of experiment and theory, we study the electrical percolation of carbon nanotubes introduced into a polymer matrix, and show that the percolation threshold can be substantially lowered by adding small quantities of a conductive polymer latex. Mixing colloidal particles of different sizes and shapes (in this case, spherical latex particles and rod-like nanotubes) introduces competing length scales that can strongly influence the formation of the system-spanning networks that are needed to produce electrically conductive composites. Interplay between the different species in the dispersions leads to synergetic or antagonistic percolation, depending on the ease of charge transport between the various conductive components.

Lowering the percolation threshold of single-walled carbon nanotubes using polystyrene/poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) blends

Single-walled carbon nanotubes (SWCNTs) are introduced into a polymer matrix via a latex-based route resulting in a conductive composite. The percolation threshold for a polystyrene (PS)-based composite prepared with SWCNTs dispersed in water using a conventional surfactant like sodium dodecyl sulfate (SDS) is approximately 0.4 wt%. In this study, SDS is substituted by a conductive polymer latex, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) also known as PEDOT:PSS. This latex can effectively stabilize individual SWCNTs in water and composites prepared with these dispersions show a lower percolation threshold value of 0.2 wt%. The percolation of PEDOT:PSS in PS in a binary polymer blend without SWCNTs is also investigated, and found to occur at a remarkably low loading of 2.2 wt% of the conductive latex. The morphology of the final polymer-filled blend is further investigated and the findings provide an explanation as to why PEDOT:PSS lowers the percolation threshold of the SWCNTs, and in fact has such a low threshold itself without the presence of the nanotubes.

Influence of the molecular weight distribution on the percolation threshold of carbon nanotube – polystyrene composites

Abstract Carbon nanotubes were introduced into insulating polystyrene (PS) and poly(methyl methacrylate) (PMMA) by means of a latex-based technique. A systematic study of the effect of the polydispersity index, more particularly the presence of different amounts of low molar mass polymer, on the final composite conductivity was performed. Six latexes with varying molecular weight distributions were prepared by means of conventional free radical emulsion polymerization in the presence of different amounts of chain transfer agent, namely n-dodecyl mercaptan. Composites were prepared with both multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs). Shifts in the percolation threshold from 0.9 to 0.6 wt% for MWCNTs and from 0.7 to 0.4 wt% for SWCNTs were observed for PS matrix material, whereas for PMMA matrix material the percolation thresholds shifted from 0.6 to 0.3 wt% for MWCNTs and 0.35 to 0.2 wt% for SWCNTs upon increasing the amount of low molecular weight polymer in the polymer matrix.