(73d) Viscoelasticity and Stability of Single Walled Carbon Nanotube – Unsaturated Polyester Resin Dispersions

We have investigated the mechanical property enhancement resulting from the high shear dispersion of Single-Walled Carbon Nanotubes (SWNTs) into a viscous unsaturated polyester resin matrix. Specifically, the complex structure, dispersion state, and flow behavior of this material was characterized using bulk rheological properties. Under controlled strain oscillatory shear viscoelastic behavior was observed from the lower semi-dilute to isotropic concentrated regime spanning the percolation threshold. Network elasticity was found to scale with increasing SWNT concentration and identifiable by the development of frequency independent linear viscoelastic moduli. The concentration dependence was removed using colloidal scaling for weakly attractive particles resulting in universal loss and storage moduli for the system. Transmission electron microscopy was performed to probe the dispersion state. As predicted by the rotational Peclet number, non-Brownian behavior was observed for SWNT bundles in a viscous medium.

In the dilute regime the application of low strain rates, over long time scales, resulted the formation of SWNT aggregates identifiable by a sharp increase in apparent viscosity. The low shear aggregation was reversible, to some extent, by the application of a shear stress great enough to overcome the aggregate attractive forces. To identify the dominant phenomena controlling the aggregation process dispersions were studied with varying SWNT purity and production type (HiPCO, laser ablation). Thermogravimetric Analysis, X-Ray Photoelectron Spectroscopy, and Raman Spectroscopy were performed to characterize the various SWNTs. Additionally, Electrostatic Force Microscopy was used to determine the magnitude of the various SWNT surface charges and to correlate aggregation behavior with the dominant Van der Waals attractive forces.