Abstract

An effective, yet simple, method for creating nanocomposite coatings, fibres, and adhesives is to blend an aqueous suspension of carbon nanotubes (CNTs) with either a polymer solution or waterborne colloidal polymer particles (i.e. latex). In processing these waterborne nanocomposites, there is a wide choice of water-soluble polymers to disperse CNTs in water. Surfactants are frequently used, however, because they are highly effective dispersants. To what extent – or why – the choice of dispersant might influence nanocomposite mechanical properties has not been considered. In this lecture, I will show that the dispersant can increase the stress transfer between a nanotube and the matrix, which is essential for achieving high stiffness, while still allowing interfacial slippage to increase energy dissipation. I will demonstrate that the mechanism of stress transfer is through interfacial friction from molecular entanglements. A high molecular-weight polymer dispersant creates a polymer brush that entangles with the soft matrix. Surfactants and low molecular-weight polymers cannot entangle, therefore yielding far inferior mechanical properties. The dispersant’s molecular weight thus provides a means to tune the mechanical and adhesive performance of waterborne nanocomposites.