Abstract Submitted to the    NANOTUBE'04 Conference:

A detailed study of the physical and chemical properties of selected polymer-nanotube composites has been carried out. We have studied composite formation and polymer-nanotube interactions for a range of nanotube types from SWNT to large diameter MWNT and both conjugated and non-conjugated polymers. Certain polymers such as polyphenylenevinylene derivatives, and vinyl based polymers such as polyvinylalcohol and polyvinylpyrrolidone tend to disperse nanotubes while rejecting other carbon based impurities. In many cases interaction with nanotubes tends to nucleate the formation of a crystalline polymer coating in the solution phase. This coating has a strong influence on the physical properties of the subsequent solid state composite materials. We have modeled the formation of the first mono-layer and found that that the energy is minimized as the polymer coating on the nanotube is maximized. Geometric constraints mean that the coverage can only be maximized for ordered coatings at some magic angles. In addition we have developed a new spectroscopic method the study the adsorption/desorption kinetics for organic molecules in SWNT composite solutions. This work shows that as the nanotube concentration is lowered in these solutions, the SWNT bundle size tends to decrease until individual nanotubes are stable at low concentration. The concentration at which individual SWNT become stable is strongly dependent on the nature of the dispersant molecules. In addition, larger diameter NT such as DWNT and MWNT can be isolated at higher concentrations as expected. In addition, tensile tests were carried out on free-standing composite films of polyvinyl alcohol and six different types of carbon nanotubes for different nanotube loading levels. Significant increases in Young’s modulus by up to a factor of two were observed in all cases. Theories such as Krenchel’s rule-of-mixtures or the Halpin-Tsai-theory could not explain the relative differences between composites made from different tube types. However, it is possible to show that the reinforcement scales linearly with the total nanotube surface area in the films. In addition, in all cases crystalline coatings around the nanotubes were detected by calorimetry suggesting comparible polymer-nanotube interfaces. Thus, the reinforcement appears to be critically dependent on the polymer-nanotube interfacial interaction as previously suggested. Furthermore, additional polymer-multiwall nanotube composite films were fabricated using polyvinylalcohol and chlorinated polypropylene. As observed previously polyvinylalcohol formed a crystalline coating around the nanotubes, maximising interfacial stress transfer. In the second case the interface was engineered by covalently attaching chlorinated polypropylene chains to the nanotubes, again resulting in large stress transfer. Increases in Young’s modulus, tensile strength and toughness of ´3.7, ´4.3 and ´1.7 respectively were observed for the polyvinylalcohol based materials. Similarily for the polypropylene based composites, increases in Young’s modulus, tensile strength and toughness of ´3.0, ´3.9 and ´4.4 respectively were observed. In addition a model to describe composite strength was derived. This model shows that the tensile strength increases in proportion to the thickness of the interface region. This suggests that composite strength can be optimised by maximising the thickness of the crystalline coating or the thickness of the interfacial volume partially occupied by functional groups.