The influence of the structure of carbon nanotubes in the polymer matrix on interfacial effects in nanocomposites

Abstract

It is now a well-known fact that interfacial effects play a decisive role in the formation of the properties of polymer composites on the whole and nanocomposites in particular. Therefore, this article investigates the relations between the structure of carbon nanotubes in the polymer matrix of a nanocomposite and the level of interfacial adhesion which is characterisedby dimensionless parameter ba. It was shown that carbon nanotubes form ring-like structures, which are analogous to macromolecular coils of branched polymer chains and represent a specific type of aggregates for nanofillers of this type. Such ring-like structures can be geometrically described either by a full circle (“closed” structures) or by a part of it (arc) (“open” structures). The amplification of the aggregation process of carbon nanotubes characterised by a decrease in the radius of the ring-like structures is accompanied by a decrease in the fractal dimension of their surface compared to the nominal maximum value. When the ring-like structures reach the smallest possible (about 130 nm) radius, their surface is perceived by the polymer matrix as absolutely smooth, i.e. with a dimension of d=2. This determines the transition of the level of interfacial adhesion from nanoadhesion to perfect adhesion by Kerner. The nanoadhesion effect allows significantly improving the properties of polymer/carbon nanotube nanocomposites. The nanoadhesion effect only takes place if the surface of the ring-like structures of nanotubes is fractal. Parameter ba, which characterises the level of interfacial adhesion in polymer nanocomposites, linearly increases with an increase in the fractal dimension of the surface of carbon nanotube aggregates. In this case, the highest attainable nominal dimension of the nanotubes surface, equal to ~ 2.85, is only achieved for “open” ring-like structures. The proposed analytical methods make it possible to predict both interfacial characteristics and the properties of polymer/carbon nanotube nanocomposites

Keywords

• nanocomposite
• carbon nanotubes
• ring-like structures
• aggregation
• interfacial adhesion
• surface
• fractal dimension