The Physics of Interfacial Adhesion between a Polymer Matrix and Carbon Nanotubes (Nanofi bers) in Nanocomposites

Abstract

The aim of this study was to investigate the physics of interfacial adhesion in polymer/carbon nanotube systems. The studywas carried out on polypropylene/carbon nanotube (nanofi ber) nanocomposites employing fractal analysis.
Due to a high degree of anisotropy and low bending stiffness, carbon nanotubes (nanofi bers) form ring-like structures in the polymer matrix of the nanocomposite, which are structural analogue of  macromolecular coils of branched polymers. This allowed us to simulate the structure of polymer/carbon nanotube (nanofi ber) nanocomposites as a polymer solution, using the methods of fractal physical chemistry. Using this approach we assume that macromolecular coils are represented by the ring-like structures of carbon nanotubes and the solvent is represented by the polymer matrix. The suggested model can be used to perform structural analysis of the level of interfacial interaction between the polymer matrix and the nanofi ller, i.e. the level of interfacial adhesion. The analysis demonstrated that most contacts between carbon nanotubes and the polymer matrix, which determine the adhesion level, take place inside the ring-like structures. The fractal analysis showed that a decrease in the radius of the ring-like structures or their compactization increases the fractal dimension, which makes it diffi cult for the matrix polymer to penetrate into these structures. This results in a decrease in the number of contacts between the polymer and the nanofi ller and a signifi cant reduction of the level of interfacial adhesion. This effect can also be described as the consequence of compactization of the ring-like structures, demonstrated by the increased density. The article shows a direct correlation between the value of interfacial adhesion (dimensionless parameter b_a), the number of contacts between the polymer and carbon nanotubes, and the volume of the ring-like structures, accessible for penetration by the polymer. The quantitative analysis demonstrated, that the number of interactions occurring on the
surface of ring-like structures of carbon nanotubes (nanofi bers) is only ~ 7–10 %. The suggested model allowed us to determine the correlation between the structure of the nanofi ller in the polymer matrix and the level of interfacial adhesion for this class of nanocomposites.
The results of our study can be used to defi ne the structure of carbon nanotubes (nanofi bers) necessary to obtain the highest level of interfacial adhesion.

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