Molecular engineering of interphases in polymer/carbon nanotube composites to reach the limits of mechanical performance

After more than 50 years of development, carbon fiber composites exhibit an order of magnitude higher specific strength as compared to structural metals such as steel. However, the strength of the current state-of-the-art carbon fiber composites remains less than 10% of their theoretical value. Recent studies show that the polymer-carbon nanotube (CNT) interphase, i.e., the region of carbon components in contact with multiple organic components in its vicinity, plays a major role. Engineering the polymer-CNT interphase at the molecular level is a promising pathway to improve the mechanical properties of nano-composite materials on the way to fully realize the potential of mechanical properties of carbon nanotubes. Examples for using pristine and flattened CNTs, combinations of polymers, and surface grafting, as well as analogies to biological systems to prepare strong polymer/CNT composites are reviewed. In support of these developments, molecular simulations have revealed the binding mechanisms of polymers to CNTs and relationships to mechanical properties such as modulus, tensile strength, and interfacial shear strength in the interphase. Recent computational models enable increasingly quantitative predictions, and examples that explain the influence of the type of polymers, polymer crystallinity, carbon nanotubes, and nanotube surface modification on the interphase properties are discussed. The developments in molecular engineering of interphases by experiment and simulations advance rational composite design.