Nanomechanical investigation of deformation behavior of π–π stacked helical polymers

Abstract

Helical polymers (HPs) have high potential as functional engineering materials according to the emulation of the nature of helix at the nanometer scale. However, there is still a lack of research directly identifying the factors that influence both the structural characteristics of the spiral and the mechanical stiffness of HPs. This study is the first to reveal the effect of the diameter of HPs on changes in the mechanical properties. We constructed three HP models with different diameters but with the same chemical unit. During tensile stretching, the structure of the HP preserves the interlayer distance while tilting diagonally. The diameter of HPs was identified as a key factor in determining structural stability and mechanical stiffness. Microscopic observation of HPs showed that the weakening of the π–π interactions due to the interlayer in-plane slippage ultimately leads to fracture of the structure. The non-bonded potential energy analysis clearly shows the high anisotropy of the deformation modes, namely slip and detachment. In addition, we designed HP models with helical reversal defects to evaluate the weakening effect of HP stiffness. Our results suggest that mechanical stiffness is a promising strategy for modulating the response kinetics of HPs from an engineering design perspective. In conclusion, this study provides a theoretical basis for designing the mechanical stiffness of HPs suitable for specific applications.