London dispersion forces and steric effects within nanocomposites tune interaction energies and chain conformation
Baode Zhang, Snežana D. Zarić, Sonja S. Zrilić, И. В. Гофман, Barbara Heck, Günter Reiter
Abstract
The interplay between attractive London dispersion forces and steric effects due to repulsive forces resulting from the Pauli principle often determines the geometry and stability of nanostructures. Aromatic polyimides (PI) and carbon nanotubes (CNT) were chosen as building blocks as two components in the hetero delocalized electron nanostructures. Two PIs, having the same diamine part and different linkage substituents between two phenyl rings of dianhydride part, one linked with ether bond (C-O-C) (OPI), the other with C-(CF3)2 (FPI), were investigated. Surprisingly, two CNT/PI nanocomposites show distinct failure mode from CNT yielding to CNT pull-out failure. Calculation of the interaction energy and chain conformations of each PI upon CNT was performed by accurate density functional theory (DFT) calculations and molecular dynamic simulation (MDS). OPI chain adopt helically wrapping conformation around CNT with relatively strong interaction energy. FPI chain take the one-side wavelike conformation upon CNT with relatively weak interaction energy. The interplay between attractive London dispersion forces and steric effects due to repulsive forces often determines the geometry and stability of nanostructures, but for nanocomposites consisting of hetero-molecular nanostructures with delocalized π electrons this interplay is highly complex. Here, the authors study the interaction energies between aromatic polyimides and carbon nanotubes, with a focus on the influence of substituent groups on London dispersion forces and steric effects.