Abstract
Previous studies from a macroscopic point of view have indicated that minor incorporation of single-walled carbon nanotubes (SWCNT) may result in enhanced crystallinity development as well as increased charge mobility in poly(3-hexylthiophene) (P3HT) thin films. However, the molecular origin is not fully understood although adsorption of P3HT onto SWCNT to serve as heterogeneous nucleation sites is intuitively a possible explanation. The aim of this study is to explore the interac-tion between SWCNT and P3HT chains from a microscopic point of view via molecular mechan-ics/dynamics simulation. We use molecular mechanics (MM) calculation to firstly explored interac-tion between oligothiophene (electron-rich) and π-conjugated system on graphene sheet (elec-tron-poor). Our approach is illustrated by a contacting model, in which we examine the variation of the potential energy with inter-molecular distance and rotational angle between tetrathiophene and SWCNT. Furthermore, in order to understand energetic contribution by alkyl arm-SWCNT or by backbone-SWCNT interactions to poly(3-alkylthiophene) (P3AT) adsorption, we study the variation of adsorption with rotational angle between P3AT and SWCNT, comparing with adsorption between PT and SWCNT. We also use an NPT ensemble under DREIDING force field and periodic boundary conditions with an MD box containing 6548 atoms at 300 K and at 450 K via the molecular dynamics (MD) simulation to simulate the interaction between P3HT and SWCNT. The MM and MD results indicate that P3HT chain segments indeed tend to be adsorbed (at a molecular separations less than 4 Å due to π-π interaction without chiral preference) onto SWCNT; this is more clearly observed at the higher temperature 450 K (where higher mobility facilitates ad-justment of molecular rearrangement), which is closer to empirical observation of Tc = 473 K. Be-sides, we observed sulfur atoms (possessing lone-pair electrons) tend to sit on top of the 6-membered conjugated ring (electron deficiency) center of the SWCNT due to lone-pair/π interac-tion; consequently the bending angles of adsorbed S−C−C on backbone tends to be concentrated around 120˚. Finally, for the general case of P3AT with long side-chains, lowered energy barriers were observed to indicate adsorption on SWCNT without orientation preference. In particular, for side-chains containing more than 8 carbons, the energetic contribution by alkyl arm-SWCNT inter-actions to P3AT adsorption may outweigh those from thiophene ring-SWCNT interactions.