(534d) Atomistic Simulations of Carbon Nanotube Deposition on Functionalized Silica Substrates

Authors: 
Shen, Z., University of Wisconsin-Madison
Van Lehn, R. C., University of Wisconsin-Madison
Dwyer, J., University of Wisconsin-Madison
Gopalan, P., University of Wisconsin at Madison
Single-walled carbon nanotubes (SWCNTs) have wide applications in semiconducting devices due to their exceptional electronic properties. SWCNTs can be dispersed in organic solvents by wrapping them with the copolymer PFO-BPy (9,9-dioctylfluorenyl-2,7-diyl and bipyridine), which has been shown to be an highly selective agent for semiconducting SWCNTs. However, utilizing SWCNTs for semiconducting devices requires the ordered deposition of SWCNTs on substrates because randomly distributed SWCNT thin films demonstrate suboptimal electronic properties. Therefore, it is essential to understand the interactions between PFO-BPy-wrapped SWCNTs and functionalized substrates to predict SWCNT deposition and interfacial assembly.

In this work, we study the liquid-phase deposition of SWCNTs on silica surfaces functionalized by self-assembled monolayers (SAMs) composed of organic molecules grafted to the silica substrate. Experiments find that SWCNT deposition depends on both the SAM chemistry and choice of organic solvent. However, no linear correlation is found between the hydrophobicity/hydrophilicity of the SAMs and the deposition density and pattern. In order to provide mechanistic insights into this deposition phenomenon, we apply molecular dynamics (MD) simulations to study the adsorption of PFO-BPy wrapped SWCNT on different SAM-protected silica surfaces in chloroform or toluene solutions. We focus on model SAMs that differ in extremes of observed deposition and wettability. Potential of mean force calculations reveal the different free energy landscapes for adsorption to each SAM in each solvent composition, which we relate to the solvent organization and interactions at the interface. Our findings provide new insight into the how the interplay of copolymer, SAM, and solvent interactions influence CNT deposition.