Predictive model for alignment and deposition of functionalized nanotubes using applied electric field

Abstract

Myriad applications, including sensors and supercapacitors, employ substrates decorated with patterned carbon nanotubes (CNTs) in order to leverage the significant anisotropy in their properties. In the present study, a unique continuum mechanics based model was developed to predict the alignment and migration timescales of CNTs for realistic lab-scale electrophoretic deposition (EPD), which is a popular technique to create aligned deposits of pristine and functionalized CNTs without embedded catalysts. This model was initially validated based on results from molecular dynamics simulations to check for mutual consistency. EPD is a complex process that involves electrophoretic alignment and migration of CNTs towards the substrate, displacement of solvent molecules from the surface of substrate by overcoming an energy barrier, followed by deposition. We simulated COOH functionalized CNTs of varying length under a range of applied electric fields (1 V/nm to 5 V/nm) to understand the mechanics of electrophoretic alignment and deposition. The dynamics of alignment and deposition were related to the molecular interactions between the various constituents by calculating friction parameters. The results from the parametric study, which is limited to length scales accessible to molecular dynamics simulations, was scaled up to CNTs of micrometer-scale length by comparing the results with solutions to the continuum scale model. The results indicate that the timescale for rotational alignment of realistic CNTs is of the order of seconds and several orders of magnitudes faster compared to the timescale for migration, which is of the order of thousands of seconds for a channel of diameter of 100 μm.