A MEAN DENSITY MODEL OF IONIC SURFACTANTS FOR DISPERSION OF CARBON NANOTUBES IN AQUEOUS SOLUTIONS
Young Soo Joung
Department of Mechanical Systems Engineering, Sookmyung Women's University, 100, Cheongpa-ro 47-gil, Yongsan-gu, Seoul, Republic of Korea
Abstract
We propose a new analytical model of ionic surfactants used for the dispersion of carbon nanotubes (CNTs) in aqueous solutions. Although ionic surfactants are commonly used to facilitate the dispersion of CNTs in aqueous solutions, understanding the dispersion process is challenging and time-consuming owing to its complexity and nonlinearity. In this work, we develop a mean-density model of ionic surfactants to simplify the calculation of interaction forces between CNTs stabilized by ionic surfactants. Using this model, we can evaluate various interaction forces between the CNTs and ionic surfactants under different conditions. The dispersion mechanism is investigated by estimating the potential of mean force (PMF) as a function of van der Waals forces, electrostatic forces, interfacial tension, and osmotic pressure. To verify the proposed model, we compare the PMFs derived using our method with those derived from molecular dynamics simulations using comparable CNTs and ionic surfactants. Notably, for stable dispersions, the osmotic pressure and interfacial energy are important for long-range and short-range interactions, respectively, in comparison with the effect of electrostatic forces. Our model effectively prescribes specific surfactants and their concentrations to achieve stable aqueous suspensions of CNTs.
In this work, we present a mean-density model of surfactants to illuminate the mechanism of carbon nanotube (CNT) dispersion in aqueous solutions of ionic surfactants. Ionic surfactants have been widely used to make well dispersed CNT suspensions in aqueous solutions. However, the mechanism of the dispersion is not clear. To understand the mechanism, molecular dynamic (MD) simulations were recently employed but it needs high computing performance and time cost to obtain final results. With the mean-density model, we can effectively estimate the potential of mean force between CNTs stabilized with surfactants. Notably, we found that the osmotic pressure between CNTs plays important role to determine the stability of dispersion. The mean-density model can effectively help to determine appropriate surfactants and their concentrations for stable dispersion of CNTs.
https://www.sciencedirect.com/science/article/pii/S0169433218300448