Simulations of Adsorption and In-plane Ordering of Electrostatically Adsorbed Charged Colloidal Nanoparticles
Luna Singh, Jennifer A
Doctor of Philosophy
Self-limiting assembly of nanoparticle arrays promises to revolutionize compliant device fabrication by enabling print-on-demand. Presently, quantitative understanding of the relationship between the array order, nanoparticle size, surface characteristics, and process conditions remain elusive. Previous simulations have shown that tuning particle and surface potentials, screening lengths, and particle concentrations can lead to ordering. However, identifying the experimental conditions to observe these in-plane order-disorder and order-order transitions for nanoparticles remains a challenge. This study focuses on the ordering process during absorption of electrostatically stabilized nanoparticles onto an attractive surface with varying bulk concentrations of the nanoparticles in solution. The bond orientational correlation function as well as Voronoi and 2D structure factor analysis is used to determine the transition points between liquid, hexatic, and crystalline nanoparticle arrays. Brownian dynamics simulations demonstrated that the critical effective surface coverage required for the liquid-hexatic or hexatic-crystalline transition point increases with increasing bulk concentration, while the critical timestep decreases with increasing bulk concentration. To better understand the role of hydrodynamic interactions between the particles simulations using Fast Lubrication dynamics were compared to the Brownian dynamics simulations. Computational cost of Fast Lubrication dynamics is approximately an order of magnitude greater than that of Brownian dynamics. The inclusion of particle-particle hydrodynamic interactions revealed a reduced bulk diffusion coefficient and the stochastic nature of the ordering process. The Fast Lubrication dynamics simulations demonstrate the complex role of not only the bulk concentration but also the bulk solvent on the ordering process. Identifying and understanding these transition points will help elucidate experimental conditions necessary to create high resolution patterns and smaller devices.
Adsorption; Colloidal system; Surface phase transitions; Surface structure