Hierarchical Assemblies and Cluster Growth Regimes of Bipolar Janus Nanoparticles: Effect of Particle Characteristics

There has been significant interest on properties of colloidal Janus particles (JP) in recent years. As a result of their current and potential applications in fields such as drug delivery, water waste treatment, oil recovery, etc. In addition to experimental studies investigating structure formation in colloidal systems composed of particles in the range of several nanometers in diameter up to micron sizes, a number of Monte Carlo and Brownian dynamics simulations have also been performed to elucidate the underlying principals which determine structure formation of Janus particles. However most of these studies are based on relatively simple models and lack inclusion of long range columbic interactions.

In this work, molecular dynamic simulation, which includes long range columbic interaction, is performed in order to elucidate the self assembly of bipolar JP at different surface charge density (0.2~1.3 e/nm²) , salt concentration(0~3 mM) and particle sizes. Results clearly indicate formation of two distinct sub structures in very low JP concentration, namely: strings and rings. As concentration of JP increases these sub structures joins and/or hierarchically assemble into larger clusters.

To further understand the underlying principals of JP self assembly, namely string versus ring formation we have carefully examined the sequential cluster growth as a function of surface charge density, particle size and steric hindrance of surface ions by cluster potential energy minimization technique.