Modelling thermochemical reversible dot-to-rod transformation in colloidal nanomaterials

Recently a nanorod-to-nanodot reversible transformation was reported by Niya et al. in case of nano-ZnO colloidal dispersion. The reversibility of this transformation, coupled with the need for a specific surfactant and solvent, indicates thermo-chemical origins of the phenomenon. Results indicate that surfactants play a critical role in the process. However, an explanation for this phenomena has not been reported yet. In this work, we derive and develop the chemical potential expressions that capture the roles played by surface-interactions, in driving this reversible transformation. Equations associated with both the dot (spherical) and rod (cylindrical) morphologies are reported. Using agent based modelling, and realistic parameters, we indeed observe a temperature induced morphology transformation that is consistent with experiment. The transition temperature is shown to vary slowly for a wide range of surfactant-surface chemistries and surface charges, which are parametrically captured. We indicate that such rod-to-dot transitions in colloids can be expected across other compositions as well.