Instability patterns of evaporative dendrimer deposits.

Abstract

The purpose of this project is to understand the instability mechanism behind dendrimer pattern formation in evaporating micro-meter size droplets. Evaporation of droplets of alcohol-dendrimer solution leaves a unique solute pattern on a substrate, where the detailed structure depends on the system variables. We are interested in developing a theory of the morphology of the dendrimer deposits that encompasses evaporation effects, solvent hydrodynamics, and solute particle chemistry. Our approach is to consider a two-dimensional coarse-grained model of dendrimer particle deposition that involves two mechanisms: transfer of solute particles by a convective flow and an inter-particle attraction competing with the convective flow. The configuration of a drying droplet is determined by the distribution of particles on a substrate and the volume fraction of them in a droplet. The Hamiltonian of each configuration is defined to account for both a convective flow and an inter-particle attraction. The evolution of the Hamiltonian is computed by Monte Carlo method to simulate the dendrimer pattern formation and associate patterns with system parameters. We found four basic regimes of morphologies that range from ringlike, wavelike, and fingerlike to islandlike patterns depending on the number of particles and the relative strength of a convective flow and an interaction.