Growth kinetics of NaCl crystals in a drying drop of gelatin: transition from faceted to dendritic growth

TL;DR

This study investigates the drying process of gelatin droplets with NaCl, revealing a transition from faceted to dendritic crystal growth, modeled through simulations and characterized by the Euler number.

Contribution

It introduces a simple growth simulation capturing the transition between faceted and dendritic crystal patterns during drying.

Findings

Large faceted crystals form initially

Transition to dendritic, fractal patterns occurs during evaporation

Euler number effectively characterizes the growth regime transition

Abstract

We report a study on the kinetics of drying of a droplet of aqueous gelatin containing sodium chloride. The process of drying recorded on video, clearly shows different regimes of growth leading to a variety of crystalline patterns. Large faceted crystals of $\sim$mm size form in the early stages of evaporation, followed by highly branched multi-fractal patterns with micron sized features. We simulate the growth using a simple algorithm incorporating aggregation and evaporation, which reproduces the cross-over between the two growth regimes. As evaporation proceeds, voids form in the gel film. The time development of the fluid-void system can be characterized by an Euler number. A minimum in the Euler number marks the transition between the two regimes of growth.