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

Abstract

We report a study on the kinetics of drying of a droplet of aqueous gelatin containing sodium chloride. The process of drying recorded as a video clearly shows different regimes of growth leading to a variety of crystalline patterns. Large faceted crystals of ∼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 the Euler number. A minimum in the Euler number marks the transition between the two regimes of growth.

Droplet Drying Patterns on Solid Substrates: From Hydrophilic to Superhydrophobic Contact to Levitating Drops

“…Sodium chloride in gelatinized potato starch solution forms dendrites or hopper crystals of different morphology, depending on experimental conditions [24]. In gelatin, two distinct modes of pattern formation were observed [26,142]. Formation of initial faceted rectilinear crystals of macroscopic dimensions (of ∼mm) size was followed by a fine dendritic network observable only under a microscope.…”

“…A simple Monte Carlo algorithm for evaporation and pattern formation has been developed by Dutta Choudhury et al to reproduce the formation of faceted salt crystals and dendritic aggregates in drying droplets of aqueous gelatin containing NaCl [142]. The pattern formation can be correlated to the topological concept of the Euler number [220].…”

“…Depending on the nature of the fluid and substrate, the film either sticks to the substrate or can be cleanly pulled off [142].…”

“…After complete drying of the droplet, a protein precipitate remains on the substrate in the form of a ring; the width of the ring depends on concentrations of the protein and the salt [3,171,172]. Salt crystals can form fractal (dendritic) structures [24,29,142,173,174]. In the later stages of drying, a sample may crack [8,28,29]; the characteristic pattern of the cracks also helps in diagnosing diseases from which the subject may be suffering [175].…”

Aggregation of Crystalline Copper Sulphate Salt in a Gelatin Medium

“…[16][17][18][19] Besides knowing the underlying principles of growth morphology of crystals in drying drops, 20-24 pattern formation procedure during evaporation is a topic of considerable interest in many practical applications. [25][26][27][28] In this experiment, we found the pattern of aggregation of CuSO 4 salt in a viscous medium on a hydrophilic solid substrate.…”