Chemical composition from photos: Dried solution drops reveal a morphogenetic tree.

Area of Science:

• * Inorganic chemistry and materials science.
• * Non-equilibrium pattern formation.
• * Crystallization dynamics.

Background:

• * Inorganic systems under nonequilibrium conditions can generate complex, life-like patterns.
• * The study of salt deposit patterns from evaporating sessile droplets remains underexplored.
• * Evaporite patterns exhibit significant variation, including rings, creep, fractals, and disks.

Purpose of the Study:

• * To explore and classify the diverse patterns formed by 42 different salts during droplet evaporation.
• * To investigate the relationship between salt composition and deposit pattern.
• * To assess the potential for pattern-based chemical analysis.

Main Methods:

• * Systematic evaporation of 42 different salts under controlled conditions.
• * Acquisition and analysis of 7,500 images of salt deposit patterns.
• * Statistical analysis to identify pattern families and bifurcations.

Main Results:

• * Distinct families of salt deposit patterns were identified.
• * Some salts, such as sodium sulfate (Na2SO4) and ammonium nitrate (NH4NO3), exhibited bifurcated patterns.
• * Salt chemical composition could be predicted from deposit patterns with high accuracy, even with limited reference data.

Conclusions:

• * Salt deposit patterns are emergent properties arising from complex interactions of evaporation, crystallization, thermodynamics, capillarity, and fluid flow.
• * Pattern-family affiliations are not predictable from composition alone.
• * The findings suggest potential applications in smartphone-based chemical analysis and space exploration tools.