Gypsum heterogenous nucleation pathways regulated by surface functional groups and hydrophobicity

Area of Science:

• Materials Science
• Surface Chemistry
• Crystallization Science

Background:

• Gypsum (CaSO4·2H2O) is crucial in natural and industrial settings.
• Understanding gypsum nucleation on diverse surfaces is limited by resolution.
• Surface chemistry significantly influences crystal formation.

Purpose of the Study:

• To investigate real-time gypsum nucleation on various functionalized surfaces.
• To elucidate the role of surface functional groups and hydrophobicity in gypsum formation.
• To differentiate nucleation mechanisms on hydrophilic versus hydrophobic substrates.

Main Methods:

• In situ microscopy for real-time observation.
• Utilizing self-assembled monolayers (SAMs) with diverse functional groups (-CH3, -hybrid, -COOH, -SO3, -NH3, -OH).
• Classical nucleation theory and molecular dynamics simulations.

Main Results:

• Gypsum formation rate follows the order: -CH3 > -hybrid > -COOH > -SO3 ≈ -NH3 > -OH.
• Hydrophilic surfaces exhibit surface-induced nucleation with vertical cluster growth.
• Hydrophobic surfaces show bulk nucleation with horizontal cluster formation.

Conclusions:

• Surface functional groups and hydrophobicity are key regulators of gypsum nucleation.
• Distinct nucleation pathways (surface-induced vs. bulk) are identified based on surface properties.
• Findings offer insights into gypsum formation mechanisms and surface interactions.