Mechanisms of L-cysteine–mediated CO₂ hydrate nucleation: role of thermodynamic driving force and interfacial effects
Journal
Journal of Colloid and Interface Science
Journal Volume
724
Start Page
141077
ISSN
0021-9797
Date Issued
2026-12-15
Author(s)
Abstract
Hypothesis: Many reported kinetic promoters of hydrate nucleation are surface-active additives, reinforcing the prevailing view that nucleation enhancement is governed by interfacial effects. However, this assumption remains unresolved for weakly surface-active molecules such as L-cysteine. We test whether nucleation promotion originates from changes in bulk thermodynamic driving force or interfacial free energy by quantitatively resolving both contributions. Calculations: Large-scale molecular dynamics simulations combined with a rigorous mean first-passage time framework are used to quantify nucleation kinetics and thermodynamics in CO₂ hydrate systems with and without L-cysteine. Homogeneous nucleation is ensured by initializing from a supersaturated aqueous solution under high pressure (300 MPa), enabling direct determination of the nucleation free energy landscape, critical nucleus size, interfacial tension, and chemical potential difference. Findings: L-cysteine exhibits a multifaceted influence on hydrate formation, acting as a thermodynamic inhibitor (lowering the melting temperature) and a kinetic inhibitor for growth (reducing molecular transport), while simultaneously promoting nucleation under identical subcooling conditions. Quantitative decomposition shows that the enhanced nucleation rate originates from an increased bulk chemical potential driving force, whereas the interfacial free energy remains essentially unchanged. These results challenge the prevailing interfacial-dominated paradigm by demonstrating that bulk and interfacial contributions can be decoupled, providing a mechanistic framework for understanding additive-controlled nucleation.
Subjects
Amino acid
Chemical potential driving force
CO₂ hydrate
Free energy landscape
Interfacial tension
Nucleation barrier
Nucleation rate
Publisher
Elsevier BV
Type
journal article