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Activated Wetting of Nanostructured Surfaces: Reaction Coordinates, Finite Size Effects, and Simulation Pitfalls
M Amabili1, S Meloni1, A Giacomello1
1Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , 00184 Rome, Italy.
The Journal of Physical Chemistry. B
|December 5, 2017
Summary
Understanding the Cassie-Wenzel transition is key for superhydrophobic applications. This study reveals simulation artifacts from common collective variables and finite system sizes, impacting free energy calculations and wetting mechanisms.
Area of Science:
- Surface Science and Physical Chemistry
- Computational Materials Science
- Fluid Dynamics
Background:
- Liquids on textured surfaces exist in Cassie (non-wetting) or Wenzel (wetting) states.
- Cassie state offers superhydrophobic properties like self-cleaning and drag reduction, lost in the Wenzel state.
- Investigating the Cassie-Wenzel transition is crucial for exploiting superhydrophobicity.
Purpose of the Study:
- To identify simulation artifacts in studying the Cassie-Wenzel transition using collective variables (CVs).
- To analyze artifacts introduced by coarse-grained density fields and finite system sizes.
- To provide guidelines for accurate computational studies of wetting phenomena.
Main Methods:
- Computational investigation using enhanced sampling techniques (rare events) with collective variables.
- Analysis of average particle density and coarse-grained density fields as CVs.
- Examination of finite size effects in simulations with pillared surfaces.
Main Results:
- Highly coarse-grained density CVs introduce significant artifacts: large errors in free energy differences and barriers, and incorrect wetting mechanisms.
- Accurate Cassie-Wenzel transition energetics and mechanisms require fine discretization of the density field.
- Simulations with single pillars under periodic boundary conditions hinder capturing the meniscus symmetry break, crucial for transition state analysis.
Conclusions:
- Commonly used coarse-grained CVs and finite system sizes can lead to severe artifacts in Cassie-Wenzel transition simulations.
- Careful selection of CVs, specifically fine-grained density fields, is essential for reliable free energy and mechanism evaluation.
- Accurate simulation of the Cassie-Wenzel transition requires addressing both CV choice and system size limitations to capture critical symmetry breaking events.
