Moving contact lines and Langevin formalism
| Autor: | J. C. Fernández-Toledano, T. D. Blake, J. De Coninck |
|---|---|
| Rok vydání: | 2020 |
| Předmět: |
Physics
Mechanical equilibrium Condensed matter physics Capillary action 02 engineering and technology Dissipation 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences 0104 chemical sciences Surfaces Coatings and Films Electronic Optical and Magnetic Materials law.invention Biomaterials Surface tension Molecular dynamics Colloid and Surface Chemistry law Thermal Wetting 0210 nano-technology Harmonic oscillator |
| Zdroj: | Journal of Colloid and Interface Science. 562:287-292 |
| ISSN: | 0021-9797 |
| DOI: | 10.1016/j.jcis.2019.11.123 |
| Popis: | Hypothesis In previous work [J.-C. Fernandez-Toledano, T. D. Blake, J. De Coninck, J. Colloid Interface Sci. 540 (2019) 322–329], **we used molecular dynamics (MD) to show that the thermal oscillations of a contact line formed between a liquid and a solid at equilibrium may be interpreted in terms of an overdamped 1-D Langevin harmonic oscillator. The variance of the contact-line position and the rate of damping of its self-correlation function enabled us to determine the coefficient of contact-line friction ζ and so predict the dynamics of wetting. We now propose that the same approach may be applied to a moving contact line. Methods We use the same MD system as before, a liquid bridge formed between two solid plates, but now we move the plates at a steady velocity U plate in opposite directions to generate advancing and receding contact lines and their associated dynamic contact angles θ d . The fluctuations of the contact-line positions and the dynamic contact angles are then recorded and analyzed for a range of plate velocities and solid-liquid interaction. Findings We confirm that the fluctuations of a moving contact line may also be interpreted in terms of a 1-D harmonic oscillator and derive a Langevin expression analogous to that obtained for the equilibrium case, but with the harmonic term centered about the mean location of the dynamic contact line x d , rather than its equilibrium position x 0 , and a fluctuating capillary force arising from the fluctuations of the dynamic contact angle around θ d , rather than the equilibrium angle θ 0 . We also confirm a direct relationship between the variance of the fluctuations over the length of contact line considered L y , the time decay of the oscillations, and the friction ζ . In addition, we demonstrate a new relationship for our systems between the distance to equilibrium x d - x 0 and the out of equilibrium capillary force γ L cos θ 0 - cos θ d , where γ L is the surface tension of the liquid, and show that neither the variance of the fluctuations nor their time decay depend on U plate . Our analysis yields values of ζ nearly identical to those obtained for simulations of spreading drops confirming the common nature of the dissipation mechanism at the contact line. |
| Databáze: | OpenAIRE |
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