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Wetting of flat gradient surfaces.

Edward Bormashenko1

  • 1Ariel University, Faculty of Engineering, Chemical Engineering, Biotechnology and Materials Department, P.O.B. 3, 40700 Ariel, Israel.

Journal of Colloid and Interface Science
|January 20, 2018
PubMed
Summary
This summary is machine-generated.

Chemically modified, gradient surfaces facilitate droplet transport. A new variational approach reveals that apparent contact angles on these surfaces depend on contact line radius and interfacial tension gradients, inevitably causing contact angle hysteresis.

Keywords:
Contact angle hysteresisGradient surfacesTransversality conditionsWetting

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Area of Science:

  • Surface Science and Engineering
  • Fluid Dynamics
  • Materials Chemistry

Background:

  • Gradient, chemically modified, flat surfaces are key for directed droplet transport.
  • Calculating apparent contact angles on gradient surfaces presents significant challenges, even for atomically flat substrates.

Purpose of the Study:

  • To develop a theoretical framework for understanding the wetting behavior of droplets on gradient flat solid surfaces.
  • To derive a generalized Young equation applicable to gradient surfaces.
  • To investigate the factors influencing apparent contact angles and the phenomenon of contact angle hysteresis.

Main Methods:

  • Application of a variational approach to model droplet wetting, allowing free movement of the contact line.
  • Derivation of a generalized Young equation using transversality conditions from the variational problem.
  • Analysis of the linear approximation to determine the dependence of apparent contact angle on contact line radius and interfacial tension derivatives.

Main Results:

  • A generalized Young equation valid for gradient solid surfaces was derived.
  • The apparent (equilibrium) contact angle is shown to depend on the contact line radius and the derivatives of interfacial tensions.
  • Contact angle hysteresis is demonstrated to be an inevitable characteristic of gradient surfaces.

Conclusions:

  • The variational approach provides a robust method for analyzing wetting on gradient surfaces.
  • Understanding the relationship between surface properties and apparent contact angles is crucial for controlling droplet behavior.
  • The inevitability of contact angle hysteresis on gradient surfaces has significant implications for applications such as microfluidics and lab-on-a-chip devices.