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Michael Newton - One of the best experts on this subject based on the ideXlab platform.

  • Contact Angle Hysteresis on super hydrophobic surfaces
    Langmuir, 2004
    Co-Authors: Glen Mchale, Neil J Shirtcliffe, Michael Newton
    Abstract:

    The relationship between perturbations to Contact Angles on a rough or textured surface and the super-hydrophobic enhancement of the equilibrium Contact Angle is discussed theoretically. Two models are considered. In the first (Wenzel) case, the super-hydrophobic surface has a very high Contact Angle and the droplet completely Contacts the surface upon which it rests. In the second (Cassie-Baxter) case, the super-hydrophobic surface has a very high Contact Angle, but the droplet bridges across surface protrusions. The theoretical treatment emphasizes the concept of Contact-Angle amplification or attenuation and distinguishes between the increases in Contact Angles due to roughening or texturing surfaces and perturbations to the resulting Contact Angles. The theory is applied to predicting Contact-Angle Hysteresis on rough surfaces from the Hysteresis observable on smooth surfaces and is therefore relevant to predicting roll-off Angles for droplets on tilted surfaces. The theory quantitatively predicts a "sticky" surface for Wenzel-type surfaces and a "slippy" surface for Cassie-Baxter-type surfaces.

Frieder Mugele - One of the best experts on this subject based on the ideXlab platform.

  • Contact Angle Hysteresis and oil film lubrication in electrowetting with two immiscible liquids
    Applied Physics Letters, 2018
    Co-Authors: Niels Mendel, Davood Baratian, Frieder Mugele
    Abstract:

    Electrowetting (EW) of water drops in ambient oil has found a wide range of applications including lab-on-a-chip devices, display screens, and variable focus lenses. The efficacy of all these applications is dependent on the Contact Angle Hysteresis (CAH), which is generally reduced in the presence of ambient oil due to thin lubrication layers. While it is well-known that AC voltage reduces the effective Contact Angle Hysteresis (CAH) for EW in ambient air, we demonstrate here that CAH for EW in ambient oil increases with increasing AC and DC voltage. Taking into account the disjoining pressure of the fluoropolymer-oil-water system, short range chemical interactions, viscous oil entrainment, and electrostatic stresses, we find that this observation can be explained by progressive thinning of the oil layer underneath the drop with increasing voltage. This exposes the droplet to the roughness of the underlying solid and thereby increases Hysteresis.

  • Contact Angle Hysteresis and oil film lubrication in electrowetting with two immiscible liquids
    arXiv: Fluid Dynamics, 2018
    Co-Authors: Niels Mendel, Davood Baratian, Frieder Mugele
    Abstract:

    Electrowetting (EW) of water drops in ambient oil has found a wide range of applications including lab-on-a-chip devices, display screens, and variable focus lenses. The efficacy of all these applications is dependent on the Contact Angle Hysteresis (CAH), which is generally reduced in the presence of ambient oil due to thin lubrication layers. While it is well-known that AC voltage reduces the effective Contact Angle Hysteresis (CAH) for EW in ambient air, we demonstrate here that CAH for EW in ambient oil increases with increasing AC and DC voltage. Taking into account the disjoining pressure of the fluoropolymer-oil-water system, viscous oil entrainment and electrostatic stresses, we find that this observation can be explained by progressive thinning with increasing voltage of the oil layer underneath the drop. This exposes the droplet to the roughness of the underlying solid and thereby increases Hysteresis.

  • Stability Limits of Capillary Bridges: How Contact Angle Hysteresis Affects Morphology Transitions of Liquid Microstructures.
    Physical Review Letters, 2015
    Co-Authors: Riëlle De Ruiter, Ciro Semprebon, Mathijs Van Gorcum, Michael H.g. Duits, Martin Brinkmann, Frieder Mugele
    Abstract:

    The equilibrium shape of a drop in Contact with solid surfaces can undergo continuous or discontinuous transitions upon changes in either drop volume or surface energies. In many instances, such transitions involve the motion of the three-phase Contact line and are thus sensitive to Contact Angle Hysteresis. Using a combination of electrowetting-based experiments and numerical calculations, we demonstrate for a generic sphere-plate confinement geometry how Contact Angle Hysteresis affects the mechanical stability of competing axisymmetric and nonaxisymmetric drop conformations and qualitatively changes the character of transitions between them.

  • How to make sticky surfaces slippery: Contact Angle Hysteresis in electrowetting with alternating voltage
    Applied Physics Letters, 2008
    Co-Authors: Li Fahong, Frieder Mugele
    Abstract:

    Contact Angle Hysteresis caused by random pinning forces is a major obstacle in moving small quantities of liquid on solid surfaces. Here, we demonstrate that the Contact Angle Hysteresis for sessile drops in electrowetting almost disappears with increasing alternating voltage, whereas for direct voltage it remains constant. This observation is explained in terms of a balance of surface tension, pinning, and (time-dependent) electrostatic forces at the Contact line.

  • How to make sticky surfaces slippery? Contact Angle Hysteresis in AC electrowetting
    Bulletin of the American Physical Society, 2007
    Co-Authors: Frieder Mugele, Adrian Staicu
    Abstract:

    Contact Angle Hysteresis caused by random pinning forces is a major obstacle in moving small quantities of liquid on solid surfaces. Here, we demonstrate that the Contact Angle Hysteresis for sessile drops in electrowetting almost disappears with increasing AC voltage, whereas it remains essentially unaffected by DC voltage. This observation is explained in terms of a balance of surface tension, pinning, and (time-dependent) electrostatic forces at the Contact line.

Savvas G. Hatzikiriakos - One of the best experts on this subject based on the ideXlab platform.

  • Contact Angle Hysteresis of non-flattened-top micro/nanostructures.
    Langmuir, 2014
    Co-Authors: Sona Moradi, Peter Englezos, Savvas G. Hatzikiriakos
    Abstract:

    A two-dimensional (2D) thermodynamic model is proposed to predict the Contact Angle (CA) and Contact Angle Hysteresis (CAH) of different types of surface geometries, particularly those with asperities having nonflattened tops. The model is evaluated by micro/nano sinusoidal and parabolic patterns fabricated by laser ablation. These microstructures are analyzed thermodynamically through the use of the Gibbs free energy to obtain the equilibrium Contact Angle (CA) and Contact Angle Hysteresis (CAH). The effects of the geometrical details of two types of microstructures on maximizing the superhydrophobicity of the nanopatterned surface are also discussed in an attempt to design surfaces with desired and/or optimum wetting characteristics. The analysis of the various surfaces reveals the important geometrical parameters that may lead to the lotus effect (high CA > 150° and low CAH 150° and high CAH ≫ 10°).

  • Contact Angle Hysteresis of non flattened top micro nanostructures
    Langmuir, 2014
    Co-Authors: Sona Moradi, Peter Englezos, Savvas G. Hatzikiriakos
    Abstract:

    A two-dimensional (2D) thermodynamic model is proposed to predict the Contact Angle (CA) and Contact Angle Hysteresis (CAH) of different types of surface geometries, particularly those with asperities having nonflattened tops. The model is evaluated by micro/nano sinusoidal and parabolic patterns fabricated by laser ablation. These microstructures are analyzed thermodynamically through the use of the Gibbs free energy to obtain the equilibrium Contact Angle (CA) and Contact Angle Hysteresis (CAH). The effects of the geometrical details of two types of microstructures on maximizing the superhydrophobicity of the nanopatterned surface are also discussed in an attempt to design surfaces with desired and/or optimum wetting characteristics. The analysis of the various surfaces reveals the important geometrical parameters that may lead to the lotus effect (high CA > 150° and low CAH 150° and high CAH ≫ 10°).

  • Contact Angle Hysteresis: surface morphology effects
    Colloid and Polymer Science, 2012
    Co-Authors: Sona Moradi, Peter Englezos, Savvas G. Hatzikiriakos
    Abstract:

    Irradiation of metallic surfaces using ultra- short pulse laser results in a dual-scale structure. While metallic surfaces are superhydrophilic immediately after laser irradiation, prolonged exposure to air renders sur- faces superhydrophobic due to surface reactions and deposition of carbonaceous materials onto the surface. In this work, we have fabricated a paraboloid micro- structure, which is analyzed thermodynamically through the use of the Gibbs free energy to obtain the equilib- rium Contact Angle and Contact Angle Hysteresis. The effects of the geometrical details on maximizing the superhydrophobicity of the nanopatterned surface are also discussed in an attempt to design surfaces with desired and/or optimum wetting characteristics.

Glen Mchale - One of the best experts on this subject based on the ideXlab platform.

  • apparent Contact Angle and Contact Angle Hysteresis on liquid infused surfaces
    arXiv: Soft Condensed Matter, 2016
    Co-Authors: Ciro Semprebon, Glen Mchale, Halim Kusumaatmaja
    Abstract:

    We theoretically investigate the apparent Contact Angle and Contact Angle Hysteresis of a droplet placed on a liquid infused surface. We show that the apparent Contact Angle is not uniquely defined by material parameters, but also has a dependence on the relative size between the droplet and its surrounding wetting ridge formed by the infusing liquid. We derive a closed form expression for the Contact Angle in the limit of vanishing wetting ridge, and compute the correction for small but finite ridge, which corresponds to an effective line tension term. We also predict Contact Angle Hysteresis on liquid infused surfaces generated by the pinning of the Contact lines by the surface corrugations. Our analytical expressions for both the apparent Contact Angle and Contact Angle Hysteresis can be interpreted as ‘weighted sums’ between the Contact Angles of the infusing liquid relative to the droplet and surrounding gas phases, where the weighting coefficients are given by ratios of the fluid surface tensions.

  • Contact Angle Hysteresis on super hydrophobic surfaces
    Langmuir, 2004
    Co-Authors: Glen Mchale, Neil J Shirtcliffe, Michael Newton
    Abstract:

    The relationship between perturbations to Contact Angles on a rough or textured surface and the super-hydrophobic enhancement of the equilibrium Contact Angle is discussed theoretically. Two models are considered. In the first (Wenzel) case, the super-hydrophobic surface has a very high Contact Angle and the droplet completely Contacts the surface upon which it rests. In the second (Cassie-Baxter) case, the super-hydrophobic surface has a very high Contact Angle, but the droplet bridges across surface protrusions. The theoretical treatment emphasizes the concept of Contact-Angle amplification or attenuation and distinguishes between the increases in Contact Angles due to roughening or texturing surfaces and perturbations to the resulting Contact Angles. The theory is applied to predicting Contact-Angle Hysteresis on rough surfaces from the Hysteresis observable on smooth surfaces and is therefore relevant to predicting roll-off Angles for droplets on tilted surfaces. The theory quantitatively predicts a "sticky" surface for Wenzel-type surfaces and a "slippy" surface for Cassie-Baxter-type surfaces.

Victor Starov - One of the best experts on this subject based on the ideXlab platform.

  • Static Contact Angle Hysteresis on smooth, homogeneous solid substrates
    Colloid and Polymer Science, 2013
    Co-Authors: Victor Starov
    Abstract:

    A theory of Contact Angle Hysteresis on smooth, homogeneous solid substrates is developed in terms of shape of disjoining/conjoining pressure isotherm and quasi-equilibrium phenomena. It is shown that all Contact Angles, θ , in the range θ _r 

  • static Contact Angle Hysteresis on smooth homogeneous solid substrates
    Colloid and Polymer Science, 2013
    Co-Authors: Victor Starov
    Abstract:

    A theory of Contact Angle Hysteresis on smooth, homogeneous solid substrates is developed in terms of shape of disjoining/conjoining pressure isotherm and quasi-equilibrium phenomena. It is shown that all Contact Angles, θ, in the range θr < θ < θa, which are different from the unique equilibrium Contact Angle θ ≠ θe, correspond to the state of slow “microscopic” advancing or receding motion of the liquid if θe < θ < θa or θr < θ < θe, respectively. This “microscopic” motion almost abruptly becomes fast “macroscopic” advancing or receding motion after the Contact Angle reaches the critical values θ = θa or θr = θ, correspondingly. The values of the static receding, θr, and static advancing, θa, Contact Angles in cylindrical capillaries were calculated earlier, based on the shape of disjoining pressure isotherm. It is shown that an advancing Contact Angle of a droplet on a solid substrate depends on the drop volume and is not a unique characteristic of the liquid–solid system. The suggested mechanism of Contact Angle Hysteresis has direct experimental confirmation.