Related Experiment Video
Updated: Feb 17, 2026
07:18
Measuring the Interaction Force Between a Droplet and a Super-hydrophobic Substrate by the Optical Lever Method
Published on: June 14, 2019
7.1K
Experimental study of dynamic contact angles on rough hydrophobic surfaces
Alireza Mohammad Karim1, Jonathan P Rothstein2, H Pirouz Kavehpour1
1Department of Mechanical and Aerospace Engineering, UCLA, Los Angeles, CA 90025, USA.
Journal of Colloid and Interface Science
|December 6, 2017
Summary
This study investigated the spreading of polyethylene glycol (PEG) solutions on rough Teflon surfaces. Surface roughness significantly impacts dynamic contact angles, with receding angles decreasing as capillary number increases.
Area of Science:
- Surface science
- Materials science
- Fluid dynamics
Background:
- Rough hydrophobic surfaces are crucial in various industrial applications.
- Understanding liquid behavior on these surfaces is essential for technological advancements.
- Polyethylene glycol (PEG) solutions are widely used and exhibit unique surface properties.
Purpose of the Study:
- To experimentally investigate the spreading dynamics of polyethylene glycol (PEG) solutions.
- To analyze the influence of surface roughness and PEG concentration on dynamic contact angles.
- To determine the relationship between capillary number and dynamic contact angles on rough hydrophobic surfaces.
Main Methods:
- Utilized the Wilhelmy plate method for precise contact angle measurements.
- Conducted experiments with varying concentrations of PEG solutions.
- Employed Teflon plates with controlled, differing degrees of surface roughness.
Main Results:
- Advancing dynamic contact angles showed weak dependence on the capillary number.
- Receding dynamic contact angles decreased with increasing capillary number.
- Surface roughness played a significant role in determining dynamic contact angles.
- Receding motion dynamics aligned with the molecular-kinetic theory.
- A power law relationship was established between receding dynamic contact angle and capillary number.
Conclusions:
- Surface roughness is a critical factor influencing liquid spreading dynamics on hydrophobic surfaces.
- The observed receding contact angle behavior supports theoretical models like the molecular-kinetic theory.
- Established a predictive power law for receding contact angles, valuable for surface design and applications.
Related Concept Videos
01:13Contact Angle
26.8K
When a solid is dipped inside a liquid, the liquid surface becomes curved near the contact. For some solid–liquid interfaces, the liquid is pulled up along the solid, while for others, the liquid surface is convex or depressed near the solid surface. This phenomenon can be explained using the concept of cohesive and adhesive forces.
The adhesive force is the molecular force between molecules of different materials, that is, between the molecules of the solid and the liquid. The cohesive...
The adhesive force is the molecular force between molecules of different materials, that is, between the molecules of the solid and the liquid. The cohesive...
26.8K
01:04Hydrostatic Pressure Force on a Curved Surface
2.6K
Hydrostatic pressure on curved surfaces is a fundamental concept in fluid mechanics with broad applications in the civil engineering field. When fluid is in contact with a curved surface, as in a reservoir, dam, or storage tank, it exerts pressure that varies in magnitude and direction along the curved surface. To assess the total hydrostatic force exerted by the fluid on a curved structure, engineers typically isolate the fluid volume adjacent to the surface and analyze the forces acting on...
2.6K
01:04Hydrostatic Pressure Force on a Plane Surface
1.5K
When a plane surface is submerged in a fluid, hydrostatic forces develop on the surface due to the fluid's pressure. For horizontal surfaces, the pressure exerted by the fluid is uniform because the depth remains constant. The resultant force is determined by the pressure at the given depth multiplied by the area of the surface, and it acts through the centroid of the surface. For vertical surfaces, the pressure varies with depth, increasing as the distance from the fluid's free surface...
1.5K
01:21Characteristics of Dry Friction
1.0K
Dry friction occurs when two solid surfaces slide against each other without any lubrication or fluid present. It causes resistance when pushing objects along a surface, like a gardener pushing a wheelbarrow. The force applied to move the cart causes dry friction between the wheel and the ground.
Before the wheelbarrow starts moving, the static frictional force acts tangentially to the contact surface, opposing the force that is about to induce the motion. This frictional force prevents the...
Before the wheelbarrow starts moving, the static frictional force acts tangentially to the contact surface, opposing the force that is about to induce the motion. This frictional force prevents the...
1.0K
01:22Surface Tension of Fluid
1.7K
Surface tension is a fundamental property of fluids, occurring at the boundary between a liquid and a gas or between two immiscible liquids. This phenomenon arises from the cohesive forces between molecules at the fluid's surface, creating an effect similar to a stretched elastic membrane. Inside each fluid, molecules are equally attracted in all directions by neighboring molecules, but surface molecules experience a net inward force, resulting in surface tension.
Surface tension varies...
Surface tension varies...
1.7K