Unsteady Wetting on a Rough Surface due to Electrically Altered Surface Tension

Area of Science:

• Physics
• Materials Science
• Surface Science

Background:

• Understanding wetting dynamics is crucial in various applications, including microfluidics and coatings.
• Surface roughness significantly impacts liquid spreading behavior, often deviating from ideal smooth surface models.
• Electrically controlling surface tension offers a method to initiate and manipulate wetting processes.

Purpose of the Study:

• To experimentally measure unsteady wetting phenomena on a rough surface.
• To develop a theoretical model that accounts for surface roughness effects on wetting.
• To investigate the relationship between surface roughness, interface shape, and capillary number.

Main Methods:

• Measurements of unsteady wetting dynamics were performed on a rough solid surface.
• Solid-liquid surface tension was dynamically altered using electrical control to initiate spreading.
• The time-dependent interface shape was analyzed and compared to theoretical models.

Main Results:

• The unsteady wetting process on a rough surface was successfully measured.
• A steady-state theory, augmented with a model for surface roughness, accurately described the observed interface shape.
• Interface flattening, attributed to pinning effects, was observed and modeled as an effective slip, reducing the capillary number.

Conclusions:

• Surface roughness plays a critical role in unsteady wetting, necessitating specialized models.
• Electrically induced surface tension changes provide a controllable method for studying wetting dynamics.
• The concept of 'slip' effectively captures the influence of pinning on rough surfaces, impacting effective capillary numbers.