Time-Dependent Wetting Behavior of PDMS Surfaces with Bioinspired, Hierarchical Structures

Area of Science:

• Surface Science
• Materials Science
• Biomimetics

Background:

• Wetting of rough surfaces is crucial for applications like oil-water separation and anti-fouling coatings.
• Conventional models (Cassie-Baxter, Wenzel) do not fully capture time-dependent wetting phenomena.
• Understanding these dynamics is key for designing durable and effective surface treatments.

Purpose of the Study:

• To investigate the time-dependent wetting behavior of water on rough polydimethylsiloxane (PDMS) surfaces.
• To analyze how surface topography and material properties influence contact angle changes over time.
• To compare experimental results with existing wetting models and identify their limitations.

Main Methods:

• Fabrication of hierarchical rough PDMS surfaces using sand dollar shells as lithography-free templates.
• Measurement of sessile water droplet contact angles over extended periods (minutes to hours).
• Utilized fluorescent confocal microscopy to observe pore filling dynamics and water droplet behavior.

Main Results:

• Initial contact angles ( < 1 min) on templated PDMS align with the Cassie-Baxter model.
• Contact angles decrease over time, transitioning towards the Wenzel state as pores fill.
• Significant long-term decrease in contact angle (to 65° over 48h) due to pore filling and potential PDMS deformation, deviating from established models.

Conclusions:

• Time-dependent wetting on rough PDMS surfaces cannot be solely explained by static models.
• Pore filling and surface viscoelasticity play critical roles in long-term wetting behavior.
• Insights gained can inform the development of advanced coatings with tailored wetting properties for specific applications.