Flexibly designable wettability gradient for passive control of fluid motion via physical surface modification

Area of Science:

• Surface science and materials engineering
• Microfluidics and lab-on-a-chip technologies
• Fluid dynamics and transport phenomena

Background:

• Modified solid surfaces display distinct wetting properties like hydrophobicity and hydrophilicity.
• Surface wettability can be leveraged for passive control of fluid flow in microchannels.
• Designing precise fluid pathways is essential for advanced microfluidic applications.

Purpose of the Study:

• To experimentally demonstrate a wettability-designable cell array on a silicon substrate.
• To engineer one- and two-dimensional wettability gradients for fluid channels.
• To achieve passive control of fluid motion, including unidirectional and curved paths.

Main Methods:

• Utilizing reactive ion etching to create physically etched surfaces with altered roughness on a silicon substrate.
• Fabricating a cell array comprising both unetched and etched silicon surfaces.
• Adjusting the ratio of unetched to etched surface areas to design wettability gradients.

Main Results:

• The etching process significantly altered the surface roughness, leading to distinct wettabilities between unetched and etched regions.
• Successfully designed and implemented one- and two-dimensional wettability gradients within fluid channels.
• Demonstrated passive realization of unidirectional and curved fluid motions by fine-tuning the wettability gradients.

Conclusions:

• Wettability gradients on engineered surfaces provide a powerful method for passive fluid control.
• The developed wettability-designable cell array enables precise manipulation of fluid trajectories.
• This approach is crucial for the development of practical and portable integrated fluidic systems.