Underwater Curvature-Driven Transport between Oil Droplets on Patterned Substrates

Area of Science:

• Materials Science
• Surface Chemistry
• Microfluidics

Background:

• Controlling liquid behavior on surfaces is crucial for microfluidic devices.
• Developing simple methods for creating patterned surfaces with tunable wettability is an ongoing challenge.

Purpose of the Study:

• To develop a facile method for creating roughness contrast patterns on copper surfaces.
• To investigate the transport of oil droplets on these patterned surfaces under saturated oil-in-water conditions.
• To explore the potential of this technique for lab-on-a-chip applications.

Main Methods:

• Site-selective oxidation using an ink pen masking method to create roughness contrast on copper.
• Utilizing saturated oil-in-water solutions to prevent oil dissolution.
• Investigating oil transport dynamics (volume, flow rate) influenced by pattern geometry and oil viscosity.
• Comparing experimental results with a Laplace pressure-driven flow model.

Main Results:

• Successfully generated roughness contrast patterns on copper surfaces.
• Demonstrated spontaneous oil droplet transport between reservoirs driven by Laplace pressure differences.
• Observed good agreement between experimental data and the Laplace pressure model.
• Showcased the ability to control oil transport direction based on droplet curvature and reservoir size.
• Extended the patterning technique to create complex multi-reservoir patterns.

Conclusions:

• The developed patterning technique offers a simple and effective way to control underwater oil transport.
• Laplace pressure-driven flow is a viable mechanism for manipulating oil droplets on patterned surfaces.
• The technology holds promise for applications in oil separation, mixing, and lab-on-a-chip systems.