Multi-Modal Droplet Manipulation on Laser-Patterned Stimulus-Responsive Gradient Surfaces: Enabling Anti-Gravity...

Area of Science:

• Materials Science
• Surface Engineering
• Microfluidics

Background:

• Superhydrophobic surfaces mimic natural structures like lotus leaves for water repellency.
• Controlling droplet movement on surfaces is crucial for microfluidic applications.
• Existing methods often lack multimodal control or adaptability to complex surfaces.

Purpose of the Study:

• To develop laser-ablated multigradient bionic superhydrophobic surfaces (MGBs) for advanced droplet manipulation.
• To integrate passive structural gradients with active stimuli-responsiveness.
• To achieve multimodal control over droplet transport, including autonomous and gravity-defying movement.

Main Methods:

• Fabrication of MGBs on Fe3O4@PDMS membranes using laser ablation.
• Achieving superhydrophobicity (contact angle ≈ 156°) with wedge-step structures.
• Surface wettability switching to superslippery states via silicone-oil infusion for liquid-liquid slippage (sliding angle < 3°).
• Utilizing passive Laplace pressure gradients and active magnetic/near-infrared (NIR) responses for control.

Main Results:

• Demonstrated autonomous droplet transport with a peak velocity of 87.75 mm/s using wettability gradients.
• Magnetic actuation reduced contact angle hysteresis (Δθ = 10°), enabling long-distance transport.
• NIR-triggered Marangoni flow achieved antigravity droplet climbing on a 43° incline at 0.24 mm/s.
• The platform showed adaptability to curved and irregular surfaces.

Conclusions:

• The developed MGB platform offers synergistic bioinspired design with magnetic/photothermal stimulation for microfluidic control.
• This approach overcomes limitations of traditional single-mode droplet manipulation.
• The technology enables self-propelled, gravity-defying microfluidic operations on diverse surfaces.