Hierarchically Structured, All-Aqueous-Coated Hydrophobic Surfaces with pH-Selective Droplet Transfer Capability.

Area of Science:

• Materials Science and Engineering
• Surface Chemistry
• Nanotechnology

Background:

• Precise droplet manipulation is crucial for microfluidics, microreactors, and water harvesting.
• Existing surface modification strategies often lack simultaneous hydrophobicity and pH-sensitivity under environmentally friendly conditions.

Purpose of the Study:

• To develop a widely applicable strategy for surface modification combining hydrophobicity and pH-sensitivity.
• To create environmentally friendly coatings for controlled droplet capture and transfer.

Main Methods:

• Utilized all-aqueous layer-by-layer (LbL) deposition of polyelectrolytes to create hydrophobic coatings.
• Incorporated pH-responsive groups into fluorinated polyphosphazenes (PPZs) for pH-selective properties.
• Investigated the influence of fluorination degree, deposition pH, and coating thickness on hydrophobicity.

Main Results:

• Achieved hydrophobic coatings with water contact angles exceeding 120° on flat surfaces and 150° on structured surfaces.
• Demonstrated tunable adhesivity and rose petal-like superhydrophobicity with attenuated contact angle hysteresis on microstructured surfaces.
• Successfully enabled pH-selective droplet capture and transfer between surfaces with varying microstructures or assembly pH.

Conclusions:

• Developed versatile, environmentally friendly hydrophobic coatings with tunable pH-sensitivity.
• The coatings facilitate precise control over water droplet adhesion and transfer, applicable to microfluidics and water harvesting.
• The approach offers a novel method for creating advanced functional surfaces through aqueous LbL assembly.