Hydrochannel-Containing Hydrophobic Polymers by Inverse Emulsion Polymerization for Moisture-Driven Actuators

Area of Science:

• Polymer Science
• Materials Science
• Biomimicry

Background:

• Polymers typically exhibit either hydrophobic (water-repelling) or water-absorptive properties, but not both simultaneously.
• Human skin presents a natural example of a hydrophobic surface with underlying hydrophilic pathways for water absorption.
• Synthesizing polymers with both incompatible properties is challenging due to poor wettability and material immiscibility.

Purpose of the Study:

• To develop a novel method for creating a polymer that combines hydrophobic and water-absorptive characteristics.
• To overcome the inherent incompatibility between hydrophobic and hydrophilic materials in synthetic polymers.
• To create a material mimicking natural skin for advanced applications.

Main Methods:

• Developed a new method by increasing the hydrophobicity of reaction sites in hydrophilic monomers.
• Utilized methacrylate structures in hydrophilic monomers (polyethyleneglycol methacrylate and dimethacrylate) to stabilize reverse emulsions.
• Incorporated these stabilized emulsions within a hydrophobic matrix of polymethylhydrosiloxane and divinylpolydimethylsiloxane (PDMS).

Main Results:

• Created a hydrophobic absorptive polymer (HPHG) film exhibiting water repellency (contact angle > 100°) and significant water absorption (19.1% by weight).
• The HPHG surface maintained decent hydrophobicity (78° water contact angle) despite its absorptive capacity.
• Successfully demonstrated a delamination-free, moisture-driven actuator using an HPHG and PDMS bilayer, which transforms into a curved shape.

Conclusions:

• The novel HPHG material successfully overcomes the incompatibility of hydrophobic and absorptive properties.
• The developed polymer mimics natural skin's functionality, offering a hydrophobic barrier while allowing water absorption.
• HPHG shows promise for applications in soft robotics and smart actuators requiring a protective, yet moisture-interactive, artificial skin.