Diffusiophoretic Fast Swelling of Chemically Responsive Hydrogels

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Polyacrylic acid hydrogels release stored ions when exposed to acid.
• This ion release influences the gel's osmotic pressure and swelling behavior.
• Existing models do not fully capture the rapid swelling dynamics observed.

Purpose of the Study:

• To investigate the mechanism behind acid-induced rapid swelling and contraction cycles in polyacrylic acid hydrogels.
• To develop a theoretical framework explaining the observed hydrogel actuation.
• To explore the potential of this mechanism for advanced hydrogel applications.

Main Methods:

• Experimental observation of ion release and hydrogel swelling dynamics.
• Development of a continuum poroelastic theory.
• Introduction and analysis of the
• gel diffusiophoresis
• mechanism.

Main Results:

• Acid-induced ion release significantly increases gel osmotic pressure, leading to swelling rates exceeding solvent absorption.
• A novel
• gel diffusiophoresis
• mechanism, driven by steric repulsion between gel polymers and ions, explains the rapid solvent intake and network expansion.
• Gel expansion ceases as ion concentration gradients dissipate, followed by gel contraction.

Conclusions:

• The developed poroelastic theory accurately explains the experimental hydrogel actuation cycles.
• Engineering
• gel diffusiophoresis
• offers a pathway to stimuli-responsive hydrogels with enhanced strain rates and power output.
• This mechanism has significant implications for drug delivery systems and soft robotics.