Shape-programmed folding of stimuli-responsive polymer bilayers.

Area of Science:

• Materials Science
• Polymer Science
• Soft Matter Physics

Background:

• Hydrogel-based polymer bilayers are responsive materials with tunable properties.
• Their folding and rolling behavior on substrates is crucial for applications in soft robotics and actuators.
• Understanding the factors influencing these shape transformations is essential for material design.

Purpose of the Study:

• To investigate the folding and rolling mechanisms of rectangular hydrogel-polymer bilayers on a substrate.
• To identify the key parameters governing different rolling morphologies.
• To elucidate the roles of non-uniform swelling and substrate adhesion in these phenomena.

Main Methods:

• Experimental fabrication and observation of hydrogel-polymer bilayers with varying aspect ratios and thicknesses.
• Finite-element modeling to simulate bilayer deformation and rolling.
• Energetic analysis to understand the driving forces behind different rolling behaviors.

Main Results:

• Observed distinct rolling behaviors: long-side rolling (high aspect ratio, low strain), all-side rolling (high actuation), and diagonal rolling (moderate actuation).
• Short-side rolling occurred rarely, often with diagonal rolling.
• Identified non-homogenous swelling and polymer-substrate adhesion as primary drivers for varied rolling scenarios.

Conclusions:

• The substrate-induced non-uniform swelling and adhesion significantly influence hydrogel bilayer rolling.
• Aspect ratio and actuation strain are critical in determining the dominant rolling direction.
• The findings provide insights into controlling the self-shaping of hydrogel-based materials.