Shell-Forming Stimulus-Active Hydrogel Composite Membranes: Concept and Modeling.

Adrian Ehrenhofer,Thomas Wallmersperger

doi:10.3390/mi11060541

Abstract

The swelling of active hydrogels combined with passive layers allows the design of shell-forming structures. A shell-like structure offers different properties than a flat structure, e.g., variations in bending stiffness across different directions. A drastic increase of the bending stiffness is favorable e.g., in rollable/flexible displays: in their unrolled form, they have to be stiff enough to resist bending due to dead weight. At the same time, they have to be flexible enough to be rolled-up. This can be achieved by shell-forming. In the current modeling and simulation work, we present a basic concept of combined active–passive composites and demonstrate how they form shells. As the example material class, we use hydrogels with isotropic swelling capabilities. We demonstrate how to model the combined mechanical behavior with the Temperature-Expansion-Model. Afterwards, we show numerical results obtained by Finite Element simulations. We conclude that the envisioned structure has a great potential for obtaining soft rollable sheets that can be stiffened by intrinsic activation.

Highlights

Introduction to Hydrogel Composite Membranes andShellsStimulus-active hydrogels can be combined with passive layers to form active composite membranes [1]
We investigated a setup composed of the temperature-sensitive hydrogel poly(N-isopropyl acrylamide) (PNiPAAm), which was combined with polyethylene terephtalate (PET)
Please note that in the following simulation studies, we focus on the swelling of hydrogels inside the structures, i.e., a positive volume expansion

Summary

Introduction

Stimulus-active hydrogels can be combined with passive layers to form active composite membranes [1]. The isotropic swelling capabilities that characterize hydrogels [2] can be used in combination with the high stiffness of the passive material. The system shows high potential in the application as switchable membrane for the handling of blood samples [1,3,4]. We demonstrate the potential of active–passive composites for structures with switchable stiffness to stabilize rollable displays. Rollable/flexible displays are a current trend in portable devices [5,6,7]. In their actual form, they are mostly combined with hard casings for stabilization. Other approaches use e.g., bistability mechanisms [8]

Objectives

Results

Conclusion