Swelling-induced folds in soft microchannels #

Haolin Li, Aidan Retallick, Anne Juel, Matthias Heil, Draga Pihler-Puzovic

12:10 Monday in 2Q48.

Part of the Mechanics of hydrogels and poroelastic media session.

Abstract #

A membrane-like soft material can easily undergo rich surface instabilities such as wrinkling when subjected to axial or biaxial compressions. The base state of the membrane plays a crucial role in the wrinkling pattern evolution. In a core-shell system, the curvature effect enables more intricate wrinkling patterns than the ones of initially flat membranes. In order to explore a more nontrivial base state, we study the swelling-induced instability of a pre-inflated membrane bonding on top of a microchannel, which features not only non-zero curvatures but also heterogeneous stress distributions to begin with. Under continuous swelling, the constrained membrane initially buckles into a small amplitude sinusoidal wrinkling pattern, and then transitions to a novel secondary pattern of alternating folds or connected folds depending on the inflating pressure. We show that the initial wrinkling resembles periodic wrinkles which arise on a pressurised thin-walled cylindrical shell when compressed axially, from which we obtain a scaling prediction of the initial wavelength that agrees well with extensive experimental results. It is also identified that the secondary wrinkling comes through a period-doubling/tripling bifurcation of the initial wrinkling. The system can evolve into alternating folds at moderate pressures via buckling of valleys created by initial wrinkling, or concentrated folds at high pressures while the swelling-induced compression is insufficient to initiate the similar buckling and ensuing symmetry breaking. This pressure-responsive transition of secondary pattern may shed light on the design of pressure-driven microfluidic devices.