arXiv subjects

Martin H. Essink

Publications and source records attributed to Martin H. Essink.

3 recordsLinked to original sources

arXiv2024

Wetting ridge dissipation at large deformations

Liquid drops slide more slowly over soft, deformable substrates than over rigid solids. This phenomenon can be attributed to the viscoelastic dissipation induced by the moving wetting ridge, which inhibits a rapid motion, and is called "viscoelastic braking". Experiments on soft dynamical wetting have thus far been modelled using linear theory, assuming small deformations, which captures the essential scaling laws. Quantitatively, however, some important disparities have suggested the importance of large deformations induced by the sliding drops. Here we compute the dissipation occurring below a contact line moving at constant velocity over a viscoelastic substrate, for the first time explicitly accounting for large deformations. It is found that linear theory becomes inaccurate especially for thin layers, and we discuss our findings in the light of recent experiments.

cond-mat.soft↗

arXiv2021

Pinning-induced folding-unfolding asymmetry in adhesive creases

The compression of soft elastic matter and biological tissue can lead to creasing, an instability where a surface folds sharply into periodic self-contacts. Intriguingly, the unfolding of the surface upon releasing the strain is usually not perfect: small scars remain that serve as nuclei for creases during repeated compressions. Here we present creasing experiments with sticky polymer surfaces, using confocal microscopy, which resolve the contact line region where folding and unfolding occurs. It is found that surface tension induces a second fold, at the edge of the self-contact, which leads to a singular elastic stress and self-similar crease morphologies. However, these profiles exhibit an intrinsic folding-unfolding asymmetry that is caused by contact line pinning, in a way that resembles wetting of liquids on imperfect solids. Contact line pinning is therefore a key element of creasing: it inhibits complete unfolding and gives soft surfaces a folding memory.

cond-mat.soft↗

arXiv2021

How to unloop a self-adherent sheet

The mechanics of adherent sheets is central to applications ranging from patching a band aid, coating technology, to the breakthrough discovery of peeling graphene flakes using sticky tape. These processes are often hindered by the formation of blisters and loops, which are notoriously difficult to remove. Here we describe and explain a remarkable phenomenon that arises when one attempts to remove a loop in a self-adherent sheet that is formed by, e.g., folding two adhesive sides of a tape together. One would expect the loop to simply unloop when pulling on its free ends. Surprisingly, however, the loop does not immediately open up but shrinks in size, held together by a tenuous contact region that propagates along the tape. This adhesive contact region only ruptures once the loop is reduced to a critical size. We experimentally show that the loop-shrinkage results from an interaction between the peeling front and the loop, across the contact zone. This new type of interaction falls outside the realm of the classical elastica theory and is responsible for a highly nonlinear increase in the peeling force. Our results reveal and quantify the increased force required to remove loops in self-adherent media, which is of importance for blister removal and exfoliation of graphene sheets.

cond-mat.soft↗