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<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" dir="ltr" lang="en-US">
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<title>Martin Essink</title>
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<div id="head">
<h1>Martin Essink</h1>
<div id="links">
<a href="//www.linkedin.com/in/martinessink/">LinkedIn</a>
—
<a href="//scholar.google.com/citations?user=mPPZ4H8AAAAJ">Google Scholar</a>
—
<a href="//github.com/MartinEssink">Github</a>
</div>
</div>
<div id="content">
<div id="entry">
<h2>About</h2>
<p>.</p>
<!-- <img src="./IMG_2556_sq.jpg" width="200" height="200" alt="Profile Picture" /> -->
</div>
<div id="entry">
<h2>Academic Work & Publications</h2>
<div class="publication paper">
<h3><a target="_blank" rel="noopener noreferrer" href="https://arxiv.org/abs/2307.05991">
Unsteady drag force on an immersed sphere oscillating near a wall
</a></h3>
<p class="ref">
Zhang, Z., Bertin, V., <b>Essink, M.H.</b>, Zhang, H., Fares, N., Shen, Z., Bickel, T., Salez, T, & Maali, A.<br />
Submitted (2023) [arXiv]
</p>
<p class="abs">
The unsteady hydrodynamic drag exerted on an oscillating sphere near a planar wall is addressed experimentally, theoretically, and numerically. The experiments are performed by using colloidal-probe Atomic Force Microscopy (AFM) in thermal noise mode. The natural resonance frequencies and quality factors are extracted from the measurement of the power spectrum density of the probe oscillation for a broad range of gap distances and Womersley numbers. The shift in the natural resonance frequency of the colloidal probe as the probe goes close to a solid wall infers the wall-induced variations of the effective mass of the probe. Interestingly, a crossover from a positive to a negative shift is observed as the Womersley number increases. In order to rationalize the results, the confined unsteady Stokes equation is solved numerically using a finite-element method, as well as asymptotic calculations. The in-phase and out-of-phase terms of the hydrodynamic drag acting on the sphere are obtained and agree well to the experimental results. All together, the experimental, theoretical, and numerical results show that the hydrodynamic force felt by an immersed sphere oscillating near a wall is highly dependent on the Womersley number.
</p>
</div>
<div class="publication paper">
<h3><a target="_blank" rel="noopener noreferrer" href="https://pubs.rsc.org/en/content/articlelanding/2023/sm/d2sm01389d#!divAbstract">
Adhesive creases: bifurcation, morphology and their (apparent) self-similarity
</a></h3>
<p class="ref">
<b>Essink, M. H.</b>, van Limbeek, M. A., Pandey, A., Karpitschka, S., & Snoeijer, J. H.<br />
Soft Matter, 19(27), 5524-5528 (2023)
</p>
<p class="abs">
An elastic material that experiences strong compression parallel to its free surface can exhibit sharp surface folds. Such creases arise due to an instability where a self-contacting fold appears on the surface, often observed in growing tissues or swelling gels. Self-adhesion of the contact is known to affect the bifurcation behavior and morphology of these structures, yet a quantitative description remains elusive. From numerical simulations and an energy analysis we resolve how adhesion quantitatively affects both morphology and bifurcation behavior. It is found that a reduced energy is able to accurately describe the bifurcation, in terms of an effective scaling that collapses the data very well. The model accurately describes how adhesion hinders crease nucleation. Furthermore, we show that the free surface profiles in the presence of surface tension exhibit self-similarity, and can be collapsed onto a universal curve.
</p>
</div>
<div class="publication paper">
<h3><a target="_blank" rel="noopener noreferrer" href="https://doi.org/10.1103/physrevlett.130.228201">
Reversal of Solvent Migration in Poroelastic Folds
</a></h3>
<p class="ref">
Flapper, M. M., Pandey, A., <b>Essink, M. H.</b>, van Brummelen, E. H., Karpitschka, S., & Snoeijer, J. H.<br />
Physical Review Letters, 130(22), 228201 (2023)
</p>
<p class="abs">
Polymer networks and biological tissues are often swollen by a solvent such that their properties emerge from a coupling between swelling and elastic stress. This poroelastic coupling becomes particularly intricate in wetting, adhesion, and creasing, for which sharp folds appear that can even lead to phase separation. Here, we resolve the singular nature of poroelastic surface folds and determine the solvent distribution in the vicinity of the fold tip. Surprisingly, two opposite scenarios emerge depending on the angle of the fold. In obtuse folds such as creases, it is found that the solvent is completely expelled near the crease tip, according to a nontrivial spatial distribution. For wetting ridges with acute fold angles, the solvent migration is reversed as compared to creasing, and the degree of swelling is maximal at the fold tip. We discuss how our poroelastic fold analysis offers an explanation for phase separation, fracture, and contact angle hysteresis.
</p>
</div>
<div class="publication thesis">
<h3><a target="_blank" rel="noopener noreferrer" href="https://research.utwente.nl/en/publications/soft-contact-from-wetting-to-adhesion">
Soft Contact: from wetting to adhesion
</a></h3>
<p class="ref">
University of Twente — November 4th, 2022
</p>
<p class="abs">
The interplay between elastic deformations and capillary forces are an important property of soft gels and tissues. In soft contact we consider the situation when such materials contact other solids or liquids, and capillary forces at the interfaces are able to significantly deform the solids. A number of these interactions have been explored in detail, ranging from wetting to adhesion problems. Numerical simulations, theory and experiments all show the importance of elastocapillary action at the edge of a soft contact.
<br /><br />
First, we describe the influence of the Shuttleworth effect on a droplet wetting a soft surface. We find the deformations near the wetting ridge, and thus the wetting properties of the solid, are strongly dependent on the (a)symmetry of the Shuttleworth coefficients. After, the viscoelastic dissipation in the wetting ridge is investigated. Recent experiments have shown that this effect is not accurately captured for thin substrates by linear theory. We have been able to model the dissipation in the substrate, and demonstrate how nonlinear effects alter the dissipative properties of a wetting ridge.
<br /><br />
In the following chapters the effect of self-adhesion on an elastic crease is studied. Experiments allow the measurement of the free surface morphology, showing that the free interface at the contact line is flattened due to adhesion. Folding and unfolding experiments reveal an asymmetry in morphology that can be explained by contact line pinning. From a numerical perspective, we are able to precisely describe the influence of adhesion on bifurcation behavior and morphology. We show that the bifurcation behavior of an adhesive crease is accurately explained by a reduced energy expression.
<br /><br />
Finally, we look at the adhesion of slender substrates, for which the adhesive forces couple to the bending of the substrate. Specifically, we have taken interest in the problem where a loop of self-adhered tape shrinks when pulling on the ends of the tape, instead of simply breaking apart. Using data from a large number of peeling experiments we are able to propose a model that explains the interaction between the contact lines, and the corresponding increase in peeling forces.
</p>
</div>
<div class="publication news">
<h3><a target="_blank" rel="noopener noreferrer" href="https://www.ntvn.nl/2022/11/hoe-open-je-een-plakbandlus/">
Hoe open je een plakbandlus?
</a></h3>
<p class="ref">
NTVN — Nederlands Tijdschrift voor Natuurkunde (November 2022)
</p>
<p class="abs">
Waarom laat een plakbandlus niet zomaar los? Wellicht is het je nog nooit opgevallen, maar als je een lus maakt van plakband en die probeert open te trekken gebeurt er iets geks: in plaats van open te springen wordt de lus eerst een heel stuk kleiner. Experimenten met in totaal een halve kilometer plakband en een theoretisch model laten zien waarom.
</p>
</div>
<div class="publication paper">
<h3><a target="_blank" rel="noopener noreferrer" href="https://doi.org/10.1098/rspa.2022.0132">
Soft wetting with (a)symmetric Shuttleworth effect
</a></h3>
<p class="ref">
Henkel, C., <b>Essink, M. H.</b>, Hoang, T., Van Zwieten, G. J., Van Brummelen, E. H., Thiele, U., & Snoeijer, J. H.<br />
Proceedings of the Royal Society A, 478(2264), 20220132 (2022)
</p>
<p class="abs">
The wetting of soft polymer substrates brings in multiple complexities when compared with the wetting on rigid substrates. The contact angle of the liquid is no longer governed by Young’s Law, but is affected by the substrate’s bulk and surface deformations. On top of that, elastic interfaces exhibit a surface energy that depends on how much they are stretched—a feature known as the Shuttleworth effect (or as surface-elasticity). Here, we present two models through which we explore the wetting of drops in the presence of a strong Shuttleworth effect. The first model is macroscopic in character and consistently accounts for large deformations via a neo-Hookean elasticity. The second model is based on a mesoscopic description of wetting, using a reduced description of the substrate’s elasticity. While the second model is more empirical in terms of the elasticity, it enables a gradient dynamics formulation for soft wetting dynamics. We provide a detailed comparison between the equilibrium states predicted by the two models, from which we deduce robust features of soft wetting in the presence of a strong Shuttleworth effect. Specifically, we show that the (a)symmetry of the Shuttleworth effect between the ‘dry’ and ‘wet’ states governs horizontal deformations in the substrate. Our results are discussed in the light of recent experiments on the wettability of stretched substrates.
</p>
</div>
<div class="publication paper">
<h3><a target="_blank" rel="noopener noreferrer" href="https://doi.org/10.1209/0295-5075/134/56001">
How to unloop a self-adherent sheet
</a></h3>
<p class="ref">
Wilting, T. J., <b>Essink, M. H.</b>, Gelderblom, H., & Snoeijer, J. H.<br />
Europhysics letters, 134(5), 56001 (2021)
</p>
<p class="abs">
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.
</p>
</div>
<div class="publication paper">
<h3><a target="_blank" rel="noopener noreferrer" href="https://doi.org/10.1103/physrevlett.127.028001">
Pinning-Induced Folding-Unfolding Asymmetry in Adhesive Creases
</a></h3>
<p class="ref">
Van Limbeek, M. A., <b>Essink, M. H.</b>, Pandey, A., Snoeijer, J. H., & Karpitschka, S.<br />
Physical review letters, 127(2), 028001 (2021)
</p>
<p class="abs">
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.
</p>
</div>
<div class="publication paper">
<h3><a target="_blank" rel="noopener noreferrer" href="https://doi.org/10.1017/jfm.2021.96">
Regimes of soft lubrication
</a></h3>
<p class="ref">
<b>Essink, M. H.</b>, Pandey, A., Karpitschka, S., Venner, C. H., & Snoeijer, J. H.<br />
Journal of fluid mechanics, 915, A49 (2021)
</p>
<p class="abs">
Elastohydrodynamic lubrication, or simply soft lubrication, refers to the motion of deformable objects near a boundary lubricated by a fluid, and is one of the key physical mechanisms to minimise friction and wear in natural and engineered systems. Hence, it is of particular interest to relate the thickness of the lubricant layer to the entrainment (sliding/rolling) velocity, the mechanical loading exerted onto the contacting elements and the properties of the elastic boundary. In this work, we provide an overview of the various regimes of soft lubrication for two-dimensional cylinders in lubricated contact with compliant walls. We discuss the limits of small and large entrainment velocity, which are equivalent to large and small elastic deformations, as the cylinder moves near thick or thin elastic layers. The analysis focusses on thin elastic coatings, both compressible and incompressible, for which analytical scaling laws are not yet available in the regime of large deformations. By analysing the elastohydrodynamic boundary layers that appear at the edge of the contact, we establish the missing scaling laws – including prefactors. As such, we offer a rather complete overview of the physically relevant limits of soft lubrication.
</p>
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<div id="foot">
<p>© 2023 Martin Essink.</p>
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