arXiv subjects

Lawrence A. Wilen

Publications and source records attributed to Lawrence A. Wilen.

6 recordsLinked to original sources

arXiv2026

Unravelling the multiscale surface mechanics of soft solids

Soft solids and their surface deformations control the response of many natural and artificial systems. Yet, their underlying properties are vigorously debated, particularly for polymer networks. While molecular-scale theories predict no interfacial changes with macroscopic deformation, multiple experiments suggest otherwise. To settle this issue, we measure displacement fields near the interface of a silicone gel, in the limit of small deformations. We discover an unexpected multiscale response. The shear modulus decreases smoothly by half with 20 microns of the interface. At the same time we observe a surface excess elasticity, that depends on history and outer medium composition. These results reveal the fundamentally multiscale nature of polymeric surfaces, and call for further experimental and theoretical investigations into the basic understanding of soft solid interfaces

cond-mat.soft↗

arXiv2024

Droplets sliding on soft solids shed elastocapillary rails

The surface tension of partially wetting droplets deforms soft substrates. These deformations are usually localized to a narrow region near the contact line, forming a so-called `elastocapillary ridge.' When a droplet slides along a substrate, the movement of the elastocapillary ridge dissipates energy in the substrate and slows the droplet down. Previous studies have analyzed isotropically spreading droplets and found that the advancing contact line `surfs' the elastocapillary ridge, with a velocity determined by a local balance of capillary forces and bulk rheology. Here, we experimentally explore the dynamics of a droplet sliding across soft substrates. At low velocities, the contact line is nearly circular, and dissipation increases logarithmically with speed. At higher droplet velocities, the contact line adopts a bullet-like shape, and the dissipation levels off. At the same time, droplets shed a pair of `elastocapillary rails' that fade away slowly behind it. These results suggest that droplets favor sliding along a stationary ridge over surfing atop a translating one.

cond-mat.soft↗

arXiv2023

Polycrystallinity enhances stress build-up around ice

Damage caused by freezing wet, porous materials is a widespread problem, but is hard to predict or control. Here, we show that polycrystallinity makes a great difference to the stress build-up process that underpins this damage. Unfrozen water in grain-boundary grooves feeds ice growth at temperatures below the freezing temperature, leading to the fast build-up of localized stresses. The process is very variable, which we ascribe to local differences in ice-grain orientation, and to the surprising mobility of many grooves -- which further accelerates stress build-up. Our work will help understand how freezing damage occurs, and in developing accurate models and effective damage-mitigation strategies.

cond-mat.soft↗

arXiv2021

Stress accumulation around ice in a temperature gradient

When materials freeze, they often undergo damage due to ice growth. Although this damage is commonly ascribed to the volumetric expansion of water upon freezing, it is usually driven by suction of water towards growing ice crystals. The freezing of this additional water can cause a large build up of stress. Here, we study this process by producing a stable ice/water interface in a controlled temperature gradient, and measuring the deformation of the confining boundary. Analysis of the deformation field reveals stresses applied to the boundary with $\mathcal{O}(μ\mathrm{m})$ resolution. Globally, stresses increase steadily over time as liquid water is transported to more deeply undercooled regions. Locally, stresses increase until ice growth is stalled by the confining stresses. In accordance with the Clapeyron equation, the local limiting stress is proportional to the local undercooling. These results are closely connected to the crystallization pressure for growing crystals and condensation pressure during liquid-liquid phase separation.

cond-mat.soft↗

arXiv2020

Viscoelastic and poroelastic relaxations of soft solid surfaces

Understanding surface mechanics of soft solids, such as soft polymeric gels, is crucial in many engineering processes, such as dynamic wetting and adhesive failure. In these situations, a combination of capillary and elastic forces drives the motion, which is balanced by dissipative mechanisms to determine the rate. While shear rheology (i.e. viscoelasticity) has long been assumed to dominate the dissipation, recent works have suggested that compressibility effects (i.e. poroelasticity) could play roles in swollen networks. We use fast interferometric imaging to quantify the relaxation of surface deformations due to a displaced contact line. By systematically measuring the profiles at different time and length scales, we experimentally observe a crossover from viscoelastic to poroelastic surface relaxations.

cond-mat.soft↗

arXiv2017

Liquid-Liquid Phase Separation in an Elastic Network

Living and engineered systems rely on the stable coexistence of two interspersed liquid phases. Yet surface tension drives their complete separation. Here we show that stable droplets of uniform and tuneable size can be produced through arrested phase separation in an elastic matrix. Starting with an elastic polymer network swollen by a solvent mixture, we change the temperature or composition to drive demixing. Droplets nucleate and grow to a stable size that is tuneable by the network cross-linking density, the cooling rate, and the composition of the solvent mixture. We discuss thermodynamic and mechanical constraints on the process. In particular, we show that the threshold for macroscopic phase separation is altered by the elasticity of the polymer network, and we highlight the role of internuclear correlations in determining the droplet size and polydispersity. This phenomenon has potential applications ranging from colloid synthesis and structural colour to phase separation in biological cells.

cond-mat.soft↗