arXiv subjects

John M. Kolinski

Publications and source records attributed to John M. Kolinski.

14 recordsLinked to original sources

arXiv2026

Following the thread: surface and bulk solvent migration in silicone elastomers from local volumetric swelling

Poroelastic materials, consisting of a permeable solid matrix infiltrated with fluid, are ubiquitous in natural and engineering contexts. In poroelastic polymer solids, the elastic matrix swells to equilibrium when immersed in a solvent bath; thus, the network elasticity couples to the solvent transport. Despite the ubiquity and importance of poroelastic theory in describing phenomena as diverse as earthquakes and biological tissues, there is a paucity of experimental data that probe the local network response to controlled stress and solvent boundary conditions. Here, we first probe the baseline diffusion kinetics of a polymeric solvent during free swelling of a polydimethylsiloxane (PDMS) network with well-characterized silicone oils. In situ 3D spatiotemporal measurements identify a flux-limited interfacial boundary condition, contradicting the canonical fully drained assumption. This correction eliminates an order-of-magnitude underestimation of diffusivity in standard bulk analysis. The swelling equilibrium is accurately captured by a Flory-Rehner theory that requires modification to include the effective finite extensibility of the filled network. Solvent migration is then studied using a bending configuration for three material preparations: as-prepared, mobile-phase-free, and fully swollen in silicone oils. The as-prepared and mobile-phase-free beams show no discernible volumetric change or force relaxation, whereas local in situ measurements directly resolve tensile-side dilation and compressive-side contraction, yielding the effective diffusivities in agreement with the force-relaxation data. These measurements rigorously benchmark solvent diffusivity in polymer networks, underscoring the importance of unambiguous interfacial boundary conditions and shedding light on mechanics and engineering across poroelastic polymers and geomaterials.

cond-mat.soft↗

arXiv2025

Drops can Perpetually Bounce over a Vibrating Wettable Solid

On the surface of a vibrating liquid bath, instead of coalescing, a drop will continually bounce on a thin film of air between the drop and the free surface, giving rise to rich chaotic dynamics and quantum analog behavior. However, perpetual bouncing is yet to be demonstrated on a vibrating rigid solid, where the control of the drop's motion is not limited by the bath dynamics. Here we show that vibration of an atomically smooth mica surface prolongs a drop's hovering state by several orders of magnitude, increasing the time to wet from less than a second to several minutes. The excitation of the second spherical harmonic mode determines a transition between a bouncing state with high-amplitude rebounds, and a bound state, where the drop's motion is locked onto the vibrating solid above a thin air layer. We further develop a coupled linear spring model, accounting for the drop's deformation, that predicts bouncing trajectories without fitting parameters. Our results extend the scope of bouncing drop studies beyond the liquid bath and highlight the potential for precision manipulation of small liquid quantities in air.

physics.flu-dyn↗

arXiv2025

Falling through the cracks: energy storage along segmented brittle crack fronts

During brittle crack propagation, a smooth crack front curve frequently becomes disjoint, generating a stepped crack and a material ligament that unites the newly formed crack fronts. These universal features fundamentally alter the singular field structure and stability of propagating cracks; however, a quantitative analysis of their mechanics is lacking. Here, we perform in-situ 3D measurements to resolve the deformation field around stepped cracks, and crucially, within the ligament feature. The 3D kinematic data are obtained by scanning a thin laser sheet through the brittle hydrogel samples, while recording the scattered intensity from the embedded tracer particles. We find that the ligament concentrates the strain energy density, and moreover, the apparent fracture energy increases proportionally to the strain energy within the ligament.

cs.CE↗

arXiv2025

Marangoni-driven flow instability accelerates liquid-solid contact on atomically smooth mica

A droplet falling toward a solid surface displaces the surrounding air until it encounters a defect, and contact nucleates. On atomically smooth surfaces devoid of defects, contact can be delayed until the droplet rebounds; however, above a critical impact velocity the droplet always contacts the surface. Here we show that for alcohol droplets in a humid atmosphere, the surface of the droplet above the solid develops patterns as a consequence of an instability; consequently, the liquid approaches the surface more closely in some places than others, accelerating contact formation. We demonstrate the attenuation and even suppression of this instability by varying the liquid composition, and characterize the growth rate and length scale of the patterns on liquid-air interface.

physics.flu-dyn↗

arXiv2024

Coating thickness prediction for a viscous film on a rough plate

Surface roughness significantly modifies the liquid film thickness entrained when dip coating a solid surface, particularly at low coating velocity. Using a homogenization approach, we present a predictive model for determining the liquid film thickness coated on a rough plate. A homogenized boundary condition at an equivalent flat surface is used to model the rough boundary, accounting for both flow through the rough texture layer, through an interface permeability term, and slip at the equivalent surface. While the slip term accounts for tangential velocity induced by viscous shear stress, accurately predicting the film thickness requires the interface permeability term to account for additional tangential flow driven by pressure gradients along the interface. We find that a greater degree of slip and interface permeability signifies less viscous stress that would promote deposition, thus reducing the amount of free film coated above the textures. The model is found to be in good agreement with experimental measurements and requires no fitting parameters. Furthermore, our model may be applied to arbitrary periodic roughness patterns, opening the door to flexible characterization of surfaces found in natural and industrial coating processes.

physics.flu-dyn↗

arXiv2024

3D characterization of kinematic fields and poroelastic swelling near the tip of a propagating crack in a hydrogel

In fracture mechanics, polyacrylamide hydrogels have been widely used as a model material for experiments, benefited from its optical transparency, fracture brittleness, and low Rayleigh wave velocity. To describe the brittle fracture in the hydrogels, linear elastic fracture mechanics comes as the first choice. However, in soft materials such as hydrogels, the crack opening can be extremely large, leading to substantial geometric nonlinearity and material nonlinearity at the crack tip. Furthermore, poroelasticity may also modify the local mechanical state within the polymer network. Direct characterization of the kinematic fields and poroelastic effect at the crack tip is lacking. Here, based on a hybrid method of digital image correlation and particle tracking technique, we retrieved high-resolution 3D particle trajectories near the tip of a slowly propagating crack and measured the near-tip 3D kinematic fields, including the displacement fields, rotation fields, stretch fields, strain fields, and swelling fields. Results confirmed the complex multi-axial stretching near the crack tip and the substantial geometric nonlinearity, particularly on the two wakes of the crack where rotation exceeds $30^{\circ}$. Comparison between the measured and predicted displacement and strain fields, derived from linear elastic fracture mechanics, highlights a disagreement in the direct vicinity of the crack tip, particularly for displacement component $u_x$ and through-thickness strain component $\varepsilon_{zz}$. Significant swelling, due to the poroelastic solvent migration, is also observed, with a strong correlation to the local stretch. Our experimental method, without any assumption of the material properties, can be readily extended to study 3D crack tips in a huge varieties of materials, and our results can shed light on the fundamental fracture mechanics.

cond-mat.soft↗

arXiv2023

The characteristic rupture height of the mediating air film beneath an impacting drop on atomically smooth mica

Before a droplet can contact a surface during impact, it must first displace the air beneath it. Over a wide range of impact velocities, the air is compressed into a thin film, slowing the progress of the liquid toward the surface. Below a critical impact velocity, the air film remains intact; the droplet rebounds off of the air film without making contact. Above this critical impact velocity, the droplet always makes contact. The initiation of contact formation occurs via a topological transition, whereby the initially connected gas domain is ruptured, and a liquid capillary bridge forms, binding the droplet to the surface. Here we probe this transition in detail around the critical impact velocity using calibrated total internal reflection (TIR) microscopy to monitor the air film profile at high speed during the impact process. Two air film rupture modalities are observed: nucleated contacts, which are isolated and don't correspond to the global minimum air film thickness, and spontaneous contacts, that occur always on a ring centered upon the impact axis where the air film reaches its global minimum. Our measurements show that for impact velocities exceeding the critical velocity for contact initiation, the air film ruptures at a nearly identical height h min ~ 20 nm, for two fluids - silicone oil and a water glycerol mixture. The height and time duration of the air film prior to contact, analyzed for over 180 droplet impact experiments, are consistent with a linear instability driven by van der Waals forces. Impact events of water solution droplets show different statistics for contact nucleation than the silicon oil; nevertheless, a critical impact velocity above which contact always occurs is identified for both liquids.

physics.flu-dyn↗

arXiv2023

Crack tip kinematics reveal the cohesive zone structure in brittle hydrogel fracture

When brittle hydrogels fail, several mechanisms conspire to alter the state of stress near the tip of a crack, and it is challenging to identify which mechanism is dominant. In the fracture of brittle solids, a sufficient far-field stress results in the complete loss of structural strength as the material `unzips' at the tip of a crack, where stresses are concentrated. Direct studies of the so-called small-scale yielding zone, where deformation is large, are sparing. Using hydrogels as a model brittle solid, we probe the small-scale yielding region with a combination of microscopy methods that resolve the kinematics of the deformation. A zone over which most of the energy is dissipated through the loss of cohesion is identified in the immediate surroundings of the crack tip. With direct measurements, we determine the scale and structure of this zone, and identify how the specific loss mechanisms in this hydrogel material might generalize for brittle material failure.

cond-mat.mtrl-sci↗

arXiv2022

How hidden 3D structure within crack fronts reveals energy balance

Griffith's energetic criterion, or `energy balance', has for a century formed the basis for fracture mechanics; the energy flowing into a crack front is precisely balanced by the dissipation (fracture energy) at the front. If the crack front structure is not properly accounted for, energy balance will either appear to fail or lead to unrealistic results. Here, we study the influence of the secondary structure of low-speed crack propagation in hydrogels under tensile loading conditions. We first show that these cracks are bistable; either simple (cracks having no secondary structure) or faceted crack states (formed by steps propagating along crack fronts) can be generated under identical loading conditions. The selection of either crack state is determined by the form of the initial `seed' crack; perfect seed cracks generate simple cracks while a small local mode~III component generates crack fronts having multiple steps. Step coarsening eventually leads to single steps that propagate along crack fronts. As they evolve, steps locally change the instantaneous structure and motion of the crack front, breaking transverse translational invariance. In contrast to simple cracks, faceted cracks can, therefore, no longer be considered as existing in a quasi-2D system. For both simple and faceted cracks we simultaneously measure the energy flux and local dissipation along these crack fronts over velocities, $v$, spanning $0<v<0.2c_R$ ($c_R$ is the Rayleigh wave speed). We find that, in the presence of secondary structure within the crack front, the implementation of energy balance must be generalized for 3D systems; faceted cracks reveal energy balance, only when we account for the local dynamic dissipation at each point along the crack front.

cond-mat.soft↗

arXiv2020

Superspreading events suggest aerosol transmission of SARS-CoV-2 by accumulation in enclosed spaces

Viral transmission pathways have profound implications for public safety; it is thus imperative to establish a complete understanding of viable infectious avenues. Mounting evidence suggests SARS-CoV-2 can be transmitted via the air; however, this has not yet been demonstrated. Here we quantitatively analyze virion accumulation by accounting for aerosolized virion emission and destabilization. Reported superspreading events analyzed within this framework point towards aerosol mediated transmission of SARS-CoV-2. Virion exposure calculated for these events is found to trace out a single value, suggesting a universal minimum infective dose (MID) via aerosol that is comparable to the MIDs measured for other respiratory viruses; thus, the consistent infectious exposure levels and their commensurability to known aerosol-MIDs establishes the plausibility of aerosol transmission of SARS-CoV-2. Using filtration at a rate exceeding the destabilization rate of aerosolized SARS-CoV-2 can reduce exposure below this infective dose.

q-bio.PE↗

arXiv2020

How moving cracks in brittle solids choose their path

While we fundamentally understand the dynamics of 'simple' cracks propagating in brittle solids within perfect (homogeneous) materials, we do not understand how paths of moving cracks are determined. We experimentally study strongly perturbed cracks that propagate between 10-95\% of their limiting velocity within a brittle material. These cracks are deflected by either interaction with sparsely implanted defects or via an intrinsic oscillatory instability in defect-free media. Dense, high-speed measurements of the strain fields surrounding the crack tips reveal that crack paths are governed by the direction of maximal strain energy density. This fundamentally important result may be utilized to either direct or guide running cracks.

cond-mat.soft↗

arXiv2020

Dilute concentrations of submicron particles do not alter the brittle fracture of polyacrylamide hydrogels

In studies of the dynamic failure of brittle hydrogels, a bound has been placed on the process zone scale - the scale where material separation and ultimate failure occur. For the polyacrylamide hydrogel system under study, this bound is set at 20 microns. Thus, any subtle alterations to the material at a \emph{smaller} scale should not in principle alter the dynamic fracture response of the hydrogel. Here we test this directly by embedding sub-micron-scale latex polystyrene microspheres within the brittle polyacrylamide hydrogel at a solids fraction of 0.1 \%. We verify that the spheres are well-distributed throughout the hydrogel material at this concentration with optical microscopy, and reconstruct the 3D distribution of these spheres using laser scanning confocal microscopy in backscatter mode. Finally, we test the fracture behavior of this gel with the dilute, embedded sub-micron spheres, and find that the brittle material failure modality common to this material \emph{without} the sub-micron spheres is indeed retained. By comparing the crack tip opening displacement, fracture energy and the crack's speed with established data from prior experimental work, we demonstrate that this material's failure is brittle, as it is in good agreement with the pure hydrogel system.

cond-mat.soft↗

arXiv2018

How super-tough gels break

Fracture of highly stretched materials challenges our view of how things break. We directly visualize rupture of tough double-network (DN) gels at >50\% strain. During fracture, crack tip shapes obey a $x\sim y^{1.6}$ power-law, in contrast to the parabolic profile observed in low-strain cracks. A new length-scale $\ell$ emerges from the power-law; we show that $\ell$ scales directly with the stored elastic energy, and diverges when the crack velocity approaches the shear wave speed. Our results show that DN gels undergo brittle fracture, and provide a testing ground for large-strain fracture mechanics.

cond-mat.soft↗

arXiv2011

Skating on a Film of Air: Drops Impacting on a Surface

Drops impacting on a surface are ubiquitous in our everyday experience. This impact is understood within a commonly accepted hydrodynamic picture: it is initiated by a rapid shock and a subsequent ejection of a sheet leading to beautiful splashing patterns. However, this picture ignores the essential role of the air that is trapped between the impacting drop and the surface. Here we describe a new imaging modality that is sensitive to the behavior right at the surface. We show that a very thin film of air, only a few tens of nanometers thick, remains trapped between the falling drop and the surface as the drop spreads. The thin film of air serves to lubricate the drop enabling the fluid to skate on the air film laterally outward at surprisingly high velocities, consistent with theoretical predictions. Eventually this thin film of air must break down as the fluid wets the surface. We suggest that this occurs in a spinodal-like fashion, and causes a very rapid spreading of a wetting front outwards; simultaneously the wetting fluid spreads inward much more slowly, trapping a bubble of air within the drop. Our results show that the dynamics of impacting drops are much more complex than previously thought and exhibit a rich array of unexpected phenomena that require rethinking classical paradigms.

physics.flu-dyn↗