Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session K09: Friction, Fracture, and Adhesion in Soft Materials II |
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Sponsoring Units: DSOFT Chair: Ahmed Elbanna, University of Illinois at Urbana-Champai Room: Room 132 |
Tuesday, March 7, 2023 3:00PM - 3:12PM |
K09.00001: Temperature-Switchable Adhesives Enabled by Thermo-Responsive Soft Active Materials Ruobing Bai, Qianfeng Yin, Yichen Wan Many biological systems, such as gecko feet, are capable of reversibly and repeatably switching their surface adherence to various external objects. By contrast, no engineering system has yet reached the same level of both robust adherence and versatile switching. This gap severely limits the capability and adaptivity of the latter to fulfil the emergent economic and societal needs in complex environments. This talk will discuss our recent progress in developing switchable adhesives with high adhesion toughness, large switching ratio, fast switching speed, and good reversibility. We start with a hypothesis of combining a PSA(Pressure Sensitive Adhesive)-like polymer network and its stimuli-responsive phase transition to achieve switchable adhesives. To test this hypothesis, we investigate the switchable adhesion of a thermo-responsive hydrogel with its polymer network containing many free-end dangling polymer chains. The hydrogel forms tough adhesion with various surfaces at ambient environment, and becomes completely non-adhering at an elevated temperature due to the thermo-induced phase separation. The adhesion switching is reversible for many cycles while maintaining a high adhesion toughness. We further study the effects of compositions and mechanical dissipation on the adhesion toughness and switching performance. We discuss the possibility of extending the general design principle to other similar polymer systems. |
Tuesday, March 7, 2023 3:12PM - 3:24PM |
K09.00002: Mechanics of Adhesion at Curvature-Resisting Interfaces for Soft Solid-Bilayer Hybrids A. Derya Bakiler, Animesh Rastogi, McKayla Torbett, Stephan A. Sarles, Berkin Dortdivanlioglu Tissue-like synthetic materials with emerging properties can be designed by assembling cell-like compartments separated by biomimetic membranes using the droplet interface bilayer (DIB) approach. DIBs mimic the structure, composition, and transport properties of cell membranes. Quantifying and improving the adhesive properties of DIBs remains a crucial but missing step toward fully harnessing their potential in functional, tissue-like material designs. Here, we aim to quantify the separation behavior of two soft compartments enclosed by curvature-resisting surfaces by developing a size-dependent, isogeometric finite element framework. The bilayer interface formed between the individual compartments will serve as an imperfect interface that can fail under loading. The load-displacement curves of the separation of DIBs will be reported for varying droplet size, interface contact areas, and bi- and mono-layer interface tensions to elucidate its complex adhesion mechanics. The numerical results, in conjunction with the experiments, will allow us to characterize the adhesive energy and toughness of the bilayers, in turn aiding the use of DIBs in multifunctional material designs. |
Tuesday, March 7, 2023 3:24PM - 3:36PM |
K09.00003: Adhesion Asymmetry in Peeling of Thin Films With Homogeneous Material Properties: A Geometry-Inspired Design Paradigm Ahmed Elbanna, Ahmed Ghareeb Peeling of thin films is a problem of great interest to scientists and engineers. Here, we study the peeling response of thin films with nonuniform thickness profile attached to a rigid substrate through a planar homogeneous interface. We show both analytically and using finite element analysis that patterning the film thickness may lead to direction-dependent adhesion such that the force required to peel the film in one direction is different from the force required in the other direction, without any change to the film material, the substrate interfacial geometry, or the adhesive material properties. Furthermore, we show that this asymmetry is tunable through modifying the geometric characteristics of the thin film to obtain higher asymmetry ratios than reported previously in the literature. We discuss our findings in the broader context of enhancing interfacial response by modulating the bulk geometric or compositional properties. |
Tuesday, March 7, 2023 3:36PM - 3:48PM |
K09.00004: Osmocapillary phase separation in the surface roughness and adhesion of gels Qihan Liu Gel is a polymer network infiltrated with a solvent. On the gel surface, the surface tension can deform the gel surface, which is known as elastocapillary deformation, or pull the solvent out from the polymer network, which is known as osmocapillary phase separation. Here we develop a linear-elasticity-based model to study how osmocapillary phase separation affects the surface roughness and surface energy of the gel. It shows that the surface behavior of a gel can be characterzed by two dimensionless groups. With the variation of these two dimensionless groups, the gel surface can be either rigid like a hard solid, flat like a liquid, deformed without phase separation like a rubber, or deformed with siginificant osmocapillary phase separation on the surface. The last type of behavior has been overlooked in many previous studies. The analysis shows that while a highly swollen hydrogel is still a solid, its surface can be mostly covered by the liquid solvent. The implication of osmocapillary phase separation on our understanding of the adhesion and friction of gels will be discusssed. |
Tuesday, March 7, 2023 3:48PM - 4:00PM |
K09.00005: Deicing with in situ Electrolysis Saurabh Nath, Henri-Louis Girard, Ha Eun David Kang, Srinivas Bengaluru Subramanyam, Yang Shao-Horn, Kripa K Varanasi The earliest experiments in ice (de-)adhesion date back to the late 1920-s in an icing tunnel in Langley, Virginia. A century of attempts later, our approaches in mitigating ice are far from developed. On one hand, anti-icing functionalizations as super-hydrophobicity or infused materials lack robustness and environmental sustainability. On the other hand, deicing strategies like chemical treatment, ohmic heating, or mechanical scrubbing are inefficient, and even crude. Here we propose a fundamentally different approach to the classical problem of deicing using in situ water electrolysis. We show with experiments how a progressing ice front can trap the electrolytically generated bubbles at the interface. Such trapped bubbles can be used to significantly diminish the energy required to fracture ice. We discuss how the proposed mechanism constitutes a self-starting, self-limiting means to reduce ice adhesion, unlike classical approaches. |
Tuesday, March 7, 2023 4:00PM - 4:12PM |
K09.00006: Crease formation in microscale friction on a soft, adhesive surface Jonathan Pham, Justin Glover, Xingwei Yang, Rong Long Studies of friction started centuries ago, yet an understanding of small-scale static friction on soft materials remains incomplete. This is partially due to the diversity in material properties that exist in soft materials, as well as with challenges in experimentally visualizing and probing the mechanics. We employ an experimental approach that combines force and confocal microscopy to combine force quantification with cross-sectional imaging. In our experiments, a glass microparticle is put in contact with a soft, adhesive polydimethylsiloxane (PDMS) surface, which is then pulled laterally. Confocal imaging reveals the emergence of creases. Creasing appears on PDMS surface exposed to ambient light as well as UV-ozone treatment. Using finite element analysis, we study what parameters govern the creasing behavior. Our experimental and numerical results show that creases are self-contacting, and move through the contact zone in a Schallamach wave-like manner, like a ruck in a rug. Yet for this to be possible and remain self-contacting, the crease interface must be adhesive in the normal direction, while allowing for self-slip. Additionally, our study shows that the interfacial strength at the particle-PDMS interface must be sufficiently high for creasing to occur. |
Tuesday, March 7, 2023 4:12PM - 4:24PM |
K09.00007: Capillary detachment of a microsphere from a liquid-liquid interface Md Sazzadul Alam Rahat The attachment and detachment of microparticles at liquid-liquid interfaces are important for a number of material systems, from capillary suspensions and emulsions to coating applications. Hence, capillary forces become relevant to develop appropriate guidelines for designing these material systems. The required work to detach microparticles from a liquid-liquid interface is related to the shape of the meniscus; however, measuring capillary forces on a single microparticle at a liquid-liquid interface, while simultaneously imaging the meniscus, can be challenging. In this study, we correlate the detachment force with the shape of the meniscus by combining colloidal probe, atomic force microscopy (AFM) and laser scanning confocal microscopy. We measure the force and visualize the capillary bridge on a hydrophilic or hydrophobic microparticle, which is being pulled from a thin glycerol film surrounded by silicone oil. A fundamental model for detachment, based on capillary theory, is verified with different conditions. Moreover, we demonstrate that the interfacial tension and the continuous change of contact angle for a pinned contact line must be considered to accurately predict the detachment force. |
Tuesday, March 7, 2023 4:24PM - 4:36PM |
K09.00008: Self-Assembled Asperities for Pressure Tunable Adhesion Chelsea S Davis, Naomi Deneke, Jamie A Booth, Edwin P Chan Control of adhesion is important in a host of applications including soft robotics, pick-and-place manufacturing, wearable devices, and transfer printing. Many studies have investigated materials able to achieve a singular but tunable adhesion strength or switchable adhesion. However, there have not been extensive studies in developing a single material with multiple, tunable adhesion strengths. In this work, we present a versatile and scalable pressure tunable adhesive (PTA) that is based on the self-assembly of stiff microscale asperities on an elastomeric substrate. The adhesive strength of the PTA is tuned by controlling the amount of pressure applied to the patterned material. To pattern the elastomer, a glassy polymer thin film (polystyrene) is dewetted from a soft elastomer (polydimethylsiloxane) by thermally annealing the bilayer system. The PS droplets arrange in a Voronoi pattern that solidify upon quenching, leaving stiff cap-shaped asperities on the elastomer surface. The patterning parameters, specifically size and spacing of the asperities, are altered by changing the pre-annealing film thickness. Flat punch indentation testing is used to characterize the adhesion strength of PTAs ranging in pattern parameter size. During testing, the PTA is compressed by the punch to a pre-defined maximum compressive load, Pm, and retracted until reaching the critical pull-off load, Pc, where separation occurs. We demonstrate that the adhesion strength of the PTA increases with the applied compressive preload due to the unique contact formation mechanism caused by the asperities. Finally, we demonstrate the applicability of precision control of adhesion strength by utilizing the PTA for pick-and-place material handling. We show that Pc increases with Pm for these PTA materials. A mechanics analysis is presented to describe the adhesive contact between a rigid body and the PTA. Our pressure tunable adhesive design based on self-assembly of asperities presents a scalable and versatile approach that is applicable to a variety of material systems having different mechanical or surface properties. |
Tuesday, March 7, 2023 4:36PM - 4:48PM |
K09.00009: Bendable adhesion: is there a better way of measuring surface energy? Andrea Giudici, Ian M Griffiths, Dominic J Vella, Janine K Nunes Evaluation of surface energy of microscale elastic objects is typically done by comparing the size of a contact patch with theoretical predictions made by the Johnson-Kendall-Roberts (JKR) theory of adhesion. However, since adhesion deformations are localised, this technique requires a precise measurement of microscale distances which may be difficult to obtain. Is there an easier way of mesuring surface energy? Here, we consider the scenario in which a slender microstructure comes into contact with a sphere; although the strains induced by adhesion remain small, the object's slenderness allows for a large and more easily measurable macroscopic deformation. For example, it has been experimentally observed that a microfibre in contact with a particle bends. We model this interaction using a revised JKR theory which includes determining the contact region and the induced bending of the fibre. This formulation reveals the link between adhesion and the easily-measurable deflection angle of the fibre and, in principle, offers an alternative and simple route to measuring surface energy at small scales. |
Tuesday, March 7, 2023 4:48PM - 5:00PM |
K09.00010: Temperature Dependence of Kinetic Friction of Thermoplastics: A Handle for Plastics Sorting? Joshua Thomas, Chad R Snyder, Kalman B Migler A crucial step in post-consumer plastics recycling (PCR) is sortation whereby properties such as density or spectral signature are used to sort plastics. However it is difficult to sort polyolefin flakes/pellets at high throughput by these properties. Here we examine friction near the melting point for four common PCRs as an alternative property for sortation. Specifically, we measure the temperature dependence of kinetic friction for three common polyolefins (high and low density polyethylene and polypropylene) and also a polyethylene terephthalate (PET). For the three polyolefins, we find strong increases in the coefficients of kinetic friction during temperature ramps as we approach the pre-melting regime. For the PET, we find a strong peak in crystallization that we associate with cold crystallization. We discuss the enhanced friction in the context of rubber friction, which exhibits comparable coefficients of kinetic frictions. |
Tuesday, March 7, 2023 5:00PM - 5:12PM |
K09.00011: Underwater friction for soft-hard contacts Utkarsh R Patil, Nityanshu Kumar, Shubhendu Kumar, Ali Dhinojwala, Hunter King Presence of lubricating liquid between two contacting surfaces has a profound influence on adhesion and friction. The current understanding in this area is summarized using a Stribeck curve that relates friction to velocity, viscosity, and applied load. Originally constructed for a hard-hard contact, the Stribeck curve has been extended to explain friction behavior in lubricated soft-hard contacts. Further, recent findings suggest that the underlying factors governing lubricated friction are microscopic contact area and the distribution of liquid trapped between the contacting pairs. |
Tuesday, March 7, 2023 5:12PM - 5:24PM |
K09.00012: Architeturally encoding adhesion in brush polymer networks Sergei Sheiko, Mitchell R Maw, Andrey V Dobrynin The diverse viscoelastic behavior of pressure sensitive adhesives (PSAs) enables their ubiquitous use in devices from office supplies to biomedical devices. Current approaches to meet these wide-ranging viscoelastic properties rely on exploratory mixing of polymers and loose additives, such as tackifiers and plasticizers. This approach results in adhesives prone to property variation over time and imprecision due to chemical migration. We have developed an alternative, additive-free PSA design platform empowering topological control over adhesive performance without altering chemical composition. By leveraging brush polymer architecture, we can concurrently regulate elastic (softness and firmness) and viscoelastic (characteristic relaxation times) properties, which allows encoding work of adhesion within five orders of magnitude. This platform bridges the gap between nanoscale molecular structure and macroscale adhesion through relaxation dynamics as a pivotal step toward universal design of both UV-cured and hot-melt PSAs. |
Tuesday, March 7, 2023 5:24PM - 5:36PM |
K09.00013: Linking Friction Scales from Nano to Macro via Avalanches Tyler M Salners Steady-state fluctuations in the friction force of molybdenum disulfide (MoS2), a prototypical lamellar solid, were analyzed experimentally for newton-scale forces and computationally via molecular dynamics simulations for nanonewton-scale forces. A mean field model links the statics and the dynamics of the friction behavior across these eight orders of magnitude in friction force and six orders of magnitude in friction force fluctuations (i.e., avalanches). Both the statistics and dynamics of the avalanches match model predictions, indicating that friction can be characterized as a series of avalanches with properties that are predictable over a wide range of scales. |
Tuesday, March 7, 2023 5:36PM - 5:48PM |
K09.00014: Scratching across ductile regimes of wear: the role of load-bearing area and friction Rosario Capozza, Kevin J Hanley Ductile wear is highly desirable in manufacturing and machining operations to achieve high finish quality. In such a ductile regime of operation, a characteristic transition from ploughing to cutting is often observed in materials with different mechanical properties. We unveil the origin of this transition through a plastic, debris free model of a tip wearing off a flat surface. The abraded volume depends on the equilibrium depth which is reached once the normal force is balanced by a lifting force during the scratching process. We show that the dependence of the equilibrium depth on the lifting force is highly non-linear and diverges above a threshold force that depends on the hardness, friction and geometry of the tip. The threshold corresponds to a characteristic depth marking the ploughing–cutting transition. When this characteristic depth is below the ductile–brittle depth of cut, ploughing, cutting and brittle modes of operation are all possible. The findings of this model, derived from theoretical considerations, are validated by DEM simulations and literature data from experiments. |
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