A Tribometric Device for the Rolling Contact of Soft Elastomers

Rolling contact experimentation is a viable and instructive method for exploring the adhesive contact between surfaces. When applied to soft elastomeric or engineered surfaces, the results of such experiments can provide insights relevant to medical robotics, soft gripping applications, and reversible dry adhesives for bandages or wearable devices. We have designed and built a tribometric device to capture normal and tangential forces between a rolling indenter and substrate correlated with contact area imaging. The device was validated using an experimental setup involving a rigid, nominally smooth acrylic cylinder rolling against a flat polydimethylsiloxame (PDMS) substrate, the results of which matched favorably with accepted contact mechanics theories. The second test involved an indenter with a rigid core and thin (3 mm) smooth shell of a highly deformable, viscoelastic polyvinyl chloride (PVC) rolling on the same PDMS substrate. This test deviated significantly from analytical predictions, highlighting the effects of finite-thickness effects, viscoelasticity, and interfacial slip. This device will facilitate experimental investigations of the rolling contact mechanics between textured surfaces and soft tissue-like materials, which is an important fundamental problem in medical robotics.

Abutment and Orthodontics for Endurance of Dental Crowns

The split-increment horizontal placement (SHP) is the popular technique being used, along with other therapeutic modus operandi. As more than adequate, SHP methods are being enhanced in barricade cavities for reducing the shrinkage stress that were generated during light polymerization. Such stress, if released unrestrained, may redress within the composite, tooth or at the adhesive contact .

Attractive forces slow contact formation between deformable bodies underwater

Thermodynamics tells us to expect underwater contact between two hydrophobic surfaces to result in stronger adhesion compared to two hydrophilic surfaces. However, the presence of water changes not only energetics but also the dynamic process of reaching a final state, which couples solid deformation and liquid evacuation. These dynamics can create challenges for achieving strong underwater adhesion/friction, which affects diverse fields including soft robotics, biolocomotion, and tire traction. Closer investigation, requiring sufficiently precise resolution of film evacuation while simultaneously controlling surface wettability, has been lacking. We perform high-resolution in situ frustrated total internal reflection imaging to track underwater contact evolution between soft-elastic hemispheres of varying stiffness and smooth–hard surfaces of varying wettability. Surprisingly, we find the exponential rate of water evacuation from hydrophobic–hydrophobic (adhesive) contact is three orders of magnitude lower than that from hydrophobic–hydrophilic (nonadhesive) contact. The trend of decreasing rate with decreasing wettability of glass sharply changes about a point where thermodynamic adhesion crosses zero, suggesting a transition in mode of evacuation, which is illuminated by three-dimensional spatiotemporal height maps. Adhesive contact is characterized by the early localization of sealed puddles, whereas nonadhesive contact remains smooth, with film-wise evacuation from one central puddle. Measurements with a human thumb and alternatively hydrophobic/hydrophilic glass surface demonstrate practical consequences of the same dynamics: adhesive interactions cause instability in valleys and lead to a state of more trapped water and less intimate solid–solid contact. These findings offer interpretation of patterned texture seen in underwater biolocomotive adaptations as well as insight toward technological implementation.

Investigations on the Adhesive Contact Behaviors between a Viscoelastic Stamp and a Transferred Element in Microtransfer Printing

Microtransfer printing is a sophisticated technique for the heterogeneous integration of separately fabricated micro/nano-elements into functional systems by virtue of an elastomeric stamp. One important factor influencing the capability of this technique depends on the adhesion between the viscoelastic stamp and the transferred element. To provide theoretical guidance for the control of adhesion in the transfer printing process, a finite element model for the viscoelastic adhesive contact between a polydimethylsiloxane (PDMS) stamp and a spherical transferred element was established, in which the adhesive interaction was modeled by the Lennard-Jones surface force law. Effects of the unloading velocity, preload, and thermodynamic work of adhesion on the adhesion strength, characterized by the pull-off force, were examined for a loading-dwelling-unloading history. Simulation results showed that the unloading path deviated from the loading path due to the viscoelastic property of the PDMS stamp. The pull-off force increased with the unloading velocity, and the increasing ratio was large at first and then became low. Furthermore, the influence of the preload on increasing the pull-off force was more significant under larger unloading velocity than that under smaller unloading velocity. In addition, the pull-off force increased remarkably with the thermodynamic work of adhesion at a fixed maximum approach.

Study of triclabendazole effects on Fasciola hepatica’s life-supporting organs, spines and suckers responsible for stable position of the parasite in the host

The purpose of the research is to study triclabendazole effects on the Fasciola’s life-supporting organs, spines and suckers which are responsible for stable position of the parasite in the host.Materials and methods. The study material was trematodes Fasciola hepatica (Linneus 1758, family Fasciolidae Railliet 1895), which were collected after the action of triclabendazole (fasinex) (chemically 5-chloro-6-(2,3-dichlorophenoxy)-2-methylthiobenzimidazole)on the 7th day after the drug administered at a single dose of 10 mg/kg for the Active Substance in the treatment of ovine fasciolosis. F. hepatica from untreated animals served as control. Mature F. hepatica collected after treatment with triclabendazole, and marita from the control groups were dehydrated in ascending alcohol series for 1–2 days after fixation; then passed through a mixture of chloroform and absolute alcohol (in a ratio of 1:1), and through pure chloroform in two portions for 10–15 minutes. The material was then soaked in a mushy mixture of chloroform and paraffin in a thermostat at 37 °C for 12–18 hours, and in paraffin in a thermostat at 56 °C for 30–45 minutes; and then embedded in paraffin with added wax. The resulting paraffin blocks were broken down into serial sections of 5–7 μm thick, then stained and examined under a light microscope.Results and discussion. Pathomicromorphological analysis of F. hepatica’s spines and suckers, organs that come into adhesive contact with the host organism revealed destructive changes in them after the action of triclabendazole. After the action of triclabendazole on fascioles, the spines look enlarged and swollen, and have a more rounded shape and some changes in color, absorbing eosin in greater concentration. The muscle fibers of the fascioles’ oral and abdominal suckers also look swollen after the action of triclabendazole. Although the musculature of the F. hepatica’s pharynx retained its structure, it has changes. It thickened sharply, which is clearly visible on the transverse and longitudinal sections of the helminths; neurosecretory cells are destroyed, and voids are observed in their place.

Survival of polymeric microstructures subjected to interrogatory touch

Polymeric arrays of microrelief structures have a range of potential applications. For example, to influence wettability, to act as biologically inspired adhesives, to resist biofouling, and to play a role in the “feel” of an object during tactile interaction. Here, we investigate the damage to micropillar arrays comprising pillars of different modulus, spacing, diameter, and aspect ratio due to the sliding of a silicone cast of a human finger. The goal is to determine the effect of these parameters on the types of damage observed, including adhesive failure and ploughing of material from the finger onto the array. Our experiments point to four principal conclusions [1]. Aspect ratio is the dominant parameter in determining survivability through its effect on the bending stiffness of micropillars [2]. All else equal, micropillars with larger diameter are less susceptible to breakage and collapse [3]. The spacing of pillars in the array largely determines which type of adhesive failure occurs in non-surviving arrays [4]. Elastic modulus plays an important role in survivability. Clear evidence of elastic recovery was seen in the more flexible polymer and this recovery led to more instances of pristine survivability where the stiffer polymer tended to ablate PDMS. We developed a simple model to describe the observed bending of micropillars, based on the quasi-static mechanics of beam-columns, that indicated they experience forces ranging from 10−4–10−7 N to deflect into adhesive contact. Taken together, results obtained using our framework should inform design considerations for microstructures intended to be handled by human users.

Theory and practice of adhesive interactions in the field of milk processing

Механизмы формирования адгезионного контакта, изучение адгезионной способности тех или других веществ и управление ею в различных технологических процессах, формирование требуемой адгезионной прочности соединений - это многообразные проблемы в области техники и технологии. Рассмотрены понятие «адгезия» и базовые теории адгезионных взаимодействий, базирующихся на различных подходах: молекулярная, которая также называется адсорбционной, диффузионная, механическая, химическая, электрическая, релаксационная, слабого граничного слоя. Универсальности в объяснении тех или иных процессов формирования адгезионных соединений нет. Адгезионные соединения, образуемые в процессе переработки молока, носят нежелательный характер и приводят к потерям продукции и нарушению санитарно-гигиенического состояния производств вследствие образования белковых, жировых и комбинированных загрязнений на поверхностях различного оборудования. Соответственно требуются глубокие научные и практические исследования как по изучению механизмов образования адгезионных соединений, так и по их удалению. Interaction with other people the mechanisms of adhesive contact, the study of the adhesive ability of different substances and the control of adhesion in various technological processes and ensuring the necessary adhesive strength of joints is a multifaceted problem in the fields of engineering and technology. The article discusses the concept of «adhesion» and the basic theory of adhesion coupled interactions, based on various approaches.Molecular, which is also called adsorptive; diffusion, mechanical, chemical, electrical, relaxation, weak boundary layer. There is no universality in explaining certain processes of the formation of adhesive joints.Adhesive joints formed during milk processing are undesirable and lead to product losses and a violation of the sanitary and hygienic state of production. This is due to the formation of protein, fat and combined contaminants on the surfaces of various equipment. Accordingly, deep scientific and practical research is required both to study the mechanisms of the formation of adhesive joints and to remove them.

Formulation and existence of weak solutions for a problem of adhesive contact with elastoplasticity and hardening

This paper presents the weak formulation of a quasi-static evolution model for two deformable bodies with uni-directional adhesive unilateral contact on which external loads act. Small deformations and linearized elastoplasticity with hardening are assumed. The adhesion component is rate-dependent or rate-independent according to the choice of the viscosity coefficient of the glue; elastoplasticity is considered rate-independent. The weak formulation is expressed as a doubly non-linear problem with unbounded multivalued operators, as a function of internal and boundary displacements, plastic and symmetric strain tensors, and the bonding field and its gradient. This paper differs from other formulations by coupling the equations defined inside and on the boundary of the solids in functional form. In addition to this novelty, we verify the existence of solutions by a path other than that displayed in similar articles. The existence of solutions is demonstrated after considering a succession of doubly non-linear problems with an unbounded operator, and verifying that the solution of one of the problems is also a solution to the objective problem. The proof is supported by previous results from non-linear Partial differential equations theory with monotone operators.

A mathematical model for evaluating adhesion contact of an elastomeric seal-on-seal structure

For low impact docking systems (LIDS) developing for rendezvous and docking of spacecraft, the main interface docking seal (MID seal) is one of the key components, and its seal and adhesion performances are crucial for mating LIDS-adapted spacecrafts. An elastomeric seal-on-seal structure is one of the mainstream designs of the MID seal and is generally made of silicone rubbers that can adapt to complex space environments. For the MID seal of seal-on-seal structure, the adhesion performance has been confirmed to have significant effects on the separation reliability of mating spacecrafts. By analyzing the sealing and adhesive mechanisms of the MID seal that is an elastomeric seal-on-seal structure, an adhesive contact model of single rough peak is derived on the grounds of Johnson, Kendall and Roberts (JKR) theory. Utilizing the asperities model and the adhesive contact model of single rough peak, an adhesive contact model of the elastomeric seal-on-seal structure is further proposed. The experiments were performed to verify the adhesion model, and the satisfied consistencies were presented in the comparative studies of the experimental data and the calculated data. Based on the proposed mathematical model, the simulation analyses were performed to disclosure adhesive performances of the MID seal. The influence rules of some parameters on adhesive performances were presented, including material parameters, geometric parameters, and parameters of surface morphology. The research findings are proven to be favorable for the design, machining, assemblage and actual service of the MID seal, and can be also used for other elastomeric seals.