Soft Rubbers Research Articles

Determination of the limits of operational loads of rubber shock absorbers during compression

Determining the limits of operational loads of rubber shock absorbers is an urgent task in the development of methods of non-destructive control of their condition. Therefore, the object of research is the influence of the limit values of the parameters of rubber shock absorbers during their static compression under harsh operating conditions. One of the most problematic issues is cylindrical shock absorbers with a form factor of less than 1.0. In the work, rubber shock absorbers of different hardness were used, which are model samples for tests of cylindrical shock absorbers with a form factor of 0.42, which were carried out on a laboratory stand. The study of compression process of rubber shock absorbers is an urgent task in modelling the conditions of their operation. The obtained results make it possible to simulate the most effective diagnostic parameter of rubber shock absorbers during compression and to establish its limit and permissible values. It has been established that different rubber hardnesses provide different compression rates, which can be used to study non-destructive testing of shock absorbers, especially under which conditions they can be used in practice. According to the indicators of relative deformation during compression, the use of rubber shock absorbers from the group of high hardness is recommended for more severe load conditions during exploitation. Soft and medium-hard rubbers are characterized by an increased relative deformation of the shock absorber's geometric size (height) during compression, which can lead to their destruction under increased loads. The obtained results on model samples can be checked on rubber shock absorbers manufactured in industrial conditions. The conducted research allows to create methods of choosing rubber shock absorbers for certain operating conditions depending on the coefficient of its shape. Limits of indicators simulating operating loads for different types of rubber shock absorbers have been established, which can be used when choosing a type of rubber for certain load conditions, and choosing a reinforcing material for the rubber array of the shock absorber and its shape.

A life off the beaten track in biomechanics: Imperfect elasticity, cytoskeletal glassiness, and epithelial unjamming.

Textbook descriptions of elasticity, viscosity, and viscoelasticity fail to account for certain mechanical behaviors that typify soft living matter. Here, we consider three examples. First, strong empirical evidence suggests that within lung parenchymal tissues, the frictional stresses expressed at the microscale are fundamentally not of viscous origin. Second, the cytoskeleton (CSK) of the airway smooth muscle cell, as well as that of all eukaryotic cells, is more solid-like than fluid-like, yet its elastic modulus is softer than the softest of soft rubbers by a factor of 104-105. Moreover, the eukaryotic CSK expresses power law rheology, innate malleability, and fluidization when sheared. For these reasons, taken together, the CSK of the living eukaryotic cell is reminiscent of the class of materials called soft glasses, thus likening it to inert materials such as clays, pastes slurries, emulsions, and foams. Third, the cellular collective comprising a confluent epithelial layer can become solid-like and jammed, fluid-like and unjammed, or something in between. Esoteric though each may seem, these discoveries are consequential insofar as they impact our understanding of bronchospasm and wound healing as well as cancer cell invasion and embryonic development. Moreover, there are reasons to suspect that certain of these phenomena first arose in the early protist as a result of evolutionary pressures exerted by the primordial microenvironment. We have hypothesized, further, that each then became passed down virtually unchanged to the present day as a conserved core process. These topics are addressed here not only because they are interesting but also because they track the journey of one laboratory along a path less traveled by.

Optimising dynamic mechanical analysis experiments on soft rubbers for use in time temperature superposition

Rubbers are ubiquitous in engineering applications where they are often subjected to loading leading to high strain rate deformation. The strong rate and temperature dependence of rubbers and their composites motivates research into understanding their mechanical response under a wide range of conditions. However, experimental characterisation of the rate-temperature dependence of soft rubbers is challenging. In this methods paper, an improved methodology is proposed for conducting Dynamic Mechanical Analysis (DMA) experiments on rubbers. The higher quality data produced can be used in time-temperature superposition (TTS) applications to derive a more accurate definition of the rubber’s rate-temperature dependence. Overall, the improvements obtained can be summarised as follows:•Reducing clamping artefacts due to volume expansion•Ensuring high quality temperature stability•Improving the contact area between the specimen and the clamps

Simultaneous measurements of ultrasound attenuation, phase velocity, thickness, and density spectra of polymeric sheets

The size distribution and mechanical properties of microparticle dispersed in liquid can be characterized by ultrasonic spectroscopy with the aid of acoustic scattering theories. In order to carry out the accurate analysis of the particles, the basic properties, such as the density, viscosity, longitudinal and shear velocities and intrinsic attenuation coefficient of the particle must be known prior to the analysis. Particularly, for soft elastomers or rubbers which exhibit complex mechanical properties with comparable real and imaginary parts, such fundamental information should be provided prior to the particle analysis to minimize the uncertainty of estimation associated with the number of adjustable parameters. In this study, we examined the acoustical properties of poly(methyl methacrylate)(PMMA) and cross-linked poly(dimethyl siloxane) sheets having different cross-linker concentrations by Multiple-Echo Reflection Ultrasonic Spectroscopy which simultaneously enabled us to acquire 4 fundamental properties, the ultrasound attenuation coefficient, phase velocity, density, and thickness (MERUS4 for solid plate). In addition, it was confirmed that the acoustic spectra of PMMA particles dispersed in water were reproduced well with the physical properties determined by MERUS4 using the PMMA plates.

Band Gap Formation and Tunability in Stretchable Serpentine Interconnects

Serpentine interconnects are highly stretchable and frequently used in flexible electronic systems. In this work, we show that the undulating geometry of the serpentine interconnects will generate phononic band gaps to manipulate elastic wave propagation. The interesting effect of “bands-sticking-together” is observed. We further illustrate that the band structures of the serpentine interconnects can be tuned by applying prestretch deformation. The discovery offers a way to design stretchable and tunable phononic crystals by using metallic interconnects instead of the conventional design with soft rubbers and unfavorable damping.

Soft porous materials with ultra-low sound speeds in acoustic metamaterials

Porous media have unique acoustic properties that have been intensively studied for many decades and found many applications in various areas. Owing to their low sound speed, porous materials have proven to be interesting key elements for the realization of acoustic metamaterials since they may act as strong Mie-type resonators, when shaped as spherical particles [1]. In that context, soft porous silicone rubbers are ideal “ultra-slow” materials since a sudden drop of the longitudinal sound speed cL with the porosity Φ has been observed in these porous materials (cL < 100 m/s for Φ < 10%). Such unusual behavior is well captured by simple models based on low-frequency approximations of multiple scattering theories [2]. Then, I will discuss the interest of these “ultra-slow” particles for acoustic metamaterials of which the acoustic index has been shown to be negative [3]. At last, I will demonstrate that the exotic values of the acoustic index may be tuned by using other porous particles such as xerogel be...

Soft porous silicone rubbers with ultra-low sound speeds in acoustic metamaterials

Soft porous silicone rubbers are demonstrated to exhibit extremely low sound speeds of tens of m/s for these dense materials, even for low porosities of the order of a few percent. Our ultrasonic experiments show a sudden drop of the longitudinal sound speed with the porosity, while the transverse sound speed remains constant. For such porous elastomeric materials, we propose simple analytical expressions for these two sound speeds, derived in the framework of Kuster and Toksöz, revealing an excellent agreement between the theoretical predictions and the experimental results for both longitudinal and shear waves. Acoustic attenuation measurements also complete the characterization of these soft porous materials.

Cellular Contractile Forces Measured a Multi-Well Silicone Device Reveal Physical Forces that Control Cell Migration in Physiology and Disease

Cell migration is a highly integrated process and basic to many biological functions ranging from development to immune response and wound healing, to metastasis in cancer. For cells to migrate, they must generate and transduce traction forces to their environment, however, no technology to date has provided a high throughput solution for measuring these traction forces. Here we present a new assay for measuring cellular contractile forces employing robust multiwall culture plates: Using a 96-well plate format, we fabricate soft (∼1-10 kPa) elastic silicone rubbers with embedded fiduciary particles; by measuring the cell-induced deformation of these particles we calculate the cellular traction stresses and work using Fourier transform cytometry. We utilize this system to quantify the traction mechanics underlying cellular migration in several diseased settings including cancer metastasis, induced epithelial to mesenchymal transition (EMT), and aging; in all instances, we find significant changes in the contractile stresses and work, suggesting that contractile force screening may become a valuable biophysical diagnostic addition. This 96-well format and the use of a non-degrading soft silicone rubber create a simple and stable assay, and we anticipate that this technology will be of broad utility in diverse quantitative biological and health sciences.

Dynamic and static tensile mechanical properties of myocardial tissue.

Event Abstract Back to Event Dynamic and static tensile mechanical properties of myocardial tissue. Sherif Ramadan1, 2, 3, Hani Naguib1, 2, 3 and Narinder Paul3, 4 1 University of Toronto, Mechanical and Industrial Engineering, Canada 2 University of Toronto, Smart and Adaptive Polymers Lab, Canada 3 University of Toronto, Institute of Biomaterials and Biomedical Engineering, Canada 4 Toronto General Hospital, Joint Department of Medical Imaging, Canada Introduction: Heart disease is a significant cause of morbidity and mortality that affects 1.3 million Canadians annually[1]. Coronary artery disease (CAD) is a leading cause of heart disease and is due to progressive accumulation of arterial plaque resulting in occlusion of the arterial lumen and abnormal myocardial contractility[2]. Computed Tomography Coronary Angiography (CTCA) is used to exclude significant CAD in patients with low-intermediate pre-test probability[3],[4]. However, dynamic anthropomorphic CT phantom devices that realistically mimic normal and diseased cardiac tissues are required to test new imaging techniques and algorithms that target ultralow radiation dose and high resolution CTCA. This study aims to quantify the mechanical properties of myocardial tissue to allow for the fabrication of phantoms that mimic the behaviour of heart tissue under varying hemodynamic conditions. Materials and Methods: The elasticity of myocardial tissue was tested under static and dynamic conditions. Tensile testing was performed to obtain the Young’s modulus and a dynamic mechanical analyzer (DMA) induced a frequency sweep to determine the complex (dynamic) modulus. A frequency range of 0.5Hz to 3.5Hz was analyzed as these frequencies correspond to human heart rates of 30 to 210bpm. Multiple tissue samples were taken from each pig and lamb heart, these animal models were chosen as they are close human analogues and are commonly used as replacements for human tissue[5],[6].The heart tissue was tested while freshly sacrificed without any intervening freeze-thaw cycles to ensure the integrity of the muscle tissue. The tissue was placed in a balanced salt solution and tested at 37°C to simulate in vitro conditions[7]. Results and Discussion: Preliminary data (mean ± SD): The tensile and complex moduli were tested on 6 pig and lamb hearts; tensile modulus of lamb = 0.06 ±0.03 (n=15 samples) and for pig =0.04 ± 0.03 (n=11 samples); the complex modulus for lamb = 0.03Mpa at 0.5Hz to 0.06 Mpa at 3.5Hz ± 0.02 (n=15 samples) and for pig = 0.03Mpa at 0.5Hz to 0.06 Mpa at 3.5Hz ± .01 (n=15 samples) and both exhibited a linear trend. These values indicate that myocardial tissue behaves similarly to soft rubbers and stiffens under higher frequency loads. Moreover, for tensile testing there was no statistical difference between individual hearts or animals (P values of 0.235, 0.483, and 0.73 between the animals, pig hearts, and lamb hearts respectively). Conclusions: The static and dynamic moduli of myocardial tissue in pig and lamb hearts is between 0.02 and 0.1Mpa which is similar to soft, rubber-like materials. This quantitative data will inform selection and fabrication of customized biomaterials for construction of the myocardium in a dynamic anthropomorphic tissue realistic heart phantom.

Soft 3D acoustic metamaterials

One of the current challenges in the field of metamaterials is to extend beyond electromagnetism in other areas such as acoustics [1]. Soft matter techniques coupled with microfluidics provide a unique tool to take up this challenge because they allow for the production of 3D locally resonant (random) materials composed of various soft resonators [2]. The Mie (or cavity) resonators are interesting key elements for acoustic metamaterials since they may induce strong acoustic resonances provided large sound-speed contrasts between the inclusions and the host matrix [3]. For example, the use of “slow” (deformable) ferrofluid-droplets allows for the tuning of sharp Mie resonances, thanks to external magnetic fields [4]. For much higher sound-speed contrasts, we have recently shown that strong Mie resonances of “ultra-slow” beads made of soft porous silicone rubbers [5] could induce strong dispersion effects leading to materials with exotic (zero, negative) values of the acoustic index [6]. [1] Wegener, Science 342, 939–940 (2013). [2] Brunet et al., Science 342, 323–324 (2013). [3] Li and Chan, Phys. Rev. E 70, 055602 (2004). [4] Brunet et al., Phys. Rev. Letters 111, 264301 (2013). [5] Zimny et al., Langmuir 31, 3215–3221 (2015). [6] Brunet et al., Nature Mater. 14, 384–388 (2015).

High friction on ice provided by elastomeric fiber composites with textured surfaces

Two main applications requiring high friction on ice are automobile tires and footwear. The main motivation behind the use of soft rubbers in these applications is the relatively high friction force generated between a smooth rubber contacting smooth ice. Unfortunately, the friction force between rubber and ice is very low at temperatures near the melting point of ice and as a result we still experience automobile accidents and pedestrian slips and falls in the winter. Here, we report on a class of compliant fiber-composite materials with textured surfaces that provide outstanding coefficients of friction on wet ice. The fibrous composites consist of a hard glass-fiber phase reinforcing a compliant thermoplastic polyurethane matrix. The glass-fiber phase is textured such that it is aligned transversally and protruding out of the elastomer surface. Our analysis indicates that the exposed fiber phase exhibits a “micro-cleat” effect, allowing for it to fracture the ice and increase the interfacial contact area thereby requiring a high force to shear the interface.

Soft porous silicone rubbers as key elements for the realization of acoustic metamaterials.

In this work, macroporous materials made of polydimethylsiloxane, a soft silicone rubber, are prepared using UV polymerization with an emulsion-templating procedure. The porosity of the final materials can be precisely controlled by adjusting the volume of the dispersed phase. We show that the porous structure of the materials is the template of the droplets of the initial emulsions. Mechanical tests show that the materials Young's moduli decrease with the porosity of the materials. Acoustic measurements indicate that, in such a porous elastomeric matrix, the sound speed also decreases dramatically as soon as the porosity increases to attain values of as low as 80 m/s. The results are compared to earlier ones on silica aerogels and are interpreted within the framework of a simple theoretical approach. We show that the very low sound speed value is a consequence of the low value of the polymer shear modulus. This explains why such porous soft silicone rubbers are so efficient at playing the role of slow-soft resonators in acoustic metamaterials. Moreover, the fast rate of polymerization of such UV-curable fluid allows for a facile shaping of the final material as beads or rods in microfluidic devices.1.

Preparation and Characterization of Micro Crystalline Cellulose Fiber Reinforced Chitosan based Polymer Composites.

Plastics are widely used in society due to low cost, light weight and excellent performance which varies from soft rubbers to fibers stronger and stiffer than steel. On the other hand their non-biodegradability creates serious environmental problems. The utilization of packaging films from bio-based compounds has received so much attention lately due to the fact that they are readily biodegradable. The two most abundant polymers on earth like cellulose and chitosan have attracted increasing attention as a source of renewable energy and functional materials. Rice straw fiber is subjected to different treatment along with chitosan to form composites. The film samples have been characterized by FTIR and SEM, thermal properties by TGA and DTA. Reinforcement of chitosan with prepared microcrystalline cellulose from rice straw enhances the moisture resistance and strength of chitosan film.

Static friction of stainless steel wire rope–rubber contacts

Little is known about static friction of stainless-steel wire ropes (‘cables’) in contact with soft rubbers, an interface of potential importance for rigidifiable medical instruments. Although friction theories imply that the size and profile of the cables affect static friction, there are no confirmative data for stainless-steel cable-rubber contacts. Static friction was measured between five cable types (0.18, 0.27 and 0.45mm diameter, twisted in 1×7, 1×19, or 7×7 strands) and latex, nitrile, and silicone rubber. Mean static friction coefficients of the cables ranged over 0.27–0.31, 0.25–0.27, and 0.44–0.53 for nitrile, silicone, and latex, respectively. Overall, the cable type had little effect on static friction. For all cables, friction was twice as high for latex as for nitrile rubber, which had slightly higher friction than silicone rubber. The higher static friction for nitrile compared to silicone rubber despite silicone rubber being significantly softer could be caused by the high polar surface free energy of nitrile rubber. Common friction theories were valuable in predicting the effect of cable profiles and rubber properties on static friction but should not be applied without considering interaction effects. Static friction seems to be a minor factor when selecting cables for practical applications involving cable-rubber contacts.

Decay Kinetics of Benzophenone Triplets and Corresponding Free Radicals in Soft and Rigid Polymers Studied by Laser Flash Photolysis

The kinetics of transients formed under photoexcitation of benzophenone (B) dissolved in three different polymers was studied by ns laser flash photolysis. These polymers were the soft rubbers poly (ethylene-co-butylene) (EB), polystyrene block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) and hard polystyrene (PS). We monitored the decay kinetics of triplet state (3)B(*) and of ketyl radicals BH(●). We observed exponential decay of (3)B(*) and two-stage decay kinetics of BH(●) in EB. The first stage is a fast cage recombination of a radical pair (BH(●), radical of polymer R(●)). The second slow stage of BH(●) decay follows the second-order law with a relatively high rate constant, which corresponds to recombination of BH(●) in a homogeneous liquid with a viscosity of only ~0.1 P (about five times of 2-propanol viscosity). Application of a magnetic field (MF) of 0.2 T leads to deceleration of both stages of BH(●) decay in EB by approximately 20%. Decay kinetics of both transients were observed in SEBS. There was no MF effect on BH(●) decay in SEBS. We only observed (3)B(*) in PS. Decay kinetics of (3)B(*) in this case were described as polychromatic dispersive first-order kinetics. We discuss the effects of polymer structure on transient kinetics and the MF effect.

Soybean oil‐based shape‐memory polyurethanes: Synthesis and characterization

AbstractShape‐memory polymers (SMPs) have wide range of applications due to their ability to sense environmental stimuli and reshape from a temporary shape to a permanent shape. Plant oil‐based polymeric materials are highly concerned in recent years in consideration of petroleum depletion and environmental pollution. However, plant oil‐based polymers are rarely investigated regarding their shape‐memory characteristics though bio‐based SMPs are highly desired nowadays. In this study, a series of soybean oil‐based shape‐memory polyurethanes (SSMPUs) are prepared through a mild chemo‐enzymatic synthetic route, and their properties are fully characterized with tensile testing, DSC, dynamic mechanical analysis (DMA), and shape‐memory testing. Results show that SSMPUs are soft rubbers with tensile strength in the range of 1.9–2.2 MPa and glass transition temperature in the range of 2–5°C, and possess good shape recoveries at RT when stretching ratio is 10, 20, and 30%, respectively. This work would promote the development of high‐value‐added plant oil‐based shape‐memory polyurethanes.Practical applications: Using annual renewable plant oil as feedstock, the synthesized SSMPUs show good shape recovery properties, which will make them applicable as potential alternatives to petroleum‐based shape‐memory materials. The simple and mild preparation process also contributes to the further exploration of plant oil to value‐added functional materials.

Vegetable oil thermosets reinforced by tannin–lipid formulations

Totally bio-based thermosetting polymers which are comparable to synthetic polyester thermosets have been prepared from copolymerization of condensed tannin–fatty acid esters with vegetable oils. Oxidative copolymerization of tannin linoleate/acetate mixed esters with linseed oil and tung oil produced polymer films ranging from soft rubbers to rigid thermosets. Tannin incorporation into the formulations was essential for the final product to achieve necessary mechanical strength. Films had ambient modulus values between 0.12 and 1.6GPa, with glass transition temperatures ranging from 32 to 72°C and calculated crosslink densities of 1020–57,700molm−3. Film stiffness, Tg and crosslink density increase with greater tannin linoeate/acetate content due mainly to this tannin component providing rigidity through polyphenolic aromatic rings and unsaturated chains as crosslinking sites.

Vegetable oil cast resins via click chemistry: Effects of cross‐linkers

AbstractPolymerization of azidated castor, canola, corn, soybean, and linseed oils with two diynes under thermal click chemistry conditions (without a solvent or a catalyst) yielded fully cross‐linked polymers (1–10) with similar density. The use of an aromatic diyne (1,4‐diethynylbenzene) as a cross‐linker resulted in polymers (1–5) that showed higher glass transition and strength and lower swelling, water absorption, and sol fraction than corresponding polymers (6–10) resulting from an aliphatic diyne (1,7‐octadiyne). These polymers exhibited behaviors ranging from soft rubbers to hard plastics.Practical applications: Vegetable oil cast resins prepared by click chemistry are potentially useful electroinsulating materials as potting or encapsulating compounds since no by‐products are generated.

Activation and deactivation of self-healing in supramolecular rubbers

A remarkable self-healing property has been achieved recently with rubbers formed by a supramolecular network of oligomers. Here we explore this property through a tack-like experiment where two parts of supramolecular rubber are simply brought into contact and then taken apart. These experiments reveal that the self-adhesive strength of rubber surfaces is significantly enhanced by fracture or other damaging processes. The mechanical energy required to separate two fracture surfaces that were brought back into contact is about one order of magnitude larger than that for surfaces close to thermodynamic equilibrium. Moreover, we find that fracture faces stored apart at room temperature still self-heal after 12 h but that this self-healing can be fully deactivated within a couple of hours by annealing around 90 °C. More generally, these results provide useful quantitative data to investigate the intensity and kinetics of self-healing in these soft rubbers.

Vegetable oil-based polymeric materials: synthesis, properties, and applications

The use of vegetable oils as renewable raw materials for the synthesis of various monomers and polymeric materials is reviewed. Vegetable oils are generally considered to be the most important class of renewable resources, because of their ready availability and numerous applications. Recently, a variety of vegetable oil-based polymers have been prepared by free radical, cationic, olefin metathesis, and condensation polymerization. The polymers obtained display a wide range of thermophysical and mechanical properties from soft and flexible rubbers to hard and rigid plastics, which show promise as alternatives to petroleum-based plastics.