Use Of Elastomers Research Articles

New integrated silicon-PDMS process for compliant micro-mechanisms

Polydimethylsiloxane (PDMS) elastomers are used for many applications, such as microfluidics and micro-engineering. This paper presents a new process of integrating soft elastomers into a silicon structure without any assembly steps. The novelty of this process is the use of only one deep reactive ion etch (DRIE) instead of two or more as developed in previous works. Thus, this fabrication process allows the use of elastomers that are usually not compatible with some fabrication processes. Compliant flexures with different interference shapes have been designed, simulated, fabricated, and characterized for generic use and notably for micro-robot joints and compliant micro-systems. The experimental results show that the 400 μm × 400 μm cross-sectional area samples can be bended more than without delamination.

Twisted and coiled polymer (TCP) muscles embedded in silicone elastomer for use in soft robot

Researchers are seeking to create robots that could conform to non-uniform objects during handling and manipulation. High performance artificial muscles are the key factors that determine the capabilities of a robot. Twisted and coiled polymeric (TCP) muscle embedded in soft silicone skin solves some of the problems of soft robots in attaining morphed structure using low voltages, contrary to other technologies such as dielectric elastomer and piezoelectric. Furthermore, the TCP actuation system does not generate noise like pneumatic systems. The TCP embedded skin shows great promise for robotics to mimic the flexible appendages of certain animals. In this paper, we present experimental results on the effect of muscle placement and the thickness of the artificial skin on the actuation behavior, which can be used as a benchmark for modeling. We demonstrate the effect of three different skin thicknesses and three different muscle locations within the skin, by taking experimental deformation data from stereo camera. In general, two modes of actuations (undulatory and bending) were observed depending on the muscle placement, skin thickness, applied voltage, and actuation time. The thinner skin showed two-wave undulatory actuation in most cases, whereas the 4 mm skins showed mixed actuation and the 5 mm skins exhibited one-wave undulatory actuation. In all cases, the increase in voltage resulted in higher magnitudes of actuation. In addition, we showed consistent strain of the TCP muscles from 18 samples from two batches that produced an average strain of 22% (batch 1) to 20% (batch 2) with standard deviation of 2.5–1.8% respectively.

A pH-responsive supramolecular polymer gel as an enteric elastomer for use in gastric devices.

Devices resident in the stomach -- which are used for a variety of clinical applications including nutritional modulation for bariatrics, ingestible electronics for diagnosis and monitoring, and gastric retentive dosage forms for prolonged drug delivery -- typically incorporate elastic polymers to compress the devices during delivery through the esophagus and other narrow orifices in the digestive system. However, in the event of accidental device fracture or migration, the non-degradable nature of these materials risks intestinal obstruction. Here, we show that an elastic, pH-responsive supramolecular gel remains stable and elastic in the acidic environment of the stomach but can be dissolved in the neutral-pH environment of the small and large intestines. In a large animal model, prototype devices with these materials as the key component demonstrated prolonged gastric retention and safe passage. These enteric elastomers should increase the safety profile for a wide range of gastric retentive devices.

Tunable Flexible Pressure Sensors using Microstructured Elastomer Geometries for Intuitive Electronics

Pressure and touch sensitivity is crucial for intuitive human‐machine interfaces. Here, we investigate the use of different microstructured elastomers for use as dielectric material in capacitive pressure sensors. We use finite element modeling to simulate how different microstructures can reduce the effective mechanical modulus. We found that pyramidal structures are optimal shapes that reduce the effective mechanical modulus of the elastomer by an order of magnitude. We also investigate the dependence of spacing of the pyramidal microstructures and how it impacts mechanical sensitivity. We further demonstrate the use of these elastomeric microstructures as the dielectric material on a variety of flexible and stretchable substrates to capture touch information in order to enable large area human‐computer interfaces for next generation input devices, as well as continuous health‐monitoring sensors.

All-silicone prestrain-locked interpenetrating polymer network elastomers: free-standing silicone artificial muscles with improved performance and robustness

We present a novel all-silicone prestrain-locked interpenetrating polymer network (all-S-IPN) elastomer for use as a muscle-like actuator. The elastomer is fabricated using a combination of two silicones: a soft room temperature vulcanizing (RTV) silicone that serves as the host elastomer matrix, and a more rigid high temperature vulcanizing (HTV) silicone that acts to preserve the prestrain in the host network. In our novel S-IPN fabrication procedure we co-dissolve the RTV and HTV silicones in a common solvent, cast thin films, and allow the RTV silicone to cure before applying prestrain and finally curing the HTV silicone to lock in the prestrain. The free-standing prestrain-locked silicones show a performance improvement over standard free-standing silicone films, with a linear strain of 25% and an area strain of 45% when tested in a diaphragm configuration. We show that the process can also be used to improve electrode adhesion and stability as well as improve the interlayer adhesion in multilayer actuators. We demonstrate that, when coupled with carbon nanotube electrodes, fault-tolerance through self-clearing can be observed. We use the fault-tolerance and improved interlayer adhesion to demonstrate stable long-life (>30 000 cycles at >20% strain) actuation and repeated high-performance actuation (>500 cycles at ∼40% strain) of prestrained free-standing multilayer actuators driving a load.

Manufacturing technology for cast inserts of new wear-resistant alloys for combined mill linings

The efficiency of combined use of elastomers (rubbers) and wear-resistant steels and cast iron for mining and metallurgical equipment is studied: mill lining, hydrocyclones, modular screens, conveyor belt grids, crushers, etc. Rubber absorbs impact loads, dampens them, and thereby prevents breakage of high-hardness wear-resistant steels and cast iron. It is established by research that combination within the structure of chromium-manganese alloys of the transition class (1.6–2.2% C) types 200G4Kh5L, 200G5Kh2L (200G5Kh2TFL) with a sufficient amount of hard carbide phases and a ductile austenite-pearlite matrix provides high indices for impact-abrasive and impact-abrasive-corrosion resistance. Inserts of combined rubber and metal linings of metals of the transition class type are effective.

Influence of Combined Use of Elastomer on Mechanical Properties of PP/Elastomer/CaCO3 Ternary Composite

Influence of Combined Use of Elastomer on Mechanical Properties of PP/Elastomer/CaCO<SUB>3</SUB> Ternary Composite

Manipulation of mechanical compliance of elastomeric PGS by incorporation of halloysite nanotubes for soft tissue engineering applications

Poly (glycerol sebacate) (PGS) is a promising elastomer for use in soft tissue engineering. However, it is difficult to achieve with PGS a satisfactory balance of mechanical compliance and degradation rate that meet the requirements of soft tissue engineering. In this work, we have synthesised a new PGS nanocomposite system filled with halloysite nanotubes, and mechanical properties, as well as related chemical characters, of the nanocomposites were investigated. It was found that the addition of nanotubular halloysite did not compromise the extensibility of material, compared with the pure PGS counterpart; instead the elongation at rupture was increased from 110 (in the pure PGS) to 225% (in the 20 wt% composite). Second, Young’s modulus and resilience of 3–5 wt% composites were ∼0.8 MPa and >94% respectively, remaining close to the level of pure PGS which is desired for applications in soft tissue engineering. Third, an important feature of the 1–5 wt% composites was their stable mechanical properties over an extended period, which could allow the provision of reliable mechanical support to damaged tissues during the lag phase of the healing process. Finally, the in vitro study indicated that the addition of halloysite slowed down the degradation rate of the composites. In conclusion, the good compliance, enhanced stretchability, stable mechanical behavior over an extended period, and reduced degradation rates make the 3–5 wt% composites promising candidates for application in soft tissue engineering.

New perfluoroelastomer for sealing at low temperatures

A new fluorinated monomer technology is now extending the low-temperature capability of perfluoroelastomers down to −30°C, but retaining the fluid resistance typical of a standard perfluoroelastomer. This feature article describes the technology and a new low-temperature polymer that is capable of extending the use of elastomer sealing to a number of industries which handle aggressive media at low temperatures.

Bearing isolators – meeting tough demands

There has been a progressive change in the sealing of bearings for industrial equipment – from the use of elastomer, radial shaft seals to alternatives such as labyrinths. This feature discusses some of the designs of labyrinth bearing isolators, looks at the specifications for levels of protection and provides details of an application in an aggressive environment in the steel industry.

A novel approach to use of elastomer for monitoring of pressure using plastic optical fiber

Elastomer has become a material of much interest for use as a deformation element in pressure and force monitoring devices. In the present work, we fabricated and characterized a pressure sensor that uses the polydimethylsiloxane (PDMS) elastomer and the plastic optical fiber (POF). The POF is used to guide light through the 10 mm thick PDMS block and collect the transmitted light and deliver it to the detector. In the force sensor, an applied pressure deforms the PDMS block, increasing the transmissivity of the device. The fabricated pressure sensor shows satisfactory response up to 478 kPa with excellent sensitivity and repeatability. The present pressure sensor is simple to fabricate and can be used for a wide range industrial and automobile applications.

Advances and Applications of Biodegradable Elastomers in Regenerative Medicine

AbstractWhen elastomers were first proposed as useful materials for regenerative medicine a few decades ago, their high versatility and suitability for a diverse and wide range of in vivo applications could not have been predicted. Due to their ability to recover after deformation, these materials were first introduced in tissue engineering in an attempt to mimic the mechanical properties of the extracellular matrix. Furthermore, elastomeric characteristics have been described as important criteria for cell interaction by modulating cellular behavior. From soft to hard tissues, elastomers have demonstrated degradation, mechanical, and biocompatibility requirements in accordance with the target tissue. In this feature article, biodegradable synthetic polyester elastomers that have been reported in the literature are discussed, with special focus on those that show promise for in vivo tissue replacement. Their satisfactory performance in vivo shows the promise of elastomers for use in regenerative medicine. However, further investigation is required to demonstrate the prospect of elastomer‐based therapies in clinical trials.

Investigation of Elastomer Graphite Composite Material for Proton Exchange Membrane Fuel Cell Bipolar Plate

The bipolar plate is an important and integral part of the proton exchange membrane (PEM) fuel cell and PEM fuel cell stacks. Currently bipolar plates represent more than 80% by weight and 40% by cost of the fuel cell stack. Traditional materials used for bipolar plates are primarily graphite and metal. Search for alternative materials to improve weight and cost considerations is needed. This paper discusses the results of an investigation of two elastomeric materials being developed for bipolar plate applications. Perceived advantages of the use of elastomers for this application include improved sealability without additional gasket material, reduction in the contact resistance between individual cells, improved formability, and weight reduction. The first elastomer investigated is a two component liquid silicone rubber, and the second is a polyolefin thermoplastic elastomer. These polymer matrix materials are made electrically conductive by the addition of conductive fillers including thermal graphite fibers (Cytec DKD &amp; CKD), high surface area conductive carbon black nanoparticles (Cabot Black Pearls 2000), and graphite flakes (Asbury 4012). Electrical conductivity, processability, and elastic behavior measurements of the composites have been conducted. Some of silicone-graphite fiber composites material exhibit conductivity values comparable to those of the traditional graphite plate materials. Elasticity of all composites is maintained even at high filler concentrations.

Crack initiation and propagation under multiaxial fatigue in a natural rubber

The ever growing use of elastomers and polymers in structures leads to the need of pertinent multiaxial fatigue life criteria for such materials. Thus, the understanding of the fatigue crack initiation micro-mechanisms and their link to the local stress and/or strain history is essential. Scanning electron microscopy and Energy Dispersive Spectroscopy (EDS) have been used to investigate those micromechanisms on a natural rubber. Rigid inclusions were systematically found at the crack initiation. Depending on the type of inclusion (identified by EDS), cavitation at the poles or decohesion are the very first damage processes observed. Cracks orientations are compared to local principal stress orientation history, the later being obtained from finite element calculations (FE). It is shown that if large strain conditions are correctly taken into account, cracks are found to propagate systematically in the direction given by the maximal first principal stress reached during a cycle, even under non-proportional loading. A fatigue life criterion is proposed.

Durability Review of Elastomers for Severe Fluid Duties

Abstract Durability aspects of elastomers when exposed to fluids under severe conditions for Offshore Oil Production and other applications have been reviewed. Examples are provided of situations where estimations of residual life might be made, and of others where different considerations might be the overriding factors. The approach has been to extend previously-presented overviews focused on the use of elastomers in the hostile conditions of the oil field industry, and made largely from personal experience, to include some work of others with reference to other application areas as well.

Polymer Microvalve Based on Anisotropic Expansion of Polypyrrole

ABSTRACTAn actuator fabricated from the conductive polymer polypyrrole using microfabrication techniques is presented. This actuator utilizes the anisotropic volume change, which occurs under application of an electric field in polypyrrole grown in the presence of NaDBS. This volume change is in direction normal to the substrate, and is several times larger than lateral volume change utilized in polypyrrole microactuators to date. The actuator is applied in a microfluidic valve where membrane and microchannels are fabricated from a transparent elastomer using soft lithography. The use of elastomer enabled a good valve seal and encapsulation of the electrolyte used for polypyrrole actuation.

Biocompatibility Testing of Thermoplastic Elastomers for Use in Hard Tissue Replacements

The resistance of two types of thermoplastic elastomers to the near-realistic combined action of compressive and shear fatigue was assessed as part of an overall study of the biocompatibility of this class of elastomers. After fatigue the SEM of the low temperature fractured surface, the kinetics of swelling in a 3% acetic add solution, the dynamic mechanical properties (DMTA), the change in crystallinity (by FT-IR and WAXS) and the change in size of the voids (SANS) revealed subtle but small fatigue damage after cyclic loading between 150 and 1500 kPa over about 107 cycles. It may be concluded tentatively that the elastomers studied are potential candidate materials for endoprosthetic use.

Exploratory materials development for towed array sensor systems

Extended towed array sensor systems are used for geophysical sensing and exploration in the petroleum industry, and for detection of submersible objects in naval applications. Many of the polymeric materials considered for use in towed array hoses either did not possess the necessary aging and weathering resistance; provided satisfactory self‐noise performance at higher temperatures but were unacceptable in cold water; or experienced changes in self‐noise through fill‐fluid permeation and chemical reaction. There has been a need to develop and evaluate new classes of elastomers for use as hose wall materials. Array self‐noise performance can also be improved through proper selection of polymers for use in vibration isolation modules for low‐frequency towline excitation. Thermoplastic elastomers offer significant advantages over other types of elastomers in cost and ease of processing. Results are presented for both conventional elastomers and thermoplastics to show how these materials can be selected for ...

Photosynthesis and application of polyfunctional poly(n‐butyl acrylate) elastomers for use in epoxy resin toughening

AbstractMedium molecular weight, novel polyfunctional elastomers, namely epoxy groups on poly(n‐butylacrylate) (ETPnBA) and carboxyl groups on poly(n‐butylacrylate) (CTPnBA) were photosynthesized for evaluation as the toughening agents in epoxy resins. The effect of the functionality and kind of functional group of the elastomers upon the toughening of epoxy resins modified with these rubbery copolymers as a second phase was investigated by tensile tests, impact test, and electron microscopy. It was found that there exists an optimum functionality of elastomers for maximum impact resistance in epoxy groups (ETPnBA) and carboxyl groups (CTPnBA) copolymer‐modified systems. Studies on morphology of the modified epoxy resin system indicated that the better toughening effects of multiple distribution of particle sizes. The aggregation of rubber particles occurring in carboxyl group CTPnBA modified epoxy resin caused a loss of toughness.

Biocompatibility of the Vascugraft ®: evaluation of a novel polyester methane vascular substitute by an organotypic culture technique

To evaluate the biocompatibility of chemically and structurally modified polyurethane elastomers for use as blood vessel replacements, small squares of vascular prostheses were cultured in direct contact with endothelium from chick embryo aorta using an organotypic culture assay. The polyurethane materials tested were: Vascugraft ® (fibrous, open pore structure); commercial Hydrophilic Mitrathane ® prosthesis (high porosity, smooth surface, non-permeable, closed pore structure); experimental hydrophobic Mitrathane (less porosity but a fibrous, open pore structure, similar to Vascugraft). The commercial expanded polytetrafluoroethylene prostheses Impra ® and reinforced GORETEX ® were included as controls on account of their extensive clinical application in the femoropopliteal position. After 5 d incubation at 37°C biocompatibility was assessed in terms of average area of migrating cells on the biomaterial, total number of cells surrounding the expiant and level of adhesion between the cells and the biomaterial. The Vascugraft prosthesis promoted the growth of a continuous monolayer of cells on its surface. This behaviour was equivalent to Impra and reinforced GORETEX materials in terms of cell density and area of cell migration but appeared to be superior for cell adhesion. From a second series of cell culture tests, in which the extractables leached from the biomaterials were added to the nutrient medium, it was concluded that none of the biomaterials tested released cytotoxic contaminants.