Elastomer Layer Research Articles

Robust control of novel pendulum-type vibration isolation system

A novel pendulum-type vibration isolation system is proposed consisting of three active cables with embedded piezoelectric actuators and a passive elastomer layer. The dynamic response of the isolation module in the vertical and horizontal directions is modeled using the Lagrangian approach. The validity of the dynamic model is confirmed by comparing the simulation results for the frequency response in the vertical and horizontal directions with the experimental results. An approximate model is proposed to take into account system uncertainties such as payload changes and hysteresis effects. A robust quantitative feedback theory (QFT)-based active controller is then designed to ensure that the active control can achieve a high level of disturbance rejection in the low-frequency range even under variable loading conditions. It is shown that the controller achieves average disturbance rejection of −14 dB in the 2–60 Hz bandwidth range and −35 dB at the resonance frequency. The experimental results confirm that the proposed system achieves a robust vibration isolation performance under the payload in the range of 40–60 kg.

Co-extruded mechanically tunable multilayer elastomer laser

We have fabricated and studied mechanically tunable elastomer dye lasers constructed in large area sheets by a single-step layer-multiplying co-extrusion process. The laser films consist of a central dye-doped (Rhodamine-6G) elastomer layer between two 128-layer distributed Bragg reflector (DBR) films comprised of alternating elastomer layers with different refractive indices. The central gain layer is formed by folding the coextruded DBR film to enclose a dye-doped skin layer. By mechanically stretching the elastomer laser film from 0% to 19%, a tunable miniature laser source was obtained with ~50 nm continuous tunability from red to green. Optically pumped by a frequency-doubled Nd:YAG laser, the elastomer laser showed a lasing threshold of 0.9 mJ/cm2 at 600 nm.

Investigation of the influence of textiles and surface treatments on blistering using a novel simulant

Friction blisters occur when shear loading causes the separation of dermal layers. Consequences range from minor pain to life-threatening infection. Past research in blister formation has focused on in vivo experiments, which complicate a mechanics-based study of the phenomenon. A Synthetic Skin Simulant Platform (3SP) approach was developed to investigate the effect of textile fabrics (t-shirt knit and denim cottons) and surface treatments (dry and wet lubricants) on blister formation. 3SP samples consist of bonded elastomeric layers that are surrogates for various dermal layers. These layers display frictional and mechanical properties similar to their anatomical analogues. Blistering was assessed by the measurement of deboned area between layers. Denim caused greater blistering than did the t-shirt knit cotton, and both lubricants significantly reduced blister area and surface damage. A triglyceride-based lubricant had a more pronounced effect on blister reduction than corn starch. The triglyceride lubricant used with t-shirt knit cotton resulted in no blisters being formed. The performance of the 3SP approach follows previously reported frictional behavior of skin in vivo. The results of textile and surface treatment performance suggest that future 3SP iterations can be focused on specific anatomical sites based on application type.

Spray deposited multilayered dielectric elastomer actuators

Dielectric elastomer electroactive polymers are an emerging class of actuation technology which is inherently compliant and capable of large actuation stresses and strains. Despite promising performance characteristics, their fabrication has been inhibited by two significant factors: (i) the requirement for consistently thin dielectric layers, to minimise activation voltages; (ii) automated production of multilayered configurations, to increase the actuation power. This paper presents a robust, low-cost fabrication technique that overcomes these issues by utilising optimised spray deposition. Spray deposition of silicone dielectric elastomer actuators (DEAs) offers numerous benefits including scalability, flexibility for different DEA configurations and multilayered assembly with a high degree of automation. A predictive model based on the Gaussian distribution is used to characterise the profile of deposited elastomer layers for principal fabrication parameters. This model enables individual dielectric layers to be composed from multiple parallel depositions, which greatly increases scalability as demonstrated by fabricated DEA films with planar dimensions from 25 mm 2 to over 10,000 mm 2. Using the predictive model, a new figure of merit is introduced for analyzing DEA film profiles by considering the estimated mean Maxwell stress that is feasible for a specific dielectric breakdown strength. The analysis suggests that compared to a single deposition, a film composed of four parallel depositions will increase the maximum characteristic DEA dimension by an order of magnitude, while producing a comparable mean Maxwell stress. A significant advantage of the presented spray deposition technique is the semi-automated layering process, creating stratified solid-state actuators. By eliminating the stacking of layers from the fabrication process, inherent electrical isolation, good layer-to-layer bonding and capacity for more complex 3D geometries is achieved. A proof-of-concept multilayer unimorph and stack DEA is presented to validate the fabrication technique through static and dynamic displacement tests.

Stability of fiber-reinforced elastomeric bearings in an unbonded application

Stable unbonded fiber-reinforced elastomeric isolators (SU-FREIs) are a viable device for seismic mitigation purposes in low-rise structures. SU-FREI bearings consist of alternating layers of elastomer and fiber fabric with shape factor and aspect ratio such that stable rollover occurs during lateral displacement. This study investigates the stability of SU-FREI bearings through experimental testing. Two experimental test procedures are employed. The first investigates stability during incrementally increasing axial loads under lateral cyclic excitation, and the second investigates the ultimate shear properties of SU-FREI bearings through monotonic lateral displacement under design axial load. Dynamic stability testing reveals that the tested SU-FREIs remain stable at axial loads significantly greater than the design load under a wide range of cyclic lateral displacement amplitudes. In addition, an increase in axial load results in lower effective stiffness and greater effective damping in the SU-FREI bearings. Although rollout instability was not encountered during ultimate shear property testing, shear tests provide insight into the stiffening effect encountered as the originally vertical faces of the SU-FREI bearings make contact with the top and bottom contact supports.

Preparation, characterization and frictional properties of silane self-assembled elastomeric nanocomposite polymer layers

A novel surface modification method was proposed to improve the tribological property of Si. Multilayers were grown on Si(100) substrate by self-assembling monolayer (SAMs) method and filtered catholic vacuum arc (FCVA) technique. The film composition and structure were characterized by using x-ray photoelectron spectroscope (XPS) and Raman spectroscopy (Raman). Surface morphology and the roughness were also analyzed by an atomic force microscope (AFM) and a scanning electron microscopy (SEM). The frictional behaviors of the films were evaluated by a UMT tester. Results showed that elastomeric nanocomposite monolayer prepared by SAM was uniformly distributed and isotropy, and the diamond-like carbon (DLC) film was successfully deposited by the FCVA technique. The friction coefficients of the prepared samples were in the range of 0.108–0.188. Furthermore, the friction coefficient slightly increased but the surface quality of the wear trace was improved after adding the copolymer elastomeric macromolecules SEBS on aminopropyl-triethoxysilane (APS) layer due to the inherent long chain of SEBS which abated the immediate impulsion at the interface and changed the kinetic energy into elastic potential energy, and stored it in SEBS.

Polychloroprene: a new material for Dielectric Elastomer Actuators.

ABSTRACTDielectric Elastomer Actuators (DEAs) consist of an elastomeric layer sandwiched between two compliant electrodes. An electric field applied between the two electrodes will lead to a compression of the elastomer due to the Maxwell’s pressure. DEA can be used for many active applications such as pumps, muscles and so on, where the voltage drives the motion, but they can also operate inversely for energy harvesting or for sensor applications, when the displacement of charges due to a change in thickness is stored or detected. Energy harvesting systems like buoys using wave energy or shoe soles extracting energy from walking have been demonstrated. In this contribution we investigate polychloroprene (CR) as a new material for DEA and describe its potential for use in energy harvesting. To this end, a full characterization of the material properties was undertaken. We find that the very high permittivity combined with good mechanical properties makes this material a promising novel candidate for the energy harvesting application.

Tailoring the Surface Properties of Silicone Elastomers to Improve Adhesion of Epoxy Topcoat

Two modification routes have been applied to control the surface properties of spin-coated and screen-printed poly(dimethylsiloxane) (PDMS) layers and to improve their adhesion to a photopatternable epoxy resin topcoat. The first route is based on the optimization of low-pressure oxygen and ammonia plasma treatments to generate acidic or basic reactive surface groups capable of forming covalent bonds with the epoxy groups of the topcoat. The main disadvantage of these fast and practicable processes is the instability of the modification effects. Therefore, the plasma-activated PDMS surfaces were used for subsequent 'grafting to' procedures with reactive polymers. The functional surface groups generated by oxygen or ammonia plasma treatments of PDMS (SiOH, OH, COOH and NH2) were used as anchors to graft epoxy group containing homopolymers and copolymers as well as maleic anhydride copolymers. All of grafted materials provided thin barrier layers that prevented the hydrophobic recovery of the modified PDMS surface. A very promising concept to tailor the surface properties of PDMS is the grafting of epoxy group containing methacrylate copolymers. Depending on the molar ratio of the monomers used the epoxy groups will act mainly as anchor groups. The surface properties of the grafted layer will, then, be controlled by the functionality of the second comonomer. In order to study the effect of the surface modifications on the surface properties of the silicone elastomer layers we used a combination of various surface-sensitive characterization techniques, namely, X-ray photoelectron spectroscopy (XPS), contact angle and electrokinetic measurements as well as roughness analysis. Additionally, pull-off tests were carried out to quantify the effect of the surface modification on the adhesion between an epoxy resin and PDMS.

Microfluidic immobilization of physiologically active Caenorhabditis elegans

We present a protocol for building and operating a microfluidic device for mechanical immobilization of Caenorhabditis elegans in its physiologically active state. The system can be used for in vivo imaging of dynamic cellular processes such as cell division and migration, degeneration, aging and regeneration, as well as for laser microsurgery, Ca2+ imaging and three-dimensional microscopy. The device linearly orients C. elegans, and then completely restrains its motion by pressing a flexible membrane against the animal. This technique does not involve any potentially harmful anesthetics, gases or cooling procedures. The system can be installed on any microscope and operated using only one syringe and one external valve, making it accessible to most laboratories. The device fabrication begins by patterning photoresist structures on silicon wafers, which are then used to mold features in elastomeric layers that are thermally bonded to form the device. The system can be assembled within 3 d.

Modeling of electrically actuated elastomer structures for electro-optical modulation

A transparent elastomer layer sandwiched between two metal electrodes deforms upon voltage application due to electrostatic forces. This structure can be used as tunable waveguide. We investigate structures of a polydimethylsiloxane (PDMS) layer with 1–30 μm thickness and 40 nm gold electrodes. For extended electrodes the effect size may be calculated analytically as a function of the Poisson ratio. A fully coupled finite-element method (FEM) is used for calculation of the position-dependent deformation in case of structured electrodes. Different geometries are compared concerning actuation effect size and homogeneity. Structuring of the top electrode results in high effect magnitude, but non-uniform deformation concentrated at the electrode edges. Structured bottom electrodes provide good compromise between effect size and homogeneity for electrode widths of 2.75 times the elastomer thickness.

Research on Power Generation of Electroactive Acrylic Elastomer

The power generation characteristics of electroactive acrylic elastomer (EAE) were studied by experiments based on theoretical analysis. The generator mode theory fundamentals of EAE were discussed and studied. A power conversion control system for EAE was designed. The experimental results show that energy generated as nearly incompressible elastomer layers increase in area and decrease in thickness when EAE stretched, and power generated when EAE relaxed. The voltage of generation increased with the bias voltage increasing. The experimental results accorded with analytical model and lay the foundation for generator of EAE.

Microtextured Surfaces with Gradient Wetting Properties

Patterned surfaces with microwrinkled surface structures were prepared by thermally evaporating thin aluminum (10-300 nm thick) (Al) layers onto thick prestrained layers of a silicone elastomer and subsequently releasing the strain. This resulted in the formation of sinusoidal periodic surface wrinkles with characteristic wavelengths in the 3-42 μm range and amplitudes as large as 3.6 ± 0.4 μm. The Al thickness dependence of the wrinkle wavelengths and amplitudes was determined for different values of the applied prestrain and compared to a recent large-amplitude deflection theory of wrinkle formation. The results were found to be in good agreement with theory. Samples with spatial gradients in wrinkle wavelength and amplitude were also produced by applying mechanical strain gradients to the silicone elastomer layers prior to deposition of the Al capping layers. Sessile water droplets that were placed on these surfaces were found to have contact angles that were dependent upon their position. Moreover, these samples were shown to direct the motion of small water droplets when the substrates were vibrated.

Adhesives with patterned sub-surface microstructures

Inspired by the complex hierarchical structures found in natural adhesives, we have embedded monolithic stack of several microchannels inside soft layers of silicon elastomers. These channels are rectangular in cross-section and their internal surfaces are textured with microscopic pillars arranged in regular arrays. Displacement controlled indentation experiment on these adhesives shows that adhesion and debonding occur not only on the surface of the adhesive but also at the interfaces of the embedded layers. These textures on the channel surface enhance adhesion via “crack arrest and initiation” mechanism. Furthermore, the adhesive is treated by hydrochloric acid so that the siloxane bonds present on the exposed surfaces are hydrolyzed generating silanol groups which on two contacting surfaces increase the effect of self adhesion hysteresis. Thus, the combined effect of surface texturing is integrated with the chemical treatment to increase adhesion.

Increasing pumping efficiency in a micro throttle pump by enhancing displacement amplification in an elastomeric substrate

Fluid transport is accomplished in a micro throttle pump (MTP) by alternating deformation of a micro channel cast into a polydimethylsiloxane (PDMS) elastomeric substrate. The active deformation is achieved using a bimorph PZT piezoelectric disc actuator bonded to a glass diaphragm. The bimorph PZT deflects the diaphragm as well as alternately pushing and pulling the elastomer layer providing displacement amplification in the PDMS directly surrounding the micro channel. In order to improve pumping rates we have embedded a polymethylmethacrylate (PMMA) ring into the PMDS substrate which increases the magnitude of the displacement amplification achieved. FEM simulation of the elastomeric substrate deformation predicts that the inclusion of the PMMA ring should increase the channel deformation. We experimentally demonstrate that inclusion of a PMMA ring, having a diameter equal to that of the circular node of the PZT/glass/PDMS composite, increases in the throttle resistance ratio by 40% and the maximum pumping rate by 90% compared to an MTP with no ring.

COMPARISON OF STRESS RELIEF MECHANISMS OF METAL FILMS DEPOSITED ON LIQUID SUBSTRATES BY THERMAL EVAPORATING AND SPUTTERING

Various metal film systems, deposited on liquid (silicone oil) substrates by thermal evaporating and DC-magnetron sputtering methods, have been successfully fabricated and the stress relief mechanisms are systematically studied by analyzing the characteristic surface morphologies. The experiment shows that the evaporating metal films can move on silicone oil surfaces freely due to the nearly zero adhesion of solid–liquid interface, which results in spontaneous formation of ordered surface patterns with a characteristic sandwiched structure driven by the internal stress. For the sputtering metal film system, however, the top surface of silicone oil can be modified to form an elastomeric polymer layer on the liquid substrate during deposition. Subsequent cooling of the system creates a higher compressive stress in the film, which is relieved by buckling of the film to form periodic wavy structures because the adhesion of solid–elastomer interface is quite strong.

Preparation and properties of polyurethane‐coated talcum/polypropylene composite materials

AbstractIn order to improve the toughness of polypropylene (PP) and expand its applications, a layer of polyurethane (PU) elastomer was coated on the surface of ultrafine talcum powder by an in‐situ synthesis method. In this way, an organic‐inorganic composite particle was formed. Then the surface‐treated talcum powder was mixed with melted PP to prepare PP composite materials through extrusion, granulation, and injection molding. Infrared spectral characterization and energy‐dispersive X‐ray analysis showed that there was a layer of PU elastomer on the surface of the talcum powder. Impact fracture analysis indicated that there was good compatibility between the talcum powder and the PP matrix. With the incorporation of PU elastomer coated on the surface of talcum powder, the toughness of PP was significantly improved, while the tensile strength decreased slightly. The optimum properties of the composite material were obtained when the weight fraction of talcum powder was 20% and the PU coating coverage was 25%. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers

Microchannel Induced Surface Bulging of a Soft Elastomeric Layer

When a wetting liquid fills in microchannels embedded inside a thin elastomeric layer, the surface of the layer does not remain smooth but bulges out in the vicinity of the channels. The height of the bulge depends on the deformability of the layer and the surface tension of liquid; in addition, it depends also on the vertical location of the channel from the surface of the layer and the channel diameter. While, for liquids of low viscosity ∼500 cP bulging occurs instantaneously, for liquids of high viscosity ∼4000 cP, it occurs over a period of time. Concomitant to bulging of the layer, the cross section of the channel alters too in its shape and size suggesting that the elastic energy penalty associated with the bulging of the layer is supplied by the interfacial energy of the liquid–air and liquid–solid interfaces. Local bulging of the layer alters also its local deformability which is demonstrated by contact mechanics experiments: indentation with a spherical indenter yields a non-circular contact area, the shape and size of which vary with the depth of indentation. Thus, sub-surface microchannels can be suitably used for generating surface patterns on the elastomer and also for modulating its modulus.

Structured hydrophilic domains on silicone elastomers

The controlled generation of hydrophilic structures within hydrophobic polymers can be challenging. Very few examples of such structures have been described for silicones. We now report that such structures can be encoded in the air-contacting layer of a silicone elastomer by the formation of silica domains from tetraethoxysilane, optionally in the presence of poly(ethylene glycol) (PEG), using a surface active aminopropylsilicone catalyst and moisture cure. The control of the relative modulus at the upper versus lower layers and the degree and type of hydrophilic structuring requires control over the efficiency of delivery of water to the core of the pre-elastomer, which is facilitated by the surface active catalyst and may additionally be manipulated by the addition of PEG.

Structured metal films on silicone elastomers

The ability to control surface morphology at nano- and micrometre length scales is required in many applications. It has previously been demonstrated that surface wave patterns are spontaneously generated when heated, layered metal-on-silicone materials are cooled, because of the stress that builds up between two materials of different modulus and coefficients of thermal expansion. We have examined the behaviour of metals sputtered on silicone elastomer surfaces and found that, unlike previous reports, the patterns are encoded by the first 5 nm of the coating layer. While gold coatings did not induce wave formation, platinum and tungsten led to single wavelength (peak to peak distance between adjacent waves) patterns, while chromium and carbon gave surfaces with two strikingly different wavelengths (0.5 μm to 4 μm). Amplitudes (difference between wave peak and trough, 8 nm to 950 nm) of the wavelengths correlated reasonably well with coating thickness. Key to controlling the patterns is the fact that only a very thin upper layer of the silicone elastomer becomes heated during the sputtering process.

MEMS-based contact stress field measurements at a rough elastomeric layer: local test of Amontons’ friction law in static and steady sliding regimes

We present the results of recent friction experiments in which a MEMS-based sensing device is used to measure both the normal and tangential stress fields at the base of a rough elastomer film in frictional contact with smooth, rigid, glass indentors. We con- sider successively multicontacts under (i) static normal loading by a spherical indentor and (ii) frictional steady sliding conditions against a cylindrical indentor, for an increas- ing normal load. In both cases, the measured fields are compared to elastic calculations assuming (i) a smooth interface and (ii) Amontons' friction law. In the static case, signifi- cant deviations are observed which decrease with increasing load and which vanish when a lubricant is used. In the steady sliding case, Amontons' law reproduces rather satisfacto- rily the experiments provided that the normal/tangential coupling at the contact interface is taken into account. We discuss the origin of the difference between the Amontons fields and the measured ones, in particular the effect of the finite normal and tangential compli- ances of the multicontact interface.