Acrylic Elastomer Research Articles

A spontaneously healable robust ABA tri-block polyacrylate elastomer with a multiphase structure

Multiphase structural designed acrylate elastomer capable of autonomously repairing structures and restoring functions upon damage was developed via an effective method, realizing good mechanical properties.

High humidity sensing by ‘hygromorphic’ dielectric elastomer actuator

Many capacitive or resistive humidity sensors cannot accurately measure high humidity because of surface water condensation and saturation of hygrosopic material in the sensors. Here, we propose a novel method of high humidity measurement using a ‘hydromorphic’ dielectric elastomer actuator (DEA). This novel humidity sensor consists of a ‘relatively water-inert’ acrylic dielectric elastomer layer (3M VHB 4910) sandwiched by a pair of hygroscopic polymer electrodes. The hygroscopic polymer electrodes are made of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS); they become softer upon moisture absorption while enabling moisture permeation into the dielectric elastomer substrate during electrical activation and read-out. While the dielectric elastomeric actuation (under constant voltage) enlarged with increasing humidity, the current leaked through it rose more significantly. This suggests a strong humidity dependence of dielectric resistivity. Experimental correlation showed the dielectric resistance be a piecewise linear function of humidity. Further, this DEA-based humidity sensor remained working when both its electrodes were sprayed with a mist of water droplets.

Effects of Thinner Compliant Electrodes on Self-Clearability of Dielectric Elastomer Actuators

A metalized plastic capacitor stands a higher chance to clear faults when embodied with thinner electrodes. However, it is not clear whether the same thickness effect applies to carbon-based compliant electrodes in clearing the defects in dielectric elastomer actuators (DEA). This experimental study showed that charcoal-powder compliant electrodes act like fuses and current limiters to successfully clear the defects of an acrylic dielectric elastomer actuator, provided a very thin electrode coating. For example, DEAs with 3 μm thick (average) charcoal-powder electrodes fast cleared faults and sustained high breakdown strength (300 to 400 MV/m), but the ones with thicker charcoal-powder electrodes (30 μm thick on average) succumbed to persisting breakdowns in a weaker electric field (200 to 300 MV/m). Thermo-gravitational analysis and differential scanning calorimetry showed that dielectric elastomer (3M VHB F9473PC) started to ignite at 350 ∘C, and charcoal powders (Mungyo charcoal pastel MP-12CP) started burning above 450 ∘C. This confirmed that flash ignition and its damping of charcoal powder is possible only with a very thin electrode coating relative to acrylic elastomer substrate thickness. Too thick of a charcoal-powder coating could lead to the spread of burning beyond the initial flash point, and incomplete burning that punctures the dielectric layer but shorts across opposite electrodes. With this insight, one can design self-clearable electrodes to improve the dielectric strength of dielectric elastomer actuators.

Rapid Fabrication Method for Soft Devices Using Off‐the‐Shelf Conductive and Dielectric Acrylic Elastomers

Herein, a method to fabricate soft and stretchable devices rapidly by using only commercially available conductive and dielectric elastomer materials with the aid of laser cutting and a layer‐by‐layer process is presented. The conductive acrylic elastomer is first characterized in terms of its mechanical and electrical characteristics and then applied to various devices, such as soft electrostatic actuators, strain sensors, and stretchable pumps. These devices, which can be fabricated within 15–30 min, exhibit areal actuated strains of up to 163.0 ± 1.0% at 4 kV in the actuators, a highly linear response (R2 = 0.995) for strains of up to 100% with a gauge factor of 0.98 in the sensors, and an output pressure of 0.11 ± 0.08 kPa and flow rate of 20 ± 4 μL s−1 at 7 kV in the pumps. These performance characteristics are comparable to those reported in the literature. To demonstrate the potential for soft robotic applications, a wearable device is developed (fabrication time of ≈15 min), which exhibits multiple functionalities, such as detection of deformations of a human finger, haptic presentation through vibration, and electroadhesion. The results illustrate the high applicability of the presented strategy in soft intelligent systems.

Triboelectric and Piezoelectric Nanogenerators for Future Soft Robots and Machines.

SummaryThe triboelectric nanogenerator (TENG) and piezoelectric nanogenerator (PENG) are two recently developed technologies for effective harvesting of ambient mechanical energy for the creation of self-powered systems. The advantages of TENGs and PENGs which include large open-circuit output voltage, low cost, ease of fabrication, and high conversion efficiency enable their application as new flexible sensors, wearable devices, soft robotics, and machines. This perspective provides an overview of the current state of the art in triboelectric and piezoelectric devices that are used as self-powered sensors and energy harvesters for soft robots and machines; hybrid approaches that combine the advantages of both mechanisms are also discussed. To improve system performance and efficiency, the potential of providing self-powered soft systems with a degree of multifunctionality is investigated. This includes optical sensing, transparency, self-healing, water resistance, photo-luminescence, or an ability to operate in hostile environments such as low temperature, high humidity, or high strain/stretch. Finally, areas for future research directions are identified.

Fabrication of radiation crosslinked and MWCNT reinforced ethylene acrylic elastomer nanocomposites: Evaluation of mechanical, dynamic mechanical, thermal and dielectric properties

Abstract The electron beam (EB) crosslinked and MWCNT reinforced ethylene acrylic elastomer (AEM) nanocomposites have been developed with varying the EB dose (50–250 kGy) and MWCNT loading level (0–8 parts per hundred gram of rubber (phr)) for various applications. The crosslink density and gel fraction significantly increase with increase in EB dose and MWCNT loading which ensures the radiation sensitizing effects of MWCNT. The chain scission to crosslink density has been check by using Flory–Rehner relationship at room temperature and the decrease in slope of the plots again confirms the predominance of crosslinking over chain scission at higher EB dose. The dispersion patterns of the MWCNT phase in bulk AEM matrix have been analyzed by using FESEM technique. Uniformly dispersed MWCNT with closely spaced network structures has been found in the FESEM photomicrographs at 4 phr loading level. The tensile strength and tensile modulus are extensively increased with increasing EB dose and up to 6 phr of MWCNT loading which ensures the reinforcing nature of MWCNT. Increase in tensile modulus (M100) and storage modulus (E ') with increase in EB dose and MWCNT indicates the absorption of applied load due to decrease in free volume of the systems. Increase in decomposition temperature with MWCNT loading of the nanocomposites has been confirmed from the thermal analysis. The significant increase in dielectric permittivity (eʹ) on increasing the MWCNT loading is mostly due to the increase accumulation of charge particles at the interface as well as increase in polarizable dipoles. The improvement in AC conductivity (σac) of these nanocomposites is mostly due to the easy electron tunnelling and hopping transport processes executed through the constructed networks by MWCNT in the bulk as well as interface.

Effect of PMMA/Silica Hybrid Particles on Interfacial Adhesion and Crystallization Properties of Poly(lactic acid)/Block Acrylic Elastomer Composites.

Poly(lactic acid) (PLA) is a relatively brittle polymer, and its low melt strength, ductility, and thermal stability limit its use in various industrial applications. This study aimed to investigate the effect of poly(methyl methacrylate) (PMMA) and PMMA/silica hybrid particles on the mechanical properties, interfacial adhesion, and crystallization behavior of PLA/block acrylic elastomer. PLA/block acrylic elastomer blends exhibit improved flexibility; however, phase separation occurs between PLA and block acrylic elastomer domains. Valid time-temperature superposition (TTS) measurements of viscoelastic behavior were obtained and exhibited interfacial adhesion with the addition of PMMA or PMMA/silica in PLA/block acrylic elastomer blends. In particular, the phase separation temperature was increased by the incorporation of PMMA/silica hybrid particles, which suggests a potential role for these particles in improving the phase stability. In addition, PMMA inhibits crystallization, while PMMA/silica acts as a nucleating agent, thus increasing the crystallization rate and crystallinity degree.

Environmentally friendly synthesis route of terpolymers derived from alkyl acrylates and their performance as additives for liquid hydrocarbon products

In this work acrylic terpolymers with different alkyl radicals were synthesized to find out the alkyl radicals with the lowest average carbon number in poly (alkyl acrylate) (PAA) samples to reach the highest viscosity index with lower concentration of the polymer. Firstly, esters of acrylic monomers are synthesized with a heteroazeotrope forming solvent not miscible with methanol, alleviating the separation process. It was followed the syntheses of terpolymers to be evaluated the solubility of them in petroleum products. After being conducted the solubility tests of these polymers in several lube oil base stocks, the suitable PAA with different molecular weights were chosen and sent them for ultrasonic testing to check their shear stability indices or the stability to mechanical destruction. Found the polymer with boundary solubility in lube oil base stocks in order to attain the highest viscosity index and mechanical destruction stability. Found low temperature, electrical conductivity and wear resistance properties of GTL (Gas to Liquid) diesel dosed with these additives. Laboratory equipment’s illustrations as well as an environmentally friendly synthesis route of the copolymers were given.

Soft sensors and actuators based on conductive acrylic elastomer

Soft sensors and actuators based on conductive acrylic elastomer

Dynamic cell culture device using electroactive polymer actuators with composite electrodes to transfer in-plane mechanical strain to cells

Living tissues in the body receive various types of stimuli, including mechanical strain, pressure, and varied chemical environments. In contrast, conventional cell cultures are processed under in vitro conditions, which are not similar to the actual body’s environment. To precisely simulate the human body environment, a dynamic cell culture device capable of applying mechanical stimulation to cells is needed. In this study, an acrylic dielectric elastomer electroactive polymer (EAP), is introduced as a driving component for a dynamic cell culture device with a simple structure. The device is composed of separated upper and lower modules with a driving film at the center, By assembling these components, the electrodes on the surface of the driving film are isolated but still connected by columns that can transfer the deformation of the driving apparatus to the culture membrane. The culturing performance of cells according to the mechanical stimuli was experimentally investigated and compared. Tensile strain was found to provide the highest improvement in cell development rate, reaching up to 32.3%. These results highlight the utility of EAPs for compact and biocompatible dynamic cell culture device design.

Electrically tunable directional light scattering from soft thin membranes.

The possibility of electrically tuning the scattering of light from surfaces by dynamically varying their properties is desirable for controllable transparency devices and diffusion filters. As a difference from state-of-the-art approaches where scattering is changed isotropically, this paper presents the first smart-material-based technology enabling electrical modulations in a single or multiple directions, which can be selected dynamically. The effect is achieved from thin soft membranes with transparent PEDOT:PSS coatings, which are electrically deformed along a single or multiple axes, using dielectric elastomer actuation. Anisotropic scattering is induced by electrically tuning the formation of directional surface wrinkles. As a proof of concept, a bi-directional device is obtained by overlapping two 90°-shifted mono-directional layers that can be controlled independently. According to the activation of the layers, light can be scattered along either direction, as well as both of them. Prototypes made of an acrylic elastomer were demonstrated with mono- and bi-directional operations. Devices with a window-to-total area ratio of 1:4 also showed a maximum electrical reduction of optical transmittance from 75% to 4%. This functionality and possible extensions to more than two controllable directions suggest applicability as electrically controllable anisotropic light diffusers for dynamic light shaping, as well as tunable transparency surfaces.

On the two-potential constitutive modeling of dielectric elastomers

This work lays out the two-potential framework for the constitutive modeling of dielectric elastomers. After its general presentation, where the constraints imposed by even electromechanical coupling, material frame indifference, material symmetry, and entropy imbalance are all spelled out, the framework is utilized to put forth a specific constitutive model for the prominent class of isotropic incompressible dielectric elastomers. The model accounts for the non-Gaussian elasticity and electrostriction typical of such materials, as well as for their deformation-enhanced shear thinning due to viscous dissipation and their time-dependent polarization due to electric dissipation. The key theoretical and practical features of the model are discussed, with special emphasis on its specialization in the limit of small deformations and moderate electric fields. The last part of this paper is devoted to the deployment of the model to fully describe the electromechanical behavior of a commercially significant dielectric elastomer, namely, the acrylate elastomer VHB 4910 from 3M.

Styrenic-Rubber Dielectric Elastomer Actuator with Inherent Stiffness Compensation

Up to date, Dielectric Elastomer Actuators (DEA) have been mostly based on either silicone or acrylic elastomers, whereas the potential of DEAs based on inexpensive, wide-spread natural and synthetic rubbers has been scarcely investigated. In this paper, a DEA based on a styrene-based rubber is demonstrated for the first time. Using a Lozenge-Shaped DEA (LS-DEA) layout and following a design procedure previously proposed by the authors, we develop prototypes featuring nearly-zero mechanical stiffness, in spite of the large elastic modulus of styrenic rubber. Stiffness compensation is achieved by simply taking advantage of a biaxial pre-stretching of the rubber DE membrane, with no need for additional stiffness cancellation mechanical elements. In the paper, we present a characterization of the styrene rubber-based LS-DEA in different loading conditions (namely, isopotential, isometric, and isotonic), and we prove that actuation strokes of at least 18% the actuator side length can be achieved, thanks to the proposed stiffness-compensated design.

Toughened Composite of Polycarbonate/Wollastonite with Styrene–Butadiene Copolymer and Ethylene‐Methyl Acrylate Elastomers

AbstractTwo kinds of elastomers, styrene–butadiene copolymer (SBC) and ethylene‐methyl acrylate (EMA) were compounded by melt mixing wollastonite into polycarbonate (PC). The result demonstrated that EMA‐filled composites showed better mechanical properties compared to SBC‐filled composites, particularly elongation and impact strength. We observed a 53% increase in Izod impact strength, that is, 5.3‐fold increase in elongation of the PC/wollastonite/EMA composite by incorporating (7%) EMA. The composite also has an encouraging blending effect with a lower decrease in tensile strength of only 13%. Incorporation of EMA and SBC decreased the glass‐transition temperature (Tg) of the system from 148°C to 141°C. The rheological behavior of composites was also examined using a parallel plate rheometer. By increasing the SBC and EMA elastomer content, we observed an increase in shear viscosity, storage, and loss modulus of the composites. Scanning electron micrographs were used to study the phase structure of Izod‐fractured samples. A multiphase morphology was seen with good dispersion of wollastonite and EMA granules in the PC matrix.

Enhanced Heat Resistance and Adhesive Strength of Styrene-Acrylic Triblock Copolymer Elastomers by Incorporating Acrylic Acid.

Herein, we present an industrially applicable strategy to enhance the heat resistance and adhesive properties of ABA triblock copolymer-based elastomers composed of styrene (St) and n-butyl acrylate (nBA) by incorporating acrylic acid (AA) at different segments. Three types of triblock copolymers, namely, poly(St-r-AA)-b-poly(nBA)-b-poly(St-r-AA), poly(St)-b-poly(nBA-r-AA)-b-poly(St), and poly(St)-b-poly(nBA)-b-poly(St), were synthesized by reversible addition–fragmentation chain-transfer (RAFT) polymerization. Large-scale RAFT polymerization afforded industrially applicable AA-containing triblock copolymers with moderate molecular weights and predetermined comonomer compositions (St/nBA/AA = 15/83/2–24/73/3, number-average molecular weight (Mn) = 30,000–110,000, and resulting product > 200 g). The heat resistance and pressure-sensitive adhesive properties of the triblock copolymers were evaluated. Among them, poly(St-r-AA)-b-poly(nBA)-b-poly(St-r-AA), having poly(nBA) as the middle soft segment and poly(St-r-AA) as hard segments at both ends, exhibited excellent heat creep resistance and increased adhesiveness to stainless steel. The feasibility to manipulate the heat resistance and adhesive properties by incorporating AA units into hard and soft segments, in addition to the ease of operation, high block efficiency, and metal-free nature owing to the RAFT process, is highly beneficial for practical applications of these copolymers.

Characterizing chain-end structures formed during initiation reactions of radical polymerization for MMA-St-BA terpolymer using pyrolysis-gas chromatography/atmospheric pressure chemical ionization high-resolution time-of-flight mass spectrometry.

Analyzing polymer end groups using pyrolysis (Py) gas chromatography/mass spectrometry (GC/MS) in multi-component polymer samples is not an easy task because of the insufficient sensitivity, selectivity, and mass resolution of conventional Py-GC/MS systems. A new Py-GC/MS system using an atmospheric pressure chemical ionization (APCI) source combined with high-resolution time-of-flight mass spectrometry (TOFMS) was used for end-group analysis of a methyl methacrylate (MMA)-styrene (St)-butyl acrylate (BA) terpolymer (P (MMA-St-BA)), which was radically polymerized using 2,2'-azobis(2-methylbutyronitrile) (AMBN) as an initiator. Five possible pyrolyzates, comprising an AMBN fragment and a monomer unit, formed during the initiation reactions from one of the three types of end groups, were selectively detected and exclusively identified in their respective extracted ion chromatograms for molecule-related ions, such as M+ and [M + H]+ , with a narrow mass window of ±2 milli m/z units. It was demonstrated that Py-APCI-TOFMS is a powerful technique to characterize in detail the complex end groups in multi-component polymer samples, because of the soft ionization nature of APCI and the high mass resolution of TOFMS.

Improving the performance of dielectric-elastomer actuators at elevated operating temperatures by means of thermal softening

Dielectric elastomer devices operate on the principle of Maxwell stress and their operating performance significantly rely on the elastomer and compliant electrode’s electrical and mechanical properties. This paper reports that performing actuation tests at elevated temperatures resulted in an enhanced performance due to the reduction of Young’s modulus and the increase of dielectric permittivity. As a result, considerably higher isometric forces and isotonic strains were achieved above the ambient operating temperature. For actuators made of silicone, polyurethane and acrylic elastomers, 166%, 70% and 266% higher isometric forces and 450%, 250% and 54% higher isotonic strains were observed, respectively, when tested at the temperature of 100 °C in comparison to ambient temperature values using the same operating voltages. Values of up to 0.4 J kg−1 and 3.1 W kg−1 were achieved for the work and power outputs per mass, respectively, on a silicone elastomer driven with a voltage of 1.5 kV at a temperature of 100 °C.

Adhesion Performance and Recovery of Acrylic PSA with Acrylic Elastomer (AE) Blends via Thermal Crosslinking for Application in Flexible Displays.

Acrylic pressure-sensitive adhesive (PSA) is used to fix each layer of a flexible display. Acrylic PSA needs to satisfy specific elongation and recovery requirements so that reliability of the flexible display can be achieved. For this reason, we aimed to design an acrylic PSA/acrylic elastomer (AE) blend and to study how some viscoelastic and adhesion properties are influenced by the AE content into the mixed, blended system. Samples were characterized by UV–Vis spectrophotometry for transmittance, texture analysis for adhesion performances, and dynamic mechanical analysis (DMA) for recovery and viscoelasticity. When acrylic PSA/AE was simply blended, the adhesion performance changed due to the influence of the long molecular chains of AE. Based on this result, the AE content was fixed at 10 wt %, and acrylic PSA prepolymer was crosslinked at different concentrations of crosslinking agent. Peel strength and probe tack decreased as the concentration of crosslinking agent increased, as reported in previous studies. On the other hand, as the content of the crosslinking agent increased, recovery characteristics were improved. Additionally, as the content of the crosslinking agent increased, the storage modulus also increased, although the glass-transition temperature was not affected. According to these findings, we successfully proved the possibility of using AE to adjust adhesion performance and recovery of acrylic PSA for designing flexible displays.

Sensitivity Improvement of Highly Stretchable Capacitive Strain Sensors by Hierarchical Auxetic Structures.

Highly stretchable sensors that can detect large strains are useful in deformable systems, such as soft robots and wearable devices. For stretchable strain sensors, two types of sensing methods exist, namely, resistive and capacitive. Capacitive sensing has several advantages over the resistive type, such as high linearity, repeatability, and low hysteresis. However, the sensitivity (gauge factor) of capacitive strain sensors is theoretically limited to 1, which is much lower than that of the resistive-type sensors. The objective of this study is to improve the sensitivity of highly stretchable capacitive strain sensors by integrating hierarchical auxetic structures into them. Auxetic structures have a negative Poisson's ratio that causes increase in change in capacitance with applied strains, and thereby improving sensitivity. In order to prove this concept, we fabricate and characterize two sensor samples with planar dimensions 60 mm × 16 mm. The samples have an acrylic elastomer (3M, VHB 4905) as the dielectric layer and a liquid metal (eutectic gallium-indium) for electrodes. On both sides of the sensor samples, hierarchical auxetic structures made of a silicone elastomer (Dow Corning, Sylgard 184) are attached. The samples are tested under strains up to 50% and the experimental results show that the sensitivity of the sensor with the auxetic structure exceeds the theoretical limit. In addition, it is observed that the sensitivity of this sensor is roughly two times higher than that of a sensor without the auxetic structure, while maintaining high linearity (R2 = 0.995), repeatability (≥104 cycles), and low hysteresis.

Colloidal films of SiO2 in elastomeric polyacrylates by photopolymerization: A strain sensor application

Thin layer SiO2 colloidal films show angle-dependent coloration (iridescence) based on constructive interference, rather than absorption, without the existence of pigments. The transfer of thin layered colloidal film into a transparent elastomeric matrix maintaining its color may allow the fabrication of colorimetric strain sensors. In this study, trilayer SiO2 colloidal films were prepared by Langmuir-Blodgett deposition using a binary solvent system (chloroform/methanol) and this structure is successfully transferred into poly(ethylene glycol) phenyl ether acrylate elastomer via lateral capillary force. The resulting composite films exhibit iridescence depending on the particle size, therefore, film thickness as similar in mere colloidal films with a slight difference due to change in efficient refractive index (neff). Uniaxial extension of the composite film up to 50 % strain causes a remarkable linear shift in reflection signal from 568 to 496 nm. The change in thickness of the composite film accordingly intercolloidal distance normal to the application of mechanical stretching causes variation of the reflection of light.