Polyacrylate Elastomers Research Articles

A high-response-frequency bimodal network polyacrylate elastomer with ultrahigh power density under low electric field

Dielectric elastomers, used as driver modules, require high power density to enable fast movement and efficient work of soft robots. Polyacrylate elastomers usually suffer from low power density under low electric fields due to limited response frequency. Here, we propose a bimodal network polyacrylate dielectric elastomer which breaks the intrinsic coupling relationship between dielectric and mechanical properties, featuring relatively high dielectric constant, low Young’s modulus, and wide driving frequency bandwidth (~200 Hz) like silicones. Therefore, an ultrahigh power density (154 W kg−1@20 MV m−1, 200 Hz) is realized at low electric field and high resonance frequency, 75 times greater than at 10 Hz. Further, a rotary motor is developed, reaching an impressive speed of 1245 rpm at 19.6 MV m−1 and 125 Hz, surpassing previous acrylate-based motors and entering the high-speed domain of silicone-based motors. These findings offer a versatile strategy to fabricate high-power-density dielectric elastomers for low-electric-field soft actuators.

Preparation and study on electrical/thermal properties of epoxy/polyacrylate rubber composite dielectric

AbstractWith the development of power systems and electronic devices, epoxy resin (EP) is facing increasingly severe operating environments, and its performance may not meet expectations. In order to broaden the application of EP, the DE/EP composite films were prepared with EP as matrix, polyacrylic rubber dielectric elastomer (DE) as reinforcement materials. The structure of DE/EP composite films was characterized by XRD, SEM, and other methods, and the electrical and thermal properties of the materials were tested and studied. The study found that with appropriate dissolution and stirring treatment, DE can be evenly dispersed in the EP matrix, and the introduction of DE does not significantly affect the structure of the EP molecular chain, also found the introduction of DE improve the electrical and thermal properties of EP. The breakdown strength of the 4% DE/EP composite film surpasses that of the pure EP film by 15.58%. Additionally, the thermal conductivity of the 8% DE/EP composite film is elevated by 41.6% compared to the pure EP film, while its dielectric constant is also enhanced by 8.2%. This work may provide a theoretical basis for studying the application of EP modified system in electrical engineering, integrated circuit packaging and other fields.

A super-toughened polyethylene naphthalene (PEN) enabled by polyacrylate elastomer with low crosslink density and reactivity

In elastomer toughening of polyester plastics, both the particle size distribution of the elastomer and the interfacial strength between the elastomer and matrix are key factors for toughness. In this work, bi-functional polyacrylate elastomers with controllable crosslinking density and reactivity were designed for enhancing the toughness of polyethylene naphthalene (PEN) matrix. Firstly, the elastomers with crosslinked structure possess increased melt viscosity and endowed wide particle size distribution, which contribute to the construct of thin matrix ligament and make PEN matrix more susceptible to shear-yield. Secondly, the high interfacial strength between elastomer and matrix can facilitate the transfer of external stress from PEN matrix to the elastomer, protecting the matrix from destroying. The resulted PEN blends exhibit an excellent impact resistance of 45.20 kJ/m2 and a high tensile toughness of 3.586 MJ/m3, which are 21.73 times and 47.81 times higher, respectively, than the virgin PEN. The present work may provide an effective approach for designing polyester blends with enhanced impact resistance and tensile toughness.

Mechanical Properties and Non-Isothermal Crystallization Kinetics of Polylactic Acid Modified by Polyacrylic Elastomers and Cellulose Nanocrystals.

In this paper, a polyacrylic elastomer latex with butyl acrylate (BA) as the core and methyl methacrylate (MMA) copolymerized with glycidyl methacrylate (GMA) as the shell, named poly(BA-MMA-GMA) (PBMG), was synthesized by seeded emulsion polymerization. Cellulose nanocrystal (CNC) was dispersed in the polyacrylic latex to prepare PBMG/CNC dispersions with different CNC contents. The dried product was mixed with polylactic acid (PLA) to fabricate PLA/PBMG/CNC blends. The addition of PBMG and PBMG/CNC improved the mechanical properties of the PLA matrix. Differential scanning calorimetry (DSC) was used to investigate the non-isothermal crystallization kinetics. The Avrami equation modified by the Jeziorny, Ozawa and Mo equations was used to analyze the non-isothermal crystallization kinetics of PLA and its blends. Analysis of the crystallization halftime of non-isothermal conditions indicated that the overall rate of crystallization increased significantly at 1 wt% content of CNC. This seemed to result from the increase of nucleation density and the acceleration of segment movement in the presence of the CNC component. This phenomenon was verified by polarizing microscope observation.

Polyacrylate-graft-polypyrrole Copolymer as Intrinsically Elastic Electrodes for Stretchable Supercapacitors.

Constructing elastic electrodes with high mechanical and electrochemical stability remains a challenge in developing flexible supercapacitors. Instability of elastic composite electrodes stems from detachment of noncovalently associated electroactive components from elastic substrates under cyclic deformations. Herein, a novel all-organic copolymer consisting of polypyrrole grafted from a polyacrylate elastomer is proposed as elastic electrodes for stretchable supercapacitors. The single copolymer is obtained by graft polymerization in the swollen state, characterized by a wrinkled polypyrrole coating covalently attached on an elastic core. The copolymer is intrinsically elastic and maintains structural integrity under bending, twisting, and stretching deformations to ensure stable electrochemical performance. In addition, the grafted polypyrrole aggregates densely under the constraint of the backbone and gives a competitive conductivity of 41.6 S cm-1. A stretchable supercapacitor is constructed using the copolymer as electrodes and an acid hydrogel as an electrolyte, resulting in a specific capacitance of 430 mF cm-2. The supercapacitor delivers a capacitance retention of 100% after 1000 stretching-releasing cycles, exhibiting mechanical and electrochemical reliability under elastic deformations.

Transparent and Stretchable Piezoresistive Strain Sensors with Buckled Indium Tin Oxide Film

AbstractOwing to excellent performance and a simple mechanism, stretchable piezoresistive strain sensors have been applied to human skin for monitoring physical activities, physiological activities, etc. However, it is still a challenge to simultaneously realize highly sensitive and stretchable piezoresistive strain sensors with high optical transparency. This study reports a transparent and stretchable piezoresistive strain sensor with 2D surface buckling by fabricating ultrathin indium tin oxide (ITO) film on the biaxially pre‐stretched polyacrylate (VHB) elastomer followed by pre‐stretch releasing. To the authors' knowledge, semiconductors are applied for a stretchable piezoresistive strain sensor for the first time. Furthermore, this strain sensor exhibits a high sensitivity of 569, a high transparency of 88% and a high biaxial stretchability of 110% at the same time. This device demonstrates the good long‐term stability over 500 stretching–relaxing cycles. The high sensitivity can be mainly attributed to the piezoresistive effect of the semiconductor where carrier mobility and the resulting resistivity can be significantly changed by the strain. The strain sensors attached to human skin are used to monitor many human motions such as chewing, swallowing, breathing, and walking. ITO‐based strain sensors pave the way toward the development of highly stretchable and sensitive wearable electronics.

Facile Synthesis of Fluorinated Polyacrylate Elastomer via Emulsion Polymerization Using Adjustable Amphiphilic Star Macro‐RAFT Agent as Surfactant

AbstractNovel thermoplastic fluorinated polyacrylate films possessing excellent mechanical performance are prepared by emulsion polymerization latex using adjustable amphiphilic star macro‐reversible addition‐fragmentation chain‐transfer (macro‐RAFT) agent as surfactants in this work. First, star macro‐RAFT agent equipped with six amphiphilic arms is synthesized via two‐step RAFT polymerization of acrylic acid (AA) and 2,2,2‐trifluoroethyl acrylate (TFEA) in the presence of hexa‐functional RAFT agents. The surface activities of the as‐synthesized amphiphilic star macro‐RAFT agents in aqueous solutions are studied. Subsequently, various fluorinated polyacrylate latexes are obtained by conducting emulsion polymerization of 2,2,3,4,4,4‐hexafluorobutyl acrylate (HFBA) and butyl acrylate (BA) using the amphiphilic star macro‐RAFT agents as both RAFT agents and surfactants. The latex particle morphologies are studied by transmission electron microscope (TEM) and particle size is measured by dynamic light scattering (DLS). The effects of PAA segment length, HFBA/BA mole ratio, and TFEA segment length on the surface morphologies of the fluorinated polyacrylate films are illustrated by investigating the surface properties using water contact angle test and atomic force microscopy (AFM). Finally, the elastomeric films obtained by directly casting the prepared fluorinated polyacrylate latexes show excellent comprehensive properties such as tensile strength over 4 MPa, elongation at break ≈700%, permanent deformation below 25%. Water absorption test is also provided as a reference.

Mill Processability, Rheology and Structure Differences of Polyacrylate Elastomers

Abstract Two commercial polyacrylate elastomers, one having epoxide (EP) crosslinking sites and the other ethylidene norbornene (ENB) were selected. It was demonstrated that the former was more difficult to mill-process than the latter. The viscoelastic properties measured at very small strain in shear oscillation indicated that the ENB polymer was more branched than the EP polymer. The gel determination by filteration confirmed this. The tensile stress-strain measurements were conducted at four different deformation rates. These data were treated according to the strain-time correspondence principle to see if this principle applies to the data of these samples. The data of EP polymer did not form a master curve, thus, the above principle is not applicable; at the larger deformation the strain-hardening tendencies were observed. This indicates that the EP polymer has a rather extensive long branching, a type of which usually results from a chain transfer reaction. The data of the ENB polymer, on the other hand, form a master-curve; that is, the strain-time correspondence principle is applicable, in spite of the presence of the large amount of gel. This means that the gel in the ENB polymer is microgel. The micro-gel in this case is polymer-latex particle, crosslinked during emulsion polymerization with a difunctional comonomer. Thus, in this work polymer rheology was effectively used to find a major difference in the polymer chain structure. In this way it was shown that the results of polymerization may be related to mill processability.

Stretchable interfaces with conformal contact

Without conformal contact, stretchable electronic devices are significantly degraded during device operation and post treatment, due to air trapping and the resulting formation of uneven surface. In this work, under the hard condition that a stretchable polyacrylate elastomer (VHB) layer with high porosity which can lead to more pore formation at the VHB interface is introduced in the stretchable device preparation, conformal contact is achieved by vacuum process (VP). Planar images indicate that, although the conventional process results in the formation of pore with a size of 0.1 mm at the vacuum pressure of 10-6 Torr, the VP prevents it until 10-6 Torr. Surface analysis using near-edge X-ray absorption fine structure indicates the VP leads to less corrugation in the surface of graphene electrode located near the VHB; thus, finally resulting in significantly higher performance of an organic light emitting diode having the VHB and the graphene.

Achieving high breakdown strength and energy density in all-organic sandwich-structured dielectrics by introducing polyacrylate elastomers

Our research provides a potential pathway to develop advanced polymer capacitors for various electric applications based on ferroelectric polymers with a layered architecture and organic elastomer fillers.

Multifunctional Enhancement of Proton-Conductive, Stretchable, and Adhesive Performance in Hybrid Polymer Electrolytes by Polyoxometalate Nanoclusters.

High ionic conductivity, good mechanical strength, strong electrode adhesion, and low volatilization are highly desired properties for flexible solid electrolytes. However, it is difficult to realize all these properties simultaneously, which needs a rational synergy of different electrolyte constituents. Here, we present the use of polyoxometalates as versatile enhancers to fabricate nonvolatile flexible hybrid polymer electrolytes with improved conductive, stretchable, and adhesive properties. These electrolytes are based on the molecular hybridization of a polyacrylate elastomer, phosphoric acid, and a commercial polyoxometalate H3PW12O40 (PW). PW can serve as a nanosized plasticizer to favor the chain relaxation of polyacrylate and improve stretchability. Meanwhile, PW as a solid acid can increase the proton concentration and form a hybrid hydrogen-bonding network to facilitate proton conduction. Besides, the strong adsorption ability of PW on solid surfaces enables the electrolytes with enhanced adhesion. The hybrid electrolyte with 30 wt % PW shows a break stress of 0.28 MPa, a break elongation of 990%, and a conductivity of 0.01 S cm-1 at 298 K, which are 1.8, 1.8, and 2.5 times higher compared to the case without PW, respectively. Moreover, PW enhances the adhesive strength of hybrid electrolytes on polypropylene, steel, and glass substrates. The flexible supercapacitors based on the hybrid electrolytes and polyaniline electrodes hold a stable electrode-electrolyte interface and exhibit a high specific capacitance of 592 mF cm-2 and an excellent capacitance retention of 84% after 6000 charge-discharge cycles. These results demonstrate great potential of polyoxometalates as multifunctional enhancers to design hybrid electrolyte materials for energy and electronic applications.

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.

Understanding thermo-oxidative degradation of polyacrylic ester elastomer and its nanocomposites through molecular dynamics simulation and experiments

Acrylic rubber is a special class of synthetic rubber with outstanding hydraulic oils, engine oils and transmission fluids resistant properties. A further improvement in the heat resistance of the elastomer is required in view of the stringent application requirements. This can be achieved by adding suitable nanofillers inside the elastomer matrix to enhance the degradation resistance of polyacrylicester elastomer under thermo-oxidative condition. However, polymer recycling and sustainability require knowledge of degradation behaviour. Reactive molecular dynamics simulations were executed on a polyacrylicester model compound composed of ten monomer units (ACM10) to study its thermal decomposition in the presence of oxygen. With the addition of model silica and graphene oxide, initial as well as final decomposition temperature was improved, while the rate of degradation was reduced for ACM10. The simulation method gave an insight into the degradation pathway of ACM10 by analysing different fragmented products like alkenes, alkyl radicals, and carbon dioxide. Pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) technique was employed to verify the results further. The activation energy of degradation calculated both from the simulation and thermogravimetric analysis were also comparable. This investigation would assist to understand and enhance the heat-resistant properties of different elastomers for industrial applications.

Hydrogen Bonding-Derived Healable Polyacrylate Elastomers via On-demand Copolymerization of n-Butyl Acrylate and tert-Butyl Acrylate.

Achieving a desirable combination of good mechanical properties and healing efficiency is a great challenge in the development of self-healing elastomers. Herein, a class of tough and strong self-healing polyacrylate elastomers (denoted as HPs) was developed simply by free-radical copolymerization of n-butyl acrylate (nBA) and tert-butyl acrylate (tBA) and a subsequent hydrolysis reaction rather than direct copolymerization of nBA and acrylic acid (AA). The tiny difference in reactivity between nBA and tBA makes the structural units of the copolymer easy to control. Precise regulation of molecular composition can be realized just by varying the relative monomer content, making its mechanical properties to vary from ductile to robust. Strikingly, when HP samples are cut off within the gauge length, they can heal into coherent and smooth samples and recover at least 79% of the original strength. Hydrogen bond interactions serve as physical cross-linking points, contributing to the high mechanical performance (fracture energy of up to 73.78 MJ·m-3 and tensile strength of up to 17.80 MPa) as well as shape memory function. Moreover, the HP samples emit strong fluorescence when exposed to a 365 nm UV lamp and exhibit an aggregation-enhanced emission effect in the state of dissolution.

Robust, Transparent, Thermally Healable Copolyacrylate Elastomer: The Effect of β‐Hydroxyethyl Acrylate on its Properties

AbstractThe contradiction between mechanical properties, transparency, and healing effects for polyacrylate elastomers is not solved yet. The copolyacrylate elastomers are prepared based on the bulk copolymerization with methyl methacrylate (MMA) and butyl acrylate (BA), incorporating the β‐hydroxyethyl acrylate (HEA) monomer. Compared with PMMA‐co‐PBA, with the incorporation of HEA, the copolymer elastomer decreases in tensile strength, while increasing in healing efficiency and visible‐light transmittance. Therefore, the high transparency and healing efficiency of the copolyacrylate elastomer are achieved under the condition of ensuring robust mechanical properties.

Sandwich structured poly(vinylidene fluoride)/polyacrylate elastomers with significantly enhanced electric displacement and energy density

A multilayered film is capable of an ultra-high energy density of 20.9 J cm−3 with an efficiency of 72%, outperforming the current ferroelectric polymers.

Evaluation of properties of elastomer seal for fuel systems exposed to effects of rapeseed methyl ester

Elastomer seals in fuel systems have to evince required mechanical properties also at exposure to fuels. The aim of the research was to determine an influence of various concentrations of rapeseed methyl ester (RME) on a change of mechanical properties of sealing O-rings made from polyacrylate elastomer (an indication ACM). A permanent deformation – compression set (CS), a tensile strength and an elongation after the exposure to the tested environment for the time 20 months were evaluated within the experiment. A fall of the tensile strength, the elongation and the permanent deformation – compression set CS was proved depending on the type of the fuel. The increased negative influence of various concentrations of RME (20% to 100%) on the tested properties of the sealing O-rings compared with the diesel oil complying with the standard EN 590:2004 was not proved. So a significant negative influence of degradation aspects on the tested properties of the O-rings of the ACM type (polyacrylate elastomer) was not proved.

A Constitutive Model for Soft Materials Incorporating Viscoelasticity and Mullins Effect

Soft materials including elastomers and gels are widely used in applications of energy absorption, soft robotics, bioengineering, and medical instruments. For many soft materials subject to loading and unloading cycles, the stress required on reloading is often less than that on the initial loading, known as Mullins effect. Meanwhile, soft materials usually exhibit rate-dependent viscous behavior. Both effects were recently reported on a new kind of synthesized tough gel, with capability of large deformation, high strength, and extremely high toughness. In this work, we develop a coupled viscoelastic and Mullins-effect model to characterize the deformation behavior of the tough gel. We modify one of the elastic components in Zener model to be a damageable spring to incorporate the Mullins effect and model the viscous effect to behave as a Newtonian fluid. We synthesized the tough gel described in the literature (Sun et al., Nature 2012) and conducted uniaxial tensile tests and stress relaxation tests. We also investigated the two effects on three other soft materials, polyacrylate elastomer, Nitrile-Butadiene Rubber, and polyurethane. We find that our presented model is so robust that it can characterize all the four materials, with modulus ranging from a few tens of kilopascal to megapascal. The theory and experiment for all tested materials agree very well.

Preparation and Structure of Poly(vinyl alcohol)/Polyacrylate Elastomer Composite Hydrogels and Their Application in Wastewater Treatment by Immobilizing with Microorganisms

Poly(vinyl alcohol) (PVA)/powdered ethyl acrylate rubber (ACM) composite hydrogels were prepared through in situ chemical cross-linking. The addition of ACM could accelerate the cross-linking reaction of PVA, and increase pore nucleus, resulting in a decrease of pore size and formation of a homogeneous and compact porous network structure. Under proper content of ACM, the shear elastic modulus (G′) and network density (νe) of the composite hydrogels can be improved, leading to an enhancement of the mechanical property and hydraulic shock resistance. The PVA/1.5 wt % ACM hydrogel presented the best long-term hydraulic stability, and the toughening mechanism was studied. The values of oxygen uptake rate and chemical oxygen demand removal rate of PVA/ACM composite hydrogels embedded with microorganism fluctuated with the addition of ACM, and a high microorganism activity can be retained.

Blood-Vessel Mimicking Structures by Stereolithographic Fabrication of Small Porous Tubes Using Cytocompatible Polyacrylate Elastomers, Biofunctionalization and Endothelialization.

Blood vessel reconstruction is still an elusive goal for the development of in vitro models as well as artificial vascular grafts. In this study, we used a novel photo-curable cytocompatible polyacrylate material (PA) for freeform generation of synthetic vessels. We applied stereolithography for the fabrication of arbitrary 3D tubular structures with total dimensions in the centimeter range, 300 µm wall thickness, inner diameters of 1 to 2 mm and defined pores with a constant diameter of approximately 100 µm or 200 µm. We established a rinsing protocol to remove remaining cytotoxic substances from the photo-cured PA and applied thio-modified heparin and RGDC-peptides to functionalize the PA surface for enhanced endothelial cell adhesion. A rotating seeding procedure was introduced to ensure homogenous endothelial monolayer formation at the inner luminal tube wall. We showed that endothelial cells stayed viable and adherent and aligned along the medium flow under fluid-flow conditions comparable to native capillaries. The combined technology approach comprising of freeform additive manufacturing (AM), biomimetic design, cytocompatible materials which are applicable to AM, and biofunctionalization of AM constructs has been introduced as BioRap® technology by the authors.