Compatibilization of porphyrins for use as high permittivity fillers in low voltage actuating silicone dielectric elastomers

Structural Decoration of Porphyrin/Phthalocyanine Photovoltaic Materials

Porphyrin/phthalocyanine compounds with fascinating molecular structures have attracted widespread attention in the field of solar cells in recent years. In this review, we focus on the pivotal role of porphyrin and phthalocyanine compounds in enhancing the efficiency of solar cells. The review seamlessly integrates the intricate molecular structures of porphyrins and phthalocyanines with their proficiency in absorbing visible light and facilitating electron transfer, key processes in converting sunlight into electricity. By delving into the nuances of intramolecular regulation, aggregated states, and surface/interface structure manipulation, it elucidates how various levels of molecular modifications enhance solar cell efficiency through improved charge transfer, stability, and overall performance. This comprehensive exploration provides a detailed understanding of the complex relationship between molecular design and solar cell performance, discussing current advancements and potential future applications of these molecules in solar energy technology.

Network Formation, Properties, and Actuation Performance of Functionalized Liquid Isoprene Rubber

Due to some useful mechanical, dynamic, and dielectric properties along with the ease of processing and forming, liquid rubbers are ideal materials for fabricating dielectric elastomer actuators in various configurations and for many potential applications ranging from automation to automobile and medical industry. In this study, we present a cross-linkable liquid rubber composition where amine-catalyzed esterification reactions lead to the formation of a network structure based on anhydride functional isoprene rubber, carboxyl-terminated nitrile-butadiene rubber, and epoxy end-capped prepolymers. The success of this intricate network formation procedure was verified by HR-MAS NMR spectroscopy. The new isoprene-based elastomeric material exhibits actuation-relevant attributes including a low elastic modulus of 0.45 MPa, soft response to an applied load up to a large deformation of 300%, and a dielectric constant value (2.6) higher than the conventional Elastosil silicone (2.2). A dot actuator comprising of an isoprene dielectric elastomer film in unstretched state and carbon paste electrodes was fabricated that demonstrated an electrode deformation of 0.63%, which is nearly twice as high as for the commercial Elastosil 2030 film (∼0.30%) at 5 kV. Compared to the Elastosil silicone film, the enhanced performance is attributed to the low modulus and high dielectric constant value of the new isoprene elastomer.

Tris(pentafluorophenyl)borane-catalyzed Hydride Transfer Reactions in Polysiloxane Chemistry-Piers-Rubinsztajn Reaction and Related Processes

Tris(pentafluorophenyl)borane (TPFPB) is a unique Lewis acid that catalyzes the condensation between hydrosilanes (Si-H) and alkoxysilanes (Si-OR), leading to the formation of siloxane bonds (Si-OSi) with the release of hydrocarbon (R-H) as a byproduct-the so-called Piers-Rubinsztajn reaction. The analogous reactions of hydrosilanes with silanols (Si-OH), alcohols (R-OH), ethers (R-OR') or water in the presence of TPFPB leads to the formation of a siloxane bond, alkoxysilane (Si-OR or Si-OR') or silanol (Si-OH), respectively. The above processes, often referred to as Piers-Rubinsztajn reactions, provide new synthetic tools for the controlled synthesis of siloxane materials under mild conditions with high yields. The common feature of these reactions is the TPFPB-mediated hydride transfer from silicon to carbon or hydrogen. This review presents a summary of 20 years of research efforts related to this field, with a focus on new synthetic methodologies leading to numerous previously difficult to synthesize well-defined siloxane oligomers, polymers and copolymers of a complex structure and potential applications of these new materials. In addition, the mechanistic aspects of the recently discovered reactions involving hydride transfer from silicon to silicon are discussed in more detail.

A New Molecular Mechanism for Understanding the Actuated Strain of Dielectric Elastomers and Their Impacts

Dielectric elastomers (DEs) are a special material that deform responding to an electric field. The induced strain is known as actuated strain (AS). This phenomenon is totally different from electrostriction, for there is no crystal lattice in elastomers and the AS of DEs is much greater. The most accepted mechanism holds the view that the AS of DEs is induced by the Maxwell stress. According to this mechanism, materials exhibiting similar ratios of permittivity and Young's modulus should have similar ASs, while the experimental AS isn't relevant to the ideal value, contradicting this mechanism. The direction of uniaxial pre-strained DE's AS cannot be explained by this mechanism either. The electric field and DE are only regarded as a source of stress and a deformable body respectively in this mechanism, which ignores the interaction between those two. Recently, a new molecular mechanism for AS is proposed, in which the electric field first orient dipoles of chains, therefore the conformation of chains will be changed, finally leading to AS. With thermodynamical derivation and experiment, entropy-dominated elasticity is found to account for more during AS. This mechanism is systematically introduced in this perspective and presents current challenges and outlooks of DE.

Crosslinking Methodology for Imidazole-Grafted Silicone Elastomers Allowing for Dielectric Elastomers Operated at Low Electrical Fields with High Strains

For improved actuation at low voltages of dielectric elastomers, a high dielectric permittivity has been targeted for several years but most successful methods then either increase the stiffness of the elastomer and/or introduce notable losses of both mechanical and dielectric nature. For polydimethylsiloxane (PDMS)-based elastomers, most high-permittivity moieties inhibit the sensitive platinum catalyst used in the addition curing scheme. In contrast to the classical addition curing pathway to prepare PDMS elastomers, here, an alternative strategy is reported to prepare PDMS elastomers via the crosslinking reaction between multifunctional imidazole-grafted PDMS with difunctional bis(1-ethylene-imidazole-3-ium) bromide ionic liquid (bis-IL). The prepared IL-elastomer entails uniformly dispersed IL and presents stable mechanical and dielectric properties due to the covalent nature of the crosslinking as opposed to previously reported physical mixing in of ILs. The relative permittivity was improved up to 200% by including the bis-IL in the elastomer, and Young's modulus was around 0.04 MPa. As a result of the excellent combination of properties, the dielectric actuator developed exhibits an area strain of 20% at 15 V/μm. The novel strategy to prepare PDMS elastomers provides a new paradigm for achieving high-performance dielectric elastomer actuators by a simple methodology.

The ultimate Lewis acid catalyst: using tris(pentafluorophenyl) borane to create bespoke siloxane architectures

The breadth of utility of a commercially available and stable strong Lewis acid catalyst, tris(pentafluorophenyl)borane, has been explored, highlighting its use towards a wide range of unique siloxane products and their corresponding applications. This article focuses on the variety of different outcomes that this impressive borane offers in controlled and selective manners by the variation of reaction conditions, precursor functionalities, reagent or catalyst loading, and the mechanistic considerations that contribute. With a predominant focus on the Piers-Rubinsztajn reaction and its modifications, tris(pentaflurophenyl)borane's utility is highlighted in the synthesis of linear, cyclic and macrocyclic siloxanes, aryl-/alkoxysiloxanes, and other bespoke products. The significance of the catalytic transformation within the field of siloxane chemistry is discussed alongside some of the challenges that arise from using the borane catalyst.

Evaluation of dielectric elastomers to develop materials suitable for actuation

Electroactive polymers based on dielectric elastomers are stretchable and compressible capacitors that can act as transducers between electrical and mechanical energies. Depending on the targeted application, soft actuators, sensors or mechanical-energy harvesters can be developed. Compared with conventional technologies, they present a promising combination of properties such as being soft, silent, light and miniaturizable. Most of the research on dielectric elastomer actuators has focused on obtaining the highest strain, either from technological solutions using commercially available materials or through the development of new materials. It is commonly accepted that a high electrical breakdown field, a low Young's modulus and a high dielectric constant are targets. However, the interdependency of these properties makes the evaluation and comparison of these materials complex. In addition, dielectric elastomers can suffer from electromechanical instability, which amplifies their complexity. The scope of this review is to tackle these difficulties. Thus, first, two physical parameters are introduced, one related to the energy converted by the dielectric elastomer and another to its electromechanical stability. These numbers are then used to compare dielectric elastomers according to a general and rational methodology considering their physicochemical and electromechanical properties. Based on this methodology, different families of commercially available dielectric elastomers are first analyzed. Then, different polymer modification methods are presented, and the resulting modified elastomers are screened. Finally, we conclude on the trends enabling the choice of the most suitable modification procedure to obtain the desired elastomer. From this review work, we would like to contribute to affording a quick identification method, including a graphic representation, to evaluate and develop the dielectric materials that are suitable for a desired actuator.

Dynamic Polymer Networks: A New Avenue towards Sustainable and Advanced Soft Machines

While the fascinating field of soft machines has grown rapidly over the last two decades, the materials they are constructed from have remained largely unchanged during this time. Parallel activities have led to significant advances in the field of dynamic polymer networks, leading to the design of three-dimensionally cross-linked polymeric materials that are able to adapt and transform through stimuli-induced bond exchange. Recent work has begun to merge these two fields of research by incorporating the stimuli-responsive properties of dynamic polymer networks into soft machine components. These include dielectric elastomers, stretchable electrodes, nanogenerators, and energy storage devices. In this Minireview, we outline recent progress made in this emerging research area and discuss future directions for the field.

On the understanding of dielectric elastomer and its application for all-soft artificial heart

Although dielectric elastomer (DE) with substantial actuated strain (AS) has been reported 20 years ago, its scientific understanding remains unclear. The most accepted theory of DE, which is proposed in 2000, holds the view that AS of DE is induced by the Maxwell stress. According to this theory, materials have similar ratios of permittivity and Young's modulus should have similar AS, while the experimental results are on contrary to this theory, and the experimental AS has no relationship with ideal AS. Here, a new dipole-conformation-actuated strain cross-scale model is proposed, which can be generally applied to explain the AS of DE without pre-strain. According to this model, several characteristics of an ideal DE are listed in this work and a new DE based on polyphosphazene (PPZ) is synthesized. The AS of PPZ can reach 84% without any pre-strain. At last, a PPZ-based all soft artificial heart (ASAH) is built, which works in the similar way with natural myocardium, indicating that this material has great application potential and possibility in the construction of an ASAH for heart failure (HF) patients.

Reliable Condensation Curing Silicone Elastomers with Tailorable Properties

The long-term stability of condensation curing silicone elastomers can be affected by many factors such as curing environment, cross-linker type and concentration, and catalyst concentration. Mechanically unstable silicone elastomers may lead to undesirable application failure or reduced lifetime. This study investigates the stability of different condensation curing silicone elastomer compositions. Elastomers are prepared via the reaction of telechelic silanol-terminated polydimethylsiloxane (HO-PDMS-OH) with trimethoxysilane-terminated polysiloxane ((MeO)3Si-PDMS-Si(OMe)3) and ethoxy-terminated octakis(dimethylsiloxy)-T8-silsesquioxane ((QMOEt)8), respectively. Two post-curing reactions are found to significantly affect both the stability of mechanical properties over time and final properties of the resulting elastomers: Namely, the condensation of dangling and/or unreacted polymer chains, and the reaction between cross-linker molecules. Findings from the stability study are then used to prepare reliable silicone elastomer coatings. Coating properties are tailored by varying the cross-linker molecular weight, type, and concentration. Finally, it is shown that, by proper choice of all three parameters, a coating with excellent scratch resistance and electrical breakdown strength can be produced even without an addition of fillers.