Contact Electrification Spectrum for Performance Enhancement Mechanism Investigation of Triboelectric Nanogenerators based on Silicone Elastomers with Different Surface Microstructures

Triboelectric nanogenerators(TENGs)based on conjunctive effects of contact electrification(CE)and electrostatic induction are emerging as a new mechanical energy harvesting and sensing technique for promising applications in smart wearables,Internet of Things(IoTs),etc.The surface microstructure of a flexible triboelectric material for the increase of surface area is a common strategy for performance enhancement of TENGs,but the real roles of surface microstructures on their output performance are still not explicit due to the lack of suitable analysis tool and rational experimental design.Taking advantages of the surface-sensitive characteristic of CE effect,this work exploited and developed the electric signal patterns generated by single impact of TENGs as a kind of CE spectrum to analyze and speculate the real roles of surface microstructures of flexible triboelectric materials on the output performance of TENGs.Firstly,four different kinds of surface microstructures,namely planar surface(PS)and three combinations of two basic surface microstructures,i.e.,micro lens arrays(MLAs),fabric textures(FTs),and hierarchical structures of MLAs on FTs(MLA/FTs),were elaborately designed and introduced for an identical triboelectric material(i.e.,silicone elastomer)by a(micro)molding synthesis route.Then they were used for assembly of TENGs based on vertical contact mode to conduct performance evaluation under the same triggering conditions.Through systematic analysis and comparison of their highly repeatable CE spectra by programmed machine,it was found that the surface microstructure for a flexible triboelectric material to maximally enhance the output performance of a TENG shall achieve a positive synergistic effect of increasing triboelectric charge density,effective contact area and contacting/separating velocity,rather than simple increase of its surface area.

Fouling-release Property of Water-filled Porous Elastomers

Since the fouling-releasing ability of silicone elastomers increased as their modulus decreases, we designed and prepared composites with embedded tiny NaC1 crytals that were soluble after their immersion in water, resulting in water-filled porous elastomers. The scanning electron microscope images confirmed such a designed water-filling porous structure. The existence of many micro-drops of water in these specially designed elastomers decreased the shear storage modulus and increased the loss factors. The decrease of shear modulus plays a leading role here and is directly related to a lower critical peeling-off stress of a pseudo-barnacle on them. Therefore, such a novel preparation with cheap salts instead of an expensive silicone provides a better way to make fouling-release paints with a lower modulus, a lower critical peeling-off stress and a better fouling-release property without a significant decrease of the cross-linking density.

Temperature dependence of dielectric breakdown of silicone-based dielectric elastomers

A large number of insulation/dielectric failures in power systems are related to thermally-induced dielectrical breakdown,also known as‘thermal breakdown’,at higher operating temperatures.In this work,the thermal breakdown behavior of typical silicone formulations,used as dielectrics in stretchable electronic devices,is analyzed at practically relevant operating temperatures ranging from 20℃ to 80℃.An effective way of delaying the thermal breakdown of insulating materials is to blend micro-or nano-sized inorganic particles with high thermal conductivity,to dissipate better any losses generated during energy transduction.Therefore,two types of commercial silicone formulations,blended with two types of rutile hydrophobic,high-dielectric TiO_(2) fillers,are investigated in relation to their dielectric properties,namely,relative permittivity,the dissipation factor,and electrical breakdown strength.The breakdown strengths of these silicone composites are subsequently evaluated using Weibull analysis,which indicates a negative correlation between temperature and shape parameter for all compositions,thus illustrating that the homogeneity of the samples decreases in line with temperature,but the breakdown strengths nevertheless increase initially due to the trapping effect from the high-permittivity fillers.

Degradation patterns of silicone-based dielectric elastomers in electrical fields

Silicone elastomers have been heavily investigated as candidates for the flexible insulator material in dielectric elastomer transducers and are as such almost ideal candidates because of their inherent softness and compliance.However,silicone elastomers suffer from low dielectric permittivity.This shortcoming has been attempted optimized through different approaches during recent years.Material optimization with the sole purpose of increasing the dielectric permittivity may lead to the introduction of problematic phenomena such as premature electrical breakdown due to high leakage currents of the thin elastomer film.Within this work,electrical breakdown phenomena of various types of permittivity-enhanced silicone elastomers are investigated.Results showed that different types of polymer backbone chemistries lead to differences in electrical breakdown patterns,which were revealed through SEM imaging.This may pave the way towards a better understanding of electrical breakdown mechanisms of dielectric elastomers and potentially lead to materials with increased electrical breakdown strengths.

Silicone Elastomer with High Elongation at Break Used in Digital Light Processing 3D Printing

3D printing silicone elastomer has demonstrated great potential in diverse areas such as medical devices,flexible electronics and soft robotics.It is of great value to investigate how to improve the mechanical properties,including tensile strength and elongation at break of printed parts.In this work,a light curing system that can be applied in silicone elastomer 3D printing is explored,which is composed of vinyl terminated polysiloxane as the macromer and thiol containing polysiloxane as the crosslinking agent,and a chain extension reaction is also introduced into this light curing system via the addition of the chain extender dithiol molecules,and a light curing system accompanied with chain extension is designed and realized based on the thiol-ene click reaction mechanism.After reinforced with silica fillers,the obtained light curing system can endow the light curing silicone elastomer with better mechanical properties under the condition of a lower viscosity of the precursor,the tensile strength and elongation at break can reach 525.5 k Pa and 601%,respectively.This light curing system provides a feasible method to solve the contradiction between the viscosity of the precursor and the mechanical properties of the light curing elastomer in the digital light processing(DLP)3D printing field.

Fault-tolerant silicone dielectric elastomers

Soft silicone films have garnered a great deal of interest for use in dielectric elastomer transducers due to their excellent properties,including high elongation to rupture,low viscoelasticity,and broad application temperature range.However,silicone films generally have higher stiffness and lower dielectric strength than VHB acrylic elastomers,which limits the achievable actuation strain.Devices based on silicone dielectric elastomers always experience high rates of premature dielectric failure when operated at high strains.The premature failure is characterized by the loss of functionality or mechanical rupture of the material when operated below the material’s dielectric strength and elongation to rupture.The use is reported of ultrathin coatings of single-walled carbon nanotubes(SWNTs)as the compliant electrodes,which can overcome the issue of premature failure.The self-clearing of the SWNT electrodes in the event of localized dielectric breakdown improves the apparent dielectric strength of the material by isolating the regions of reduced dielectric strength.The actuators may be operated at higher than 50%area strain with reasonably long lifetimes.High strains were measured between-40 and 80℃and in a broad frequency range up to 100 Hz.The fault tolerance introduced by the SWNT electrodes should broaden the application scope of silicone dielectric elastomers.

Constructing a biomimetic robust bi-layered hydrophilic lubrication coating on surface of silicone elastomer

Silicone elastomers-based materials have been extensively involved in the field of biomedical devices,while their use is extremely restricted due to the poor surface lubricity and inherent hydrophobicity.This paper describes a novel strategy for generating a robust layered soft matter lubrication coating on the surface of the polydimethylsiloxane(PDMS)silicone elastomer,by entangling thick polyzwitterionic polyelectrolyte brush of poly(sulfobetaine methacrylate)(PSBMA)into the sub-surface of the initiator-embedded stiff hydrogel coating layer of P(AAm-co-AA-co-HEMA-Br)/Fe,to achieve a unified low friction and high load-bearing properties.Meanwhile,the stiff hydrogel layer with controllable thickness is covalently anchored on the surface of PDMS by adding iron powder to provide catalytic sites through surface catalytically initiated radical polymerization(SCIRP)method and provides high load-bearing capacity,while the topmost brush/hydrogel composite layer is highly effective for aqueous lubrication.Their synergy effects are capable of attaining low friction coefficient(COFs)under wide range of loaded condition in water environment with steel ball as sliding pair.Furthermore,the influence of mechanical modulus of the stiff hydrogel layer on the lubrication performance of layered coating is investigated,for which the COF is the lowest only when the modulus of the stiff hydrogel layer well matches the PDMS substrate.Surprisingly,the COF of the modified PDMS could remain low friction(COF<0.05)stably after encountering 50,000 sliding cycles under 10 N load.Finally,the surface wear characterizations prove the robustness of the layered lubricating coating.This work provides a new route for engineering lubricious silicon elastomer with low friction,high load-bearing capacity,and considerable durability.