Elastomers are widely used in various fields owing to their excellent tensile properties.Recyclable and self-healing properties are key to extending the service life of elastomers.Accumulating evidence indicates that dynamic covalent chemistry has emerged as a powerful tool for constructing recyclable and self-healing materials.In this work,we demonstrate the preparation of a recyclable and self-healable polydimethylsiloxane(PDMS)elastomer based on the Knoevenagel condensation(KC)reaction.This PDMS elastomer was prepared by the KC reaction catalyzed by 4-dimethylaminopyridine(DMAP).The obtained PDMS elastomer exhibited an elongation at break of 266%,a tensile strength of 0.57 MPa,and a good thermal stability(Td=357℃).In addition,because of the presence of dynamic C=C bonds formed by the KC reaction and low glass transition temperature(Tg=-117℃).This PDMS exhibited good self-healing and recycling properties at room temperature and could be reprocessed by hot pressing.In addition,the PDMS elastomer exhibits good application prospects in the fields of adhesives and flexible electronic devices.
Herein,the electromagnetic shielding performance of surface concave-convex(SC)and zig-zag micro-arrays was studied by using a simulation prediction and a three-dimensional(3D)printing custom model.Firstly,surface stripe concaveconvex(SSC)and surface cylindrical concave-convex(SCC)micro-arrays with or without zig-zag micro-arrays are designed,and their shielding performance is simulated in multi-bands(C-,X-band).The multiwalled carbon nanotubes/polydimethylsiloxane composites(MWCNT/PDMS)with different SC structures and different electrical conductivity are molded in acrylonitrile-butadiene-styrene copolymer(ABS)molds which are printed by a 3D printer.The results show that the electromagnetic interference shielding effectiveness(EMI SE)of the samples can be enhanced by constructing the SC micro-arrays with zig-zag micro-arrays,and improving with the increase of conductivity and frequency.In addition,the shielding mechanism of the SC-MWCNT/PDMS composites is investigated and discussed by an electromagnetic simulation.
Ke JiangZhi Chen JiYu Chen ZhengShan HuangMing Wang
Flexible electronic technology has laid the foundation for complex human-computer interaction system,and has attracted great attention in the field of human motion detection and soft robotics.Graphene has received an extensive attention due to its excellent electrical conductivity;however,how to use it to fabricate wearable flexible sensors with complex structures remains challenging.In this study,we studied the rheological behavior of graphene/polydimethylsiloxane ink and proposed an optimal graphene ratio,which makes the ink have an good printability and conductivity at the same time.Then,based on the theory of Peano fractal layout,we proposed a two-dimensional structure that can withstand multi-directional tension by replacing the traditional arris structure with the arc structure.After that,we manufactured circular arc fractal structure sensor by adjusting ink composition and printing structure through direct ink writing method.Finally,we evaluated the detection performance and repeatability of the sensor.This method provides a simple and effective solution for fabricating wearable flexible sensors and exhibits the potential to fabricate 3D complex flexible electronic devices.
This paper systematically investigates the effective parameter ontheperformanceof polydimethylsiloxane/graphene(PDMS@Gr)-based triboelectric nanogenerators(TENGs)as well as their applications.PDMS@Gr films containing 0,0.05,0.5,1,and 1.5 wt.%graphene are synthesized,and their sur-face characteristics,mechanical behavior,and electrical prop-erties are characterized.Vertical contact-separation mode TENGs are fabricated,and their performance is evaluated.The results demonstrate that the surface roughness and sur-face charge density are the most critical parameters for the performance of PDMS@Gr-based TENGs compared to the elec-trical and mechanical properties of the friction layers.The PDMS@Gr-based TENG with 1 wt.%graphene shows the high-est power output of 2.6 W/m?at an optimized working con-dition(5 Hz and 15 N).It also exhibits stable power output until 15,oo0 working cycles and displays battery-free applica-tions by powering a light-emitting diode(LED)array,a calculator,a digital watch,and a digital thermometer.
Fattaneh SalemiFathallah KarimzadehMohammad-Hasan AbbasiFatemeh MoradiDuc Hoa PhamJaehwan Kim
