“Solid-Liquid” Vitrimers Based on Dynamic Boronic Ester Networks

The "solid-liquid" behavior of vitrimers have not been systematically investigated. Herein, a series of "solid-liquid" vitrimers bearing varying contents of dynamic boronic ester bonds were synthesized via thiol-ene click reactions. These vitrimers allow for flexibile modulation of their network structures and thus show a range of intriguing properties including high stretchability, flexible transition from elasticity to plasticity, strong strain rate dependence, and solid-liquid performance. Th...     

Stretchable Perovskite Solar Cells with Recoverable Performance

Perovskite solar cells (PSCs) are a promising photovoltaic technology for stretchable applications because of their flexible, light‐weight, and low‐cost characteristics. However, the fragility of crystals and poor crystallinity of perovskite on stretchable substrates results in performance loss. In fact, grain boundary defects are the “Achilles’ heel” of optoelectronic and mechanical stability. We incorporate a self‐healing polyurethane (s‐PU) with dynamic oxime–carbamate bonds as a scaffold into the perovskite films, which simultaneously enhances crystallinity and passivates the grain boundary of the perovskite films. The stretchable PSCs with s‐PU deliver a stabilized efficiency of 19.15 % with negligible hysteresis, which is comparable to the performance on rigid substrates. The PSCs can maintain over 90 % of their initial efficiency after 3000 hours in air because of their self‐encapsulating structure. Importantly, the self‐healing function of the s‐PU scaffold was verified in situ. The s‐PU can release mechanical stress and repair cracks at the grain boundary on multiple levels. The devices recover 88 % of their original efficiency after 1000 cycles at 20 % stretch. We believe that this ingenious growth strategy for crystalline semiconductors will facilitate development of flexible and stretchable electronics.     

Electrically Conductive Polymeric Materials with High Stretchability and Excellent Elasticity by a Surface Coating Method

Electrically conductive polymer films with high stretchability and excellent elasticity were simply fabricated by coating a conductive layer on the surface of an elastomer film. The material used for the conductive layer was a high‐shear processed poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] triblock copolymer (SEBS)/multiwalled carbon nanotubes (MWCNTs) nanocomposite with 20 wt.‐% MWCNTs loading. The nanocomposites were first dissolved in toluene to form a stable solution and then were coated onto the SEBS film by spin coating. The alignment of MWCNTs in the coated layer and the interface between the base film and the coated layer were investigated. It was found that almost all the MWCNTs are aligned parallel to the base film and that there is good adhesion between the two layers. The fabricated films show high electrical conductivity and almost same stretchability and elasticity as the base film. Moreover, the films exhibit extremely high electrical conductive retention after applying high strain.

     

柔性电子封装结构中夹杂对延展性的影响分析

以岛-桥型柔性电子封装结构为研究对象,从封装材料中夹杂的刚度、位置、封装方式三个方面探讨了夹杂对柔性电子结构延展性的影响。有限元分析结果表明:随着夹杂刚度的增大,桥的最大主应变增大,整体结构最大延伸量可减小30%;夹杂埋藏位置越深,桥顶局部的整体应变水平越大,最大延伸量可减小20%;相对"硬"封装情形,相同的夹杂对"软"封装中桥的最大延伸量的影响更严重。本文所得结论对于柔性电子器件结构的设计和材料选用具有参考和指导意义。     

Dynamic cross‐links to facilitate recyclable polybutadiene elastomer with excellent toughness and stretchability

A facile cross‐linking strategy of using small molecules as physcial crosslinkers to facilitate recyclable polybutadiene (PB) elastomer with excellent toughness and stretchability is demonstrated. Carboxylic acid groups were incorporated along the PB backbone via thiol‐ene reaction, and then the polymer can be cross‐linked by ionic hydrogen bonds between the carboxylic acid groups from PB and the amine groups of the cross‐linkers. The ionic hydrogen bonds can dynamiclly break and reconstruct upon deformation, thus endowing the resultant polymer with not only high toughness and stretchability (～1800%), but also good self‐recovery and enhanced damping properties. Remarkably, the dynamically cross‐linked PB elastomer can be thermally recycled owing to the thermal reversibility of the ionic hydrogen bonds and the mechanical properties can be largely recovered after reprocessing. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1357‐1366     

Highly conductive and transparent carbon nanotube-based electrodes for ultrathin and stretchable organic solar cells

In this work, we have presented a freestanding and flexible CNT-based film with sheet resistance of 60 ?/ and transmittance of 82% treated by nitric acid and chloroauric acid in sequence. Based on modified CNT film as a transparent electrode, we have demonstrated an ultrathin, flexible organic solar cell(OSC) fabricated on 2.5-μm PET substrate. The efficiency of OSC, combined with a composite film of poly(3-hexylthiophene)(P3HT) and phenyl-C61 butyric acid methyl ester(PCBM) as an active layer and with a thin layer of methanol soluble biuret inserted between the photoactive layer and the cathode, can be up to 2.74% which is approximate to that of the reference solar cell fabricated with ITO-coated glass(2.93%). Incorporating the as-fabricated ITO-free OSC with pre-stretched elastomer, 50% compressive deformation can apply to the solar cells. The results show that the as-prepared CNT-based hybrid film with outstanding electrical and optical properties could serve as a promising transparent electrode for low cost, flexible and stretchable OSCs, which will broaden the applications of OSC and generate more solar power than it now does.     

Stretchable and flexible resistive behavior of poly(3,4‐ethylenedioxythiophene):Poly(styrenesulfonate) thin film on ultra‐low modulus polydimethylsiloxane with trench‐type roughness

This study investigates the resistive behavior of rod‐coated micrometer thick films of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on ultra‐low modulus (120– 130 kPa) polydimethylsiloxane (PDMS) substrate having scratch or microtrench‐type roughness patterns. On average, the films were found to remain electrically functional up to 23% axial strain with an average increase of three times in the value of the normalized resistance. The films were also found to remain conductive up to bending diameter of 4 mm with an average increase of 1.12 times their initial resistance. The rod‐coated PEDOT:PSS films on ultra‐low modulus PDMS having microtrench‐type roughness were also found to remain functional even after 1000 bending cycles at a bending diameter of 4 mm and even smaller with an increase in resistance that was on average 1.15 times their initial resistance. The films were found to fail firstly by cracking and thereby debonding from the substrate under the application of axial strain. On the other hand, the films exhibit no delamination under bending strains. The results from this investigation suggest that the polymer–polymer laminate has potential applicability in stretchable and flexible electronics and related applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 226–233     

Structurally Enhanced Self‐Plasticization of Poly(vinyl chloride) via Click Grafting of Hyperbranched Polyglycerol

A highly self‐plasticized poly(vinyl chloride) (PVC) is demonstrated for the first time via click grafting of hyperbranched polyglycerol (HPG). The plasticizing effect of the grafted HPG on PVC is systematically investigated by various analytical methods. The amorphous and bulky dendritic structure of HPG efficiently increases the free volume of the grafted PVC, which leads to a remarkably lower glass transition temperature comparable to that of the conventional plasticized PVC. Viscoelastic analysis reveals that HPG considerably improves the softness of the grafted PVC at room temperature and promotes the segmental motion in the system. The HPG‐grafted PVC films exhibit an exceptional stretchability unlike the mixture of PVC and HPG because the covalent attachment of HPG to PVC allows it to maintain its homogeneous and well‐organized architecture under tensile stretching. The work provides valuable insights into the design of highly flexible and stretchable polymeric materials by means of introducing hyperbranched side chains.

     

Wet-spun porous fibers from high internal phase emulsions: Continuous preparation and high stretchability

Although high internal phase emulsion (HIPE)-templating is promising to prepare macroporous materials (polyHIPEs) with controllable shapes and tuneable property, fibrous polyHIPEs with stretchability and their continuous preparation are still challenging. Here, we report the fabrication of polyHIPE fibers in a continuous manner through wet spinning of HIPEs. The successful fabrication of polyHIPE fibers depends on HIPE dispersed phase fractions, ammonia-catalyzed interfacial reaction and wet spinning. Dry polyHIPE fibers exhibit tunable diameters, hierarchically porous structures, high stability to temperature and to various solutions, and high stretchability (with a high tensile strain of 155%), which is hard to achieve for polyHIPEs. The polyHIPE fibers show enhanced uptakes to both water (14.4 ml g⁻¹) and organic solvents (up to 26.3 ml g⁻¹), and the amphiphilic swelling is rare for polyHIPEs. Moreover, the dry polyHIPE fibers show good thermal insulation, similar to that of cotton. Simple wet spinning, combining with HIPEs with tuneable composition, is promising for preparing various polyHIPE fibers for various potential applications.