Baoping Lin

Enhanced dielectric properties of amino-modified-CNT/polyimide composite films with a sandwich structure

Novel amino-modified-CNT/polyimide (NH2-MWNT/PI) flexile composite films with a sandwich structure were prepared through step-by-step casting, in which a dielectric layer (NH2-MWNT/PI composites) intercalated between the two insulating layers (pure PI, acting as both the bottom and the top layers). Due to the high capacitance of the dielectric layer and the effective blocking off conductive paths by the insulating layers, the sandwich composite films show a high dielectric constant and ultralow dielectric loss, and the dielectric constants of the composite films are almost frequency independent between 1 and 1000 kHz. It is notable that the NH2-MWNT/PI ratio of the mid-layer markedly influences the dielectric property of the composite film. When the NH2-MWNT content of the mid-layer is 10 wt%, the multi-layer composite film (P-10-P) shows the highest dielectric constant (e′) of 31.3 at 1 kHz, while the dielectric loss (tan δ) of the P-10-P is only 0.0016. Furthermore, the obtained multi-layer composite films have high breakdown strength and maximum energy storage density. The mechanical properties and thermal properties of the composite films were also examined in this work.

A plant tendril mimic soft actuator with phototunable bending and chiral twisting motion modes.

In nature, plant tendrils can produce two fundamental motion modes, bending and chiral twisting (helical curling) distortions, under the stimuli of sunlight, humidity, wetting or other atmospheric conditions. To date, many artificial plant-like mechanical machines have been developed. Although some previously reported materials could realize bending or chiral twisting through tailoring the samples into various ribbons along different orientations, each single ribbon could execute only one deformation mode. The challenging task is how to endow one individual plant tendril mimic material with two different, fully tunable and reversible motion modes (bending and chiral twisting). Here we show a dual-layer, dual-composition polysiloxane-based liquid crystal soft actuator strategy to synthesize a plant tendril mimic material capable of performing two different three-dimensional reversible transformations (bending versus chiral twisting) through modulation of the wavelength band of light stimuli (ultraviolet versus near-infrared). This material has broad application prospects in biomimetic control devices.

All-solid-state asymmetric supercapacitors based on ZnO quantum dots/carbon/CNT and porous N-doped carbon/CNT electrodes derived from a single ZIF-8/CNT template

Currently, the development of two kinds of materials from a single precursor has been an important frontier in material synthesis. In this study, we have successfully fabricated a single precursor using metal–organic frameworks (MOFs) (zeolitic imidazolate framework, ZIF-8) and carbon nanotubes (CNTs). ZnO quantum dots (QDs)/carbon/CNTs and porous N-doped carbon/CNTs have been selectively synthesized from a single ZIF-8/CNTs template. When the two derived materials were used for supercapacitor electrodes, they showed high capacitance values (185 F g−1 g for ZnO QDs/carbon/CNTs at 0.5 A g−1 and 250 F g−1 g for porous N-doped carbon/CNTs at 1 A g−1, respectively). Further, an all-solid-state asymmetric supercapacitor (ASC) device using ZnO QDs/carbon/CNTs as the positive electrode and porous N-doped carbon/CNTs as the negative electrode was fabricated, and this device could reach a working potential of 1.7 V, delivering a maximum energy density of 23.6 W h kg−1 and a maximum power density of 16.9 kW kg−1, which are better than those of the ZnO-based symmetric or asymmetric supercapacitor devices.

Self-host thermally activated delayed fluorescent dendrimers with flexible chains: an effective strategy for non-doped electroluminescent devices based on solution processing

Two self-host dendrimers TZ-Cz and TZ-3Cz with TADF nature were designed and synthesized for solution-processed nondoped fluorescent organic light-emitting diodes (OLEDs). The first and second generation carbazole dendrons were conveniently introduced into the TADF core through non-conjugated aliphatic chains, which favourably make the fluorescence of the core independent of the peripheral dendrons. Photophysical investigation showed that the prevalent concentration quenching effect of the TADF materials can be effectively restrained by the encapsulation of the emissive core. Moreover, the key role of the end-capping moieties on the molecular frontier orbital of the dendrimers was revealed by electrochemical testing and theoretical calculations. Solution-processed OLEDs featuring TZ-3Cz as the host-free emitter achieved a superior external quantum efficiency of 10.1%, which is almost ten times higher than that of the emissive core TZ (1.09%). Thus, a facile strategy to design a solution-process with highly emissive self-host TADF materials for nondoped OLEDs by flexible alkyl chain is demonstrated.

Self-Host Blue Dendrimer Comprised of Thermally Activated Delayed Fluorescence Core and Bipolar Dendrons for Efficient Solution-Processable Nondoped Electroluminescence

A self-host thermally activated delayed fluorescence (TADF) dendrimer POCz-DPS for solution-processed nondoped blue organic light-emitting diodes (OLEDs) was designed and synthesized, in which the bipolar phosphine oxide carbazole moiety was introduced by alkyl chain to ensure balanced charge transfer. The investigation of physical properties showed that the bipolar dendrons not only improve the morphological stability but also restrain the concentration quenching effect of the TADF emissive core. The spin-coated OLEDs featuring POCz-DPS as the host-free blue emitter achieved the highest external quantum efficiency (7.3%) and color purity compared with those of doped or nondoped devices based on the parent molecule DMOC-DPS, which indicates that incorporating the merits of encapsulation and bipolar dendron is an effective way to improve the electroluminescent performance of the TADF emitter used for a solution-processed nondoped device.

Carbon nanotubes@metal–organic frameworks as Mn-based symmetrical supercapacitor electrodes for enhanced charge storage

A hybrid material of carbon nanotubes (CNTs) and Mn-based metal organic frameworks (Mn-MOF) was synthesized and used as a Mn-based supercapacitor electrode material. The incorporation of CNTs into Mn-MOF led to an inherent improvement in conductivity and an intrinsic increase in specific capacitance (from 43.2 F g−1 for pure Mn-MOF to 203.1 F g−1 for CNTs@Mn-MOF). Furthermore, the symmetrical supercapacitor based on the CNTs@Mn-MOF exhibited excellent power density and outstanding stability even after 3000 cycles with 88% retention of the initial capacitance. This research exploited a new direction for developing Mn-based supercapacitor materials and provided an effective method to improve capacitive performance of MOFs materials.

Synthesis and properties of UV-curable hyperbranched polyurethane acrylate oligomers containing photoinitiator

The hyperbranched polyurethane acrylate oligomers containing photoinitiator were synthesized by modifying the second-generation hyperbranched poly(amine-ester) with isophorone diisocyanate-2-hydroxyethylacrylate and isophorone diisocyanate-2-hydroxy-2-methylpropiophenone at different feed ratio. The elemental analysis, FT-IR and NMR methods are used for structural characterization, molecular weights, and polydispersities, photosensitive groups and thermal properties of the oligomers were analyzed by gel permeation chromatography, UV–Vis spectra and thermogravimetric analysis, respectively. UV-curing properties were characterized by FT-IR at different curing time. In addition, the solubilities of the oligomers were also examined.

Solution processable low bandgap thienoisoindigo-based small molecules for organic electronic devices

Two donor–acceptor conjugated small molecules that consist of thienoisoindigo as an acceptor unit and benzofuran or naphthalene as a donor building block have been synthesized via a Suzuki coupling reaction. The small molecules, TII(BFu)2 and TII(Na)2, exhibit broad and near-infrared absorption in the range of 500–900 nm while their absorption maxima locate at around 620 nm in films. Optical band gaps calculated from the solid state absorption cutoff value are 1.49 eV for TII(BFu)2 and 1.53 eV for TII(Na)2, respectively. These small molecules possess p-channel charge transport characteristics when used as the active semiconductor in organic thin-film transistors (OFETs). The highest hole mobilities of 1.28 × 10−3 cm2 V−1 s−1 for TII(BFu)2 and 1.29 × 10−3 cm2 V−1 s−1 for TII(Na)2 have been achieved in top-contact-bottom-gate OFET devices. The preliminary characterization of bulk heterojunction photovoltaic devices consisting of small molecules and PC71BM yield power conversion efficiencies (PCE) of 1.24% for TII(BFu)2 and 1.04% for TII(Na)2. Moreover, the relationships between the semiconductor devices performance and film morphology, and energy levels are discussed.

Side Chain Liquid Crystalline Polymers with an Optically Active Polynorbornene Backbone and Achiral Mesogenic Side Groups

Most of the traditional chiral side-chain liquid crystalline polymers (SCLCPs) depend on pendant chiral mesogenic units to introduce chirality into their structure, with the polymer backbones being usually achiral. In this work, we asymmetrically synthesize several enantiomerically pure norbornene monomers functionalized with achiral mesogenic units, and further apply a ring-opening metathesis polymerization technique to prepare a series of side-on and end-on SCLCPs with an optically active polynorbornene main chain and achiral mesogens. Their physical properties are fully characterized by NMR, UV, CD, GPC, TGA, DSC, polarimetry, polarized optical microscopy and small-angle X-ray scattering. The obtained side-on SCLCPs display the tendency to form nematic, i.e. achiral mesophases, in strong contrast to the chiral nematic (cholesteric) mesophase exhibited by their comparative end-on analogues. The proposed explanation for this phenomenon is that the chiral backbones and the laterally attached mesogens of side-on SCLCPs can concurrently exist in a parallel arrangement so that the mesogenic directors might not be affected by the chirality information, while the mesogenic directors of end-on SCLCPs always tilt to the backbone orientation so that the twisting power of chiral main chains might force the terminally attached mesogens to form helical structures.

Near-Infrared Chromophore Functionalized Soft Actuator with Ultrafast Photoresponsive Speed and Superior Mechanical Property

In this Communication, we develop a two-step acyclic diene metathesis in situ polymerization/cross-linking method to synthesize uniaxially aligned main-chain liquid crystal elastomers with chemically bonded near-infrared absorbing four-alkenyl-tailed croconaine-core cross-linkers. Because of the extraordinary photothermal conversion property, such a soft actuator material can raise its local temperature from 18 to 260 °C in 8 s, and lift up burdens 5600 times heavier than its own weight, under 808 nm near-infrared irradiation.