Lijie Dong

Property−Structure Relationship of Nanoscale Ionic Materials Based on Multiwalled Carbon Nanotubes

Two categories of nanoscale ionic materials (NIMs) based on multiwalled carbon nanotubes (MWCNTs) were obtained. According to the nature of organic modifier and the type of interaction, these NIMs can be divided into two categories referred to as A-MWCNTs-Fs and I-MWCNTs-Fs, respectively. These MWCNT derivatives were virtually solvent-free and showed good flowability even at room temperature. The liquidlike manner of these MWCNT derivatives was from their relatively high organic content and continual departing-recombining motion of the large organic ions as suggested by the comparison of rheological response of the two categories of MWCNT-based NIMs. Thermal property and temperature-dependent and strain-dependent viscoelasticity of MWCNT derivatives were related to the microscopic structure of their coating layer and subsequently related to the configuration, chemistry, and molecular dimension of modifying molecules to establish the property-structure relationship of MWCNT-based NIMs, which could guide our future work on NIMs to appropriate and promising applications based on their tunable and controllable physical properties.

Solvent-free Fluids Based on Rhombohedral Nanoparticles of Calcium Carbonate

Calcium carbonate nanoparticles are one of the most economical nanomaterials. However, the ease of agglomeration and lack of functionalities are obstacles to their widespread application. Here we report the preparation and characterization of the solvent-free fluids based on rhombohedral nanoparticles of calcium carbonate, with a soft organic shell on the inorganic particle surface. For the first time, solvent-free fluids based on an inorganic salt are demonstrated. The fluidity of this nanosystem derived from the soft shell will be of great value for processability, manipulation, and ease of dispersion. Moreover, the solvent-free fluids are intrinsically conductive, which is a new functionality for calcium carbonate nanoparticles. The core/shell structure is clearly revealed by the high-resolution transmission electron microscopy images, and this verifies the presumed structure of this family of functionalized nanostructures.

Enhancement of dielectric constant and piezoelectric coefficient of ceramic-polymer composites by interface chelation

Ferroelectric ceramics (e.g., lead zirconate titanate, PZT) and polymers exhibit extraordinary dielectric and piezoelectric properties and processability, respectively. It is, however, difficult to retain the ideal dielectric constant (er) and piezoelectric coefficient (d33) in their composites. Here we show that an interfacial adhesion mechanism (afforded by the chelation technique) in PZT-polymer composites can lead to a dielectric constant that is, remarkably, seven times greater than what is usually found. At frequencies below 40 Hz, the dielectric constant of the composite is higher than in PZT alone (i.e., er > 1300), and this is the first achievement of the ceramic–polymer 0–3 composites as reported. Additionally, a super-high piezoelectric coefficient (d33 > 170) is also obtained owing to the interfacial mechanism. Our finding can lead to a novel way for preparing ceramic–polymer composites with an ultrahigh dielectric constant and ultrahigh piezoelectric coefficient, which are required in many modern electric systems and energy converters.

Controlled Viscoelastic Carbon Nanotube Fluids

It is generally assumed that some qualitative factors, including high organic fraction, size, density, and surface chemistry of the core etc., will dominate the liquid-like behavior of the hybrid nanofluids. For quasi one-dimensional PEG-functionalized carbon nanotubes (PEG-CNTs), this paradigm may be quite different. Our investigations show that controlling the functional density, CNT contents, and aspect ratio of the nanopipes will extremely change the rheological properties of the nanofluids. Namely, a highly viscous longer PEG-MCNT system exhibits a liquid-like behavior throughout all the temperature range of 20−80 °C, but a low viscous shorter PEG-MCNT behaves as an elastic solid and even can give a solid−liquid transition at 56.7 °C. As we model the response of the nanofluids with a deformation mechanism governed by viscous interaction, we have 1/Jx = K × exp(−Ea/RT) (or a/x = K‘ × exp(−Ea/RT)). Then we gain a quantitative understanding of the relationship between functional density, CNT volume frac...

Suppression of energy dissipation and enhancement of breakdown strength in ferroelectric polymer–graphene percolative composites

The percolative polymer composites have recently exhibited great potential in energy storage due to their high dielectric permittivities in the neighborhood of the percolation threshold. Yet high energy dissipation and poor voltage endurance of the percolative composites resulting from electrical conduction are still open issues to be addressed before full potential can be realized. Herein we report the percolative composites based on ferroelectric poly(vinylidene fluoride-co-chlorotrifluoroethylene) as the matrix and SiO2 coated reduced graphene oxide nanosheets as the filler. By capitalizing on the SiO2 surface layers which have high electrical resistivity and breakdown strength, the composites exhibit superior dielectric performance as compared to the respective composites containing bare reduced graphene oxide nanosheet fillers. In addition to greatly reduced dielectric loss, little change in dielectric loss has been observed within the medium frequency range (i.e. 300 kHz–3 MHz) in the prepared composites even with a filler concentration beyond the percolation threshold, indicating significantly suppressed energy dissipation and the feasibility of using the conductor–insulator composites beyond the percolation threshold. Moreover, these composites exhibit a remarkable breakdown strength of 80 MV m−1 at the percolation threshold, which far exceeds those of conventional percolative composites (lower than 0.1 MV m−1 in most cases) and thus enables the applications of the percolative composites at high electric fields. This work offers a new avenue to the percolative polymer composites exhibiting high permittivity, reduced loss and excellent breakdown strength for electrical energy storage applications.

Fluxible Nanoclusters of Fe3O4 Nanocrystal-Embedded Polyaniline by Macromolecule-Induced Self-Assembly

We have prepared Fe3O4 nanocrystal-embedded polyaniline hybrids with well-defined cluster-like morphology through macromolecule-induced self-assembly. These magnetic and electrically conductive composite nanoclusters show flowability at room temperature in the absence of any solvent, which offers great potential in applications such as microwave absorbents and electromagnetic shielding coatings. This macromolecule-induced self-assembly strategy can be readily applied on the fabrication of other ion oxide/conjugated polymer composites to achieve robust multifunctional materials.

Synthesis of poly(vinylidene fluoride-co-bromotrifluoroethylene) and effects of molecular defects on microstructure and dielectric properties

A series of copolymers composed of vinylidene fluoride (VDF) and bromotrifluoroethylene (BTFE) have been synthesized via suspension polymerization up to crystallinity inhibition. P(VDF-co-BTFE) copolymers exhibit different regioregularity in comparison to previously reported PVDF based copolymers owing to differences in size and reactivity of BTFE. The polymerization of the comonomers result in molecular defects that are shown to be both included (single BTFE defects) and excluded (runs of BTFE monomers) from the crystalline phase. The effects of increasing defect concentrations determined by 19F NMR were evaluated on the resulting microstructures by using Fourier transformed infrared spectroscopy, differential scanning calorimetry, and wide-angle X-ray diffraction. Dielectric properties have been investigated in terms of complex permittivity as a function of frequency and temperature. The results indicate that the single BTFE defects are incorporated into the crystalline phase and destabilize the ferroelectric β phase, while the excluded defects reduce both lamellar and lateral crystallite sizes though also resulting in a significant drop in crystallinity. The excluded defects are found to expand the interlamellar region of the crystalline phase, which increases both temperature and frequency dependence of the dielectric β relaxation.

Particle Size Dependence of the Dielectric Properties of Polyvinyledene Fluoride/Silver Composites

The dependence of the dielectric properties of micro- (m-) and nano- (n-) silver (Ag)/poly(vinylidene fluoride) (PVDF) composites on the Ag particle size was determined. The magnitude of dielectric constant and conductivity for the PVDF/n-Ag composites was much higher than that of the PVDF/m-Ag composites at the same Ag volume loading. Our results suggest that the percolative behaviors were quite different for the m- and n-systems owing to the Ag particle size effect. The dielectric property depends on the synergistic effects of interfacial area, interparticle distance, and interfacial adhesion, all of which are highly dependent on the Ag particle size. The increased interfacial area, reduced interparticle distance, and improved interfacial adhesion contributed to the better dielectric properties of the PVDF/n-Ag composites.

NiO hierarchical hollow nanofibers as high-performance supercapacitor electrodes

NiO hierarchical hollow nanofibers (hhNFs) consisting of nanosized NiO particles have been synthesized with electrospun poly(amic acid) nanofiber templates through a simple ion-exchange process and subsequent thermal annealing. By virtue of the hierarchical porous fiber-like morphology, as confirmed by the microstructure analysis, the hhNFs possess dense ion transportation channels, interconnected electron diffusion paths, as well as good structure stability, which are conducive to electrochemical capacitor (i.e., supercapacitor) applications. Electrochemical measurements have validated the excellent electrochemical performance of as-prepared hhNFs, including a high specific capacitance of 700 F g−1 at a discharge current of 2 A g−1, a good cyclic stability (96% capacity retention after 5000 cycles at 5 A g−1), and a remarkable rate capability (80% capacitance retention with the current density increasing from 1 to 5 A g−1). These results along with the simplicity and high efficiency of the material preparation demonstrate that NiO hhNFs are promising electrode materials for high-performance supercapacitor applications. The method presented in this work could be extended to the fabrication of other hierarchical fiber-like nanomaterials for applications including electrochemical capacitors and secondary batteries.

Self-Suspended Polyaniline Doped with a Protonic Acid Containing a Polyethylene Glycol Segment

Self-suspended nanoparticles (NPs) are flowable at or near room temperature without the presence of any solvent. The zero vapor pressure of self-suspended NPs eliminates the environmental concerns associated with using various solvents, and has attracted extensive research interests recently. Various hybrid self-suspended NPs have been synthesized from surface modification of the nanostructures, for example, SiO2, g-Fe2O3, [1,2] TiO2, [3] ZnO, quantum dots, gold, platinum, palladium, CaCO3, [7] and carbon nanotubes. The intrinsic electronic, magnetic, and luminescent properties of various nanostructures have made the self-suspended NPs a promising alternative to conducting lubricants, heat-transfer fluids, batteries, and printing electronics. Aside from the above mentioned self-suspended NPs and their corresponding liquid-like behavior, herein we report a self-suspended polyaniline (PANI) that exhibits a unique thermoreversible gel-like rheological response. Owing to the intrinsic electrical properties of PANI, the self-suspended PANI might exhibit high electroconductivity, excellent electroluminescence, unique electrochromism, and outstanding processability, which could have widespread application in electrochromic devices, medical diagnostic transducers, lightweight batteries, electroluminescent devices, fuel cells, sensors, and actuators. We anticipate that the technique reported here is also applicable to other polymers for exhibiting this unique structure and properties. The self-suspended PANI was prepared using a long-chain protonic acid containing a polyethylene glycol segment (CH3 ACHTUNGTRENNUNG(CH2)8-C6H4 ACHTUNGTRENNUNG(OCH2CH2)10OCH2CH2CH2SO3H) (NPES) as the dopant during the polymerization of the aniline monomers, and then removed the excess of NPES in the polymer solution through extensive dialysis. A dialysis experiment was carried out to investigate the removal of NPES, and the result indicates that all the unreacted NPES molecules can be extracted out of the dialysis bag (see the Supporting Information, Figure S1), which resulted in a solvent-free system. The doped PANI derivatives can self-assemble into nanofibrils. By controlling the average doping ratio of the PANI molecule chain within a system, the PANI nanofibrils can further organize into micelles and exhibit unique thermoreversible gel-like rheology behavior. Although such thermoreversible rheology behavior resembles those of previously reported thermoreversible gels, the two categories are essentially different in that a real thermoreversible gel possesses a fibrillar network morphology. The micelle morphology may originate from the nature of NPES which is quite different from those used in previously reported work involving sulfonic acid doped PANI; for example, NPES contains a long flexible chain segment of polyethylene glycol. These NPES molecules with high flexibility significantly alter the assembly behavior of doped PANI and thus results in PANI derivatives with unexpected properties. The doping ratio of NPES to PANI is represented by the average weight fraction of NPES, fNPES. PANI can exist in a variety of forms which differ in their oxidation state and consist of the reduced unit and the oxidized unit (see the Supporting Information, Figure S2). The reduced unit and the oxidized unit are present in a 1:1 ratio for the as-synthesized PANI molecule because a 1:1 molar ratio of aniline/ ammonium peroxydisulphate is used in the polymerization reaction. Therefore, every two nitrogen atoms in the assynthesized PANI molecule can only be doped by one [a] Dr. J. Huang, Dr. Q. Li, Y. Wang, Y. Wang, Prof. Dr. L. Dong, Dr. H. Xie, Prof. Dr. C. Xiong State Key Laboratory of Advanced Technology for Materials Synthesis and Processing and School of Materials Science and Engineering Wuhan University of Technology Wuhan 430070 (People s Republic of China) Fax: (+86) 27-8765-2879 E-mail : qili@live.whut.edu.cn [b] Prof. Dr. C. Xiong School of Materials Science and Engineering Wuhan Textile University Wuhan 430073 (People s Republic of China) E-mail : cxx@live.whut.edu.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201100437.