Wangshu Tong

Green dielectric materials composed of natural graphite minerals and biodegradable polymer

Polymeric nanocomposites are a promising dielectric due to their low cost, easy processability and flexibility but most polymers are difficult to treat and recycle leading to “white pollution”. Here, we report an eco-friendly “green” dielectric material made from natural graphite minerals and biodegradable poly(butylene succinate) synthesized by solution casting and hot pressing. Dielectric constant of resulting composite films agreed quite well with percolation theory and a low percolation threshold fc = 5.98% was obtained due to a high aspect ratio of natural graphite minerals. Composite films possessed a high dielectric constant of 113, around 28 times higher than that of pristine PBS (103) when volume fraction reached 5.5%. Furthermore, dynamic mechanical properties of composite films can be improved at the same time. Dielectric constant of composite films can be greatly improved by incorporating natural graphite minerals while mechanical flexibility can be maintained to be as good as that of pure polymer matrix.

Polyimide composites composed of covalently bonded BaTiO3@GO hybrids with high dielectric constant and low dielectric loss

Novel flexible three-phase high-k polyimide (PI) composites were fabricated by the incorporation of covalently bonded BaTiO3@graphene oxide (BaTiO3@GO) hybrids in which the BaTiO3@GO hybrids were prepared by the reaction of amino modified BaTiO3 particles and GO. A series of analyses, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman and XRD demonstrated that amino modified BaTiO3 particles were successfully grafted onto the surface of GO. A dielectric constant as high as 285 (100 Hz), which was eighty times that of a pure PI film, a lower dielectric loss as low as 0.25 and high-frequency-shift dielectric relaxation were obtained for BaTiO3@RGO/PI composites as the fraction of BaTiO3@GO was 20 wt% (the corresponding volume fraction is 8 vol%). The flexible, high-k BaTiO3@RGO/PI composites have promising potential applications for capacitors and electronic devices in the fields of micro electron.

Constructing the magnetic bifunctional graphene/titania nanosheet-based composite photocatalysts for enhanced visible-light photodegradation of MB and electrochemical ORR from polluted water

Photocatalysis is a promising strategy to address the global environmental and energy challenges. However, the studies on the application of the photocatalytically degraded dye-polluted water and the multi-purpose use of one type of catalyst have remained sparse. In this report, we try to demonstrate a concept of multiple and cyclic application of materials and resources in environmentally relevant catalyst reactions. A magnetic composite catalyst prepared from exfoliated titania nanosheets, graphene, the magnetic iron oxide nanoparticles, and a polyelectrolyte enabled such a cyclic application. The composite catalyst decomposed a methylene blue-polluted water under visible light, and then the catalyst was collected and removed from the treated water using a magnet. The photocatalytically treated water was then used to prepare the electrolyte in electrochemical reductive reactions and presented superior electrochemical performance compared with the dye-polluted water. The composite catalyst was once again used as the cathode catalyst in the electrochemical reaction. Each component in the composite catalyst was indispensable in its catalytic activity, but each component played different roles in the photochemical, magnetic recycling, and electrochemical processes. We expect the report inspire the study on the multi-functional catalyst and cyclic use of the catalytically cleaned water, which should contribute for the environmental and energy remedy from a novel perspective.

Surface-Enhanced Raman Spectra Promoted by a Finger Press in an All-Solid-State Flexible Energy Conversion and Storage Film

Electrochemically up-regulated surface-enhanced Raman spectroscopy (E-SERS) effectively increases Raman signal intensities. However, the instrumental requirements and the conventional measurement conditions in an electrolyte cell have hampered its application in fast and on-site detection. To circumvent the inconveniences of E-SERS, we propose a self-energizing substrate that provides electrical potential by converting film deformation from a finger press into stored electrical energy. The substrate combines an energy conversion film and a SERS-active Ag nanowire layer. A composite film prepared from a piezoelectric polymer matrix and surface-engineered rGO that simultaneously presents high permittivity and low dielectric loss is the key component herein. Using our substrate, increased E-SERS signals up to 10 times from a variety of molecules were obtained in the open air. Various tests on real-life sample surfaces demonstrated the potentials of the substrate in fast on-site detection.

A New Way to Promote Molecular Drug Release during Medical Treatment: A Polyelectrolyte Matrix on a Piezoelectric-Dielectric Energy Conversion Substrate

Enhanced drug releases in a timely manner during urgent medical treatments would significantly enhance the prognosis of patients. Inspired by the facilitated molecular transports by the potentials, an enhanced drug release strategy driven by mechanical disturbances that widely exist in medical treatment processes is proposed. This strategy is enabled by a functional material comprised of multilayers of dendrimers as the drug reservoir, which are built on a piezoelectric-dielectric flexible film with reduced graphene oxide fillers. The generated voltages are higher and last longer than that in regular piezoelectric films. Photochemical crosslinking leads to a stable drug matrix which is even sustained in electric fields and high ionic strengths. The device enhances releases of positively, negatively, and zwitterionically charged molecules in response to mechanical stimuli and supports high cell viabilities. An illustrative application is demonstrated by preparing the material on the surface of a gastric lavage tube. The results show that the release of antiemetic drug increased by 200% within 60 min in response to forces mimicking human swallowing. This study contributes an integrative material that can realize electrically triggered releases that are previously only realized using complicated electrochemical setups. It is believed that this material can facilitate medicine applications in various emergent situations.

A Promising Material by Using Residue Waste from Bisphenol A Manufacturing to Prepare Fluid-Loss-Control Additive in Oil Well Drilling Fluid

The residues mixture from Bisphenol A manufacturing process was analyzed. Fourier transform infrared (FTIR) spectroscopy, gas chromatography-mass spectrometry (GC-MS), and nuclear magnetic resonance (NMR) were used to characterize the residues. The results indicated that the residues were complex mixture of several molecules. 3-(2-Hydroxyphenyl)-1,1,3-trimethyl-2,3-dihydro-1H-inden-5-ol and phenol were the main components of the residues. The technical feasibility of using it as phenol replacement in fluid-loss-control additive production was also investigated. The fluid-loss-control capacity of the novel additive was systematically investigated. It was discovered that the well fluid-loss performance of the prepared additive can be achieved, especially at high temperature.

Dielectric property of all-organic composite film composed of cobalt phthalocyanine and poly(vinylidene fluoride)

Due to the mechanical flexibility, tunable properties and easy processing, polymer based composites, especially the electroactive polymer composites based on the poly(vinylidene fluoride), which can be applied in the sensors, transistors and the capacitors, have been widely investigated. In this paper, all-organic composite films composed of cobalt phthalocyanine and poly(vinylidene fluoride) with high dielectric permittivity are simply synthesized by solution casting on the glass. The dielectric property over the broad frequency from 1Hz to 107Hz is investigated. The high dielectric permittivity 86.4(102Hz), about 9 times of the pure poly(vinylidene fluoride), is achieved when the fraction of the cobalt phthalocyanine is 20wt% that is similar to other semiconductors reinforced polymer composites. The significant increase of the dielectric constant and the dielectric loss tangent can be explained by the threshold theory. The origin of dramatically enhancement of dielectric permittivity and dielectric loss tangent over the low frequency is the Maxwell-Wagner-Sillars polarization. The results show that the dielectric property is very sensitive to the fraction of cobalt phthalocyanine. Additionally, when the fraction of the cobalt phthalocyanine was 10wt%, the dielectric permittivity and the conductivity of composite films are 17.1 and 1.1×10-6s/cm respectively which indicated that it is potentially applied in the capacitors.