Electrospun Fluorinated Polyimide/Polyvinylidene Fluoride Composite Membranes with High Thermal Stability for Lithium Ion Battery Separator

The separator with excellent mechanical and thermal properties are highly required for lithium ion batteries(LIBs).Therefore,it is crucial to develop novel nanofbrous membranes with enhanced mechanical strength and thermal stability.In this work,the fuorinated polyimide(FPI)was synthesized and blended with polyvinylidene fuoride(PVDF)to fabricate composite nanofbrous membranes(CNMs)via electrospinning method.Benefting from the introduction of aromatic FPI,the prepared PVDF/FPI nanofbrous membranes were endowed with enhanced mechanical strength and thermal stability.When the FPI content increased from 0 to 30 wt%,the tensile strength of composite nanofbrous membranes enhanced from 1.57 to 2.30 MPa.Moreover,there are almost no dimensional shrinkage for the CNM-30 containing 30 wt%FPI after heat treatment at 160℃ for 1 h.Furthermore,the prepared CNMs show improved electrochemical performances in comparison with neat PVDF and commercial Celgard membranes.The electrolyte uptake and ionic conductivity of the CNMs could reach to 522.4% and 1.14 ms·cm^(−1),respectively.The prepared CNMs could provide an innovative and promising approach for the development and design of high-performance separators.

Micro-mechanical model for predicting the elasto-plastic behavior of composites based on secant formulation method

To predict the Elasto-Plastic Behaviors(EPBs)of aligned inclusions reinforced composites,this paper develops an interpolative Mori-Tanaka/Double-Inclusion(MT-DI)homogenization model with the secant formulation,and gives the numerical implementation algorithms of the developed MT-DI model with the secant formulation.The Finite Element(FE)homogenization method is implemented to provide the "exact" EPBs of the composites and thus validate the MT-DI model with the secant formulation.The MT-DI model with the 2 nd-order secant formulation is validated to provide the more accurate predictions,while the MT-DI model with the 1 st-order secant formulation always gives the stiffer predictions.The results show that using the macro-stress and macrostrain as the inputs,the MT-DI model with the secant formulation gives the identical predictions.The predictions of the MT-DI model with the secant formulation vary between those of the MT and DI models with the secant formulation.Meanwhile,the MT-DI model with the secant formulation does not predict the accurate EPBs for the phases of the composites.

A Method to Adjust Dielectric Property of SiC Powder in the GHz Range

The SiC powders by AI or N doping have been synthesized by combustion synthesis, using AI powder and NH4Cl powder as the dopants and polytetrafluoroethylene as the chemical activator. Characterization by X-ray diffraction, Raman spectrometer, scanning electron microscopy and energy dispersive spectrometer demonstrates the formation of Al doped SiC, N doped SiC and the AI and N co-doped SiC solid solution powders, respectively. The electric permittivities of prepared powders have been determined in the frequency range of 8.2-12.4 GHz. It indicates that the electric permittivities of the prepared SiC powders have been improved by the pure AI or N doping and decrease by the AI and N co-doping. The paper presents a method to adjust dielectric property of SiC powders in the GHz range.

In-situ growth of gold nanoparticles on electrospun flexible multilayered PVDF nanofibers for SERS sensing of molecules and bacteria

Plasmonic surface of flexible multilayered nanofibers possesses special superiority for the surface-enhanced Raman scattering(SERS)sensing of molecules and microbial cells.However,the fabrication of flexible plasmonic nanofibers with high sensitivity and reproducibility is difficult.Herein,we report a smart strategy for fabricating flexible plasmonic fibers,in which compact and homogeneous gold nanoparticles(Au NPs)are in-situ grown on the high-curvature surface of multilayered fibers of electrospun polyvinylidene fluoride(PVDF).Firstly,the surface of PVDF fibers is changed electrically,and Au seeds are deposited on the surface of PVDF fibers using electrostatic driving force.Secondly,a stable AuI_(4)−complex is formed employing coordination between I−and AuCl4−ions,which could decrease the reduction potential of AuCl4−and restrain the self-nucleation,and then the reduction reaction of AuI4−is initiated by introducing PVDF@Au seeds to pull down the barrier of potential energy.Finally,in-situ growth of AuNPs is generated on the high-curvature surface of PVDF nanofibers,and large-scale hotspots are generated by adjacent AuNPs coupling in the three-dimensional(3D)space of multilayered fibers.Membrane of PVDF@Au nanofibers also realizes the sensitive detection of thiram molecules(low limit of detection of 0.1 nM)and good reproducibility(relative standard deviation of 10.6%).Meanwhile,due to the multilayered construction of PVDF@Au nanofibers,a valid SERS signal on 3D surface of bacteria could be generated.3D distribution of hotspots on multilayered PVDF@Au nanofibers gives a clear advantage for SERS sensing of organic molecules and microbial cells.