Electromagnetic properties of hybrid polymer composites

The effective permeability of a composite material is studied experimentally and theoretically. The composite material has a core—shell-like structure, where the core is a ferromagnetic particle and the shell is a conductive overlayer. It is established that the conducting layer partially shields the magnetic particle and changes the effective magnetization of the said particle. As a result, there is a change of the effective permeability of the hybrid composite. It is shown that both the permeability and the ferromagnetic-resonance frequency of a hybrid copmosite can be changed by the controlled overlayer conductivity and the selection of a relation between the thickness of the layer and the size of the magnetic particle.     

Influence of ionic liquid concentration on the electromechanical performance of ionic electroactive polymer actuators

We have investigated influence of ionic liquid concentration on the electromechanical response of ionic electroactive polymer actuators. Actuators were fabricated from ionomeric membrane and doped with different concentrations of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid. Samples were investigated for their electromechanical and electrochemical characteristics; and it was observed that the maximum electromechanical strain of approximately 1.4% is achieved at 22 wt% ionic liquid content. Increasing ionic liquid concentration results in saturation of the electrode–ionomer interface and formation of ionic double/multi layers, which in turn result an inward accumulation of ions; hence, generate strain in an undesired direction that deteriorates the electromechanical response of the actuator.     

Improving electroactive polymer actuator by tuning ionic liquid concentration

We have fabricated actuators from a blend of fluoropolymer (FP) with ionic liquid (IL). Here a combination of graphene, graphite, and silver nanoparticles is used to raise the electrode conductivity. As the electrode composition is fixed, we found that the actuator displacement increases with decreasing amount of ionic liquid in the polymer gel electrolyte. A maximum strain of 0.48% was observed from peak-to-peak displacement for an actuator with IL/FP = 0.3 in the polymer gel electrolyte. The simulation results indicate that lowering IL concentration leads to a more compact ion distribution in the electrode layers and hence explains the increased strain in the actuators.     

In-situ synthesis of metal nanoparticle-polymer composites and their application as efficient interfacial materials for both polymer and planar heterojunction perovskite solar cells

A new approach for the synthesis of gold nanoparticles (Au NPs) via a simple and fast in-situ generation method using an amine-containing polymer (PN4N) as both stabilizer and reducing agent is reported. The application of the Au NPs-PN4N hybrid material as efficient interfacial layer in different types of solar cells was also explored. The synthesized Au NPs show good uniformity in size and shape and the Au NPs doped PN4N hybrid composites exhibit high stability. Amine-containing polymers are good cathode interfacial materials (CIMs) in polymer solar cells (PSCs) and planar heterojunction perovskite solar cells (PVKSCs). The performance of the PSCs with Au NPs doped PN4N CIMs is largely improved when compares to devices with pristine PN4N CIM due to the enhanced electronic properties of the doped PN4N. Furthermore, by incorporating larger Au NPs into PEDOT:PSS to enhance absorption of the light harvesting layer, power conversion efficiencies (PCEs) of 6.82% and 13.7% are achieved for PSC with PCDTBT/PC₇₁BM as the light harvesting materials and PVKSC with a ∼280 nm-thick CH₃NH₃PbI_3−xCl_x perovskite layer, respectively. These results indicate that Au NPs doped into both PEDOT:PSS and PN4N interlayers exhibited a synergistic effect in performance improvement of PSCs and PVKSCs.     

石墨烯金属基复合材料研究进展

石墨烯因为其极高的导电导热性能和优异的力学性能被认为是理想的金属基复合材料增强体。本文从导电性、导热性、力学性能等方面介绍了近年来石墨烯增强金属基复合材料的研究进展,概述了产业化进程,分析总结了石墨烯金属基复合材料产品研发中的主要难点,并对石墨烯金属基复合材料的应用前景作了展望。     

Improving thermal conductivity of polymer composites in embedded LEDs systems

Polymer embedding of LEDs increases safety and waterproof levels in LED based lighting systems. The embedding allows for mechanical flexibility of these systems. The increase of polymer thermal conductivity has been a research challenge for decades. Here, we suggest materials for enhancing thermal conductivity in polymer embedded LED systems. We demonstrate that thermally conductive fillers into the polymer matrix to form a composite improved heat transfer from the LEDs to the environment. Non metallic boron nitride with a high intrinsic thermal conductivity is a good candidate. Thermal conductivity of basic polymer PDMS with various filler size and polymer ratios is reported here. Here, an in situ measurement tool to fast evaluate the quality of the composites in LED applications is demonstrated. Future work will focus on further increasing the thermal conductivity of the composites by using different mixtures.     

碳纳米材料在导热聚合物复合材料中的应用

介绍了三种具有较高热导率的碳纳米材料:碳纳米管、纳米石墨片及纳米碳纤维的结构与导热性能,概述了三种碳纳米材料在改善聚合物复合材料导热性能方面的应用,重点分析了碳纳米材料的种类、用量、表面改性方法及复合材料的制备方法对聚合物复合材料热导率的影响,并对含碳纳米材料的导热聚合物复合材料未来的发展方向进行了分析与展望。     

Study of electric heating effects on carbon nanotube polymer composites

Carbon nanotube (CNT) composites are ideal materials for electric heating (E-heating) components owing to their lightweight, rapid heating ability, and easy processability for microscale patterns. However, careful consideration of their thermal stability and the effect of E-heating on CNT composites is necessary to ensure safety and long-term durability. Thermal degradation of CNT composites as a result of E-heating was found to be much more severe than air convection heating (C-heating). Enhanced mechanical properties of CNT composite were observed after 40 h C-heating, while E-heating composites became fragile that the matrix was severely damaged at the same temperature/hours. Consequently, the electrical resistance of the CNT composite for E-heating was dramatically increased. To avoid thermal degradation and a dramatic increase in resistance, the E-heating temperature should be much lower than the temperature limit of thermally stable polymer. In addition, thermal degradation of the polymer matrix could be relieved through the addition of CNTs, which can be understood as parallel resistor model, by spreading thermal concentration throughout the polymer matrix.     

The efficiency of application of magnetic polymer composites as radio-absorbing materials

The results of investigation of the complex permittivity and permeability of polymer composite materials with different magnetic fillers in the frequency range of 1 MHz to 10 GHz are presented. The possibility of controlling the frequency characteristics of permeability and permittivity and the absolute values of these parameters via the formation of hybrid composites with multicomponent magnetic filler is shown. The efficiency of application of magnetic polymer composites as absorbing materials for the RF and microwave bands is analyzed.     

Ti金属对电磁屏蔽复合材料影响的实验研究

对于环境苛刻的电磁兼容环境下,常用电磁屏蔽材料已不能满足对设备及相关系统的保护作用,如高低温或强酸碱的特殊工作环境等,本文通过对比几种金属参数,并将Ti金属与其他性能优良的金属结合制备出高效能电磁屏蔽复合材料,利用法兰同轴测量电磁屏蔽效能法测得含Ti金属合金电磁屏蔽复合材料的电磁屏蔽效能在工作带宽7—15GHz下平均可达85d B。     

Radio absorbers based on magnetic polymer composites and frequency-selective surfaces

Polymer composites filled with carbonyl iron are considered. A method is proposed for extending the operating frequency band of such radio absorbers with the help of band-reflection frequency-selective surfaces (FSSs). A functional relationship between the reflection characteristics of a radio absorber and the generalized characteristics of an FSS—the resonance frequency and Q factor—is established. On the basis of the rigorous theory of integral equations, programs are developed for computation of the reflection coefficient of a radio absorber with an FSS implemented as a biperiodic lattice with ring elements. The reflection coefficients of a series of samples are measured in the frequency band 1–10 GHz.     

Optical absorption behaviour of metal/semiconductor hybrid nanoparticle composites

Semiconductor/metal hybrid nanoparticle composites have been prepared in a glass host by a modified melt/quench process and examined with respect to their optical properties. The coated hybrid nanoparticles exhibit surface plasmon resonance absorption spectra which are red-shifted compared with that of a dispersion of homogeneous Ag nanoparticles in the same host. The position of the plasmon resonance was a sensitive function of the heat treatment schedule. A theoretical model based on effective medium theory for the coated hybrid particles was used to describe the shift of the plasmon position in the optical spectra as a function of the coating thickness. The calculated absorption spectra of the coated hybrid particles agree well with the experimental results. © 1998 John Wiley & Sons, Ltd.     

Direct visualization of percolation paths in carbon nanotube/polymer composites

Composites of single-walled carbon nanotubes (SWNT) and conjugated polymers are highly interesting as active semiconducting layers in solution-processable and flexible electronics. Understanding the percolation behavior and percolation threshold for electrical conductivity in these composites is a prerequisite for future applications. Here, we investigate the concentration and length dependence of on-currents and apparent mobilities for selectively dispersed, semiconducting (6,5) single-walled carbon nanotubes in a matrix of the dispersing polyfluorene-bipyridine copolymer (PFO-BPy) through field-effect transistor measurements. More importantly, we directly visualize the percolation paths at and above the percolation limit by near-infrared electroluminescence (EL) imaging with high spatial resolution. EL imaging reveals the various shapes of critical percolation paths at the threshold and the non-uniformity of charge transport even at high SWNT concentrations. We also find that percolation paths differ depending on the assignment of the injecting electrodes probably due to different injection barriers and variation of nanotube density at the electrodes.     

基于金属基复合材料的硅通孔热应力仿真分析

硅通孔(TSV)技术是三维集成电路中的关键技术,对信号传输以及热量的传导起到关键的作用,其热可靠性的问题一直都是研究热点。基于Comsol Mulitiphsics平台,通过有限元仿真分析,研究了金属基复合材料对TSV热应力的影响。并进一步研究了在不同通孔直径以及不同TSV高度下,碳纳米管(CNTs)、碳纳米管铝(CNTs/Al)以及碳纳米纤维铜(CNFs/Cu)等复合材料和传统金属材料的等效热应力情况。结果表明:与传统金属材料相比,金属基复合材料CNTs/Al以及CNFs/Cu均能有效降低TSV的热应力,提高TSV的热可靠性;并且对于CNTs含量不同的金属基复合材料,其TSV的等效热应力也会有所不同,需综合考虑合理选择CNTs的含量。     

Photoconductivity of organic polymer films doped with porous silicon nanoparticles and ionic polymethine dyes

Features of electrical conductivity and photoconductivity of polyvinylbutyral films containing porous silicon nanoparticles and similar films doped with cationic and anionic polymethine dyes are studied. Sensitization of the photoelectric effect by dyes with different ionicities in films is explained by the possible photogeneration of holes and electrons from dye molecules and the intrinsic bipolar conductivity of porous silicon nanoparticles. It is assumed that the electronic conductivity in porous silicon nanoparticles is higher in comparison with p-type conductivity.     

In-situ analysis of thermal properties of polymer composites by embedded LED temperature sensor

Real time and accurate measurement of thermal conductivity of polymer composites with thermal conductive fillers challenges researchers in industrial application. Here, we present an in-situ measurement approach by embedding a LED or diode as a combined heat source and temperature sensor into the filled polymer and using the well-established transient measuring method based on forward voltage variation to determine the temperature response of the sensor in polymer. Numerical model fitting is applied to estimate the thermal conductivity of the polymer composites with different filler/polymer ratios. These findings are compared with other thermal conductivity test methods such as the laser flash method and the Modular Differential Scanning Calorimeter (MDSC). The proposed approach provides a quick way of measuring the thermal conductivity in relatively thin polymer composites and agrees well with the MDSC method. Another advantage is that it can work with the real samples made for the application in mind, so its results can be used directly.     

Numerical prediction of failure paths at a roughened metal/polymer interface

Debonding of polymer–metal interfaces often involves both interfacial and cohesive failure. This paper extends the investigation of Yao and Qu presented in [Yao Q, Qu J. Interfacial versus cohesive failure on polymer–metal interfaces in electronic packaging – effects of interface roughness. J Electr Packag 2002;124;127–34] towards a numerical fracture mechanics model that is used to quantitatively predict the relation between cohesive and adhesive failure on a metal–polymer interface. As example, an epoxy–aluminum interface is investigated. The competition between adhesive and cohesive failure depending on surface roughness parameters will be studied. Understanding of these phenomena could enable the optimization of interface properties for different applications.     

Semitransparent,thin metal grid-based hybrid electrodes for polymer solar cells

A conducting polymer/thin Au grid hybrid electrode was investigated to replace an indium tin oxide (ITO) electrode in polymer solar cells (PSCs). Semitransparent, thin Au films were combined with transparent conducting PEDOT:PTS films (70 nm thickness, ~90% of transmission), to form Au grid/conducting polymer hybrid electrodes. The mixed self-assembled monolayers coated on the Au grids and glass substrate provided uniform and adherent coating of conducting polymer on the monolayer, achieving a low contact resistance of 0.6 Ω mm. This resulted in a robust PEDOT:PTS/Au grid hybrid structure.Theoretical calculation showed the dependence of figure of merits (FM) on the filling ratio (=grid width/(grid spacing+grid width)) and Au thickness. In addition, grid spacing had an effect on the surface morphology of the conducting polymer; decreasing the grid spacing produced more flat surface of the overlayers, leading to enhanced performance of PSCs. The fabricated PSCs based on these hybrid electrodes showed that the best efficiency of 3.54%, comparable to that of devices based on an ITO electrode, was obtained at the filling ratio of 0.5 for 15 nm-thick Au electrodes, which was different from that predicted from the theoretical calculation, probably due to the grid spacing effects on the charge collection efficiency.     

Tunable permittivity in polymer composites filled with Si-based semiconductors by regulating induced polarization

Induced polarization shows a significant influence on dielectric permittivity of 0–3 polymer composites containing Si-based semi-conductive fillers. The nature of induced polarization is the increased electric conductivity or decreased band gap in Si-based semi-conductive fillers. In this work, the dependence of induced polarization onto particle size of α-SiC filler together with polarity of polymer matrix and Si-based semi-conductive filler has been elaborately investigated by detecting the permittivity of composites. It was found that increasing the grain size of SiC filler, improving the polarity of polymer matrix and reducing the band-gap of Si-based semi-conductive filler could favor the enhancement of the overall induced polarity in the composites. As a result, the significantly improved dielectric permittivity of composites higher than both of the neat polymer and filler was observed depending on the constituents of the composites. The highest dielectric permittivity of ~215@1 kHz was achieved in poly(vinyl alcohol) based composite filled with 60 vol% of 12 µm SiC particles. The dielectric permittivity of these 0–3 composites could be well tuned in a wide range through altering their constituents. This work might open a facile route to obtain the promising high-performance dielectric composite materials by regulating the degree of induced polarization.