Synthesis of graphite incorporated core–shell composite of styrene-methylacrylate/polyaniline by surfactant free mini-emulsion polymerization and evaluation of their electrical property

A series of core–shell particles (SMAP/G) having polystyrene-methylacrylate copolymer (styrene-methyl acrylate) as the core and graphite incorporated polyaniline as the shell were prepared by surfactant free mini-emulsion polymerization. Here poly (SMA) copolymer latex particles were first dispersed in water and then coated with polyaniline (PA) by in situ polymerization of aniline in presence of different percentage (0.25, 0.50 and 1.0%) of graphite. The composite particles were characterized by FTIR, XRD and TGA. TEM and SEM analysis confirms the core–shell morphology of the composite particles. DC electrical conductivity values of all the samples were measured by using a standard four-probe method. The effect of temperature and the amount of graphite incorporated into the PA shell on the dc electrical conductivity of the core–shell composites was investigated. The electro chemical behaviour of the core–shell composites was studied by using a cyclic voltammeter. Electro chemical data shows that the core–shell composites are sufficiently stable under redox potential of 50 mV/s to find applications in various electronic devices.     

碳系分散体填充聚合物基PTC复合材料的研究进展

总结了碳系分散体(包括碳黑、石墨、碳纤维)作为导电填料填充聚合物形成聚合物基PTC复合材料的研究进展。对聚合物基体及碳系导电填料进行共混或接枝改性是当前主要的研究方向。认为在碳系／聚合物体系中加入合适的金属系导电填料可能会更有利于提高复合材料的PTC强度和稳定性。     

炭黑填充多组分高分子导电复合材料的研究进展

基体为多组分高分子的填充型导电复合材料中存在“双逾渗”行为,能有效地降低导电填料的逾渗阈值,克服由填料含量过高而导致的材料加工性和力学性能下降的缺点,并能削弱材料的负温度系数(NTC)效应。本文基于国内外炭黑(CB)填充多组分高分子导电复合材料的研究进展,对CB分布、多组分高分子基体对材料体系导电性的影响、导电机理以及电导-温度依赖性等方面进行评述。     

Studies on Ag/Polypyrrole composite deposited on the surface of styrene-methyl acrylate copolymer microparticles and their electrical and electrochemical properties

The colloidal dispersion of silver nano particles with different concentration (0.5, 1.0 and 1.5%) were synthesized by chemical reduction method using citrate as reducing agent. Colloidal dispersion of Poly (Styrene-co-methylacrylate) (SMA) was synthesized by mini emulsion polymerization technique. The SMA micro particles were used as template for the polymerization of pyrrole in presence of dispersion of silver nano particles by oxidative coupling method. The Ag nano particles and the final core–shell composite particles were characterized by UV–visible, FTIR, SEM, EDX and TEM analysis. The thermal analysis revealed that the SMA-PPy-Ag core–shell particles possesses better thermal stability in comparision with bare PPy-Ag nano composite. The dc conductivity and the electro chemical behaviour of the particles were studied by using a standard four-probe method. The dependence of electrical conductivity of the composites on the concentration of silver in the polypyrrole shell and the methyl acrylate content in SMA copolymer were also investigated The core–shell particles show reversible electrochemical response as revealed by the cyclic voltammetry study.     

Enhanced thermal conductivity of epoxy nanocomposites filled with hybrid filler system of triethylenetetramine-functionalized multi-walled carbon nanotube/silane-modified nano-sized silicon carbide

Multi-walled carbon nanotubes (MWCNTs) were first treated by a 3:1 (v/v) mixture of concentrated H₂SO₄/HNO₃, and then triethylenetetramine (TETA) grafting was carried out. Nano-sized silicon carbide particles (SiC_np) were modified by the silane coupling agent. Epoxy nanocomposites filled with hybrid filler system containing TETA-functionalized MWCNTs and silane-modified SiC_np were prepared. The investigation on the thermal conductivity of epoxy nanocomposites filled with single filler system and hybrid filler system was performed. Chemical surface treatment is conducive to the enhancement of thermal conductivity of epoxy composites. The thermal conductivity of epoxy composites with hybrid filler system is higher than that of epoxy composites with any single filler system (functionalized MWCNTs or modified SiC_np), which is due to the effective combination of MWCNT-to-MWCNT and SiC_np-to-SiC_np conductive networks. Hybrid filler system could provide synergistic effect and cost reduction simultaneously.     

Preparation, characterization, and fluorescence properties of well-dispersed core–shell CdS/carbon nanoparticles

The core–shell CdS-carbon (CdS/C) nanoparticles were synthesized for the first time via a facile pyrolysis approach of bis(β-mercaptoethanol)-cadmium(II) as a single-source precursor. After using acid treatment method, well-dispersed and homogeneous core–shell CdS/C nanoparticles were obtained. The morphology, structure, and properties of CdS/C nanoparticles were investigated by X-ray diffraction (XRD), Raman spectra, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and fluorescence spectroscopy. Most of the prepared nanoparticles presented core–shell structures with core diameter of ~10 nm and shell thickness of ~4 nm. The CdS core belonged to hexagonal crystal system. The carbon shell was employed as a good dispersion medium to form well-dispersed small sized CdS particles. XRD and XPS results revealed that there is an interaction between CdS core and carbon shell. Fluorescence measurement showed that the monodispersed CdS-carbon nanoparticles exhibit remarkable fluorescence enhancement effect compared with that of the pristine CdS nanoparticles, which indicates the prepared nanoparticles are a promising photoresponsive material.     

Thermal conductivity of epoxy composites with a binary-particle system of aluminum oxide and aluminum nitride fillers

Aluminum oxide and aluminum nitride with different sizes were used alone or in combination to prepare thermally conductive polymer composites. The composites were categorized into two systems, one including composites filled with large-sized aluminum nitride and small-sized aluminum oxide particles, and the other including composites filled with large-sized aluminum oxide and small-sized aluminum nitride. The use of these hybrid fillers was found to be effective for increasing the thermal conductivity of the composite, which was probably due to the enhanced connectivity offered by the structuring filler. At a total filler content of 58.4 vol.%, the maximum values of both thermal conductivities in the two systems were 3.402 W/mK and 2.842 W/mK, respectively, when the volume ratio of large particles to small particles was 7:3. This result was represented when the composite was filled with the maximum packing density and the minimum surface area at the same volume content. As such, the proposed thermal model predicted thermal conductivity in good agreement with experimental values.     

氮化硼及其在导热复合材料中的研究进展

目的 从氮化硼的表面改性、取向结构、形态含量以及杂化填料等4个方面介绍氮化硼填充导热复合材料的基础研究进展,为导热聚合物在电子封装领域的应用提供一定的研究思路。方法 通过对近年来国内外的相关文献进行分析和总结,归纳出微/纳氮化硼的产业化制备方法以及产品性能,并介绍微/纳氮化硼填料对聚合物基复合材料导热性能影响的研究情况。结论 氮化硼各方面均具有优异的性能,可用于制备填充型高导热复合材料。     

Rheologisches Verhalten hochgefüllter Kunststoffe. Einfluss der Füllstoffe

Rheological behavior of high filled polymers. Influence of fillers The viscose properties of high filled thermoplastic composites were studied. It was shown that the rheological properties of high filled plastics depend generally on behavior of the flow of a matrix polymer, the structure of the disperse phase, the interaction between the polymer and the filler and between separate particles. In the work a theoretical relation between filled and unfilled polymer as a function of the filler content and interactions between components was presented. On the basis of the developed model a stochastic structure of filled material and non‐linear viscose properties of the polymer melt can be considered.     

炭黑结构度对HDPE/CB导电复合材料导电网络形成与破坏的影响

采用熔融混合方法制备高密度聚乙烯/炭黑(HDPE/CB)导电复合材料,比较不同结构度CB填充体系的逾渗曲线和温度-电阻行为,并研究了不同含量、不同结构度CB填充的HDPE的结晶行为。实验结果表明,高结构度CB可使填充体系逾渗值显著下降(本研究中可降低为2.7%);低结构度CB填充体系的正温度系数(PTC)效应强度比高结构度CB填充体系高出约3;降温过程中,温度-电阻率曲线上出现电阻突变峰的强度随着CB结构度的降低而增强;差示扫描量热(DSC)和广角X射线衍射(WAXD)结果显示,CB粒子的加入对HDPE的结晶行为没有显著影响。     

Three-dimensional fractal analysis of fracture surfaces in titanium–iron particulate reinforced hydroxyapatite composites: relationship between fracture toughness and fractal dimension

Fractal dimension has been considered as a measure of fracture surface roughness of materials. Three-dimensional (3D) surface analysis is anticipated to provide a better evaluation of fracture surface toughness and fractal dimension. The objective of this study was to quantify the fracture surfaces and identify a potential relationship between fracture toughness and fractal dimension in a new type of core–shell titanium–iron particulate reinforced hydroxyapatite matrix composites using SEM stereoscopy coupled with a 3D surface analysis. The obtained results showed that both fracture surface roughness and fractal dimension increased with increasing amount of core–shell Ti–Fe reinforcing particles. The fractal dimension was observed to be a direct measure of fracture surface roughness. The fracture toughness of the composites increased linearly with the square root of fractal dimensional increment (i.e., followed the Mecholsky–Mackin equation well) due to the presence of Ti–Fe particles along with the effect of porosity in brittle materials. The 3D fractal analysis was suggested to be a proper tool for quantifying the fracture surfaces and linking the microstructural parameter to fracture toughness.     

Effect of extensional strain on the resistivity of electrically conductive nitrile-rubber composites filled with carbon filler

The resistivity and mechanical properties of nitrile-rubber based conductive composites filled with short carbon fibres (SCFs) and mixed filler system (SCF + carbon black) are studied as functions of the extensional strain and the strain rate. It has been observed that both strain and strain rate have a strong influence on the resistivity of the composites. The sensitivity of the change in resistivity against the strain and strain rate depends on the concentration as well as the type of conductive filler. SCFs impart higher conductivity to the composite than a blend of SCFs and carbon black at the same level of loading parts per hundred of rubber (p.h.r.). Composites filled with a mixed filler system show high mechanical properties in contrast to those of SCF-filled composites. The change in resistivity with the degree of strain is less pronounced in mixed-filler-filled composites than in only carbon-fibre-filled composites. The mechanical properties of the composites are dependent on the polymer-filler interaction whereas change in resistivity is dependent on the transient arrangement of the conducting components in the polymer matrix. A good correlation exists between mechanical and electrical response to the strain sensitivity.     

Model representation of filled polymers

We have investigated the mechanical properties and dielectric relaxation in polyamide-6 composites with fiber glass and mica. We propose a new model for filled polymers, assuming that the material consists of two interpenetrating continuous phases. The first phase is the polymer sorbed on the surface of the filler particles, mechanically stronger and having a higher modulus of elasticity. The second phase is the unsorbed polymer. The calculated mechanical characteristics of the composites (tensile strength and modulus of elasticity) agree well with experimental data. Translated from Izmeritel'naya Tekhnika, No. 8, pp. 53–56, August, 1998.     

Carbon based conductive photoresist

A conductive photoresist for photolithographic application was studied here. The negative near-UV sensitive epoxy-based photoresist was used as a polymer matrix and conductive carbon black was used as functional filler. DC electrical resistivity of composite as a function of filler concentration has a well-known S-shape. After UV-exposure the resistivity of the composite decreases for almost five orders of magnitude, mostly at percolation threshold (approx. 0.6 vol.%). This effect can be attributed to the fully cross-linked polymer structure formed during UV-exposure of the composite. The resistivity of prepared samples also depend on the state of dispersion of the functional filler obtained using different dispersing additives. Composites with better dispersed particles have lower resistivities. This effect remained below one order of magnitude and decreased after UV-exposure. The composites with carbon black concentration of up to 1.1 vol.% are suitable for spin-coating and photolithography.     

Model filled rubber Part V Mechanical properties of rubbery composites

Monodisperse size crosslinked polymeric particles of specific chemical compositions, synthesized by emulsifier-free emulsion polymerization, were used as model fillers to study the effect of filler chemical composition on stress-strain behavior of rubbery composites. The modulus, E or G of filled composites increased while the stress and the strain at break decreased with increasing filler-matrix interactions. Physical crosslinking, either due to particle clustering or a network of filler particles with an adsorbed polymer layer supplemented chemical crosslinking. As a result, the overall crosslink density(chemical and physical) was effectively enhanced. The strength of the physical networks, and hence the stiffness of the composites increases with increasing particle-matrix interactions. However, excessively strong matrix-filler interaction would cause a loss of polymer flexibility at the particle-matrix interface, resulting in a decreased stress and elongation at break of the particle filled composites in the order PS > PMMA > PSVP.     

具有隔离结构的超高分子量聚乙烯/镍高导电复合材料

采用化学镀手段制备金属镍包覆的超高分子量聚乙烯复合粒子,通过热压成型方法制得具有隔离结构的超高分子量聚乙烯(UHMWPE)/镍(Ni)高导电复合材料。通过调节金属(镍)镀层厚度及加工温度考察不同Ni含量及加工温度对复合材料导电性能的影响。结果表明,复合材料具有明显的导电逾渗行为;通过化学镀工艺可有效提高金属填料与基体的结合力,同时实现金属镍在聚合物基体中的选择性稳定分布,构建具有隔离结构的导电网络,使得复合材料的逾渗值降低至1.02%(体积分数)。基于金属填料优异的导电性能,在Ni体积分数仅为2.53%时,复合材料的电导率达到2648S/m。此外,降低复合材料的加工成型温度有助于减少加工过程对导电网络的破坏作用,从而有效降低复合材料的导电逾渗值,对提高复合材料导电性能具有重要意义。     

Mechanisms of particulate filled polypropylene finite plastic deformation and fracture

The plastic deformation and fracture of aluminium hydroxide filled polypropylene has been investigated. A transition between two mechanisms with an increase of the filler volume fraction has been observed. Below a critical filler volume content φcr ≈ 20 vol% (designated region 1) adhesive failure processes and polymer deformation in the neighbourhoods of different particles occur in an uncorrelated manner. Above this critical value (designated region 2) exfoliation along the surface of the initial portion of inclusions causes the formation of craze-like deformation zones transverse to the direction of the loading. The concentration of craze-like zones is essentially determined by the filler content and the level of interphase interaction which in turn depends on the particle size. In region 1 deformation occurs in a macro heterogeneous way with the formation and growth of a neck. The elongation to break decreases with an increase in the mean diameter of the filler phase. At φ>φcr composites, filled with small particles, fail in quasi brittle manner with the formation of a short and narrow neck. In contrast to the case for a small filler concentration, an increase of the inclusion size leads to an increase in the ultimate elongation and a tendency to macro homogeneous yielding. An explanation of the observed behaviour is proposed based on a change in adhesive failure conditions with filler content and size. This revised version was published online in November 2006 with corrections to the Cover Date.     

Bi-layered polymer–magnetite core/shell particles: synthesis and characterization

Polymer magnetic core particles receive growing attention due to these materials owing magnetic properties which are widely used in different applications. The prepared composite particles are characterized with different properties namely: a magnetic core, a hydrophobic first shell, and finally an external second hydrophilic shell. The present study describes a method for the preparation of bi-layered polymer magnetic core particles (diameter range is 50–150 nm). This method comprises several steps including the precipitation of the magnetic iron oxide, coating the magnetite with oleic acid, attaching the first polymer shell by miniemulsion polymerization and finally introducing hydrophilic surface properties by condensation polymerization. The first step is the formation of magnetite nanoparticles within a co-precipitation process using oleic acid as the stabilizing agent for magnetite. The second step is the encapsulation of magnetite into polyvinylbenzyl chloride particles by miniemulsion polymerization to form a magnetic core with a hydrophobic polymer shell. The hydrophobic shell is desired to protect magnetite nanoparticles against chemical attack. The third step is the coating of magnetic core hydrophobic polymer shell composites with a hydrophilic layer of polyethylene glycol by condensation polymerization. Regarding the miniemulsion polymerization the influence of the amount of water, the mixing intensity and the surfactant concentration were studied with respect to the formation of particles which can be further used in chemical engineering applications. The resulting magnetic polymer nanoparticles were characterized by particle size measurement, chemical stability, iron content, TEM, SEM, and IR.     

Synthesis,extrusion and rheological behaviour of PU/HA composites for biomedical applications

Biostable polyurethane/hydroxyapatite (PU/HA) composites with potential application as bone replacement materials were synthesized in bulk and processed in a screw extruder. The polyurethanes (PU) were prepared by reacting an aliphatic diisocyanate, 4-methylene-bis-diisocyanate (MDI), with poly-(ε-caprolactone) (PCL) diols and polytetramethylene oxide (PTMO) of different molecular weights, extended with 1, 4-butanediol (BDO). Glass-transition temperatures were measured by differential scanning calorimetry (DSC). The specific PU groups were assessed by total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The effects of polymer chemistry and filler content on the rheological behaviour were studied by oscillatory rheometry. Polymers with larger chain lengths showed higher viscosity and, for identical chain lengths, polyether urethanes seem to have higher viscosities than polyester based urethanes. A lubricating effect was found for composites containing 50% weight of filler, whereas at higher filler contents a solid-like behaviour was measured. Polymer chemistry seems to be affected by ageing but not so by the presence of filler. Ageing is characterized by a decrease in the concentration of hydrogen bonds involving between urethane linkages.     

Epoxy Composites Filled with Micro-Sized AlN Particles for Microelectronic Applications

With the rapid development of the electronic information industry, better properties are required for substrate and packaging materials such as high thermal conductivity, low coefficient of thermal expansion, and low dielectric constant. Polymers are ordinarily being used for this purpose due to their high electrical resistivity and low density, but unfortunately they suffer from a disadvantage like low thermal conductivity. To offset this deficiency, adding inorganic conductive particles to polymer is a versatile method. In view of this, the present work aims at developing a class of particulate filled polymer composites with micro-sized aluminum nitride (AlN) particles having an average particle size of 60–80 µm reinforced in epoxy matrix. A set of composites, with filler content ranging from 0 to 25 vol%, have been prepared by the hand-layup technique. Effects of filler percentage on various properties like effective thermal conductivity (k_eff), coefficient of thermal expansion (CTE), glass transition temperature (T_g), and dielectric constant (ε_c) are studied. It is found that the incorporation of AlN in resin increases the k_eff and T_g, whereas CTE of the composite decreases favorably. Though dielectric constant of the matrix increases with filler content yet it remains well within the desirable limit. With modified thermal and dielectric characteristics, these composites can possibly be used for microelectronics applications.