Non-conductive Fillers Research Articles

Piezoresistive Effect of Conductive and Non-Conductive Fillers in Bi-Layer Hybrid CNT Composites under Extreme Strain.

Polymers mixed with conductive fillers hold significant potential for use in stretchable and wearable sensor devices. Enhancing the piezoresistive effect and mechanical stability is critical for these devices. To explore the changes in the electrical resistance under high strains, typically unachievable in single-layer composites, bi-layer structures were fabricated from carbon nanotubes (CNTs) and EcoFlex composites to see unobservable strain regions. Spherical types of non-conductive fillers composed of polystyrene and conductive filler, coated with Ni and Au on non-conductive fillers, were used as secondary fillers to improve the piezoresistive sensitivity of composites, and their respective impact on the conductive network was compared. The electrical and mechanical properties were examined in the static state to understand the impact of these secondary fillers. The changes in the electrical resistance under 100% and 300% tensile strain, and their dependence on the inherent electrical properties of the secondary fillers, were also investigated. Single-layer CNT composites proved incapable of withstanding 300% strain, whereas the bi-layer structures proved resilient. By implementing cyclic stretching tests, contrary to non-conductive fillers, reduced piezoresistive influence of the conductive secondary filler under extreme strain conditions could be observed.

Thermal Percolation in Well-Defined Nanocomposite Thin Films.

Thermal percolation in polymer nanocomposites─the rapid increase in thermal transport due to the formation of networks among fillers─is the subject of great interest in thermal management ranging from general utility in multifunctional nanocomposites to high-conductivity applications such as thermal interface materials. However, It remains a challenging subject encompassing both experimental and modeling hurdles. Successful reports of thermal percolation are exclusively found in high-aspect-ratio, conductive fillers such as graphene, albeit at filler loadings significantly higher than the electrical percolation threshold. This anomaly was attributed to the lower filler-matrix thermal conductivity contrast ratio kf/km ∼104 compared to electrical conductivity ∼1012-1016. In a randomly dispersed composite, the effect of a low contrast ratio is further accentuated by uncertainties in the morphology of the percolating network and presence of other phases such as disconnected aggregates and colloidal dispersions. Thus, the general properties of percolating networks are convoluted as they lack a defined structure. In contrast, a prototypical system with controllable nanofiller placement enables the elucidation of structure-property relations such as filler size, loading, and assembly. Using self-assembled nanocomposites with a controlled 1,2,3-dimension nanoparticle (NP) arrangement, we demonstrate that thermal percolation can be achieved in spite of using spherical, nonconductive fillers (kf/km ∼60) at a low volume fraction (9 vol %). We observe that the effects of volume fraction, interfacial thermal resistance, and filler conductivity on thermal conductivity depart from effective medium approximations. Most notably, contrast ratio plays a minor role in thermal percolation above kf/km ∼60─a common range for semiconducting nanoparticles/polymer ratios. Our findings bring new perspectives and insights to thermal percolation in nanocomposites, where the limits in contrast ratio, interfacial thermal conductance, and filler size are established.

Impact of Carbon Particle Character on the Cement-Based Composite Electrical Resistivity.

Electroconductive cement-based composites are modern materials that are commonly used in many industries such as the construction industry, among others. For example, these materials can be used as sensors for monitoring changes in construction, grounding suspension, and resistance heating materials, etc. The aim of the research presented in this article is to monitor the impact of carbon particle character on cement-based electroconductive composites. Four types of graphite were analyzed. Natural and synthetic types of graphite, with different particle sizes and one with improved electrically conductive properties, were tested. For the analysis of the electrical conductivity of powder raw materials, a new methodology was developed based on the experience of working with these materials. Various types of graphite were tested in pure cement paste (80% cement, 20% graphite) as well as in a composite matrix, which consisted of cement (16.8%), a mixture of silica sand 0–4 mm (56.4%), graphite filler (20.0%) ground limestone (6.7%) and super plasticizers (0.1%). The resistivity and physical-mechanical properties of the composite material were determined. Furthermore, the resistivity of the test samples was measured with a gradual decrease in saturation. It may be concluded that graphite fillers featuring very fine particles and high specific surface are most suitable and most effective for creating electrically conductive silicate composites. The amount, shape and, in particular, the fineness of the graphite filler particles thus creates suitable conditions for the creation of an integrated internal electricity-conductive network. In the case of the use of a coarse type of graphite or purely non-conductive fillers, the presence of an electrolyte, for example, in the form of water, is necessary to achieve a low resistivity. Samples with fine types of graphite fillers achieved stable resistivity values when the sample humidity changed. The addition of graphite fillers caused a large decrease in the strength of the samples.

Unveiling Interfacial Li-Ion Dynamics in Li7La3Zr2O12/PEO(LiTFSI) Composite Polymer-Ceramic Solid Electrolytes for All-Solid-State Lithium Batteries.

Unlocking the full potential of solid-state electrolytes (SSEs) is key to enabling safer and more-energy dense technologies than today's Li-ion batteries. In particular, composite materials comprising a conductive, flexible polymer matrix embedding ceramic filler particles are emerging as a good strategy to provide the combination of conductivity and mechanical and chemical stability demanded from SSEs. However, the electrochemical activity of these materials strongly depends on their polymer/ceramic interfacial Li-ion dynamics at the molecular scale, whose fundamental understanding remains elusive. While this interface has been explored for nonconductive ceramic fillers, atomistic modeling of interfaces involving a potentially more promising conductive ceramic filler is still lacking. We address this shortfall by employing molecular dynamics and enhanced Monte Carlo techniques to gain unprecedented insights into the interfacial Li-ion dynamics in a composite polymer-ceramic electrolyte, which integrates polyethylene oxide plus LiN(CF3SO2)2 lithium imide salt (LiTFSI), and Li-ion conductive cubic Li7La3Zr2O12 (LLZO) inclusions. Our simulations automatically produce the interfacial Li-ion distribution assumed in space-charge models and, for the first time, a long-range impact of the garnet surface on the Li-ion diffusivity is unveiled. Based on our calculations and experimental measurements of tensile strength and ionic conductivity, we are able to explain a previously reported drop in conductivity at a critical filler fraction well below the theoretical percolation threshold. Our results pave the way for the computational modeling of other conductive filler/polymer combinations and the rational design of composite SSEs.

Nanocomposite with fast Li+ conducting percolation network: Solid polymer electrolyte with Li+ non-conducting filler

Solid polymer electrolytes (SPEs) have attracted considerable research interest because they are expected to solve the safety problems caused by the liquid electrolytes. However, the low ionic conductivity limits their practical applications. Constructing Li + fast conducting network in SPEs with Li + highly conducting ceramic fillers following the mixed matrix membrane concept have shown their limits in raising the Li + conductivity. Herein, a new strategy using Li + non-conducting fillers like CeO 2 nanowires, is proposed to construct a Li + fast conducting network through SPEs. CeO 2 nanowires can dissociate LiTFSI, which results in a high Li + conductivity through the SPEs near to the fiber surface. This experimental finding is confirmed by analytics (FT-IR, Raman and NMR) and theoretical calculations (DFT-MD and COHP). As a result, the network of interwoven CeO 2 nanowires helps form a continuous Li + fast conducting percolation network through the SPEs. The ionic conductivity of the composite SPEs with 10 wt% CeO 2 nanowires is greatly improved (1.1 × 10 −3 S cm −1 at 60 °C). The Li symmetric cells with this composite electrolyte exhibit good cyclic stability (without short circuiting after 2000 h), and the all-solid-state LiFePO 4 /Li cells present a superior cycling performance (remained 140 mA h g −1 after 100 cycles at 1 C). • Li + non-conducting nanofillers are used to construct Li + fast conducting network. • Dissociation process of LiTFSI on the CeO 2 surface is theoretically simulated. • Novel mechanism for the enhancement of Li + conductivity is proposed.

Macroscopic Electrical Wires from Vapor Deposited Poly(3,4-ethylenedioxythiophene)

Conducting polymers represent a field of materials innovation that bridges the properties of metals (electrical conduction) with those of traditional polymers (mechanical flexibility). Although electronic properties have been studied, minimal attention is given to their mechanical properties such as tensile strength. This study presents macroscopic wires made from the vapor phase polymerization of poly(3,4-ethylenedioxythiophene) using triblock copolymers as a molecular template. These macroscopic wires are conductive (up to 5 × 104 S/m), and possess tensile properties (Young's modulus ∼1.1 GPa; tensile strength ∼90 MPa) comparable to commercially available polymers (Nylon-6 and poly(methyl methacrylate)), without need for nonconductive mechanical fillers.

Massive electrical conductivity enhancement of multilayer graphene/polystyrene composites using a nonconductive filler.

We report a massive increase in the electrical conductivity of a multilayer graphene (MLG)/polystyrene composite following the addition of nonconducting silica nanoparticles. The nonconducting filler acts as a highly effective dispersion aid, preventing the sheetlike MLG from restacking or agglomerating during the solvent casting process used to fabricate the composite. The enhanced dispersion of the MLG leads to orders of magnitude enhancement in electrical conductivity compared to samples without this filler.

ELECTRICAL CONDUCTION AND DYNAMIC RHEOLOGY OF MULTI-WALLED CARBON NANOTUBES AND HYDROPHOBIC NANOSILICA-FILLED IMMISCIBLE POLY(METHYLMETHACRYLATE)/POLYSTYRENE BLENDS

Multi-walled carbon nanotubes(MWCNTs) and hydrophobic nanosilica(SiO2) were used as conductive and nonconductive fillers to fill immiscible poly(methylmethacrylate)/polystyrene(PMMA/PS)(1/1 in volume) blends to prepare(PMMA/SiO2)/(PS/MWCNTs) quaternary conductive polymer composites(CPCs).Conductive percolation at room temperature and melt dynamic rheology of the quaternary CPCs were investigated and were compared with PMMA/(PS/MWCNTs) ternary CPCs containing 5 vol% SiO2.The ternary and the quaternary CPC exhibited similar percolation behavior with percolation threshold of MWCNTs volume fractions much smaller than that of PS/MWCNTs binary CPC.SiO2 particles could reduce the phase size and improve the melt complex modulus without influence the time-dependent dynamic conductive percolation during melt annealing.MWCNTs and SiO2 have different effects on the time-dependent dynamic modulus percolation during annealing of quaternary CPCs.It is believed that MWCNTs and SiO2 accelerated and decelerated the onset time for phase coarsening,respectively,while both significantly extended the time interval of phase coarsening.Morphological observation revealed that degree of phase coarsening decreased with increasing volume fraction of MWCNTs in ternary CPC during melt annealing.The presence of SiO2 could greatly restrain the coarsening in quaternary CPC.

Novel anticorrosion coatings prepared from polyaniline/graphene composites

We report on the exceptional application of polyaniline/graphene composites (PAGCs) for corrosion protection of steel. The composites display outstanding barrier properties against O2 and H2O compared with neat polyaniline and polyaniline/clay composites (PACCs). The conductive filler, 4-aminobenzoyl group-functionalized graphene-like sheets (ABF-G) with a relatively higher aspect ratio than organophilic clay nonconductive fillers, is a versatile platform for polymer grafting that promotes better dispersion of the graphite within the polymer matrix and lengthens the diffusion pathway that gases should effectively encounter. This concept can be used for other polymer/graphene composites.

Effect of nanofillers on the properties of a state of the art epoxy gelcoat

In this work, the effect of the inclusion of electrically conductive and non-conductive nanofillers in a state of the art epoxy gelcoat was studied. The conductive fillers used were multi-wall carbon nanotubes and exfoliated nanographite. The non-conductive ones were nanoclay and nano-titanium dioxide. The content of the nanofillers was 0.65% per weight and their inclusion took place using high shear mixing devices. The conductive fillers showed an increase in tensile and fracture properties, as well as in the thermal properties whereas the non-conductive fillers did not show any improvement on the fracture properties. The glass transition temperature was practically unaffected by the presence of the nanofillers while conversly, the coefficient of thermal expansion was decreased for all the nanofillers for temperatures above the glass transition temperature. Finally, weatherometer tests showed that the nanofillers contribute into less weight losses in com- parison with the reference epoxy gelcoat.

Conductive Carbon Loaded Polymer Film Electrodes for Pulsed Power Applications. Part II: Determination and Minimization of the Contact Resistance

Electrically conductive polymer composites consisting of a nonconductive polymer matrix and conductive fillers, such as carbon black, are widely used. This contribution describes a newly developed measurement setup that has been built to investigate the specific electrical properties of polymer composite films for pulsed conditions in the microsecond (10−6 s) range. For an industrially available volume conductive polymer film (Carbostat) the contact resistivity to copper has been investigated. Also, three methods for minimizing the contact resistivity, namely pressing, gluing, and wetting, have been compared for a wide range of applied current densities.

Conductive Carbon Loaded Polymer Film Electrodes for Pulsed-Power Applications. Part I: Determination of the Film Properties

Electrically conductive polymer composites consisting of a nonconductive polymer matrix and conductive fillers, such as carbon black, are widely used. This contribution describes the specific electrical properties of polymer composite films for pulsed conditions in the microsecond (10−6 s) range. Investigation of an industrially available volume conductive polymer film (Carbostat) showed that the electrical properties of this material, which can be considered for electrodes in pulsed power applications, are quite different from the properties for DC conditions.

Filler size and content effects on the composite properties of anisotropic conductive films (ACFs) and reliability of flip chip assembly using ACFs

Flip chip assembly on organic board using anisotropic conductive films (ACFs) is gained more attention because of its many advantages. But to obtain more reliable flip chip assembly, it is necessary to have low coefficient of thermal expansion (CTE) value of ACFs. To control the CTE of ACF materials, non-conductive silica fillers were incorporated into ACFs. The effect of non-conductive silica filler content and size on cure kinetics and thermo-mechanical properties of ACFs was studied. Furthermore, filler content and size effects on reliability of flip chip assembly using ACFs were also investigated. In accordance with increasing filler content, curing peak temperature and storage modulus ( E′) increased. But CTE decreased as the filler content increased. The effect of filler size on composite properties and assembly reliability showed similar tendency with the filler content effect. The smaller filler size was applied, the better composite properties and reliability were obtained. Conclusively, incorporation of non-conductive fillers, particularly in case of smaller size and higher content, in ACFs improves the material properties significantly, and as a result, flip chip assembly using ACFs is resulted in better reliability.

Thermally conductive rubber-based composite friction materials for railroad brakes – Thermal conduction characteristics

This study deals with the thermal conductivity of rubber-based composite friction materials used in railroad vehicles. Based on a commercially available railroad friction material, called here base material (BM), various friction materials containing different thermally conductive fillers (Cu, brass, Al, Al 2O 3 and talc) are fabricated and then their thermal conductivities are measured at various contents of the fillers. Addition of the thermally conductive fillers causes an increase in thermal conductivity of the friction material from 0.48 up to 5.8 W/m K, depending on the type and content of the filler. In addition, the experimental results reveal that the thermal conductivity of the friction material can be influenced by indirect effects including mainly the shape and size of the filler. Fillers with larger size and platelet shape are more effective in enhancing the thermal conductivity of the friction material. In order to provide an engineering tool to estimate the thermal conductivity of the friction materials, a new semi-empirical model is proposed for multiphase systems based on geometric mean model. In this model, the filler may be regarded thermally conductive or non-conductive. The model is first developed for friction material containing multi-non-conductive fillers and one thermally conductive filler and then is extended to a system containing multi-conductive and non-conductive fillers. The agreement between model predictions and experimental measurements is satisfactory.

Synergistic Physical Properties of Multiphase Nanocomposites with Carbon Nanotubes and Inorganic Particles

ABSTRACTMultiphase epoxy-nanocomposites based on multi-wall carbon nanotubes (MWCNT) and inorganic nanoparticles (TiO2) were produced. The rheological, electrical and thermo-mechanical properties were investigated in order to reveal informations about the interparticle interactions between the different types of nanoparticles. TEM-investigations reveal altered microstructures for the multiphase nanocomposites (MWCNT plus TiO2). TiO2 causes changes in the state of dispersion of MWCNT which can lead to an increase of the rheological parameters (e.g. G'). Due to changes in the formation of the percolated MWCNT network during curing, the electrical conductivity is decreased if the concentration of the non-conductive fillers exceeds a critical value. Additional synergistic effects could be found for the glass transition temperature. The presence of nanoparticles leads to a chemical inactivation of reactive groups of the matrix. Thus, the generated interphase between matrix and nanoparticles exhibits a lower curing degree which results in lower thermo-mechanical properties. For the multiphase systems the glass transition temperature is decreased less, due to an inactivation of the surface of the different types of nanoparticles by a self assembly which leads to a higher curing degree of the interphase.

Highly reliable non-conductive adhesives for flip chip CSP applications

Non-conductive adhesives (NCA), widely used in display packaging and fine pitch flip chip packaging technology, have been recommended as one of the most suitable interconnection materials for flip-chip chip size packages (CSPs) due to the advantages such as easier processing, good electrical performance, lower cost, and low temperature processing. Flip chip assembly using modified NCA materials with material property optimization such as CTEs and modulus by loading optimized content of nonconductive fillers for the good electrical, mechanical and reliability characteristics, can enable wide application of NCA materials for fine pitch first level interconnection in the flip chip CSP applications. In this paper, we have developed film type NCA materials for flip chip assembly on organic substrates. NCAs are generally mixture of epoxy polymer resin without any fillers, and have high CTE values un-like conventional underfill materials used to enhance thermal cycling reliability of solder flip chip assembly on organic boards. In order to reduce thermal and mechanical stress and strain induced by CTE mismatch between a chip and organic substrate, the CTE of NCAs was optimized by filler content. The flip chip CSP assembly using modified NCA showed high reliability in various environmental tests, such as thermal cycling test (-55/spl deg/C/+160/spl deg/C, 1000 cycle), high temperature humidity test (85/spl deg/C/85%RH, 1000 h) and high temperature storage test (125/spl deg/C, dry condition). The material properties of NCA such as the curing profile, the thermal expansion, the storage modulus and adhesion were also investigated as a function of filler content.

Effect of nonconducting filler additions on ACA properties and the reliability of ACA flip-chip on organic substrates

We investigated the effect of nonconducting fillers on the thermomechanical properties of modified anisotropic conductive adhesive (ACA) composite materials and the reliability of flip chip assembly on organic substrates using modified ACA composite materials. For the characterization of modified ACAs composites with different content of nonconducting fillers, dynamic scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and thermomechanical analysis (TMA) were utilized. As the nonconducting filler content increased, CTE values decreased and storage modulus at room temperature increased. In addition, the increase in the content of filler brought about the increase of T/sub g/(DSC) and T/sub g/(TMA). However, the TGA behaviors stayed almost the same. Contact resistance changes were measured during reliability tests such as thermal cycling, high humidity and temperature, and high temperature at dry condition. The reliability results were significantly influenced by CTEs of ACA materials, especially at the thermal cycling tests. Results showed that flip chip assembly using modified ACA composites with lower coefficients of thermal expansion (CTEs) and higher modulus by loading nonconducting fillers exhibited better contact resistance behavior than conventional ACAs without nonconducting fillers.

Reduced thermal strain in flip chip assembly on organic substrate using low CTE anisotropic conductive film

Flip chip assembly directly on organic boards offers miniaturization of package size as well as reduction in interconnection distances, resulting in a high performance and cost-competitive packaging method. This paper describes the usefulness of low cost flip-chip assembly using electroless Ni/Au bump and anisotropic conductive films on organic boards such as FR-4. As bumps for flip chip, electroless Ni/Au plating was performed as a low cost bumping method. Effect of annealing on Ni bump characteristics informed that the formation of crystalline nickel with Ni/sub 3/P precipitation above 300/spl deg/C causes an increase of hardness and an increase of the intrinsic stress. As interconnection material, modified ACFs composed of nickel conductive fillers for conductive fillers, and nonconductive fillers for modification of film properties, such as coefficient of thermal expansion (CTE), were formulated for improved electrical and mechanical properties of ACF interconnection. Three ACF materials with different CTE values were prepared and bonded between Si chips and FR-4 boards for the thermal strain measurement using moire interferometry. The thermal strain of the ACF interconnection layer, induced by temperature excursion of 80/spl deg/C, was decreased according to the decreasing CTEs of ACF materials. This result indicates that the thermal fatigue life of ACF flip chip assembly on organic boards, limited by the thermal expansion mismatch between the chip and the board, could be increased by low CTE ACF.

PEO-carbon composite lithium polymer electrolyte

The addition of fillers to lithium polymer electrolytes is a well established procedure to improve their mechanical stability as well as their interfacial stability with lithium anodes. As far only inert, non-conductive fillers have been used in the formulation of PEO-based composite electrolytes. In this report as the addition of a small volume fraction (<1.5%) of moderately high surface area (∼60 m 2 g −1) carbons results in composite lithium polymer electrolytes with excellent performance in terms of conductivity and interfacial stability is shown.

Improving the Electrical Conductivity of Composites Comprised of Short Conducting Fibers in a Nonconducting Matrix: The Addition of a Nonconducting Particulate Filler

ABSTRACTThe addition of a second discontinuous filler (silica fume) that is essentially nonconducting to a composite with a comparably non-conducting matrix (cement) and a conducting discontinuous filler (carbon fibers) was found to increase the electrical conductivity of the composite when the conducting filler volume fraction was less than 3.2%. The maximum conducting filler volume fraction for the second filler to be effective was only 0.5% when the second filler was sand, which was much coarser than silica fume. The improved conductivity due to the presence of the second filler is due to the improved dispersion of the conducting filler. The silica fume addition did not affect the percolation threshold, but the sand addition increased the threshold.