Filler Volume Fraction Research Articles

Theoretical analysis of Soft Conductive Materials for Next Generation Wearable System

Purpose of the study: Recent advances in strategies for soft materials have transformed the wearable or bioelectronics from a rigid form into a soft, having advantages in terms of mechanical similarity with human tissue. Conductive nanocomposites are promising components as conductive interconnects in stretchable electronic system. This study is about optimizations of nanocomposite for enhancing its performances without degrading mechanical properties. 
 Methodology: First, we summarize the recent advances in metallic nanocomposites. Next, we discuss the 3-dimensional percolation theory, which is basic theoretical basis to understand the random system of nanocomposite. From this, we also briefly search important parameters having potential to change percolative connections of nanoparticles.
 Main Findings: We investigated required parameters, which could affect the percolation network of conductive fillers in matrix. Dimension, shape and volume fraction of fillers are very important to realize the high conductivity of conductive composite. By calculating some parameters with theoretical formula, we analyzed the effect of shape and dimensions on performance of conductive composite.
 Implications: This study can help researchers to understand the potential parameters that could affect the performances of conductive nanocomposite and analyze them in qualitative and quantitative approaches.
 Novelty: The potential applications of optimized conductive nanocomposite, especially focused on wearable and bio-implantable system are discussed.

Carbon Modification of K1.6Fe1.6Ti6.4O16 Nanoparticles to Optimize the Dielectric Properties of PTFE-Based Composites.

In this work, polymer matrix composites with the compositions PTFE/KFTO(H) and PTFE/KFTO(H)@CB and with filler volume fractions of 2.5, 5.0, 7.5, 15, and 30% (without and with carbon modification at a content of 2.5 wt.% regarding ceramic material) were produced by calendering and hot pressing and studied using FTIR, SEM, and impedance spectroscopy methods. Ceramic filler (KFTO(H)) was synthesized using the sol–gel Pechini method. Its structure was investigated and confirmed by the XRD method with following Rietveld refinement. The carbon black (CB) modification of KFTO(H) was carried out through the calcination of a mixture of ceramic and carbon materials in an argon atmosphere. Afterwards, composites producing all the components’ structures weren’t destroyed according to the FTIR results. The effect of carbon additive at a content of 2.5 wt.% relating to ceramic filler in the system of polymer matrix composites was shown, with permittivity increasing up to ε’ = 28 with a simultaneous decrease in dielectric loss (tanδ < 0.1) at f = 103 Hz for composites of PTFE/KFTO(H)@CB (30 vol.%).

Flammability and mechanical properties of Timoho fiber-reinforced polyester composite combined with iron powder filler

Natural fiber reinforced composites are usually added with fillers to improve their performance. However, this often affects the other composite properties. This study describes the successful development of timoho fiber (TF)-reinforced polyester composites combined with iron powder (IP) filler. Composite fabrication used hot press method. Flame, thermal, mechanical, and morphological characteristics were analyzed to determine the effect of variations on the volume fraction of IP filler in polyester composites with 30% (wt) TF. The results showed that the PTF composite had the highest tensile strength of 119.26 MPa. The impact toughness and the highest compressive strength were obtained at 126.74 kJ/m2 and 155.72 MPa, respectively, for the TF10IP composite. The elongation of the polyester composite decreased with the addition of IP filler from 3.58% to 2.19%. In contrast to elongation, the modulus of elasticity of the polyester composite increased from 4.14 to 4.94 GPa with the addition of IP filler. However, the thermal stability (TGA) and flame resistance of the composite increased. Observation of composite fracture morphology revealed the appearance of voids and TF pullout which supported the analysis of composite tensile strength.

Dielectric response and molecular dynamics of nanocomposites based on TEMPO-oxidized cellulose nanofibrils and polyvinyl acetate

• Two series of nanocomposites based on Polyvinyl-acetate incorporated with two different TEMPO-oxidized cellulose nanofibrils were investigated. • The activation energy and the strength parameters were interpreted. • Electrical conductivity were evaluated using DC measurements. • The comparison between the two sets of CNF showed that PVAc/CNF-5 min films were able to build a denser CNF network and hence the highest potential of filling effect than those of PVAc/CNF-2 h films. A series of polyvinyl acetate polymer matrices (PVAc) incorporated with two different TEMPO-oxidized cellulose nanofibrils (CNF with 5 min and 2 h of oxidation) were studied. These composites have proven to be suitable for use as ion battery separators. For this purpose, dielectric properties and electrical conductivity have been investigated using impedance spectroscopy in the frequency range from 10 2 to 10 6 Hz and over the temperature range, 200–350 K. The effects of CNF loading on the molecular motion and the charge transport mobility in PVAc polymer chains were studied. Calculation of the strength parameter for the α-relaxation process revealed a threshold value of 8 % in the volume fraction of filler. A comparative study of the two nanocomposites films showed that PVAc/CNF-5 min nanocomposites were able to build a denser CNF network and hence the highest potential of filling effect than those of PVAc/CNF-2 h films. According to our results, the volume fraction of 8 % of CNF-5 min is recommended for achieving the highest performing nanocomposite with potential applications.

Predicting Dynamic Properties of Asphalt Mastic Considering Asphalt-Filler Interaction Based on 2S2P1D Model.

The relationship between the various phases of asphalt materials, from asphalt binder to mastic and mixture, has received great attention over the years, with efforts being made to establish linkages among these phases. Many methods for predicting the rheology properties of asphalt mastics from those of asphalt and filler volume fractions exist. However, most prediction methods are based on an empirical formula and on the micromechanical model. Very few research studies focus on the constitutive model. In addition, relatively little research has explored the influence of asphalt–filler interaction on mastic’s rheology properties, which is believed to be an important factor. In this study, the 2S2P1D (two springs, two parabolic elements, and one dashpot) model was applied to link the behavior of asphalt binder, filler volume fraction, asphalt–filler interaction and asphalt mastic. First, the interaction between asphalt and filler was evaluated, and the interaction parameter C of the Palierne model was used as an assessment indicator to calculate the effective filler volume fraction of asphalt mastic. Then, the relation between the 2S2P1D model parameters of asphalt mastic and those of asphalt binder and the effective filler volume fraction was analyzed. Finally, a simple relationship associating the 2S2P1D model parameters , of mastic and that of asphalt binder and the effective filler volume fraction was developed. The proposed expression was validated, and the result showed that it was an efficient model for the shear complex modulus prediction of virgin asphalt mastic.

Filler Models Revisited: Extension of the Nielson Model with Respect to the Geometric Arrangements of Fillers.

Models describing how fillers affect the barrier properties of polymers remain an important research topic to improve applications such as hydrogen storage or food preservation. The Nielsen model, one of the earliest models for such predictions, is still one of the most widely used in the literature. However, it does not provide quantitative information on arrangements of fillers inside a polymer matrix, which is crucial for the definition of suitable filler distributions in barrier materials. Therefore, the channel model was developed in this work, which extends the Nielsen model by determining the relative distances between the fillers in regular filler arrangements in polymer matrices. This allows us to relate the permeation properties of filled polymer membranes to the geometric properties of the filler arrangement in simulations and experimental measurements. Simulations with geometries defined according to the channel model showed good agreement with the predictions of the Nielsen model. This demonstrated that the channel model can be a valuable tool for predicting at least mean geometric distances in studied polymer membranes. The validity range of the channel model was limited to a value range of the filler volume fraction based on theoretical considerations.

Modeling of Modulus of elasticity of Nano-Composite Materials: Review and Evaluation

To improve the mechanical properties of polymer, the mineral particles are added to produce composite material. For example, the mineral particles are added to polymer to improve the stiffness of polymer because of the higher stiffness of mineral particles. When the micron-sized particles are used in composite usually cause a reduction in impact resistance. On the other hand, adding the nano scale minerals leads to improve the impact and wear properties of the composite materials (nanocomposites). Several factors effect on the mechanical properties of nanocomposites like adhesion between the polymer and nanoparticles. If the interfacial deboning of particles from the matrix decreases, the tensile strength of the composite could be reduced.In this article, the micromechanical models dealing with calculating modulus of elasticity of nanocomposite are reviewed and discussed using the comparison between the results of the micromechanical models with experimental data factors effect on the modulus of elasticity of nanocomposite are matrix and filler elastic modulus, volume fraction of filler, aspect ratio of filler, maximum volumetric packing and the thickness and elastic modulus of interphone surrounding the nanoparticles and these factors are studied in each mechanical models.

Evaluation of the Abrasive Resistance of Compositions Based on Polyurethane Compounds Used in the Manufacture of Diaphragms of Diaphragm-piston Pumps

Data on the study of the abrasive resistance of compositions based on the two-component polyurethane compound Advaform (grade 80) are presented. Talc, shungite and basalt fiber were used as fillers. The volume fraction of fillers varied from 1 to 5% with a step of 2%. According to the results of the study, it was proved that the composition with a volume fraction of basalt fiber of 1% demonstrated the greatest abrasive resistance compared to a pure compound, which allows us to conclude that it is expedient to use this material for the manufacture of diaphragm of diaphragm-piston pumps.

Stiffening effect of filler on asphalt mastic composite: A new insight based on nearest surface function

This study aims to provide a new insight into the reinforcement effect of filler on stiffness of asphalt mastic through the probability theory, nearest surface function and micromechanics. To implement the consideration of microphysical mechanisms in the stiffening behavior of asphalt mastic composite, a general methodological framework was developed. A new method to calculate the filler’s critical volume fraction (CVF) in asphalt mastic was constructed through the volume fraction of penetrable transition zone (PTZ) acting as a link. Particle size distribution (PSD) of filler was tested by a laser particle size analyzer. Asphalt mastics were fabricated with different filler concentrations. Distributions of filler particles in these mastics were tested by a scanning electron microscope. Complex stiffness moduli of asphalt binder and mastics were tested by a dynamic shear rheometer. Nearest surface distance (NSD) of filler particles in asphalt mastics was analyzed by nearest surface functions. Filler’s CVF in asphalt mastics was calculated through the constructed method. Results show that the shifted Rosin-Rammler distribution function allows to describe the PSD of filler with a high accuracy. Void nearest-surface exclusion probability of filler particles allows to represent the volume fraction of free asphalt in asphalt mastic. The larger the filler volume fraction, the higher the proportion of NSD making particles intercontact. A filler particle with larger radius has more likely to contact with other filler particles, and thus large particles tend to dominate the interparticle interaction in asphalt mastic. The mean NSD of filler particles decreases with increasing the filler volume fraction. The volume fraction of PTZ has an increased first and decreased afterwards trend with the filler volume fraction. The filler’s CVF decreases with the temperature increases. The constructed method is capable of determining the filler’s CVF in asphalt mastic.

Probing into why anisotropic nanoclay offers better reinforcement in natural rubber than isotropic nano zinc oxide by determining their interaction with sol and gel fractions

AbstractRole of sol–gel interaction with anisotropic nanoclay in raw natural rubber (NR) for offering higher mechanical reinforcement than isotropic nano zinc oxide was reported in this article. Experiments were carried out on four different grades of NR, having equal Mooney viscosity but different gel contents (toluene insoluble fraction), with commercial grades of nanofillers. In raw NR, the green strength was found to be influenced by higher apparent viscosity instead of higher gel content. In unvulcanised nanocomposites, however, the reinforcement was subjected to interaction between the nanofillers and the sol fraction (toluene soluble fraction, major part of the matrix) of NR. The mixing energy was decreased by approximately 2.9% for nanoclay (Cloisite 30B) and 4.4% for nano zinc oxide addition, whereas the gel content has increased upon addition of Cloisite 30B and nano zinc oxide by 12% and 49%, respectively. The ability was found higher with nano zinc oxide due to its isotropic shape and lower overall size than Cloisite 30B. Conversely, higher sol concentration of Cloisite 30B along with higher filler volume fraction offered higher mechanical reinforcement in both high and low gel grades of NR. The fact was established from extensive studies on morphology, filler crystallography, gel content, and viscoelastic responses.

Modeling of mechanical behaviors and interphase properties of polymer/nanodiamond composites for biomedical products

The interphase properties of polymer/nanodiamond (ND) composites have not been studied, although this class of materials has attracted considerable attention in recent years. In this study, we investigate models for prediction of the mechanical behaviors and interphase properties of polymer/ND composites. Various powers of the filler volume fraction in the Pukanszky model for the tensile strengths of nanocomposites are considered to find the best power representing accurate data. The best power of 0.01 is obtained for the interfacial parameter (B) for all samples. B changes between 4.2409 and 4.7628, which suggests various strengths and thicknesses of the interphases in the samples. Some parameters in the Ji model have negligible effects on the nanocomposite modulus, so that the Ji model is simplified to obtain a better accuracy. The thickness of the interphase is calculated using the Ji model. A polyamide-66/ND sample has the thickest interphase because strong adhesions such as hydrogen bonding are generated between polyamide-66 and ND. Polymer/ND composites can be applied in biomedical products owing to their outstanding mechanical, thermal, optical, and electrical properties.

Tailoring the surface energy and area surface resistance of solid-electrolyte polymer membrane for dendrite free, high-performance, and safe solid-state Li-batteries

Solid electrolyte polymer composite enabled solid-state lithium batteries have shown extensive viability for mass production and commerciality for advanced energy storage technology. Most studies of polymer composite electrolyte are produced by solution casting and free-standing methods, where ionic conductors are randomly distributed into the polymeric network, suffering from poor ionic conductivity and agglomeration during charge/discharge cycling. In this work, using the threshold percolation model and critical volume fraction requirement, we have designed a highly efficient garnet-type ion-conducting nanofibrous sheet where ionic conductors of different aspect ratios are dispersed to tune the surface roughness, area surface resistance, and wettability of the developed electrolyte membrane. Moreover, the impact of filler volume fraction and percolation threshold on the surface properties of the membrane, regulating the area interfacial resistance of the Li metal cell has also been examined, which has not been studied so far in the literature. The corresponding high potential cathode-based lithium assembled coin cells exhibit an excellent specific capacity of 170 mAh g −1 at 0.3C, with high capacity retention under ambient circumstances. By optimizing the critical aspect ratio of the fillers and the percolation threshold, a high-performing solid electrolyte membrane can be realized for advanced and safer Li-batteries technology.

Enhancement of thermal conductivity in polymer composites by maximizing surface-contact area of polymer-filler interface

Abstract In this article we discuss in detail the effective approaches to enhance the thermal conductivity in polymer composites. Numerical simulations show that maximizing interfacial area between filler and polymer enhances very significantly the effective thermal conductivity in composites. We show that among the different geometries thermal conductivity is high for those geometries for which the ratio of surface-area to volume is high. For fillers of a particular geometry, by maximizing its surface area without changing the volume fraction of the metallic filler, the effective thermal conductivity increases. Thus, the interfacial area between filler and polymer plays an important role in the enhancement of thermal conductivity. It is also observed that as this interfacial area increases, increase in effective thermal conductivity follows from linear to the logarithmic growth. It should be noted that to inherit the polymer properties there is a restriction on the upper bound of volume fraction of the fillers. The current study brings out an important step in this direction. Our results are technologically very important in designing composite polymers for better heat conduction and are very cost-effective. This study also provides a connection between the bulk and the surface area in effective determination of the thermal conductivity.

Theoretical analysis on thermal grease dry-out degradation in space environment

Silicone thermal grease can reduce the contact thermal resistance of thermal interfaces and has been widely used as a thermal interface material in the thermal design of spacecraft. Silicone thermal grease gradually degrades owing to the dry-out of silicone oil during a long service period and breaks the validity of the thermal interface and induces thermal overload in a spacecraft. In this study, a mechanism-based prediction method for the silicone thermal grease loss in a space environment is proposed. The prediction of long-term thermal grease loss is realised by evaluating the variation in its effective thermal conductivity. In the prediction method, an improved multi-component thermal conductivity model was established to determine the thermal conductivity of thermal grease with multiple filler sizes and a high filler volume fraction. Then, the silicone oil loss induced by complex penetration, crawl, and volatilisation were evaluated with an equivalent capillary model and a volatilisation model. The behaviour of the silicone oil loss, the primary cause of dry-out degradation, was clarified. The variation in the effective thermal conductivity of thermal grease under different contact angles, operating temperatures, and connection surface dimensions was investigated. The results show that the dominant factor gradually changes from capillary loss to volatilisation loss during dry-out degradation. The effective thermal conductivity decreased faster at higher operating temperatures, and the effective thermal conductivity decreased slower with an increase in the contact angle and connection interface dimensions. The present work provides insights for the design of silicone thermal greases for space utilization.

Investigating the role of filler shape on the dynamic mechanical properties of glass‐filled epoxy composites

AbstractThe influence of filler shape and volume fraction on the dynamic mechanical characteristics of rigid glass filler epoxy composites is investigated. Two variants of glass fillers, spherical particle and slender (milled) fibers, are doped into the epoxy matrix till 10% volume fraction. The composites are room temperature cured and tested to measure their viscoelastic properties. The dynamic mechanical analyses performed in the temperature range of 20–180°C at 10 Hz suggest that the milled fiber composites display consistently higher storage and loss moduli, whereas the higher loss factor peaks were noted for the spherical particle composites. The C‐factor, filler reinforcement efficiency of the composites and entanglement density, evaluated from the storage modulus values, indicate that the milled fibers composites are more effective in transferring the loads in both glassy and rubbery zones when compared against the spherical particle case. Also, the filler/matrix adhesion factor (A factor) and the interphase adhesion factor, calculated from the loss factor curves reveal stronger filler/matrix interactions in the case of milled fiber epoxy composites. Interestingly, the filler geometry or volume fraction has only marginal influence on the glass transition temperature of the composites.

High-throughput finite-element design of dielectric composites for high-frequency copper clad laminates

Dielectric substrates with low dielectric constant and good thermal stability are highly desired for high-frequency and high-speed signal transmission. It is however challenging to rationally design the demand-satisfied polymer-based composites due to the inadequate understanding of the contradictory effect of inorganic fillers on modulating dielectric-thermal-mechanical properties. In this work, taking Polytetrafluoroethylene (PTFE)-SiO2 composite as the example, we perform high-throughput finite-element calculations to systematically study the filler effects on the dielectric constant of composites εrcomposite and the coefficient of thermal expansion of composites (CTE-c). A series of influencing factors including intrinsic property, volume fraction, shape, distribution, and orientation of fillers have been considered in our models to establish the structure-property mapping of dielectric composites. It is found that CTE-c is more sensitive to the filler structure of PTFE-SiO2 composites than εrcomposite. Finally, guided by the calculation results, a skeleton structure is proposed to realize the performance targets of εrcomposite< 2.3 and CTE-c < 60 ppm/K with lower SiO2 filler content. This work provides a universal data-driven strategy for the rational design of dielectric composites with multi-objective requirements, and it is expected to spark more experimental efforts to design novel dielectric composites for high-quality signal transmission.

An elastomeric composite with tunable thermal and mechanical properties via liquid metal-flake graphite multiphase fillers

Soft composites with improved and tunable thermal conductivity, stretchability and load-bearing capacity may find fascinating applications in soft robotics and wearable devices. Unfortunately, thermally conductive soft composites with solid fillers usually show serious degradation in stretchability, while those with liquid fillers usually possess a weak load-bearing capacity. To overcome these limitations, an elastomeric composite with solid–liquid multiphase fillers, named as pre-mixed LM&amp;FG/SR composite, is proposed here by incorporating flake graphite (FG) with high thermal conductivity into liquid metal (LM) and then dispersing the mixture in a soft silicone elastomer (SR). In comparison with the LM/SR composite and the FG/SR composite, the pre-mixed LM&amp;FG/SR composite gains the highest thermal conductivity under the strain-free state as it possesses both the excellent thermal conductivity of the FG filler and the high-volume fraction of the LM filler. In addition, by controlling the volume fraction of the multiphase fillers and the volume ratio of LM to FG, the pre-mixed LM&amp;FG/SR composite can gain tunable thermal and mechanical properties under the strained state and thus be applicable to complex situations in which both excellent heat-conducting capability and certain load-bearing capacity are required.

STUDIES ON THE THERMODYNAMIC PROPERTIES OF NATURAL RUBBER COMPOSITES FILLED WITH CLAY AND CORN COB

The mechanical properties of materials such as natural rubber composites determine their usefulness as engineering or biological materials. The thermodynamic properties of natural rubber composites filled with clay and corn cob at varying volume fraction of filler were studied with a view of relating and comparing thermodynamic parameters (ΔG, ΔH and ΔS) to mechanical properties (Young’s modulus, tensile strength, elongation at break, etc) of natural rubber composites. The rubber composites were prepared using a standard compounding recipe. The tension observed for each rubber composite as a result of changes in temperature was used in evaluating thermodynamic parameters via Arrhenius equation and plot. These properties have been evaluated by measuring the thermodynamic parameters of natural rubber composites compounded with varying percent volume fractions (5% - 25%) of two fillers- clay and corn cob. The results indicated that the maximum values of ΔG and ΔH was obtained for corn cob filled composites at 10% volume fraction, while the optimal values of ΔS for the same composites was found to be at 5% and 25% volume fraction. At lower filler concentration (5 – 17.5%), corn cob filled composites were observed to have higher modulus than clay filled rubber composites, while at these concentration ranges, clay was found to impact higher tensile strength to natural rubber than corn cob filler.

Contribution of mineral filler to the fatigue damage behaviour of bituminous mastic

The objective of this research was to quantify the contribution of mineral filler to the linear shear strain amplitude sweep-based fatigue behaviour of mastic. Mastics with different volume fractions of mud (RM), marble dust (MD), and limestone dust (LS) fillers were tested in intermediate temperature domain, while the mechanical responses throughout the test sequence were compared to that of bitumen. The conspicuously high contribution of the RM filler indicated its comprehensive interaction with bitumen. The threshold of this contribution by approaching the ultimate particle interlocking was identified at the volume fraction of the RM filler of 20 %. On the contrary, the contributions of the common MD and LS fillers were moderate. The transition of the mechanical properties throughout the test sequence showed a characteristic dependency on the type of filler, its volume fraction, and test temperature. A more advanced characterisation of this transition in the zone of failure would have a considerable potential for the quantitative assessment of the type of failure, critical for the relevance of the results.

Experimental characterisation and modelling of the strain rate dependent mechanical response of a filled thermo-reversible supramolecular polyurethane

• A sugar-filled healable polyurethane composite was fabricated, characterized and modelled. Composites consisting of a polymer binder filled with various particles are widely used in industrial applications, and key to their engineering design is the ability to produce mechanical models of these materials. One limitation of many composites is the use of cross-linked elastomers as matrix materials, which reduces re-usability and recyclability. In this research, a recently developed reusable and low temperature processable supramolecular polyurethane was mixed with sugar particles to produce a model composite material with different particle sizes or volume fractions, which were subsequently characterised and modelled. Large strain mechanical properties of the material were analysed in compression at strain rates up to approximately 1800 s −1 , supported by measurements of the small strain viscoelastic response at different temperatures and frequencies. A model was developed that combined the known viscoelastic response of the supramolecular polyurethane with filler reinforcement and strain activated damage equations calibrated against quasi-static experiments. The model provided a good prediction of the high strain rate behaviour, for which the effect of adiabatic heating in the sample was also considered. The model parameters were related back to the filler particle size and volume fraction. Finally, a preliminary study of geometry and strength recovery was performed.