Filler Volume Fraction Research Articles

Synergistic enhancement of thermal and dielectric properties in PVDF films with Au-BaTiO3 hybrid nanoparticles

In our investigation of poly(vinylidene fluoride) (PVDF) films embedded with Au-BaTiO3 (AuBT) nanoparticles, we noted a synergistic improvement in both thermal stability and dielectric properties. PVDF films with varying concentrations of AuBT were expertly fabricated. Remarkably, the films retained their flexibility even at a high volume fraction of filler (f AuBT = 0.5). The predominant phases of PVDF (α, β, and γ) were observed. An increase in f AuBT resulted in a modest decrease in the melting temperature, while simultaneously causing a significant 40% increase in thermal conductivity compared to pure PVDF. The dielectric permittivity reached ∼160 at 1 kHz, while maintaining a loss tangent of ∼0.05. These improvements were attributed to discrete Au growth on BT particles, hindering conduction in PVDF. The rise in dielectric response resulted from interfacial polarization and inherent high dielectric permittivity of BT.

Experimental and numerical investigation of adhesively bonded kfrp/steel double strap joints incorporating eggshell powder-toughened epoxy adhesive

Due to the environmental concerns, the application of natural FRPs to replace synthetic fibre as a strengthening material has increased. Kenaf fibre-reinforced polymer (KFRP) has comparable specific strength with glass fibre-reinforced polymer (GFRP). Moreover, epoxy resin is widely used as a matrix of composites and adhesives; however, it has low shear strength. Improvement of epoxy properties is therefore required, for example, by incorporating biofiller such as eggshells from household waste, which contain calcite, to improve its shear strength. Testing series includes variations of KFRP bond length, KFRP thickness and eggshell filler volume fractions. All the DSJ specimens underwent a two-stage testing process, experimentally and numerically. In Stage 1, experimental work was performed on the specimens through quasi-static tensile tests, following the ASTM D3528–96. In Stage 2, numerical studies were conducted to predict the strength using the extended finite element method (XFEM) within ABAQUS CAE. Subsequently, the strength prediction from developed 2-D FEA models was validated by the experimental datasets. All testing specimens exhibited KFRP rupture mode. For all the studied overlap lengths, the joint strength increased with the increase of the studied composite's adherend thickness (1 - 4 mm); however, the overlap length reached the optimum at the overlap length of 80 mm, where beyond that overlap length, the joint strength tended to decrease. The maximum joint strength is achieved with a combination of 80 mm bond length and 4 mm KFRP thickness, resulting in a 226.5% enhancement compared to the baseline (composite thickness of 1 mm, with adhesive without filler). Moreover, it was found that volume fraction of 5% eggshell was the optimum. The strength prediction was performed using an extended finite element method (XFEM), In general, there were good agreements in both experimental datasets and XFEM models, with discrepancies of less than 16.1% (averaging less than 8%). The FEA modelling approaches are promising for predicting the joint strength of KFRP/steel DSJ.

Graphene-based phononic crystal lenses: Machine learning-assisted analysis and design

The advance of artificial intelligence and graphene-based composites brings new vitality into the conventional design of acoustic lenses which suffers from high computation cost and difficulties in achieving precise desired refractive indices. This paper presents an efficient and accurate design methodology for graphene-based gradient-index phononic crystal (GGPC) lenses by combing theoretical formulations and machine learning methods. The GGPC lenses consist of two-dimensional phononic crystals possessing square unit cells with graphene-based composite inclusions. The plane wave expansion method is exploited to obtain the dispersion relations of elastic waves in the structures and then establish the data sets of the effective refractive indices in structures with different volume fractions of graphene fillers in composite materials and filling fractions of inclusions. Based on the database established by the theoretical formulation, genetic programming, a superior machine learning algorithm, is introduced to generate explicit mathematical expressions to predict the effective refractive indices under different structural information. The design of GGPC lenses is conducted with the assistance of the machine learning prediction model, and it will be illustrated by several typical design examples. The proposed design method offers high efficiency, accuracy as well as the ability to achieve inverse design of GGPC lenses, thus significantly facilitating the development of novel phononic crystal lenses and acoustic energy focusing.

Low‐Loss Sr2Ti9O20‐Filled Butyl Rubber Composites for Miniaturized Flexible Microwave Substrate Applications

Low‐loss Sr2Ti9O20 (STO)/butyl rubber (BR) composites have been prepared by mixing and hot pressing. X‐ray diffraction and energy‐dispersive spectroscopy are employed to investigate the phases contained in the STO filler, and the microstructural characteristics of the composites are discovered using scanning electron microscopy. The STO/BR composites demonstrate a high relative permittivity of 10.98 and a low loss of 0.003 at 10 GHz, corresponding to an optimum filler volume fraction of 45%. In addition, a low coefficient of thermal expansion of 50.72 ppm °C−1 and a high thermal conductivity of 0.9603 W m−1 K−1 have been found for the optimum composition, with an acceptable moisture absorption of 0.071%. The obtained composites can be employed for miniaturized, flexible radio‐frequency substrate applications.

Revealing the Role of Chain Conformations on the Origin of the Mechanical Reinforcement in Glassy Polymer Nanocomposites.

Understanding the mechanism of mechanical reinforcement in glassy polymer nanocomposites is of paramount importance for their tailored design. Here, we present a detailed investigation, via atomistic simulation, of the coupling between density, structure, and conformations of polymer chains with respect to their role in mechanical reinforcement. Probing the properties at the molecular level reveals that the effective mass density as well as the rigidity of the matrix region changes with filler volume fraction, while that of the interphase remains constant. The origin of the mechanical reinforcement is attributed to the heterogeneous chain conformations in the vicinity of the nanoparticles, involving a 2-fold mechanism. In the low-loading regime, the reinforcement comes mainly from a thin, single-molecule, 2D-like layer of adsorbed polymer segments on the nanoparticle, whereas in the high-loading regime, the reinforcement is dominated by the coupling between train and bridge conformations; the latter involves segments connecting neighboring nanoparticles.

The Resistor Network Approach to Modeling Screen-Printed Silver Ink Under Uniaxial Stretch

Abstract Flexible electronic devices are used in a wide variety of applications that utilize their unique ability to stretch, bend, and twist. Experimental methods were developed for evaluating the piezoresistive behavior of printed conductive inks under uniaxial strain. DuPont 5025 screen-printed silver ink on Kapton and Melinex substrates was stretched until substrate failure. Kapton samples were found to rupture at around 60% strain and have a relative resistance, R/R0, of about 30–40 at substrate rupture. On Melinex substrates, the ink was found to electrically fail before the substrate ruptured but could be stretched to strains exceeding 130% or higher before failing. The relative resistance values for these high strains in the Melinex samples were erratic and could exceed 1000 and in one case more than 30,000. The ink strain to failure exhibited a dependence on conductor width with narrower conductors failing before wider ones. Finally, a 2.5D RVE model that accounts for ink filler volume fraction, particle size distribution, contact resistance, and electron tunneling was developed that accurately predicts the piezoresistive behavior of 5025 ink up to 60% axial strain. An initial parametric study found that increasing the volume fraction of the RVE results in improved electrical performance.

Multilayer functional structure design and multi-objective optimization

The current research introduces a multilayer functional structure along with its corresponding multi-objective optimization design strategy intended to improve the design efficiency of materials exhibiting remarkable properties in both load-bearing and electromagnetic wave absorption. The composite structure contains several layers of graphite oxide reinforced epoxy resin, each of which has a different thickness and volume fraction of fillers. The proposed strategy employs the volume fraction of fillers and thickness of each layer as the design variables, with the electromagnetic wave absorption bandwidth and bending stiffness of the entire structure serving as objectives. The multi-objective model was derived using the Maxwell-Garnett Model, Halpin-Tsai Model, Transmission Line Theory and Classical Laminate Theory. To efficiently optimize the multilayer structure, the JAYA, an evolutionary algorithm is employed as optimizer. The results indicate that the optimized structure exhibits a considerable increase in electromagnetic wave absorbing capacity and a slight increase in load-bearing performance relative to the original structure, while the total thickness remains constant. In addition, the whole process takes only a few seconds.

Systematic Study of the Nanostructures of Exfoliated Polymer Nanocomposites.

High-performance bioinspired materials have shown rapid development over the last decade. Examples are brick-and-mortar hierarchical structures, which are often achieved via solvent evaporation. Although good properties are claimed, most systems are composed of stacked or intercalated platelets. Exfoliation is a crucial step to give ultimate anisotropic properties, e.g., thermal, mechanical, and barrier properties. We propose a general framework for all the various types of micro-scale structures that should be distinguished for 2D filler nanocomposites. In particular, the exfoliated state is systematically explored by the immobilization of montmorillonite platelets via (gelatin) hydrogelation. Scattering techniques were used to evaluate this strategy at the level of the particle dispersion and the regularity of spatial arrangement. The gelatin/montmorillonite exfoliated nanostructures are fully controlled by the filler volume fraction since the observed gallery d-spacings perfectly fall onto the predicted values. Surprisingly, X-ray analysis also revealed short- and quasi long-range arrangement of the montmorillonite clay at high loading.

Degradation of Kapok Fiber-Reinforced Polyester Composites with Calcium Carbonate Filler in Seawater

This research investigates the development of polyester composites reinforced with kapok fiber and CaCO3 filler to reduce environmental impact. Natural fibers, valued for their lightweight, fire resistance, cost-effectiveness, and biodegradability, are commonly used in composites. However, synthetic fibers, despite their superior mechanical properties, raise environmental concerns. The study focuses on the composites' performance, stability, and endurance in harsh conditions. Kapok fibers were manually extracted, and CaCO3 powder was sieved to 80 mesh. Composite samples were created with varying volume fractions of CaCO3 powder and kapok fibers, using polyester as the matrix. Tensile and bending tests, according to ASTM D3039 and ASTM D790 standards, were conducted on these samples. Additionally, water absorption was assessed gravimetrically, and mechanical strength degradation was studied via immersion in artificial seawater at different temperatures. Results indicated that water absorption increased with higher fiber volume fractions in the composite, primarily due to the water-absorbing capabilities of natural fibers and CaCO3 particles, surpassing that of polyester resin. Increased immersion temperatures accelerated water diffusion, impacting interactions between water molecules, polymer chains, and natural fibers. Furthermore, an increase in the CaCO3 filler volume fraction negatively affected the mechanical strength of kapok polyester-fiber composites. This was attributed to the agglomeration of CaCO3 powder, disrupting the polyester resin's viscosity and damaging the bond between kapok fiber and the matrix. The composites exhibited their highest tensile strength with 10% CaCO3 filler before immersion, but this strength decreased following exposure to high temperatures.

Nonlinear dynamics of ionic liquid enhanced soft composite membrane under electro-mechanical loading

The incorporation of ionic liquids (ILs) into dielectric elastomer composites has attracted significant interest due to their potential applications in soft actuators and optical devices. Their soft and hyperelastic nature make them a distinct dynamic. In this paper, nonlinear dynamics of IL enhanced soft composite (ILESC) dielectric membrane subjected to electro-mechanical loading is investigated. A mixed micromechanical model with the incorporation of an electric double layer (EDL) and Maxwell-Wagner-Sillars (MWS) polarization is developed to estimate mechanical and electrical properties of the ILESC. Governing equations are derived via an energy method with the framework of the hyperelastic membrane theory, Neo-Hookean constitutive model and the couple dielectric theory. These equations are discretized by Taylor series expansion (TSE) and differential quadrature (DQ) methods and are solved by incremental harmonic balance (IHB) method combined with arc-length technique. The developed model and results are verified by comparing to experimental data and previous results. The influence of volume fraction, shape and size of IL fillers, static and dynamic applied electric field and excitation amplitude on forced vibration and resonant response of the ILESC membrane are comprehensively analyzed. It is found that ILESC membrane with slender ellipsoidal ILs displays larger amplitude, lower peak amplitude frequency and more obvious softening behavior.

Investigations on thermal contact resistance between filled polymer composites and solids using micro thermography

This article reports the use of a new measurement technique based on micro thermography for determining the thermal contact resistances (TCRs) between filled polymers and solids. The thermal conductivity of polymers can be significantly increased by using thermally conductive fillers. For numerous applications, not only is a high intrinsic thermal conductivity required but also a good thermal transfer between the filled polymer and an adjacent solid surface. The physical principles of thermal transport when considering this type of contact have not yet been investigated in detail, and only a few experimental results are available. The most common measurement techniques determine a macroscopic resistance and project it onto the contacting surface. However, the heterogeneous microstructure of a filled polymer causes the TCR to be a volumetric phenomenon in the overall boundary region. The utilized IR camera system takes thermal images with a spatial resolution of less than per pixel. The new method resolves the TCRs spatially and gives new insights into the microscale effects on the particle level. In addition to the common zero-gap extrapolation for the extraction of TCRs, we propose another evaluation method that considers all microscale effects of the boundary layers and evaluates TCR as a volumetric phenomenon. For the first systematic study, samples consisting of two aluminum substrates and a filled epoxy polymer were prepared and investigated. We studied the effects of filler size, filler material, filler volume fraction, and surface structure, focusing on monomodally filled polymers with filler amounts between and . The obtained results and the uncertainties of the new method are discussed within this paper.

Influence of filler topology on the thermal transport of composite materials based on similarity principle modeling: A cross-scale simulation study

The thermal conductivity parameter of the materials is a fundamental parameter for thermal design and study of heat transfer processes. In our study, we combined the homogenization theory based on the finite element with the thermal conductivity order-of-magnitude analysis and similarity principle, to construct structural models of fibers, spheres, ellipsoids, sheets, and interfaces, and establish the topology of intermingling and encapsulation of different structures. Combined thermal conductivity calculations of mesoscopic composites and microscopic interface models using finite element and molecular dynamics methods. The anisotropy model of thermal conductivity was established by coordinate transformation. Based on the numerical verification of the reliability of the method, the mechanisms of the influence on the thermal transport of composites were analyzed for parameters such as volume fraction of different structural fillers, structural shape, thermal conductivity ratio, thickness of highly thermally conductive coatings, and spatial orientation distribution. The results showed that the effective thermal conductivity (ETC) of the continuous structural reinforced composite was mainly influenced by the volume fraction of the filler; the modulation of ETC with ellipsoidal particle structure form and distribution mode was comparable to the effect of changing the volume fraction modulation; the mutual fusion between ellipsoids randomly distributed in the plane could effectively enhance the heat transport effect of the composite, and as the volume fraction increased to more than 3%, the heat transport gain from mutual fusion was more obvious; spraying high thermally conductive copper coating on ellipsoidal particles could significantly enhance the ETC of the composites. The present work could provide reference for composites in terms of structural improvement and thermal performance enhancement.

Experimental investigation of the interface interaction between asphalt binder and mineral filler from the aspects of materials properties

The strength of the interface between asphalt and filler is relatively low, making it susceptible to stress concentration and damage, which can affect the service life of the asphalt pavement. Current research indicates that there is a significant relationship between the interfacial interaction behavior and the properties of both asphalt and filler. Based on this, this study investigated the influence of both asphalt and filler properties on the interaction behavior of the asphalt-filler interface. Firstly, this study conducted research on existing interaction evaluation indicators and selected Palierne C as the optimal evaluation indicator for this study, which has the weakest correlation with filler volume fraction, in order to avoid the influence of filler volume fraction on experimental results. Secondly, this study analyzed the effects of asphalt SARA components and aging degree on the interface interaction ability between asphalt and fillers, as well as the rheological properties of asphalt. The research results found that the asphaltenes and resins fractions can enhance the interaction ability between asphalt and filler, as well as the high-temperature performance of asphalt. The content of these fractions was positively correlated with the interaction between the interfaces. In contrast, the content of aromatics and saturates fractions was negatively correlated with the interaction capacity. The strength of the interaction was negatively correlated with aging time, and long-term aging inhibited interface interaction to a greater extent than short-term aging. Finally, the mineral and chemical composition of common fillers were analyzed by X-ray diffraction (XRD) and X Ray Fluorescence (XRF). Subsequent studies were carried out on the interaction of the asphalt-filler interface in terms of the mineral composition, chemical composition, and particle size of the filler. It was found that in terms of mineral composition, albite and asphalt have the strongest ability to interact at the same temperature, followed by calcite and the weakest by quartz. In terms of chemical composition, the strongest interaction was between MgO and asphalt, followed by CaO, Fe2O3 and Al2O3, and the interaction between SiO2 and asphalt was the worst. In addition, the smaller the particle size of the filler, the greater the interaction capacity.

Assessment of mechanical properties on abaca fiber strengthened nano sandstone filler hybrid polymer composite

The experimental study here examines the mechanical characteristics of an epoxy composite with a nano sandstone reinforcement and an abaca fibre filler. The weight percentage of nano sandstone filler is varied from 0 to 8 wt% and abaca fiber is varied from 40 to 32 wt% with the interval of 2 wt% correspondingly. The chopped abaca fiber and nano sandstone composites are manufactured through the traditional hand lay-up technique. All mechanical test specimens are manufactured in accordance with ASTM specifications. Flexural, tensile strength, impact resistance, and hardness are the few of the mechanical characteristics that are measured and compared. The weight fraction of the nano sandstone filler has been considered as the significant performance parameter of the composites. A Universal Testing Machine (UTM), an impact tester, and a hardness meter were used during the preliminary research. The mechanical characteristics of the produced composites were found to be primarily influenced by the volume fraction of nano sandstone filler with fibre and epoxy resin matrix.

Salt template-assisted construction of three-dimensional interconnected network in thermally conductive EP/PVDF/NiCo@GNP composites

In this study, graphene nanoplatelets (GNP) and nickel–cobalt (NiCo) alloy were adopted as reinforcing materials to prepare epoxy (EP) resin-based composites. NiCo particles were able to achieve uniform anchoring on GNPs’ surface under the electrostatic force due to the successful introduction of oxygen defects on GNPs. With the synergistic effect of adhesive PVDF and salt particles, the system with three-dimensionally (3D) interconnected network was successfully constructed. Benefit from the formation of mechanically stable and efficient heat conduction paths, the thermal conductivity (TC) of the EP/PVDF/NiCo@GNP composite reached 1.077 W⋅m−1⋅K−1 at a filler volume fraction of 6.82 vol%, while the counterpart’s storage modulus (E’) was up to 3.22 GPa. In addition, a scaling formula was quantitatively proposed to correlate TC with E’, and the perfect agreement between the theoretical prediction and experimental data clarified the underlying mechanism of the relationship between phonons transport and stress transfer within a system with 3D ordered structures. The establishment of relationship between AHR (average heating rate) and TC made it possible to further predict TC of composites based upon the infrared thermal imaging (ITI) data. The as-prepared GNP composites show good application prospects as thermal management materials which need to experience thermally mechanical deformation.

Nonlinear elastic behaviors and deformation mechanisms of nano-structured crosslinked biopolymer networks

Cells always undergo large deformation in response to external stimulations or internal stresses in many cell functions (e.g., cell migration, cell division and cell growth). When undergoing large deformation, crosslinked actin filament networks (CAFNs) always show strong nonlinear elasticity to maintain the cell shape and integrity, known as strain stiffening, which plays a crucial role in many cell functions. To investigate the nonlinear elastic behaviors of CAFNs, a three-dimensional representative volume element model is used to perform finite element method simulations. Simulation results show that actin filament volume fraction, crosslinking density and components’ Young’s moduli show significant influences on the nonlinear elastic behaviors of CAFNs. In addition, the shear stress–strain curves of CAFNs highly depend on the bending stiffness and tensile stiffness of filamins as well as the bending stiffness of actin filaments, however, they are almost insensitive to the tensile stiffness of actin filaments. The present work not only sheds light on the nonlinear elastic behaviors of CAFNs but also provides a valuable reference for developing advanced artificial composite structures that can be used as semi-flexible biomedical scaffolds and wearable electronics.

Soft interphase volume fraction of composites containing arbitrarily shaped mono−/poly-disperse fillers: Theoretical and numerical investigations

Interphase, a crucial structural component in composite materials connecting the fillers and matrix, typically possesses unique physical properties and plays a crucial role in determining the overall transport and mechanical behaviors of the material system. In this work, we propose a generic theoretical framework to precisely determine the volume fraction fsi of soft interphase around arbitrarily shaped hard fillers, including both convex and concave shapes with arbitrary size dispersity, in three−/two-dimensional (3D/2D) heterogeneous material systems. Specifically, a composite material is regarded as a three-phase structure composed of a homogeneous matrix, hard anisotropic fillers, and their surrounding interpenetrable interphase layers with a constant “thickness” for each filler volume fraction. The seminal hard -core soft-shell (i.e., cherry-pit) model and statistical geometry theories are employed to derive explicit analytical formalism of fsi which is subsequently verified via a series of numerical experiments using Monte Carlo sampling. We systematically investigate the dependence of fsi on the filler characteristics, including filler volume fraction, geometric size factor, fineness, and filler shape and size distributions. Interestingly, we find that filler sphericity can be used as the sole shape descriptor to control the interphase volume fraction for all filler shapes, including those with irregular non-convex morphologies. Our framework provides an efficient and accurate tool for composite design that complements expansive numerical simulations, which is also readily applicable to understanding the effect of fsi on physical properties of composites.

Micromechanical modeling of damping behavior in vibration-reducible cementitious composites

Recently, some microparticles have been proven to be effective in improving the damping performance of cementitious composites, which is described by the damping loss factor. Related studies have analyzed damping loss factors of cementitious composites with microparticles to determine optimum mixing proportion, but no efficient numerical analysis method is available for cementitious composites with microparticles. In this study, the micromechanical three-phase model and finite element (FE) strain energy were applied to cementitious composites reinforced with hollow sphere and flake-shaped microparticles. These methods have been widely used with fiber composites but never used with microparticle-reinforced composites. The three-phase model was used here to estimate the damping loss of microparticles, and FE strain energy method was used to analyze the damping loss factor of microparticle-reinforced cementitious composites with the damping loss factor from the three-phase model. This research highlights that the FE strain energy method can be an effective method for estimating the damping loss factor of cementitious composites with different types of microparticles at various volume fractions of fillers with less than 0.1% the least square error between the experimental and simulation results.

Nonlinear consecutive dynamic instabilities of thermally shocked composite circular plates on the softening elastic foundation

In this research, the nonlinear dynamics of a clamped circular composite plate placed on a softening elastic foundation under rapid thermal loading is investigated. In this situation, based on the amount of temperature supplied to the structure and the coefficients of softening elastic foundation, two instabilities may happen one after the other. The structure will thermally buckle and deform dynamically if the applied temperature exceeds a critical level. If the softening coefficient of the elastic foundation is critical, the structure will completely lose its stability after a certain deformation range. A polymer containing graphene platelets (GPL) makes up the system. Based on various functions, the volume fraction of fillers varies along the thickness. The system’s nonlinear dynamic equations are obtained by applying Hamilton’s principle and the Von-Kármán theory. The transient heat conduction equation is solved by the cubic B-spline collocation (CBSC) and Crank–Nicolson procedures. The CBSC and the Newmark methods are used to solve spatially and temporally dependent governing nonlinear differential equations. Also, the Newton–Raphson method is used as a powerful tool to solve nonlinear algebraic equations. The temporal evolution, phase-plane, and post-buckling-to-maximum deflection paths are demonstrated to analyze the instabilities of the plate.

Elongation induced demonstration of the fraction dependent filler network structures in silicone rubber: An in situ SAXS study

Aiming to unveil the filler network structures in silicone rubber with various filler volume fraction (ΦSi), in situ tensile-small-angle x-ray scattering (SAXS) was conducted on composites with ΦSi of 0%, 11.9%, 18.4%, and 26.5% (S0, S30, S50, and S80). For the static state of S30, S50, and S80, the aggregates sizes decrease from 65 nm, 53 nm–42 nm, while the homogeneity of aggregates and filler network is improved. With the help of in situ SAXS, intrinsic differences of filler networks on vertical (V) and horizontal (H) of the elongation direction related to ΦSi are further unveiled. During elongation, the relative stable peak position in medium-q range of Kratky plots indicate that the aggregates as a stable unit (form factor) of the filler network. In V direction, the almost unchanged intensity of S30 indicates the insignificant changes statistically due to high heterogeneity of filler network. The decreased low-q intensity of S80 indicates the compression of relatively homogeneous filler network. While in H direction, additional peaks appear for all the samples, which are low-q shift with increasing the strain. However, for S30, the peaks mainly come from the separation of the initially adjacent aggregates. For S80, the clear increased low-q intensity suggests the initial existed correlation length is expanded.