Interphase Region Research Articles

Effects of nano-sized silica particles on the off-axis creep performance of unidirectional fiber-reinforced polymer hybrid composites

A multi-step homogenization approach is presented to predict the off-axis creep response of hybrid polymer matrix composites (HPMCs) reinforced with unidirectional carbon fibers and silica nanoparticles. The first step deals with evaluating the viscoelastic properties of silica nanoparticle-polymer nanocomposite using the Mori-Tanaka micromechanical model. Two essential features affecting the behavior, including silica nanoparticle agglomeration and interphase region generated due to the interaction between the nanoparticle and polymer are taken into account. In the second step, the off-axis viscoelastic behavior of HPMCs is extracted from the homogenized nanocomposite and carbon fiber properties using a unit cell-based micromechanical model. Some comparative studies between the predictions and available experiment are directed to verify the homogenization process. All the model predictions are in good agreement with the experimental data. The results indicate that with increasing the fiber off-axis angle from 0° to 90°, the presence of silica nanoparticles leads to a reduction in the HPMC creep compliance. Also, the proposed multi-step homogenization approach is applied to investigate the effects of volume fraction, size and agglomeration degree of silica nanoparticles; thickness and material properties of the interphase region; and off-axis angle and volume fraction of the carbon fiber on the HPMC creep response.

Silicon Monoxide As Anode Material for Lithium Ion Batteries

Silicon monoxide (SiO) is a very promising anode material for the next generation high energy lithium ion batteries due to its high theoretical specific capacity of 1710 mAh/g and volumetric capacity of 1547 Ah/L.[1] Compared to commercially used graphite, SiO can offer 18% cell stack level improvement in volumetric energy density and 11% in gravimetric energy density (calculated based on the same cell stack model), enabling utilization of smaller and lighter batteries. It also offers more stable cycle performance compared to Si due to less volume change (134% initial volume expansion and 117% reversible volume expansion), making it a more practical choice for lithium ion batteries in the near future.SiO is composed of Si nanodomains in a SiO2 matrix. An interphase region of transitional stoichiometry (SiOx, 0 < x < 2) is also present between Si and SiO2 and takes up 20-25 at.% of the entire composition.[2] During the lithiation and delithiation, the Si nanodomains react reversibly with lithium, similar to amorphous silicon, to give the reversible capacity. The SiO2 matrix reacts irreversibly with lithium to form lithium silicates and lithium oxide. Therefore, the Si domain size and interphase suboxide between Si and SiO2 have effect on the electrochemical performance of SiO. In this study, we gradually changed the microstructure of SiO via annealing treatment and thoroughly studied the change of the SiO microstructure and its impact on the electrochemical performance of the SiO. Together with electrode formulation optimization, up to 99% capacity retention during 50 cycles was obtained in full cells when using pure SiO as anode and LiNi0.5Mn0.3Co0.2O2 as cathode. Acknowledgement We gratefully acknowledge the support from Peter Faguy at the U.S. Department of Energy’s (DOE) office of Energy Efficiency & Renewable Energy (EERE) - Vehicle Technologies Office. This work is conducted under the Cell Analysis, Modeling, and Prototyping (CAMP) Facility at Argonne National Laboratory. Argonne National Laboratory is a U.S. Department of Energy Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357.Reference: Obrovac, M. N.; Chevrier, V. L., Alloy Negative Electrodes for Li-Ion Batteries. Chemical Reviews 2014, 114 (23), 11444-11502.Hirata, A.; Kohara, S.; Asada, T.; Arao, M.; Yogi, C.; Imai, H.; Tan, Y.; Fujita, T.; Chen, M., Atomic-scale disproportionation in amorphous silicon monoxide. Nature Communications 2016, 7, 11591.

An integrated computational materials engineering framework to analyze the failure behaviors of carbon fiber reinforced polymer composites for lightweight vehicle applications

A bottom-up multi-scale modeling approach is used to develop an Integrated Computational Materials Engineering (ICME) framework for carbon fiber reinforced polymer (CFRP) composites, which has the potential to reduce development to deployment lead time for structural applications in lightweight vehicles. In this work, we develop and integrate computational models comprising of four size scales to fully describe and characterize three types of CFRP composites. In detail, the properties of the interphase region are determined by an analytical gradient model and molecular dynamics analysis at the nano-scale, which is then incorporated into micro-scale unidirectional (UD) representative volume element (RVE) models to characterize the failure strengths and envelopes of UD CFRP composites. Then, the results are leveraged to propose an elasto-plastic-damage constitutive law for UD composites to study the fiber tows of woven composites as well as the chips of sheet molding compound (SMC) composites. Subsequently, the failure mechanisms and failure strengths of woven and SMC composites are predicted by the meso-scale RVE models. Finally, building upon the models and results from lower scales, we show that a homogenized macro-scale model can capture the mechanical performance of a hat-section-shaped part under four-point bending. Along with the model integration, we will also demonstrate that the computational results are in good agreement with experiments conducted at different scales. The present study illustrates the potential and significance of integrated multi-scale computational modeling tools that can virtually evaluate the performance of CFRP composites and provide design guidance for CFRP composites used in structural applications.

How Interphase Properties Control the Young’s Modulus and Yield Strength of Polymer Nanocomposites?

In this article, several models are applied to reveal the effects of volume fraction, thickness, strength and modulus of interphase region between polymer matrix and nanofiller on the Young’s modulus and yield strength of polymer nanocomposites. The properties of interphase are calculated for several samples by experimental data of mechanical properties. It is found that the concentration of interphase is higher than that of nanofiller in some samples. The Young’s modulus of nanocomposites largely depends on filler and interphase concentrations. In addition, the highest fraction and strength of interphase region produce the highest yield strength of nanocomposites.

Spectroscopic Study of Ultra High Molecular Weight Polyethylene (UHMWPE) and Mg-Ni-doped ZnFe&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt; Nano Composites

The present study aims at investigating the effect of incorporating nano scale MgxNixZn1-xFe2O3 (where x=0.15) as nano fillers on the physical and chemical stability of ultra high molecular weight polyethylene (UHMWPE). The effect of adding 1% and 2% (by weight) nano fillers on the physicochemical properties of UHMWPE/MgxNixZn1-xFe2O3 nano composites have also been investigated by using FTIR, Raman, and UV-VIS spectroscopy. FTIR data of UHMWPE/MgxNixZn1-xFe2O3 nano composites reveal that the addition of MgxNixZn1-xFe2O3 up to 1% induces significant chemical and physical structural alterations in UHMWPE matrix. However, this behavior is found to reduce on increasing the concentration of nano fillers from 1% to 2%. Raman spectroscopic data shows that crystalline contents of UHMWPE remain unaffected with the addition of nano fillers, however; a significant increase in amorphous contents and decrease in all-trans interphase region is observed. This behavior is attributed to the chain scission reactions due to addition of MgxNixZn1-xFe2O3 followed by compression moulding process at high pressure and elevated temperature. Absorption spectroscopy analysis revealed that the incorporation of MgxNixZn1-xFe2O3 results in decrease of energy band gaps from 2.14 eV to 2.08 eV (for direct transition) and from 1.54 eV to 1.38eV (for indirect transition) due to band gap energy which is induced because of MgxNixZn1-xFe2O3 incorporation as nano fillers within the PE matrix.

Investigation on the effect of GMA-graft structure in SAN-g-GMA-coSt on inter-phase behavior, thermal stability, and mechanical properties of PC/SAN/GO nanocomposites

In this study, the effect of simultaneous presence of graphene oxide (GO) nanoparticles and styrene-assisted glycidyl-methacrylate-grafted SAN copolymer (SAN-g-GMA-coSt), as a compatibilizer, on inter-phase behavior, microstructure, thermal, and mechanical properties of PC/SAN blends was investigated. First, the structure of GMA-grafts on the surface of the SAN copolymer was adjusted to improve the compatibility of the blend components. The role that processing conditions play in grafting efficiency was comprehensively studied by FTIR and H-NMR techniques. The results indicated that the optimized SAN-g-GMA-coSt contained grafted sequences consist of 5 GMA molecules dispersed in every 387 carbons of the straight SAN chains. This structure of GMA-grafts reduced phase separations of the blend components and the size of droplets. GO localization in the system, controlled by two-step mixing method, was studied theoretically and the prediction was confirmed by the experimental results. The DSC and DMTA thermograms illustrated that the inter-phase region expanded probably by interactions between functional groups on the surface of GO and the epoxy section of GMA. In addition, thermogravimetric and mechanical results indicated that incorporation of nanoparticles in the presence of SAN-g-GMA-coSt increased the residual mass (char yield) at 600 C and tensile strength of nanocomposites by 55% and 37%, respectively.

In Situ Investigation of Chemomechanical Effects in Thiophosphate Solid Electrolytes

Summary Solid-state batteries can suffer from catastrophic failure at high current densities due to solid electrolyte fracture, interface decomposition, or lithium filament growth. Failure is linked to chemomechanical material transformations that can manifest during electrochemical cycling. We systematically investigate how solid electrolyte microstructure and interfacial decomposition (e.g., interphase) affect failure mechanisms in lithium thiophosphates (Li3PS4, LPS) electrolytes. Kinetically metastable interphases are engineered with iodine doping, and microstructural control is achieved using milling and annealing processing techniques. In situ transmission electron microscopy reveals iodine diffusion to the interphase, and upon electrochemical cycling, pores are formed in the interphase region. In situ synchrotron tomography reveals that interphase pore formation drives edge fracture events, which are the origin of through-plane fracture failure. Fractures in thiophosphate electrolytes actively grow toward regions of higher porosity and are affected by heterogeneity in microstructure (e.g., porosity factor). This work provides fundamental design guidelines for high-performance solid-state batteries.

Influence of carbon black on cure properties and mechanical strength of natural rubber/butadiene rubber blends

In the present study rubber/rubber blends [RRB] of natural rubber [NR] and butadiene rubber [BR] with 50phr of carbon black [CB] in different blend ratios (70:30, 50:50, and 30:70) were prepared on a two-roll mill. Cure properties, density, morphology, and mechanical strength of CB filled NR/BR blends were analyzed. It was observed that the addition of CB improved the processing properties. A decrease in cure time in the presence of CB was observed. CB forms physical dense networks in filled RRB and increases the crosslink density as compared to the corresponding neat RRB. In addition to the improvement in processing properties, the addition of CB strengthens the interphase region within RRB thereby increasing the mechanical strength of the RRB. A correlation between the morphology driven CB partitioning within NR/BR blend would be informative to readers.

Effect of working temperature on the interfacial behavior of overmolded hybrid fiber reinforced polypropylene composites

In the present study, the interfacial behavior of overmolded hybrid fiber reinforced polypropylene composites (hybrid composites) in the working temperature range from 23 °C to 90 °C was studied by experimental and constitutive methods. Monotonic and cycle loading-unloading single-lap-shear tests were employed to determine the interfacial properties of hybrid composites. The experimental results show that both interfacial shear strength and shear stiffness decrease with increasing working temperature. A regression function was adopted to evaluate the decaying degree of interfacial properties with increasing working temperature. The shear stress-displacement relationship under monotonic loading exhibits nonlinear behavior after an initial elastic region. The envelope lines of shear stress-displacement of hybrid composites under cyclic loading indicate that the nonlinearity in the curve is caused by the plastic deformation of polypropylene in the interphase region. A constitutive model was built to describe the nonlinear shear stress-displacement relation of hybrid composites at different working temperatures. A full suite of temperature-dependent plastic parameters in the model was obtained from cyclic loading-unloading tensile tests. The predicted shear stress–displacement curves agreed well with experimental results from different working temperatures. In addition, the failure mode of hybrid composites varied with working temperature.

Correlation of nanoscale interface debonding and multimode fracture in polymer carbon composites with long-term hygrothermal effects

The correlation between nanoscale interface debonding and crack energy release rate for modes I, II, and I/II for extended exposure to hygrothermal conditions in polymer matrix composites (PMCs) needs to be understood. In this study, the effects on PMCs for two years of exposure, to a heat of 60 °C and relative humidity of 90%, were investigated. The interphase properties were studied using PF QNM. During hygrothermal treatment, the interphase region's thickness around the crack tip increases, and the morphology of the interphase changes. Nanoscale debonding of the fiber and matrix in artificially aged samples is a mix of cohesive and adhesive failure. Degradation at the nanoscale interphase and the macroscale crack initiation toughness slows after one year of aging. Interface debonding and nanoscale cracks cause intralaminar cracks, fiber bridging, and an increase in crack energy. Toughness in mode I fracture was increased in the artificially aged samples.

Enhancement of thermal, morphological, and mechanical properties of compatibilized based onPA6‐enriched graphene oxide/EPDM‐g‐MA/CR: Graphene oxide andEPDM‐g‐MAcompatibilizer role

AbstractIn this study, a series of elastomeric nanocomposites based on specific amounts of polyamide6 (PA6)/chloroprene rubber (CR) blends which are compatibilized with ethylene propylene diene monomer‐grafted‐maleic anhydride (EPDM‐g‐MA) and different amounts of graphene oxide (GO) were prepared with melt mixing method. The effect of compatibilizer and reinforcement concentration in the PA6/CR blend matrix was investigated using theoretical and experimental analysis. Dispersion of nanoplatelets within rubber blend matrix was proven with transmission electron microscopy and field emission‐scanning electron microscopy. The modified microstructure of samples showed the significant effect of EPDM‐g‐MA and GO on the size reduction of CR droplets in the PA6 continuous phase. The results from differential scanning calorimetry and dynamic mechanical thermal analysis revealed the effect of EPDM‐g‐MA and GO as an effective nucleating agent in PA6‐enriched GO/CR (PA6EGO/CR). The findings obtained from thermogravimetric analysis displayed that the GO in the presence of an EPDM‐g‐MA as a compatibilizer can cause a higher thermal stability in PA6EGO/CR. From mechanical properties, by adding a compatibilizer to the PA6/CR blend, the tensile strength changed from 39.0 to 45.1, the Young's modulus altered from 522.2 to 716.0 and the elongation at break changed from 246.8 to 222.2. While incorporation of 5 phr of GO to the compatibilized blend, the tensile strength increased by 25.2%, the Young's modulus increased by 36.6% and the elongation at break decreased by 20%. The Christensen–Lo model used for analyzing the stiffness of PA6EGO/EPDM‐g‐MA/CR with emphasis on the influence of the interphase region to predict the effect of various loadings of GO and EPDM‐g‐MA of Young's modulus. The rheology and creep tests showed a significant effect of EPDM‐g‐MA and GO content on the rheology behavior of nanocomposites.

Ultraviolet–Visible Spectroscopy: A Qualitative Tool to Predict Dispersion and Interphase Characteristics in Carbon-Based Particulate Filled Poly (Lactic Acid) Composites

Abstract Properties of polymer composites depend to a large extent on the characteristics of dispersion and interphase layers. In this work, poly (lactic acid) composites (PLAC) were prepared via the dissolution–dispersion method (DD) and oligomeric–dispersion method (OD). Ultraviolet–Visible spectroscopy (UV–VIS) was used to determine the dispersion and interphase characteristics within the PLAC. An increase in absorbance at a higher wavelength within the absorbance spectra was observed for PLAC prepared by DD and OD, which can be attributed to the formation of strong adlayers as well as “near to homogenous dispersion” for carbon-based particulate filled composites. An increase in absorbance was observed for PLAC prepared by OD in comparison to DD and can be attributed to modifications occurring at interphase regions. PLAC using carbon black, multiwalled carbon nanotubes in poly (lactic acid) were prepared via DD and OD and further characterized by UV–VIS. To study the “hybrid effect,” composites with 2.5 weight percent of carbon black with varied concentration of multiwalled carbon nanotubes and nanocellulose fibers were prepared via DD and OD, further characterized for UV–VIS. This manuscript portrays the role of UV–VIS to determine dispersion as well as the interphase characteristics for poly (lactic acid) filled carbon composites.

Effect of interphase parameters on elastic modulus prediction for cellulose nanocrystal fiber reinforced polymer composite

Abstract In this study, the effective elastic modulus (Ec ) of a cellulose nanocrystal fiber reinforced polymer composite was evaluated using the Mori-Tanaka and finite element (FE) model. The FE model was generated using a representative volume element with a periodic boundary condition. The mass fractions of the fiber in the composites (MFf ) were set to 1, 2, and 3 wt.%. Elastic modulus values for interphase were input and were either uniform or exhibited a gradient. The E c for the uniform interphase region increased significantly with MFf , but was relatively low for interphase regions exhibiting a gradient. The results show that interphase parameters must be considered carefully when predicting Ec using the FE model.

Effects of critical interfacial shear strength between polymer and nanoclay on the Pukanszky's “B” interphase factor and tensile strength of polymer nanocomposites

This paper aims to develop the “B” interphase parameter and Pukanszky model for tensile strength of polymer clay nanocomposites assuming critical interfacial shear strength (τc) providing the stress transferring between polymer and nanoparticles. The clay properties express the “τc” and both “τc” and interfacial shear strength (τ) develop the effective thickness, strength and volume fraction of interphase region as well as the effective volume fraction of clay in nanocomposites. The effective terms are applied to expand the “B” interphase parameter and Pukanszky equation. The experimental data of tensile strength for some samples and the parametric investigations validate the developed equations for “B” and tensile strength of nanocomposites. All parameters consistently control the “B” and tensile strength. Low critical interfacial shear strength, high interfacial strength, thick interphase, high interfacial shear strength, high aspect ratio (length per thickness) of clay and a small number of clay in the stacks produce a high “B” and improve the tensile strength of nanocomposites. The absence of interphase section in nanocomposites largely decreases the “B” and very thin interphase deteriorates the strengthening efficiency of nanoclay in nanocomposites.

A novel model for quantification of the moisture absorption of polymeric laminated composites

In the present study, a new model was developed that considers the amount of the environmental fluid absorption by different constituents of polymeric laminated composites including fibers, resin, fiber-matrix interphase region, ply interface region, and voids. By knowing the fluid absorption behavior of the composite constituents, the present model can predict the amount of fluid absorption of different constituents of polymeric laminated composites with an arbitrary resin volume fraction and stacking sequence. Test specimens were fabricated by glass fibers and vinyl ester resin. The environmental fluids, examined in this study, were distilled and saline water under different temperatures and salt concentrations. To investigate the absorption behavior of different constituents of polymeric composite, various tests were conducted on fibers, pure cured resin, unidirectional composite specimens, and laminated composites. Based on the results of the tests, a new theoretical model was developed to quantify and predict the amount of fluid absorption of different constituents of laminated polymeric composites. The thickness of the interphase region between the fiber and matrix was also measured using the scanning electron microscope (SEM) images and nano-indentation tests. The consistency of experimental results with the outcomes of the theoretical model indicates the accuracy of the model.

A developed theoretical model for effective electrical conductivity and percolation behavior of polymer-graphene nanocomposites with various exfoliated filleted nanoplatelets

In this paper, based on developing an analytical model, the effective electrical conductivity and percolation behavior of exfoliated polymer graphene nanocomposites (PGNs) are investigated. The graphene layers are considered as filleted cuboids which are randomly distributed in the matrix. The effects of several parameters including physical properties of graphene, matrix, interphase region, and quantum tunneling effect on the effective electrical conductivity and percolation behavior of PGNs are investigated. Moreover, comparing our results with the results obtained for graphene disc and cuboid composites, the present model makes a better prediction of the electric behavior of the compound. Afterward, our results are compared with five different experimental data sets and satisfactory agreement were found.

Influence of Graphene Platelet Aspect Ratio on the Mechanical Properties of HDPE Nanocomposites: Microscopic Observation and Micromechanical Modeling.

A series of high-density polyethylene nanocomposites filled with different diameter sizes (5, 15, and 25 μm) of graphene nanoplatelets at various amounts (0.5–5 wt.%) are prepared by the melt-mixing method. The effect of diameter size and filler content on the mechanical properties is reported, and the results are discussed in terms of morphology and the state of dispersion within the polymer matrix. The measured stiffness and strength of the nanocomposites were found to be mainly influenced by the filler aspect ratio and the filler-matrix adhesion. Fractography was utilized to study the embrittleness of the nanocomposites, and the observations revealed that a ductile to brittle transition is caused by a micro-deformation mechanism change in the nanocomposites. Several micromechanical models for the prediction of mechanical properties of nanocomposites, taking into consideration filler aspect ratio, percolation effect, and interphase regions, are considered. The three-phase model proposed by Ji accurately predicts the stiffness of graphene nanoplatelets with a higher diameter size, while Takayanagi modified model II was found to show good agreement with the experimental results of smaller ones at low filler content. This study demonstrates that the diameter size of the filler plays a central role in determining the mechanical properties.

Mini-Review: Mixed Ionic-Electronic Charge Carrier Localization and Transport in Hybrid Organic-Inorganic Nanomaterials.

In this mini-review, a comprehensive discussion on the state of the art of hybrid organic–inorganic mixed ionic–electronic conductors (hOI-MIECs) is given, focusing on conducting polymer nanocomposites comprising inorganic nanoparticles ranging from ceramic-in-polymer to polymer-in-ceramic concentration regimes. First, a brief discussion on fundamental aspects of mixed ionic–electronic transport phenomena considering the charge carrier transport at bulk regions together with the effect of the organic–inorganic interphase of hybrid nanocomposites is presented. We also make a recount of updated instrumentation techniques to characterize structure, microstructure, chemical composition, and mixed ionic–electronic transport with special focus on those relevant for hOI-MIECs. Raman imaging and impedance spectroscopy instrumentation techniques are particularly discussed as relatively simple and versatile tools to study the charge carrier localization and transport at different regions of hOI-MIECs including both bulk and interphase regions to shed some light on the mixed ionic–electronic transport mechanism. In addition, we will also refer to different device assembly configurations and in situ/operando measurements experiments to analyze mixed ionic–electronic conduction phenomena for different specific applications. Finally, we will also review the broad range of promising applications of hOI-MIECs, mainly in the field of energy storage and conversion, but also in the emerging field of electronics and bioelectronics.

Impact of interfacial properties on the viscoelastic relaxation of hard–soft block copolymers using finite element analysis

Abstract

Molecular dynamics simulation of the influence of sizing agent on the interfacial properties of sized carbon fiber/vinyl ester resin composite modified by self-migration method

ABSTRACT The interfacial property of sized carbon fiber reinforced vinyl ester resin (SCF/VE) composite was improved by a self-migration method using acrylamide (AM) as a modifier. A molecular dynamics simulation was performed to study the influence of sizing agent on the interphase formation and the interfacial modification effect. After the system equilibrium, the analysis of monomer distribution shows that an interphase region with thickness of ~2.0–2.5 nm was formed surrounding the fiber surface and the interaction energy was increased obviously. The thickness of this interphase region is obviously larger than that of unsized carbon-reinforced composite (~0.5–1.0 nm). This is mainly due to the sizing agent diffusion to the resin and the strong polar interaction between the sizing agent and AM molecule. As a consequence, the interfacial strength and toughness of the composite were enhanced jointly, which was confirmed by the test of interface shear strength and interlaminar shear strength.