Interphase Morphology Research Articles

Understanding interfacial crystallization dynamics on carbon fiber reinforced polypropylene composite manufacturing

Reinforcing polymers with discontinuous fibers improves mechanical properties, such as strength and stiffness, and in some cases achieve isotropic properties, rendering them suitable for various engineering applications. Matrix materials are generally highly engineered thermosets (e.g. crosslinked epoxies), bonded to the fiber periphery by proprietary surface and sizing chemistries. Semicrystalline thermoplastic matrices are less utilized due to poor fiber-matrix bonding resulting in inefficient interfacial load-transfer in reinforced composites. However, flexibility with melt-processing or molding conditions can be leveraged to promote non-covalent interfacial bonding between matrix and fiber via crystallization of the matrix onto fiber surface. In the present study, we utilize a co-mingle chopped carbon and isotactic polypropylene fibers to form isotropic composites, tailoring interfacial immobilized matrix or interphase morphology to optimize performance through precise control of thermal processing/molding windows. Calorimetry and optical microscopy were employed to investigate the impact of carbon fiber at various volume fractions (10, 20, and 30%) on isotactic polypropylene crystallization and mechanical performance. Variations in mechanical properties correspond to the structural evolution of the interfacial region and are correlated to underlying microstructural attributes using wide-angle X-ray scattering, thermal analysis, and low-field nuclear magnetic resonance spectroscopy. These results provide a practical framework for the manufacturing of thermoplastic matrix composites. The results presented provide a guide for the strategic optimization of interphase design, showcasing tailorable tensile strengths which outperform any isotactic polypropylene carbon fiber composites previously reported in literature.

Dependence of Thermally Activated Relaxation of Crystalline Stems on the Molecular Topology at Crystalline/Amorphous Interfaces in Polyethylene.

We investigate the relaxation dynamics of crystalline stems in relation to the molecular topology of the crystalline/amorphous interface, employing coarse-grained molecular dynamics. To efficiently generate model semicrystalline systems of linear polyethylene with a realistic interphase morphology, we simplified the Monte Carlo method by introducing molecular dynamics for faster relaxation. The structural properties of the generated systems are validated against experimental measurements, theoretical predictions, and existing simulation data. The models suggest that the probability distribution of loop-entry sites on the lamellar surface can be described by a power law in terms of the distance between the entry sites. By considering realistic interphase morphology, we are able to improve the prediction of the overall activation energy for the relaxation of crystalline stems, aligning it closely with experimental measurements. The largest model predicts that crystalline stems connected via large loops, i.e., those that exceed the entanglement length, and long tails are associated with increased activation energy; whereas stems connected to shorter tails show the lowest activation energy. These predictions can guide the future development of tougher semicrystalline polymers by providing insights into how amorphous chain morphology contributes to the activation energy and the relaxation dynamics of crystalline chains.

Effect of pre-curing on thermoplastic-thermoset interphases

This study considered adhesion between thermoplastic and thermoset laminates through interdiffusion at the interface. The influence of the degree of cure of the thermoset at the start of the process was investigated through mechanical testing and microscopy. Increasing the initial degree of cure decreased both interlaminar fracture toughness and interphase thickness. Fracture toughness decreased disproportionately to interphase thickness, attributed to changes in interphase morphology and decreasing surface contact at the interface. A simplified model was developed using gel layer thickness measurement data to predict the level of interdiffusion with increasing initial degree of cure. Compared to thermoset-thermoset co-curing, there was superior bond strength at low initial degrees of cure and a predicted increased sensitivity to the initial degree of cure, suggesting a greater influence of process variability. Hence, for specific property critical applications, the trade-off between the potential manufacturing efficiency gains from semi-curing and the reduced performance would be an important consideration.

Electrodeposited Lithiophilic Nanoparticles As Artificial Interphase for Anode-Free Lithium Ion Batteries

The world is impatiently waiting for the lithium metal or even anode free batteries - to finally make a significant step forward from current battery technology. Safer and higher in energy and power density are the targeted improvements, and while the latter is met by the choice of lithium metal as anode (or more radically, no anode at all), the safety aspect is not as easily reached (1). The anode interphase was identified long ago as the critical element to this endeavour. Consequently, alternative electrolytes (polymer, ceramic) or additives as well as numerous kinds of protective coatings are being developed (2,3). Lithiophilic metal coatings could also do the job, and it has been shown that sputtered Au or Zn layers on Li metal could prevent dendritic growth in a cell (4). The concept of artificial SEI engineering can be expanded on by using lithiophilic nanoparticles as opposed to continuous coatings. Nanoparticle decorated current collectors or lithium metal anodes can be made by electrodeposition, where the experimental conditions allow for the tuning of particle number density, size and composition (5). A precise understanding of the intermetallic phases formed between lithium and a lithiophilic-metal nanoparticle should enable their optimised design for highest performance and durability. To do so, X-ray and neutron based techniques can be great tools to follow structure and morphology of the anode interphase and correlate those properties to the electrochemical parameters.In this work, we show an investigation of electrodeposited Au or Zn nanoparticles on a current collector. Multiple configurations regarding particle size and number density are explored. Small angle X-ray scattering, electron microscopy as well as X-ray diffraction are used to characterise the anode interphase in lithium half cells under variation of the degree of lithiation.

Atomic force microscopy and scanning electron microscopy characterization of the controlling of surface morphology of epoxy‐amine‐cured spin‐coated films

AbstractAtomic force microscopy (AFM) was successfully used to study spin‐coated, amine‐cured epoxy film microstructure and morphology. The air‐epoxy and epoxy‐substrate interfaces were examined using tapping‐mode height and phase imaging AFM. The impact of relative humidity on the morphology and microstructure of the surfaces was determined. AFM was able to elucidate the changes on the surface as relative humidity during processing increased. It was observed that large nodular formations formed on the epoxy surface expose to the air but not epoxy surface formed on the substrate in addition to varying regions of more or less compliant structures, which was attributed to carbamate formation caused by the amine curing agent reaction with atmospheric CO2. Scanning electron microscopy (SEM) was used to further elucidate interface and interphase morphology of spin‐coated epoxies. Experimentation also demonstrated that post‐curing above the glass transition did not change the morphology structure, suggesting surface structures are “locked‐in.” SEM was used to further elucidate how the interface and interphase change with changing environmental conditions at both the air‐epoxy and epoxy‐substrate interface/interphases, including the impact of atmospheric CO2 on Marangoni cell formation.

Pack-boriding of Sleipner steel: microstructure analysis and kinetics modeling

Abstract In this research work, we subjected the Sleipner steel to pack-boronizing within the temperature range of 1173–1323 K, lasting from 1 to 10 h. Our study involved assessing the steel’s microstructure by examining interphase morphology and measuring the layers’ thicknesses through scanning electron microscopy. To determine the phase composition of the boronized layers, we employed X-ray diffraction analysis. Furthermore, we investigated the redistribution of certain elements during the boronizing process using EDS mapping and EDS point analysis. The boride layers were found to consist of FeB and Fe2B phases. We conducted microhardness testing using the Vickers method on the diffusion zone, Fe2B, and FeB. Lastly, we utilized a diffusion model to evaluate the activation energies of boron in FeB and Fe2B, and we presented the results in terms of activation energies.

The effect of deposition temperature of BN interphase on the tensile properties of SiC fibers

The chemical vapor infiltration (CVI) process was utilized to deposit controllable BN interphase on SiC fibers by using BCl3–NH3–H2 as precursors at low pressure from 900 °C to 1200 °C. Various characterization methods, such as SEM, Raman, XRD, XPS and TEM, are used to detect the microstructure and elemental composition of the interphases. The effects of deposition temperature on the morphology, deposition kinetics, elemental composition, and tensile properties of BN interphase coated fibers were investigated. The results indicated that the BN interphases deposited at the temperature from 900 °C to 1200 °C were compact and uniform. The growth rate increases first and then decreases with the increase of deposition temperature. The reaction rate reaches the maximum value at 1100 °C. High temperature deposition can improve the crystallinity of the BN interphase. Regardless of the deposition temperature, the tensile strength of the fiber decreases due to the increasing diameter after depositing the BN interphase. The deposition temperature had a significant impact on the tensile strength of fibers, especially at 1200 °C.

(Invited) Multiscale Interfacial Heterogeneity Explored by Advanced Spectroscopy and Imaging for Batteries Beyond Lithium-Ion

Keywords: solid-liquid interface, solid-state battery, surface-enhanced Raman spectroscopy (SERS), tip-enhanced Raman spectroscopy (TERS), neutron tomography, sulfide solid-state electrolyte, Raman imagingThe ever-growing needs for energy storage systems require batteries with even higher power and energy density with extended life and enhanced safety beyond the current Li-ion battery technologies. Fulfilling these needs requires new battery chemistries, including high-energy-density electrode materials, solid-state electrolytes, and efficient interphases to mitigate the side reactions between the electrodes and the electrolytes.Charge transport across the electrode and electrolyte interface is believed to be one of the charge/discharge rate-limiting steps. Although the composition, morphology, and structure of solid-electrolyte interphase (SEI) have been extensively studied, probing its evolution at the nanoscale is challenging to a large extent. Plasmon-enhanced Raman spectroscopy (PERS) is promising to solve this challenge. PERS is the resonant oscillation of conduction electrons at the interface between negative and positive permittivity molecules stimulated by incident light. It includes surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS). In the first part of this talk, I will show that gap-mode SERS is ideal to probe salt solvation structure in the immediate vicinity (< 20 nm) of the electrode/electrolyte interface. SERS lacks the nanoscale resolution in the sample plane. This can be compensated by TERS. TERS analysis on cycled high-energy silicon anodes indicates that the nanometer scale SEI "islands" are unevenly distributed. Even for the same SEI "island", the composition is different from point to point with inter-point distance smaller than 10 nm.All-solid-state lithium metal batteries (SSBs) promise specific energy >500 Wh/kg. A solid-state electrolyte (SSE) plays an irreplaceable role in reaching such an energy-density goal. Sulfide-based SSEs have emerged as a prominent class of soft ionic conductors that have comparable room-temperature ionic conductivity to their liquid electrolyte counterparts. However, when paring with a high voltage cathode, such as lithium nickel manganese cobalt oxide (NMC), the (electro)chemical instability of the sulfide SSE at the electrode/SSE interfaces becomes a major challenge. The interfacial instability can result in >50% initial capacity loss in a Li/sulfide SSE/NMC battery, thereby keeping the sulfide SSEs from commercialization. In the second part of this talk, I will show how we synergistically use neutron computed tomography and in situ Raman imaging, with clustering analysis to track lithium displacement at the interface of a sulfide-based SSB. Acknowledgment This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is supported by Asst. Secretary, Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (VTO) through the Advanced Battery Materials Research (BMR) Program. This research used resources at High Flux Isotope Reactor, a DOE Office of Science User Facilities operated by the Oak Ridge National Laboratory.

The effect of nonflammable electrolyte on Cu-substituted P2-type layered cathode for high safety sodium-ion batteries

Sodium-ion batteries (SIBs) have attracted a lot of attention due to abundant resources and environmental-friendly advantages. However, further improvements are needed to commercialize SIBs for poor air-stable property of cathodes and flammable risk of electrolyte. Here, we newly synthesize Na2/3Cu2/9Fe1/9Mn2/3O2, an air-stable P2-type layered cathode, using solution combustion method and investigate its electrochemical performance using triethyl phosphate (TEP), a well-known fire-retardant solvent. We confirm an air and moisture stability of cathode and nonflammable property of electrolyte. In addition, compared to a cell comprising a carbonate-based electrolyte, the TEP cell exhibits a higher capacity retention of 76.28% after 200 cycles at 2 C rate in a wide voltage range (1.5–4.6 V vs. Na/Na+). To find out the reason of superior electrochemical properties of the TEP cell, morphology and components of the cathode-electrolyte interphase (CEI) layer are characterized by morphological and spectroscopic studies.

Correlating Nanoscale Structures with Electrochemical Properties of Solid Electrolyte Interphases in Solid-State Battery Electrodes.

Here, we investigate the nonlinear relationship between the content of solid electrolytes in composite electrodes and the irreversible capacity via the degree of nanoscale uniformity of the surface morphology and chemical composition of the solid electrolyte interphase (SEI) layer. Using electrochemical strain microscopy (ESM) and X-ray photoelectron spectroscopy (XPS), changes of the chemical composition and morphology (Li and F distribution) in SEI layers on the electrodes as a function of solid electrolyte contents are analyzed. As a result, we find that the solid electrolyte content affects the variation of the SEI layer thickness and chemical distributions of Li and F ions in the SEI layer, which, in turn, influence the Coulombic efficiency. This correlation determines the composition of the composite electrode surface that can maximize the physical and chemical uniformity of the solid electrolyte on the electrode, which is a key parameter to increase electrochemical performance in solid-state batteries.

A comprehensive proposed model for gas separation prediction of mixed matrix membranes containing tubular fillers

AbstractIn this study, a comprehensive model based on composite modulus prediction model named Takayanagi is rendered which can reasonably describe gas performance of tubular filler contained mixed matrix membrane (MMMs) by considering any possible interfacial morphology. Interphase thickness (t), interphase permeability (Pi), and percolation threshold concept are included in proposed model to accurate description of the MMM performance. Since tubular fillers can be in different surface area with the same chemistry, mechanical properties are useful for determination of interphase thickness based on Pukanszky approach. On the other hand, the maximum separation potential of tubular filler can be estimated by the proposed model. In order to examine the proposed model, polyvinylidene fluoride based MMMs containing pristine and acid modified multiwalled carbon nanotube are fabricated and characterized. The interphase morphology and contribution of carbon nanotubes in gas permeability of the constructed MMMs are interpreted in details by the proposed model.

Unravelling the interphase - bond strength relationship in novel co-bonded thermoplastic - thermoset hybrid composites for leading edge protection of wind turbine blades

The relation between the bond strength of the co-bonded thermoplastics (ABS, PC) and fiber-reinforced thermoset polymers (polyester/glass) and the interphase morphology of a novel integrated leading edge protection (LEP) solution for wind turbine blades is investigated. Interphase morphology is characterized via optical microscopy and the mechanical properties of the interphase are obtained by means of nanoindentation. Bond strength of the co-bonded hybrid composites is tested via climbing drum peel test, after which, fractography is carried out to link the fracture behavior to interphase morphology. It was seen that ABS establishes a stronger bond with polyester/glass, constituting a better candidate as an LEP material. The superior bond strength of ABS was linked to its higher affinity to polyester, promoting a no-phase separated, tough interphase undergoing extensive plastic deformation. The interphase between PC and polyester/glass, however, exhibited phase separation, which triggered brittle failure at the interface between the interphase and the polyester/glass.

Novel co-bonded thermoplastic elastomer-epoxy/glass hybrid composites: The effect of cure temperature on the interphase morphology

High adhesion strength in hybrid composites is a decisive factor for their widespread use in lightweight structures. The bond strength of co-bonded thermoplastic-thermoset composites is largely influenced by the interphase thickness and morphology, which are controlled by the cure and diffusion kinetics. Hence, this study aims to characterize the interphase of a hybrid composite comprised of thermoplastic elastomer (TPE) co-bonded to glass fiber reinforced epoxy (epoxy/glass) by correlating the cure temperature with the interphase thickness and morphology. The interphase thickness is analyzed with light microscopy, while the morphology is studied with scanning electron microscopy (SEM) and atomic force microscopy (AFM) employing the PeakForce quantitative nanomechanical mapping mode (PF-QNM). The relationship between interphase thickness and cure temperature is investigated by assessing the diffusion and cure kinetics with a rheometer. It was observed that phase separation took place at the interphase, while the interphase thickness and morphology depended on cure temperature.

Fe3+-Derived Boosted Charge Transfer in an FeSi4P4 Anode for Ultradurable Li-Ion Batteries.

Ion and electron transportation determine the electrochemical performance of anodes in metal-ion batteries. This study demonstrates the advantage of charge transfer over mass transport in ensuring ultrastable electrochemical performance. Additionally, charge transfer governs the quality, composition, and morphology of a solid-electrolyte interphase (SEI) film. We develop FeSi4P4-carbon nanotube (FSPC) and reduced-FeSi4P4-carbon nanotube (R-FSPC) heterostructures. The FSPC contains abundant Fe3+ cations and negligible pore contents, whereas R-FSPC predominantly comprises Fe2+ and an abundance of nanopores and vacancies. The copious amount of Fe3+ ions in FSPC significantly improves charge transfer during Li-ion battery tests and leads to the formation of a thin monotonic SEI film. This prevents the formation of detrimental LiP and crystalline-Li3.75Si phases and the aggregation of discharging/recharging products and guarantees the reformation of FeSi4P4 nanocrystals during delithiation. Thus, FSPC delivers a high initial Coulombic efficiency (>90%), exceptional rate capability (616 mAh g-1 at 15 A g-1), and ultrastable symmetric/asymmetric cycling performance (>1000 cycles at ultrahigh current densities). This study deepens our understanding of the effects of electron transport on regulating the structural and electrochemical properties of electrode materials in high-performance batteries.

Bond Strength of Co-Bonded Thermoplastic Leading Edge Protection (LEP): The Effect of Processing-Driven Interphase Morphology

Integrated leading edge protection (InLEP) is a novel LEP method that involves co-bonding a tough thermoplastic to the blade shell of the wind turbine made of fiber-reinforced thermoset polymer. In the co-bonding process, as a result of the interdiffusion of the bonded thermoplastic and thermoset polymers, an interphase is formed between them. An important factor affecting the level of interdiffusion is the cure temperature. In this work, we investigate the influence of cure temperature on the interphase morphology and bond strength of ABS-polyester/glass and PC-polyester/glass hybrid composites. The hybrid composites are manufactured via vacuum-assisted resin transfer molding. Interphase morphology is observed and the interphase thickness is measured via optical microscopy. Bond strength is tested via climbing drum peel testing and subsequently, fractography analysis is carried out on the fractured samples. It was found that both the interphase thickness and bond strength decrease with an increase of cure temperature. The decrease in bond strength at high temperatures was accompanied by an increase in the extent of interfacial failure, while interphase failure at low temperatures promoted higher bond strength.

Enthesis Healing Is Dependent on Scaffold Interphase Morphology-Results from a Rodent Patellar Model.

The use of multiphasic scaffolds to treat injured tendon-to-bone entheses has shown promising results in vitro. Here, we used two versions of a biphasic silk fibroin scaffold to treat an enthesis defect created in a rat patellar model in vivo. One version presented a mixed transition between the bony and the tendon end of the construct (S-MT) while this transition was abrupt in the second version (S-AT). At 12 weeks after surgery, the S-MT scaffold promoted better healing of the injured enthesis, with minimal undesired ossification of the insertion area. The expression of tenogenic and chondrogenic markers was sustained for longer in the S-MT-treated group and the tangent modulus of the S-MT-treated samples was similar to the native tissue at 12 weeks while that of the S-AT-treated enthesis was lower. Our study highlights the important role of the transition zone of multiphasic scaffolds in the treatment of complex interphase tissues such as the tendon-to-bone enthesis.

Fabrication and performance of mini SiC/SiC composites with an electrophoresis-deposited BN fiber/matrix interphase

The feasibility of fabricating a BN matrix/fiber interphase of SiC/SiC composites via electrophoresis deposition (EPD) was investigated based on the simplicity and non-destructiveness of the process and the excellent interfacial modification effects of BN. The BN suspension and SiC fiber surface properties were both adjusted to generate suitable conditions for the EPD process of the BN interphase. Next, the deposition dynamics and mechanism were studied under different deposition voltages and time, and the relationship between the deposition morphology of the BN interphase and mechanical properties of the fabricated mini SiC/SiC composites were also discussed. After oxidation at high temperature (600–1000 ℃), the mechanical properties of the mini SiC/SiC composites were studied to verify the oxidation resistance effect of the EPD-deposited BN interphase, whose oxidation resistance mechanism was briefly analyzed as well.

Negating the Interfacial Resistance between Solid and Liquid Electrolytes for Next-Generation Lithium Batteries.

The combination of solid and liquid electrolytes enables the development of safe and high-energy batteries where the solid electrolyte acts as a protective barrier for a high-energy lithium metal anode, while the liquid electrolyte maintains facile electrochemical reactions with the cathode. However, the contact region between the solid and liquid electrolytes is associated with a very high resistance, which severely limits the specific energy that can be practically delivered. In this work, we demonstrate a suitable approach to virtually suppress such interfacial resistance. Using a NASICON-type solid electrolyte in a variety of liquid electrolytes (ethers, DMSO, acetonitrile, ionic liquids, etc.), we show that the addition of water as electrolyte additive decreases the interfacial resistance from >100 Ω cm2 to a negligible value (<5 Ω cm2). XPS measurements reveal that the composition of the solid-liquid electrolyte interphase is very similar in wet and dry liquid electrolytes, and thus the suppression of the associated resistance is tentatively ascribed to a plasticizer or preferential ion solvation effect of water, or to a change in the interphase morphology or porosity caused by water. Our simple estimates show that the improvement in the solid-liquid electrolyte interphase resistance observed here could translate to an enhancement of 15-22% in the practical energy density of a Li-S or Li-O2 battery and improvements in the roundtrip efficiency of 21-28 percentage points.

On the effect of stiffness/softness and morphology of interphase phase on the effective elastic properties of three-phase composite material

In the present study, Composite material consisting of an elastic homogeneous isotropic matrix in which are embedded coated elastic isotropic inclusions, widely used in many applications is investigate by homogenization approach coupled to the finite elements method. A finite element model is proposed to predict the Young and Shear modulus of the three-phase composite containing spherical inclusions surrounded by a spherical or ellipsoid interphase layer. Three cases of particles volume fractions and interphase was considered with addition of two interphase morphology. Young modulus of interphase region was varied from soft to hard than the matrix properties. We note that interphase morphology and properties plays an important role in the elastic properties of composite with increasing the volume fraction of inclusions and interphase. The results were compared to the first order bounds Voigt and Reuss, and the mean field homogenization techniques. A sensitive study of the effect of mesh density on the results of the von Mises stresses and elastic properties has been made.

Combatting rain erosion of offshore wind turbine blades by co-bonded thermoplastic-thermoset hybrid composites

An integrated thermoplastic-thermoset hybrid leading edge protection system is developed based on the co-bonding process. Co-bonding is a joining method in which a prefabricated part joints with a thermoset composite during the curing process. In such a multi-material hybrid design, the reliability of the bonding between the prefabricated protection layer and the main body of the blade is of crucial importance to prevent any delamination failures. Nevertheless, the adhesion of prefabricated thermoplastics to the thermoset remains a challenge as the interphase between two dissimilar materials is prone to form defects and irregularities. Such interface defects may lead to early failure and reduced structural integrity of the components. Therefore, the focus of this study is on achieving a strong, and reliable bonding between the prefabricated thermoplastic leading edge protection system and thermoset main body of the blade. In this study, the effect of processing temperature on the interphase quality and thickness during the co-bonding process is investigated. Next, mechanical characteristics and microstructure of the interphases are examined by Vickers’ microhardness tests. The effect of processing condition on the fracture toughness of structure is examined by climbing drum peel tests (CDP). Finally, fractography investigations are used to provide an understanding of failure mechanisms and its correlations with interphase morphology and microstructure.