Amount Of Free Volume Research Articles

Cavitation and Solid-State Post-Condensation of Polyethylene Terephthalate: Literature Review.

Polyethylene terephthalate (PET) is widely used in bottle production by stretch blow molding processes (SBM processes) due to its cost-effectiveness and low environmental impact. The presented literature review focuses on microcavitation and solid-state post-condensation effects that occur during the deformation of PET in the SBM process. The literature review describes cavitation and microcavitation effects in PET material and solid-state post-condensation of PET on the basis of a three-phase model of the PET microstructure. A three-phase model of PET microstructure (representing the amorphous phase in two ways, depending on the ratio of the trans-to-gauche conformation of the PET macromolecule and the amount of free volume) with a nucleation process, a crystallization process, and the use of positron annihilation lifetime spectroscopy (PALS) to analyze PET microstructure are discussed in detail. The conceptual model developed based on the literature combines solid-state post-condensation with microcavitation via the diffusion of the post-condensation product. This review identifies the shortcomings of the developed conceptual model and presents them with five hypotheses, which will be the basis for further research.

A molecular dynamics simulation study on the recovery performance of aged asphalt binder by waste vegetable oil rejuvenators

This study employed molecular dynamics to simulate the recovery performance of a waste vegetable oil rejuvenator on aged asphalt binder. The model's accuracy was verified through density and glass transition temperature (Tg) calculations. The Radial Distribution Function (RDF) was utilized to assess the aggregation state of different asphalt binder components. The impact of the waste vegetable oil rejuvenator on asphalt binder microstructure was evaluated using cohesive energy density (CED), relative concentration, mean square displacement (MSD), radius of gyration (Rg), and free volume amount. Changes in functional groups of the aged and recycled asphalt binder samples were analyzed using Fourier transform infrared spectroscopy (FT-IR). Results indicate that the rejuvenator significantly influences the dispersion of SARA components. Improved compatibility between aged and virgin asphalt binders is achieved through increased activity of asphaltenes and resins. The incorporation of rejuvenators into asphalt binder mildly counters the aggregation of asphalt binder molecular structure, mitigates the negative effects of aging, and restores asphalt binder structure. The rejuvenator, enriched with polar groups as per FT-IR tests, increases the proportion of polar groups in the recycled asphalt binder. The recycled asphalt binder exhibits a higher proportion of polar molecules, and the rejuvenator reacts with the polar molecules in the asphalt binder at high temperatures.

Tribocorrosion behaviors of Ti-based bulk metallic glass via laser shock peening in 3.5 wt % NaCl solutions

A Ti40Zr25Ni3Cu12Be20 bulk metallic glass (BMG) is treated by laser shock peening (LSP) with 1, 2 and 30 times, and then the phase structure, thermal, mechanical and tribocorrosion behaviors of the Ti-based BMG after LSP processing were studied in detail. The results demonstrate that although LSP did not significantly alter the phase structure of the Ti-based BMG, it facilitated rejuvenation and induced residual compressive stress within the BMG, thereby introducing internal structural heterogeneity. This heterogeneity promoted the generation of a substantial amount of free volume in the LSP-processed BMG specimens, leading to a marked improvement in plasticity and resistance to crack propagation. Consequently, the LSP-1 specimen exhibited higher surface microhardness (7.1 GPa) and plasticity, making it both plastic and tough and mitigating fatigue peeling wear caused by brittleness during reciprocating sliding wear. The average tribocorrosion volume loss rate of the LSP-1 specimen decreased by approximately 11 % to 5.73 × 10−4 mm3 N−1 m−1 (400 mV). However, excessive LSP resulted in elevated surface roughness (552.9 nm) and rejuvenation (ΔHrelax = 3.68 J g−1), rendering the surface of LSP-2 specimens more susceptible to pitting and significantly reducing their tribocorrosion resistance.

Tetramine-Based Hyperbranched Polyimide Membranes with Rigid Crosslinker for Improved Gas Permeability and Stability.

Triamine-based HBPI membranes are known for high gas separation selectivity and physical stability, but their permeabilities are still very low. In this study, we utilized a tetramine monomer called TPDA (N,N,N',N'-tetrakis(4-aminophenyl)-1,4-benzenediamine) as a crosslinking center and incorporated an additional diamine comonomer called DAM (2,4,6-trimethyl-1,3-diaminobenzene) to enhance gas separation performance, especially gas permeability. The findings demonstrated that the resultant 6FDA-DAM/TPDA membranes based on tetramine TPDA exhibited a greater amount of free volume compared to the triamine-based HBPI membranes, resulting in significantly higher gas permeabilities. Furthermore, the higher concentration of DAM component led to the generation of more fractional free volumes (FFV). Consequently, the gas permeabilities of the 6FDA-DAM/TPDA membranes increased with an increase in DAM content, with a minimal compromise on selectivity. The enhanced gas permeabilities of the 6FDA-DAM/TPDA membranes enabled them to minimize the footprint required for membrane installations in real-world applications. Moreover, the 6FDA-DAM/TPDA membranes exhibited remarkable durability against physical aging and plasticization, thanks to the incorporation of a hyperbranched network structure.

Reversible linear-compression behavior of free volume in a metallic glass

Free volume is one of the key structural concepts widely used to describe various glass phenomena. However, free volume is challenging to be rigorously defined in glass structures and directly determined by experiments. Here, we employed metallic glass as a simple glass model system and studied the structural evolution of an as-spun (hyperquenched) and another thermally annealed metallic glass with different amounts of free volume by in situ high-pressure synchrotron x-ray diffraction. Therefore, the effect of free volume on the compression behavior of metallic glasses can be clarified by comparing the two samples at identical experimental conditions. We find that a higher amount of free volume causes both lower density and bulk modulus as expected at ambient conditions. Surprisingly, during compression, the decrease of free volume has a constant rate up to $\ensuremath{\sim}30\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and appears to be mostly reversible upon decompression without obvious permanent densification after pressure release. These results suggest an elastic process in metallic glasses under pressure. Implications of these results for the structural models based on the free-volume concept are discussed. The typically assumed glass structural model with isolated domains of ``liquidlike'' (free-volume rich) region embedded in a solidlike (free-volume poor) matrix seems unlikely. Instead, a more ``homogeneous'' model over a wide range of length scales such as a nested fractal network of liquid- and solidlike regions seems more consistent with the experimental observation.

The Effect of Fluorinated Solvents on the Physicochemical Properties, Ionic Association, and Free Volume of a Prototypical Solvate Ionic Liquid.

Solvate ionic liquid (SIL) synthesis and properties depend on a delicate balancing of cation-solvent and cation-anion interactions to produce materials containing only cation-solvent complexes and solvent-separated anions. Most SILs meeting these characteristics fall within the paradigm of oligomeric ethylene oxides (e.g. glymes and glycols) and lithium salts. Targeted functionalization of solvent molecules to achieve desired properties is a relatively unexplored avenue of research. Fluorinated solvents have significantly different electric charge distributions compared to their nonfluorinated analogs. We test the impact of solvent fluorination for a SIL created from equimolar mixtures of lithium bis(trifluoromethylsulfonyl)imide (LiNTf2 ) and triethylene glycol (TEG), hereafter [(TEG)1 Li]NTf2 . In the first experiment, TEG is partially substituted with 2,2,4,4,5,5,7,7-octafluoro-3,6-dioxaoctane-1,8-diol (FTEG). This leads to a precipitous decrease in ionic conductivity and larger quantities of ionically-associated Li(NTf2 )2 - species, as detected with vibrational spectroscopy. These observations suggest FTEG does not readily coordinate Li+ ions in a manner analogous to TEG. Computational studies reinforce this conclusion. Relative complex cation stabilities are ranked as [(FTEG)1 Li]+ >[(TEG)1 Li]+ . A second experiment adds FTEG as a diluent to [(TEG)1 Li]NTf2 . This places FTEG and TEG in competition to coordinate a limited number of Li+ ions. The resulting mixtures exhibit conductivity enhancement over the parent SIL and minimal changes in ion speciation due to the poor Li+ binding by FTEG compared to TEG. Positron annihilation lifetime spectroscopic studies point to increased amounts of free volume upon dilution of FTEG. This likely explains the origin of the conductivity and viscosity enhancements.

High toughness, thermal resistance and excellent dielectric properties phenolic epoxy vinyl ester resin modified by hyperbranched polyimide

PurposePhenolic epoxy vinyl ester resin (PEVER) is an advanced resin matrix, which has excellent heat resistance, electrical insulation. However, the brittleness and poor toughness of its curing product limited its application, so this paper aims to modify the PEVER with hyperbranched polyimide (HBPI), so as to enhance the toughness, heat resistance and dielectric properties of PEVER.Design/methodology/approachHexamethylene diisocyanate trimer was used as the central reactant. Methyl tetrahydrophthalic anhydride was used as the branching unit, stannous octoate was used as the catalyst and hydroquinone was prepared as the inhibitor. Then, the hyperbranched structure of HBPI was characterized by Fourier transform infrared spectrometer and 13C-NMR. Next, PEVER was mixed with different contents of HBPI, and then the authors tested its curing product.FindingsIt is found that with the addition of HBPI, the free volume of the system was increased and the content of polar groups was decreased in each unit space, so the dielectric constant (ε) and the dielectric loss (tanδ) were decreased. In addition, PEVER could be well toughened by HBPI and the thermal stability of PEVER was improved.Originality/valueHBPI has excellent heat resistance. The addition of hyperbranched polymer increases the free volume of the system so it can slow down the transfer of stress and its nearly circular structure can absorb the impact energy from all directions. Moreover, an appropriate amount of free volume can decrease the dielectric constant of PEVER by reducing the content of polar groups.

Improved plasticity of a ZrCuAlAg bulk metallic glass by controlling the casting condition

A series of Zr50.75Cu35.75Al8.5Ag5 bulk metallic glasses (BMGs) were prepared by controlling the cooling rate and over-heating temperature. The plastic deformation behavior of the BMGs was examined. The plasticity was enhanced when the BMG was prepared at a high cooling rate and low over-heating temperature. The plasticity of the Zr-based BMGs prepared under different casting conditions was discussed based on the amount of free volume. The structural heterogeneity of the BMGs prepared with different over-heating temperatures was examined using a high-resolution transmission electron microscope and mapped by using an energy dispersive x-ray spectroscope. The results showed that a low over-heating temperature could increase the degree of heterogeneity, but an extremely low over-heating temperature could lead to nanocrystallization. The difference in the heterogeneous structures caused the distinct plastic performance of the Zr50.75Cu35.75Al8.5Ag5 BMGs prepared with different over-heating temperatures.

Dynamics across a Free Surface Reflect Interplay between Density and Cooperative Length: Application to Polystyrene

It is now generally agreed that the most dramatic influence of a free surface on local relaxation dynamics occurs over the first 10 nm from the surface. Using the cooperative free volume (CFV) rate model, we have linked a faster dynamic response to a lower density (i.e., greater available or free volume) closer to the interface. Experimental and simulation studies have shown that the relaxation profile is significantly broader than the local density profile. Here, we explain this difference using the CFV model to show that local relaxation can be enabled through accrual of a fixed amount of free volume, the value of which is a characteristic, material-dependent quantity. The process by which a relaxing segment acquires this volume involves a cooperative region whose length scale will change with density and therefore with distance from the interface. The result is a region-averaged position-dependent density profile that is significantly broadened and that links directly to the relaxation profile. Finally, we explain why these film confinement effects diminish in importance as the temperature is increased.

Strategy for improving the wear-resistance properties of detonation sprayed Fe-based amorphous coatings by cryogenic cycling treatment

Abstract Fe-based amorphous coating is deposited on invar steel substrates using detonation spray and then through the cryogenic cycling (CCT) treatment from 0 to 60 cycles with the interval 10 cycles. Effects of CCT on microstructure, thermal properties, mechanical and tribological properties were investigated. It was found that, all the coated samples with CCT are still well bonded with the invar steel substrate, except for the surface of C60 appears local cracks. Moreover, it also found that although CCT did not significantly change the phase structure of the amorphous coating, CCT promoted the rejuvenation behavior in the amorphous coating, which also led to the heterogeneity of the internal structure. Attributed to this heterogeneity, it promotes the generation of a large amount of free volume in the amorphous coating, which results in a significant change in the toughness and resistance to crack propagation of the amorphous coating. And after 50 CCT cycles, the amorphous coating has undergone an obvious ductile-brittle transition, which has the highest fracture toughness KIC and plastic work Wp value. The COF and wear rate of coatings increased initially, then followed by a decrease, but then again increased with the increase of CCT cycles. The 50-cycles coatings exhibited the lowest COF (0.60) and wear rate (0.56 × 10−5 mm3N−1 m−1). The wear mechanism of all the samples is mainly delamination wear with oxidative wear, but the degree of delamination wear is obviously different, showing a trend corresponding to the tribological behavior of the amorphous coating. Therefore, the CCT method could be an effectively strategy to ameliorate the toughness and then enhance the wear performance of the Fe-based amorphous coating.

Evolution of Shear Bands in the Structure of a Zirconium-Based Amorphous Alloy during Rolling at Different Temperatures

The effects of rolling with different reductions at room temperature, a temperature of 300°C, and the temperature of boiling of liquid nitrogen on the surface structure of the Zr62.5Cu22.5Fe5Al10 alloy on the evolution of shear bands and microhardness of this alloy have been investigated. Scanning electron microscopy, transmission electron microscopy, and X-ray structural analysis methods were used to study the changes in the structure after mechanical processing. To study the effect of rolling on the mechanical properties of ribbons, the Vickers microhardness is measured. Based on the results, conclusions on the hardness changes depending on the mode of rolling of the Zr62.5Cu22.5Fe5Al10 alloy ribbons are drawn. It is found that after rolling, the microhardness of the ribbons decreases with an increase in the degree of deformation at both room temperature and elevated and lowered temperatures, which is associated with the formation of shear bands in the structure and an increase in the amount of free volume (the greater the volume, the greater the degree of deformation). The microhardness of the alloy decreases to the greatest extent upon rolling at the temperature of liquid nitrogen.

Effect on microstructure and plastic deformation behavior of a Zr-based amorphous alloy by cooling rate control

In this study, Zr41.2Ti13.8Cu12.5Ni10Be22.5 amorphous alloys samples with the same diameter (8 mm) were prepared by using self-designed molds (viz. refractory steel, pure graphite, and copper molds) with different cooling capacities. Moreover, by eliminating the size effect, the effect of the cooling rate on the microstructure and compression deformation behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 amorphous alloys was investigated. Differentiation of the cooling curves revealed that the instantaneous cooling rates of the alloy melt at the glass transition temperature (Tg) are 45, 52, and 64 K·s―1 for refractory steel, pure graphite, and copper molds, respectively. X-ray diffraction, differential scanning calorimetry, and high-resolution transmission electron microscopy analysis revealed that with the decrease in the cooling rate, trace icosahedral-like atomic clusters and nanocrystals appear in local areas of the amorphous alloy and that the amount of free volume decreases with the increase in the amount of icosahedra-like atomic clusters and nanocrystals. Compression test results revealed that the elastic strain, yield strength, and compressive strength of the amorphous alloy marginally change with the decrease in the cooling rate, while the plastic strain gradually increases. By fitting, the effective size of the vein-like pattern was linearly related to the enthalpy released during structural relaxation and plastic strain, indicating that at a low cooling rate, the trace nanocrystals in the amorphous alloy could not effectively improve its plasticity and that the amount of free volume mainly affects its plasticity.

Interior of Amylopectin and Nano-Sized Amylopectin Fragments Probed by Viscometry, Dynamic Light Scattering, and Pyrene Excimer Fluorescence.

Nano-sized amylopectin fragments (NAFs), prepared by extrusion of waxy corn starch, were investigated by viscometry, dynamic light scattering (DLS), and pyrene excimer fluorescence (PEF). NAF57, with a hydrodynamic diameter of 57 nm, was treated with nitric acid to yield three degraded NAFs, which appeared to share the same interior and structural features as amylopectin based on their measured intrinsic viscosity and hydrodynamic diameter. This conclusion was further supported by comparing the efficiency of forming excimer between an excited and a ground-state pyrenyl label covalently attached to the NAFs (Py-NAFs) using their IE/IM ratio of the fluorescence intensity of the excimer (IE) to that of the monomer (IM). The overlapping trends obtained for all Py-NAFs and the pyrene-labeled amylopectin samples by plotting the IE/IM ratio as a function of pyrene content provided further evidence that the interior of NAFs and amylopectin shared the same structural features and contained a similar amount of free volume as predicted by the Solution-Cluster (Sol-CL) model. The presence of free volume was validated by adding linear poly(ethylene glycol) (PEG) chains that could not penetrate the interior of Py-NAFs, thus subjecting the Py-NAFs to increased osmotic pressure, which induced their compression and resulted in an increase in IE/IM.

Characterizing the Tensile Strength of Metastable Grain Boundaries in Silicon Carbide Using Machine Learning

The local atomic structure, local chemistry, and stoichiometry of grain boundaries control in part the strength and fracture toughness of silicon carbide components. The predictions of the structure and properties of these grain boundaries are generally limited to their ground-state configurations. We investigated the tensile strength behavior of metastable grain boundaries in silicon carbide using high-throughput atomistic simulations combined with machine learning techniques. We analyzed and compared the ∑5 ⟨100⟩{120} and ∑9 ⟨110⟩{122} tilt grain boundary metastable configurations to identify structural and chemical attributes that dominate their tensile strength. We characterized these metastable grain boundaries using a set of microscopic descriptors representing the local grain boundary atomic structure and the local grain boundary stoichiometry and chemical-bound types. We used a boosted regression tree surrogate model for the successful prediction of metastable grain boundary strength as a function of these descriptors. Our results show that the tensile strength of generic (i.e., any random grain boundary from the entire grain boundary population), metastable grain boundaries is primarily dominated by the grain boundary excess free volume, closely followed by the type of structure composing the boundary and the amount of C–C bonds. The 5% strongest metastable grain boundaries have particular characteristics with a low amount of free volume and the highest density of C–C bonds. Our results reveal that the 5% strongest and weakest metastable grain boundaries are most sensitive to the local stoichiometry, regardless of the local atomic structure composing the grain boundary as compared to any other generic metastable grain boundaries. We show that the strongest and weakest metastable grain boundary configurations can be identified as specific regions in a low-dimensional-representation space of their microscopic descriptors. Taken together, these findings showcase the effectiveness and validity of using a low-dimensional representation of the grain boundary structure and machine-learned surrogate models to rapidly assess metastable grain boundary strength without the need to perform actual tensile simulations.

Bending behavior and fracture surface characters for FeSiB amorphous ribbons in different free volume state

The FeSiB amorphous ribbons with monolithic amorphous structure in different free volume state were prepared by annealing the as-cast ribbons at different temperature. The results show that a fairly large amount of free volume for S25 sample, the medium amount of free volume for S250 sample, and the free volume were almost annealed out in S380 sample, and the free volume has great influence on bending behavior and the resultant fracture surface. With the decrease of free volume, the amount of shear bands on the bent crease, bending strain decrease from 1 to 0, critical shear displacement on fracture surface decrease form 3.32 mm decline to ~ 203 nm. Meanwhile, the size of micro-scale vein pattern decreases, the size of nano-scale periodic corrugations increases. The bending strain, shear band density and fracture surface characteristics were discussed via free volume content and shear transform zone size.

Relating melting temperature with structure heterogeneity and plasticity of Zr57Cu20Al10Ni8Ag5 bulk metallic glass

In the present paper, a series of Zr57Cu20Al10Ni8Ag5 BMGs are prepared by controlling the melting temperature. Glass forming ability and thermal-stability of Zr57Cu20Al10Ni8Ag5 BMGs increases continuously with the melt temperature moves to higher overheating state. However, the compressive plasticity decreases from 16.3% for the BMG with the lowest melting temperature of 1273K to 0% for the BMG with the highest melting temperature of 1573K. By structure characterization using HRTEM, the results show that nanocrystals and local segregation of atom clusters exist in the glassy matrix of the BMGs with lower melting temperature. Difference in plastic performance is considered relating with the heterogeneous structure caused by the different amount and distribution of nanocrystals and clusters. The reason for the plastic performance with respect to different melting temperature is also discussed from the aspect of cooling rate, amount of free volume, and oxygen content.

A universal natural hydroxy propyl methyl cellulose polymer additive for modifying lignocellulose-based gel polymer electrolytes and stabilizing lithium metal anodes

Defects in gel polymer electrolytes (GPEs) limit the comprehensive performance of lithium-ion batteries (LIBs). Even using an excellent lignocellulose (LC)-based GPE is not sufficient for practical applications due to its poor mechanical properties, low liquid absorption and ionic conductivity. To eliminate these limitations, in this work, a novel biodegradable hydroxy propyl methyl cellulose (HPMC) polymer with a remarkable swelling effect was added to an LC-based polymer matrix. The LC/HPMC (LCH) membrane prepared by the phase transfer method retains the excellent performance of the LC membrane. A large amount of free volume is formed in the corresponding GPE due to the swelling effect, which can remarkably improve the physical and electrochemical properties, including the absorption of the liquid electrolyte (1168 wt%), mechanical property (14.45 MPa), ionic conductivity (6.14 × 10−3 S cm−1, 25 °C), lithium ion transfer number (tLi+ = 0.75), charge/discharge performance (162 mA h g−1 at 0.2C), and excellent regulation ability of Li deposition. Moreover, the overpotential of the Li/LCH-based GPE/Li symmetric battery is stable for more than 1000 h, which illustrates that the addition of the HPMC can provide long-term protection for lithium metal electrodes.

Detection of Ring and Adatom Defects in Activated Disordered Carbon via Fluctuation Nanobeam Electron Diffraction.

How the structure of disordered porous carbons evolves during their activation is particularly poorly understood. This problem endures primarily because of a lack of high-resolution 3D techniques for the characterization of amorphous and highly disordered structure. To address this, the measurement of the 3D pair-angle distribution function using nanodiffraction patterns from high-energy electrons is demonstrated. These rich multiatom correlations are measured for a disordered carbon and they clearly show the structural evolution during activation. They provide previously inaccessible bond-angle information and direct evidence for the presence of ring and adatom defects. An increase in the short-range order and the number of fivefold ring defects with activation are observed, indicating stress relaxation by increasing curvature. These observations support models of disordered porous carbons based on curved graphene networks and explain how large amounts of free volume can be created with surprisingly small changes in the average ratios of tetrahedral to graphitic bonding.

Annealing effect on elastic and structural behavior of Tantalum monatomic metallic glass

Molecular dynamics simulation with embedded atom method (EAM) interatomic potential has been devoted to investigating the elastic and structural behavior of Tantalum (Ta) monatomic metallic glass (MG). Ta-MG samples were heat treated for periods ranging from 0 to 10 ns at three aging temperatures (500 K, 900 K and 1100 K). Our results revealed an improvement in terms of elastic constants C11 and C44, and a reduction of C12 when annealing time and temperature increase. During annealing process, the Ta monatomic MG undergoes a hardening and its yield strength increases. This has been correlated to the increase of Young's modulus (E) and shear modulus (G) which suggests the improvement of the elastic behavior and the resistance to the shear bands (SBs), respectively. We found that during aging process, the isotropic property of Ta monatomic MG remains invariants. The self-diffusion coefficient (D) has been found to be more pronounced at 1100 K near the glass transition temperature, which leads to an atomic vibration by reducing the amount of free volume accumulated during the glass transition and inhibits the localization of certain defect such as shear bands (SBs). We have also found that the <0,0,12,0> full icosahedral short-range order (SRO) increases as annealing time increases. At medium-range order (MRO), the full icosahedral cluster <0,0,12,0> has been observed to be connected by intercross-sharing (IS), face-sharing (FS), Edge-sharing (ES) and vertex-sharing (VS). These enhancements in structural properties are the principal key to interpret the achieved hardening of Ta monatomic glass under annealing process.

Atomic-scale origin of shear band multiplication in heterogeneous metallic glasses

Using molecular dynamics simulations, we provide an atomistic description of the shear band multiplication mechanisms in a heterogeneous metallic glass consisting of two distinct amorphous regions with different amounts of free volume and degrees of short-range order. The structural differences and elastic fluctuations encountered by the developing shear band while crossing the interface between the two regions alter the autocatalytic activation of the shear transformation zones (STZs) and, subsequently, lead to shear band branching. The two-unit STZ-vortex mechanism sheds light on the correlation between the strain distribution during tensile deformation and the directional characteristics of the STZ activation process.