Formation Of Free Volume Research Articles

Free volume formation and the high strength of pure Mg after room temperature core-sheath ECAP passes

The present investigation is conducted to successfully deform pure Mg by equal-channel angular pressing (ECAP: channel angle 90°, corner angle 20°) using core-sheath configuration at room temperature. The microstructure of the sample after 4 passes of ECAP contained an average grain size of ∼0.3 μm and an excess free volume of ∼0.63% due to the formation of defects and dislocations during the ECAP process. The results show that local temperature increases up to 200 °C during the ECAP process causes dynamic recovery and recrystallization in the microstructure during deformation. The texture analysis shows that the first pass activates the non-basal sliding systems and the 4 passes present a relatively strong (0002) fiber texture. The highest ever reported tensile toughness of SPD processed pure Mg of about 1.784 GPa% with remarkable mechanical properties were achieved after 4 passes with an ultimate tensile strength of 223 MPa, yield stress of 170 MPa, and an elongation to failure of 8%.

Influence of Cold Rolling Process and Chemical Composition on the Mechanical Properties and Corrosion Behavior of Zr-Based Metallic Glasses

Cold rolling (CR) with thickness reduction of 10%, 30%, and 50% was applied to Zr50Cu44Al6 and Zr49.5Cu44Al6Nb0.5 metallic glassy ribbon samples. The XRD patterns showed the amorphousness of all samples after casting and CR processes. The SEM images indicated the formation of multiple shear bands (SBs) owing to plastic deformation during CR. However, the addition of 0.5 at% Nb to the alloy changed the SBs’ density and spacing characteristics. The characterization of free volume changes caused by CR was carried out by measuring the density of Archimedes. The micro-hardness of samples was studied by investigating SBs and free volume during plastic deformation. Alloy softening occurred due to the formation of free volume during CR. X-ray photoelectron spectroscopy (XPS) confirmed the presence of oxides ZrO2, CuOx, and AlOx on the surface of the ribbons. The anodic polarization curves of the cast and R50 samples in solutions of NaCl and Na2SO4 (0.5 M) were obtained using potentiodynamic polarization measurements. Compared to CR ribbons, melt-spun ribbons after casting showed better corrosion resistance with lower anodic current densities in Na2SO4 solution.

Modeling the formation of free volume at grain boundaries and triple junctions during nickel crystallization

The molecular dynamics method was used to study the formation of free volume at grain boundaries and triple junctions during crystallization using nickel as an example. To simulate the crystallization process, crystalline nuclei were used — small ideal crystals with a fixed lattice. The orientation of the crystal lattice in the nuclei was set randomly, but so that tilt boundaries with the misorientation axis <100> or <111> were formed in the result of crystallization. It is shown that the free volume during crystallization is predominantly concentrated at grain boundaries and triple junctions, and more so in the latter ones, i. e. where the last solidification of the structure occurs and crystallization fronts are encountered. The reduced density of the structure at triple junctions compared with grain boundaries is explained by the fact that when three crystallization fronts meet, the volume is fixed, where the liquid phase having a density lower than that of the crystal solidifies. The velocity of crystallization front motion is several tens of times lower than the speed of sound in a metal, therefore, defects, as a rule, formed only in the last turn — when the fronts meet, i. e. at grain boundaries and triple junctions. Disclinations at triple junctions were not observed in this work. During crystallization, relatively small subgrains with an orientation different from the neighboring grains, and usually in a stretched state, sometimes appeared in the region of triple junctions. But they “healed” relatively quickly, being absorbed by neighboring growing grains.

Investigation of shear transformation zone and ductility of Zr-based bulk metallic glass after plasma-assisted hydrogenation

The shear transformation zone (STZ) and ductility of Zr-based bulk metallic glass with varying hydrogen content were analyzed using serrated flow in nanoindentation, with each serration representing the formation and expansion of one or more shear bands. An exponential model was employed to extract the serrations and obtain a certain range of shear stress, and STZ size was estimated via thorough statistical data analysis. The experimental results demonstrated a striking decrease in the serration number and width of the load-displacement curve after hydrogenation, which is similar to the effects of the nanoindentation loading rate. The calculated STZ volume and atomic number were in good agreement with those reported in the literature. The STZ volume, size, activation energy, and activation volume also increased with the increased hydrogen content, leading to shear band formation and proliferation as well as increased shear band density, plastic zone, and plasticity. At the microscopic level, the hydrogen addition accelerated free volume formation and enhanced flow ability between the atoms, as characterized by the improvement of plasticity. At the macroscopic level, hydrogen addition promoted shear band nucleation and multiplication and increased shear band density, plastic zones, and plasticity. The metallic glass plasticity was greatly improved after hydrogenation as assessed via compression tests at room temperature, confirming the rationale of the experimental results.

A nanoscale study of the negative strain rate dependency of the strength of metallic glasses by molecular dynamics simulations.

Compressive strength and deformation characteristics of a metallic glassy alloy related to strain rate are studied by molecular dynamics simulations. The negative strain rate dependency of strength is presented, i.e., compressive strength decreases with the increase of strain rate, which is well in line with the experimental results. The negative strain rate dependency of strength is explained from two aspects at the atomic scale of free volume and potential energy. Compressive strength is related to the free volume formation in a shear band, which is different from that in a metallic glass matrix. In addition, the relation of potential energy and temperature is also investigated, which indicates that thermal softening also plays an important role in the negative strain rate dependency of strength. The thermal-mechanical coupling mechanisms causing the negative strain rate dependency of the strength of the metallic glassy alloy are clarified. It is significant to explore the intrinsic deformation characteristics of the metallic glassy alloy under a high rate loading.

Mechanistic insights of the enhancement effect of sorbitan monooleate on olanzapine transdermal patch both in release and percutaneous absorption processes

In this paper, based on the optimized formulation of olanzapine (OLN) transdermal patch, the role of sorbitan monooleate (SP) in OLN release and percutaneous absorption processes was probed in vitro and in vivo. Rheological test, DSC, FT-IR and molecular modeling were conducted to elucidate the effect of SP on the release process of OLN from transdermal patch. Additionally, the action of SP on the percutaneous absorption process was probed using tape stripping transdermal experiment, confocal laser scanning microscopy (CLSM), ATR-FTIR and molecular docking. The results showed that the hydrogen bonding interaction between OLN and pressure sensitive adhesive (PSA) was weakened by SP, which resulted in a decrease in the cohesive interaction between polymer chains and an increase in the formation of free volume of PSA, thus, the release of OLN from patch was promoted. Meanwhile, the OH groups of SP interacted with the polar head groups of the ceramides, which increased the fluidity of the skin lipids, thereby improved the ability of OLN percutaneous absorption. In summary, this study demonstrated that not only the release but also the percutaneous absorption processes were promoted by SP. This study provided comprehensive molecular level understanding on the effect of penetration enhancer on transdermal patch and strategies for rationally selection of chemical enhancer for transdermal drug delivery systems.

Viscoelastic Properties of the Chinese Fir (Cunninghamia lanceolata) during Moisture Sorption Processes Determined by Harmonic Tests.

Measured by harmonic tests, the viscoelastic properties of Chinese fir during moisture sorption processes were examined under three relative humidity (RH) modes: RHramp, RHisohume, and RHstep. The stiffness decreased and damping increased as a function of the moisture content (MC), which is presumed to be the effect of plasticization and an unstable state. The increasing damping was associated with the breaking of hydrogen bonds and the formation of free volume within polymer networks. The changes of loss modulus ratio at 1 and 20 Hz, E″1Hz/E″20Hz, proved the changing trend of the unstable state. Higher ramping rates aggravated the unstable state at the RHramp period, and higher constant RH levels provided more recovery of the unstable state at the RHisohume period. Changes of viscoelastic properties were associated with RH (varied or remained constant), and the application of Boltzmann’s superposition principle is a good approach to simulate viscoelasticity development.

반사방지 나노구조의 성형성과 광학적 특성에 대한 이형 온도의 영향

본에서는 저반사 나노구조 필름의 열 나노임프린트 공정 최적화를 위해 나노구조의 성형성과 광학적 특성에 대한 이형 온도의 영향을 평가하였다. 이형 온도에 따른 광학적 특성을 평가한 결과 <TEX>$70^{\circ}C$</TEX>까지는 이형 온도가 증가함에 따라 투과율과 반사율 특성이 향상되는 거동을 보였으나 그 이후에는 오히려 투과율이 감소하고 반사율이 증가하는 경향을 보였다. 이와 같은 이형온도에 따른 거동은 성형성에도 유사하게 관찰되었으며 자유체적 형성과 고분자 유동에 의한 것으로 보인다. 따라서, 이형 온도에 따라 고분자의 유동과 자유체적의 형성에 의한 패턴의 성형성이 결정되며, 이로 인해 광학적 특성에 영향을 줄 수 있음을 확인하였다. In this study, effects of demolding temperature (DT) on the formability and optical properties were evaluated in order to optimize thermal nanoimprint lithography for anti-reflective film. Characterization on optical property showed that optical performance was gradually enhanced as the DT increased up to <TEX>$70^{\circ}C$</TEX> while the transmittance and the reflectance was degraded as the DT increased further to <TEX>$100^{\circ}C$</TEX>. In addition, similar behavior was observed from formability analysis. It was contributed to the formation of free volume and viscose flow. Therefore, it was concluded that the formability and optical property are highly influenced by the formation of free volume and viscous flow of polymer depending on the DT.

Probing the role of chemical enhancers in facilitating drug release from patches: Mechanistic insights based on FT-IR spectroscopy, molecular modeling and thermal analysis

In patches, a drug must release from patches prior to its percutaneous absorption. Chemical enhancers have been used for several decades, but their roles in drug release from patches are poorly understood.In this work, the roles of chemical enhancers in bisoprolol tartrate (BSP-T) release from patches were probed in vitro and in vivo. More importantly, an innovative mechanism insight of chemical enhancers in drug release process was provided at molecular level. FT-IR spectroscopy and molecular modeling were employed to investigate the influence of chemical enhancers on drug-adhesive interaction. The results showed chemical enhancers like Span 80, which had a strong ability forming hydrogen bonds, could decrease drug-adhesive interaction leading to the release of drug from adhesive of patches. Thermal analysis was conducted to research the influence of chemical enhancers on the thermodynamic properties of patch system. It showed that chemical enhancers promoted the formation of free volume of adhesive, which facilitated drug release process. By contrast, the influence on the thermodynamic properties of BSP-T was less effective in influencing BSP-T release process.In conclusion, chemical enhancers played an important role in facilitating BSP-T release from the adhesive DURO-TAK® 87-2287 of patches by decreasing drug-adhesive interaction and promoting the formation of free volume of adhesive. This work may be an important step in understanding the important roles of chemical enhancers in drug release process.

Residual Structural Stresses in Glass Bodies

A mathematical model for the quantitative description of the formation of free volume in glass bodies in the process of their inhomogeneous cooling is used to study the influence of the parameters of this process on the distribution of residual structural stresses in glass plates. It is shown that the maximal tensile stresses increase with the temperature of the onset of cooling and cooling rate.

The free volume in dried and H2O-loaded biopolymers studied by positron lifetime measurements.

We present experiments on glucose-gelatin compounds using positron annihilation lifetime spectroscopy (PALS) in order to study the behavior of the free volume dependent on H2O loading, drying, and uniaxial pressure. A semiempirical quantum mechanical model was applied in order to correlate the lifetime of orthopositronium in nanoscaled voids to the void size. This allowed us to determine the absolute value of the mean void radius in the biopolymer samples. In addition, the variation of the total free volume of the differently treated samples is quantified and illustrated by a log-normal distribution function. Most interesting results have been obtained after saturation loading with H2O that leads to the formation of voids with a mean size of 84.3(1.9) Å(3) and to an increase of the total free volume by a factor of 2.5. This observation in the swelled sample is explained by the entropy elastic regime well above the glass transition temperature that greatly facilitates the formation of free volume. Differential scanning calorimetry (DSC) measurements were performed in order to determine the glass transition temperature and to support the interpretation of the results obtained by PALS.

Contact loss in the vicinity of cylindrical and spherical inclusions in a nanocomposite material

The loss of contact in the vicinity of cylindrical and spherical inclusions in a nanocomposite material is studied. The physical basis of the process is represented by the formation of free volume at the inclusion-matrix interface caused by a diffusion vacancy flux.

Architecturing Nanospace via Thermal Rearrangement for Highly Efficient Gas Separations

The ability to monitor free volume formation during space-making treatments is critical for the ultrafine tuning of nanospace for efficient gas separation. Here, investigating the polymer thermal rearrangement using synchrotron in situ small-angle X-ray scattering for the first time and combining this information with transport theory, we elucidate the evolution of nanospace features in polymer-based gas separation membranes. The proposed nanospace monitoring technique encompasses the structure–property relationships, therefore offering a powerful tool for tuning the polymer properties for particular gas-related clean energy applications. These results demonstrate that the fine control of the nanospace dimension and magnitude leads to a drastic improvement in gas separation performance above any material to date.

Use of acetylated softwood kraft lignin as filler in synthetic polymers

Partially acetylated softwood kraft lignin (ASKL) is used as filler in synthetic polymers such as LDPE, PP, PS and PET. ASKL/synthetic polymer composites are prepared by melt-blending and compression molding with ASKL content up to 50.0 wt%. The chemical and physical properties of ASKL/synthetic polymer composites are also investigated. TGA results show that ASKL is more thermally stable than SKL up to 200 °C. FTIR spectra demonstrate a formation of free volume by crystallization of LDPE in ASKL/LDPE composite. DSC results show that the glass transition temperature of ASKL decreased by acetylation, and ASKL/synthetic polymer composites (50/50 w/w) have a single glass transition. The AFM images of ASKL/synthetic polymer composites show no significant phase separation. Young’s moduli of ASKL/synthetic polymer composites increased with ASKL content in some extents. Tensile strength and breaking strain of ASKL/PET composite are almost retained in spite of the addition of ASKL as a result of a contraction in free volume or densification.

Effect of sand blasting on structural, thermal, and mechanical properties of Zr58.3Cu18.8Al14.6Ni8.3 bulk metallic glass

Abstract In the present work sand-blasting-induced structural, thermal, and mechanical effects were studied in Zr58.3Cu18.8Al14.6Ni8.3 bulk metallic glass. It was observed that sand blasting favors disordering of the atomic configuration, formation of free volume and evolution of multiple intersecting shear bands. As a result, considerable compressive plasticity was achieved in sand-blasted samples. It was also observed that in order to superimpose the effect of pre-straining and extra free volume for improving compressive plasticity, there exists a limit to both parameters.

Limiting of photo induced changes in amorphous chalcogenide/alumino-silicate nanomultilayers

Photo induced changes in amorphous As 20Se 80/alumino-silicate nanomultilayers (NML) produced by pulsed laser deposition (PLD) method have been studied in this work. The aim was to investigate the photo induced optical and surface relief changes due to the band gap illumination under the size- and hard cover limited conditions. It was observed that the hard cover layer on the surface of the uniform film or alumino-silicate sub-layers in the NML structure influences the photo darkening and restricts surface relief formations in As 20Se 80 film or in the related NML compared with this effect in a pure chalcogenide layer. The influence of hard layers is supposed to be connected with limiting the free volume formation at the initial stage of the transformation process, which in turn limits the atomic movement and so the surface relief formation.

Characterization of dimethacrylate polymeric networks: A study of the crosslinked structure formed by monomers used in dental composites

The resin phase of dental composites is mainly composed of combinations of dimethacrylate comonomers, with final polymeric network structure defined by monomer type/reactivity and degree of conversion. This fundamental study evaluates how increasing concentrations of the flexible triethylene glycol dimethacrylate (TEGDMA) influences void formation in bisphenol A diglycidyl dimethacrylate (BisGMA) co-polymerizations and correlates this aspect of network structure with reaction kinetic parameters and macroscopic volumetric shrinkage. Photopolymerization kinetics was followed in real-time by a near-infrared (NIR) spectroscopic technique, viscosity was assessed with a viscometer, volumetric shrinkage was followed with a linometer, free volume formation was determined by positron annihilation lifetime spectroscopy (PALS) and the sol–gel composition was determined by extraction with dichloromethane followed by 1H NMR analysis. Results show that, as expected, volumetric shrinkage increases with TEGDMA concentration and monomer conversion. Extraction/ 1H NMR studies show increasing participation of the more flexible TEGDMA towards the limiting stages of conversion/crosslinking development. As the conversion progresses, either based on longer irradiation times or greater TEGDMA concentrations, the network becomes more dense, which is evidenced by the decrease in free volume and weight loss after extraction in these situations. For the same composition (BisGMA/TEGDMA 60–40 mol%) light-cured for increasing periods of time (from 10 to 600 s), free volume decreased and volumetric shrinkage increased, in a linear relationship with conversion. However, the correlation between free volume and macroscopic volumetric shrinkage was shown to be rather complex for variable compositions exposed for the same time (600 s). The addition of TEGDMA decreases free-volume up to 40 mol% (due to increased conversion), but above that concentration, in spite of the increase in conversion/crosslinking, free volume pore size increases due to the high concentration of the more flexible monomer. In those cases, the increase in volumetric shrinkage was due to higher functional group concentration, in spite of the greater free volume. Therefore, through the application of the PALS model, this study elucidates the network formation in dimethacrylates commonly used in dental materials.

New Approach for Characterization of Gelatin Biopolymer Films Using Proton Behavior Determined by Low Field 1H NMR Spectrometry

The behavior of protons in biopolymer films (BFs) formed with gelatin, water, and glycerol was investigated at various relative humidities (RHs) and concentrations of glycerol using a low field 1H NMR spectrometer. At a RH of approximately 0%, the distributed spin-spin relaxation times (T2) of protons in BFs showed two components: a rapidly relaxing proton with the shortest T2 derived from protons in the rigid backbone of the gelatin polymer such as CH1-, CH2-, and CH3-, and a slowly relaxing component with longer T2 from protons of the functional groups in amino acid residues in gelatin such as -OH, -COOH, and -NH3. These two components are referred to as nonexchangeable (T2N) and exchangeable protons (T2E), respectively, indicating the different mobility of the protons. The T2E increased as RH increased indicating the increase in relative mobility of protons due to the larger free volume in the BF matrix. Above a RH of 33%, the slowest relaxing component was found in all BFs and referred to as hydration-water protons (T2W) with the highest relative mobility of all protons in the films. It suggests that the free volume in BFs can be formed above a RH of 33% in the absence of glycerol. The behaviors of T2N, T2E, and T2W reveal the formation of free volume in the BF matrix associated with the presence of plasticizers (water and glycerol). The T2 behavior in BFs is consistent with the behavior of spin-lattice relaxation (T1). Our result is the first attempt to characterize using low field 1H NMR technology how all protons in a film matrix behave and to develop correlations between proton mobility and free volume in protein-based BFs plasticized with water and glycerol.

Temperature-resolved Fourier transform infrared study of condensation reactions and porogen decomposition in hybrid organosilicon-porogen films

Composite organosilicon/porogen thin films were deposited via pulsed-plasma chemical vapor deposition. The organosilicon monomer was polymerized using water as the oxidant, allowing incorporation of silanol (Si–OH) moieties for subsequent condensation reactions and crosslinking for enhanced mechanical properties. The porogen monomer [methylmethacrylate (MMA)] was codeposited in the same step, and the degree of MMA incorporation was shown to scale with both the peak plasma power and porogen flow rate. Fourier transform infrared (FTIR) spectroscopy spectra of the composite material show features from both the organosilicon precursor and the porogen species, indicating that both materials are successfully incorporated into the thin film. The kinetics of both the condensation reaction and porogen removal were determined by a temperature/time-resolved FTIR method. The condensation reaction and crosslinking events occur between 100 and 425 °C. Porogen decomposition occurs simultaneously between approximately 325 and 400 °C, which is consistent with the decomposition of poly(methylmethacrylate). Using these data, the activation energy for the primary decomposition mode was found to be approximately 53.6 kJ/mol (12.8 kcal/mol). Both the index of refraction and the dielectric constant scale with the degree of porogen removal, suggesting the formation of free volume in the films. The lowest index of refraction and dielectric constant obtained was 1.404 and 2.3, respectively, for a 1 h anneal at 425 °C. Worst-case thickness loss for the films was approximately 36% of the as-deposit thickness.

Compositional Trends of Radiation-Induced Effects in Ternary Systems of Chalcogenide Glasses

The effect of γ-irradiation on the optical transmittance spectra of pseudobinary stoichiometric and non-stoichiometric cuts of ternary systems of chalcogenide glasses was studied. The application of chemical-bond approach is proposed to explain the features of compositional dependencies of radiation-induced effects in these materials. It is shown that free volume concept must be taken into consideration at the presence of different radiation-sensitive structural units. The creation processes of coordination defects connected with the formation of free volume and coupled with the capability of the constituent atoms to passivation are the main factors determining the magnitude of the radiation-induced effects in chalcogenide glasses.