Positron Annihilation Lifetime Spectroscopy Analysis Research Articles

Correlation of proton conductivity and free volume in sulfonated polyether ether ketone electrolytes: A positron annihilation lifetime spectroscopy study

Proton-conducting polymers play a pivotal role in clean energy technologies and various industrial applications, with a significant emphasis on enhancing energy efficiency and minimizing environmental impact. Sulfonated polyether ether ketone (SPEEK), which is renowned for its proton conductivity, has emerged as a key material in electrochemical processes, notably in proton exchange membrane (PEM) fuel cells. This study investigated the proton conductivity and dielectric behavior of SPEEK electrolytes at varying degree of sulfonation (DS) of 65% and 80%, correlating these properties with free volume profiles determined by positron annihilation lifetime spectroscopy (PALS). The SPEEK-65 and SPEEK-80 electrolytes were prepared via a controlled sulfonation process and characterized by FTIR, TGA, and SEM analyses. Proton conductivity and dielectric measurements were conducted at temperatures ranging from 300-370 K and frequencies ranging from 20 Hz to 1 MHz. The results revealed that SPEEK-80 exhibited a maximum proton conductivity of 3.4×10-2 S/m at 300 K and 1 MHz, which was significantly greater than the 4.38×10-3 S/m observed for SPEEK-65 under the same conditions. PALS analysis demonstrated a notable increase in free volume with increasing DS, with SPEEK-80 showing a higher o-Ps lifetime and intensity, indicating larger free volume sizes and fractions. These findings underscore the critical interplay between DS, free volume, and proton conductivity, offering insights into optimizing SPEEK-based electrolytes for advanced electrochemical applications.

Probing of CoO-induced nano-sized defects in Li2SO4–MgO–P2O5 glasses: Insights from positron annihilation lifetime spectroscopy

This study investigates the influence of CoO doping on concentration and characteristics of nano-sized cavities in Li₂SO₄-MgO-P₂O₅ glasses using positron annihilation lifetime spectroscopy (PALS). These defects are known to significantly impact the physical properties of glasses. Glasses with compositions of 20 Li₂SO₄-20MgO-(60-x) P₂O₅: x CoO (0 ≤ x ≤ 1.0 mol%), were prepared using melt-quench technique. PALS analysis revealed a strong dependence of positronium (e⁺- e⁻ pair) lifetime on CoO concentration. The analysis of the results further indicated that the fraction of free volume Δf/f0) and cavity radius (R) reached minimum values between 0.6 and 0.8 mol% CoO, but increased with further CoO doping. This suggests that cobalt ions prefer Oh sites, act as network modifiers, and create a larger concentration of free volume defects when CoO is increased beyond 0.8 mol%. Notably, the PALS-derived free volume defect concentration with CoO concentration is found to follow nearly same trend exhibited by the results of optical absorption and AC conductivity studies.

Positron annihilation lifetime spectroscopy of FeCr and FeCrAl oxide dispersion strengthened (ODS) alloys

Positron annihilation lifetime spectroscopy (PALS) was performed to characterize the interfacial nanostructure between the oxide particles and ferritic matrix in two types of oxide dispersion strengthened (ODS) alloys: FeCr dispersed with Y-Ti oxide nanoparticles and FeCrAl dispersed with Y-Al oxide nanoparticles. The spectra were precisely fitted and decomposed into three components with two trapping rates. Bulk lifetime approached the theoretical value of 107 ps by taking into account the positron trapping at two types of defects. Structural characterization was performed by coincidence Doppler broadening and high-resolution transmission electron microscopy (HRTEM), revealing that two-trapping defect clusters were closely associated with Y-Ti or Y-Al oxide particles. Trapping was not detected in the non-ODS alloys. Based on Kuramotos advanced theoretical work, the shorter annihilation lifetime (179–194 ps) could be ascribed to positron trapping at vacancies and divacancies localized under the misfit dislocations associated with Y-Ti or Y-Al oxide particles. The longer annihilation lifetime (301–323 ps) could be attributed to Ar-filled gas bubbles precipitated at the oxide particle-matrix interfaces. These results of PALS analyses were consistent with the HRTEM characterization.

Proton pathways via free volumes: A positron annihilation lifetime spectroscopy (PALS) investigation of proton conductivity in SPEEK-PEG-TMOS composites

This study investigates the ionic conductivity and dielectric properties of SPEEK-PEG-TMOS solid-state polymer electrolytes across a broad frequency spectrum (0.1–1000 kHz). Proton transport mechanisms were explored over an extensive temperature range, and positron annihilation lifetime spectroscopy (PALS) was employed to elucidate the roles of free volumes in the transport mechanism. At elevated temperatures, sulfonic acid groups and free volume defects predominantly govern the conductivity in all polymer electrolytes. PEG incorporation significantly improved proton conductivity at low temperatures, while the presence of TMOS and higher PEG content have elevated conductivity at higher temperatures. Proton conductivity mechanisms at elevated temperatures are influenced by SPEEK's intrinsic proton conductivity, PEG's plasticizing effect, acid-base interactions, and the presence of free volumes. PALS analysis reveals temperature-dependent trends in the o-Ps lifetime, intensity, and free volume fraction, increasing linearly with temperature due to thermal expansion. PEG content modulated this trend, with lower PEG content samples displaying lower thermal expansion slopes, and higher PEG content samples exhibiting more substantial increases in hole-free volume. The o-Ps intensity displayed a temperature-dependent change attributed to PEG's thermal expansion limitations. These insights contributed to a comprehensive understanding of the intricate interplay between PEG content, thermal expansion, and free volume in SPEEK-PEG-TMOS composites. The study has implications for material science applications, particularly in the development of high-temperature, anhydrous proton-conductive systems.

Electrochemical characterization and structural analysis of (In2O3)/(Fe2O3) nanocomposites for high-performance supercapacitors

This study presents a comprehensive investigation of the electrochemical characteristics and structural properties of novel nanocomposites with varying compositions of (In2O3)x/(Fe2O3)1-x, where x ranges from 1 to 0. These nanocomposites were synthesized using a versatile and cost-effective co-precipitation method. The crystallographic structure and morphology of the synthesized samples were thoroughly analyzed using Powder X-ray diffraction (PXRD) and Tunneling Electron Microscopy (TEM). Advanced analytical techniques were employed including Positron Annihilation Lifetime Spectroscopy (PALS) and Coincidence Doppler Broadening Spectroscopy (CDBS) to uncover critical insights into the structural and molecular properties of these nanocomposites. PALS analysis revealed valuable insights into the pore characteristics of the nanocomposites, while CDBS identified crucial molecular interactions within the materials. Electrochemical characterization of the nanocomposites is carried out using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical-impedance-spectroscopy (EIS) measurements. The (In2O3)0.3/(Fe2O3)0.7 nanocomposite exhibits a remarkable specific capacitance of 945 F g-1 at 1 A g-1 and exceptional rate performance, retaining 93.6% of its specific capacitance at a six-fold higher current density. Moreover, this nanocomposite electrode demonstrates outstanding cyclic stability, maintaining 92.1% of its specific capacitance even after 3000 GCD cycles at 8 A g-1. These findings suggest that the novel composition and integrated electrochemical properties of the (In2O3)0.3/(Fe2O3)0.7 nanocomposite hold great promise for enhancing the performance of next-generation electrochemical capacitors. This research contributes valuable insights into the design and development of advanced energy storage materials with applications in various high-performance energy storage devices.

Zeolite‐Based Catalysts for Conversion of Oxygenated Polymer Waste by Positron Annihilation

AbstractPositron Annihilation Lifetime Spectroscopy (PALS) has been employed to investigate the catalysts HZSM‐5 and MESO−Y, which play a pivotal role in catalyzing and upgrading plastics, with a primary focus on oxygenated polymers, thereby transforming existing plastic materials into simpler, higher‐quality value‐added products. In this study, PALS was systematically compared with other complementary analytical techniques. The research outcomes have successfully demonstrated the efficacy of PALS in elucidating the morphology and topology of zeolites at micro/meso‐meter scales.The first experiment focuses on H‐ZSM‐5 zeolite subjected to treatments involving polyurethane and polypropylene. The second experiment delves into H‐ZSM‐5 zeolites with varying Si/Al ratios, both before and after conversion. The third experiment investigates Y zeolites that are surfactant templated to induce meso‐porosity, examining their fresh state as well as their post‐conversion condition.The PALS analysis was supplemented by BET (Brunauer‐Emmett‐Teller) analysis and NMR (Nuclear Magnetic Resonance) spectroscopies. Notably, PALS exhibits superior sensitivity, at the sub‐nanometer scale, suggesting its potential as a preferred complementary method for catalysis studies. In conclusion, the integration of PALS into the repertoire of analytical tools enhances our understanding of catalyst behavior and catalytic processes, offering valuable insights for the advancement of plastic recycling and catalysis research.

Sintering study of digital light process printed zeolite by positron, thermogravimetric and x-ray techniques

This study examined the sintering of digital light process (DLP)-printed zeolite 13X with two different phyllosilicate binders—bentonite and kaolin. DLP printing offers the potential for developing a robust additively manufactured zeolite structure that can improve upon typical adsorption column configurations by employing additively manufactured triply periodic minimal surface (TPMS) structures. Zeolite 13X is a crystalline alumina silicate material with applications in pressure swing adsorption (PSA) for CO2 and N2 gas refinement and for adsorption cooling systems. The present study developed a process to fabricate zeolite parts by DLP printing where the TPMS structures were found to hold together much better than the printed discs. Thermogravimetric analysis was used to develop debinding and sintering curves and x-ray diffraction was performed to confirm the crystalline structure of the zeolite was preserved. The micropore structure and distribution were characterized with positron annihilation lifetime spectroscopy (PALS) to investigate the effects of sintering on pore size and density. From the PALS analysis, it is concluded that DLP printing produces samples with a high surface area; however, the sintering process destroys a regular nanostructure into less regular, less crystalline, and more amorphous structure pores, which is visible by more trapping and less positronium formation with sintering in the PALS parameters.

Improved pervaporation dehydration performance of alginate composite membranes by embedding organo-montmorillonite

In this work, two different montmorillonite (MMT) nanoclays were incorporated in sodium alginate (Alg) solution for fabrication of hybrid membrane for pervaporative separation of aqueous isopropanol solution. Sodium-MMT (Na-MMT) was modified to organo-montmorillonite (O-MMT) using cationic surfactant dialkyldimethyl ammonium chloride (DDAC). The influence of incorporating MMTs on the membrane properties and separation performance was investigated. Intercalating of DDA+ on Na-MMT tailored the chemical structure and morphology of the MMTs. Integrating of MMTs modified the physicochemical properties of the membranes. The membrane morphology shows the homogeneous dispersion of MMTs in athe Alg matrix. Positron annihilation lifetime spectroscopy analysis revealed a tuned microstructure of the membranes. Swelling measurements showed better compatibility of O-MMT than the Na-MMT with the Alg matrix. As a result, AlgO-MMT had better separation performance than the AlgNa-MMT with permeation flux of 4764 g∙m−2∙h−1 and water concentration in permeate of 99.99 wt% on dehydrating 70 wt% IPA/water aqueous solution at 25 °C. Owing to the favorable compatibility between the polymer and filler, AlgO-MMT membrane demonstrated stability at different pervaporation operating conditions and long-term use. Our results demonstrated that the properties and separation performance of Alg membrane can be enhanced through incorporation of O-MMTs.

Microstructure and barrier properties of reactive compatibilized PLA/PA11 blends investigated by positron annihilation lifetime spectroscopy

Poly(lactic acid)/polyamide11 (PLA/PA11) blends were prepared by reactive blending with multifunctional epoxy oligomer as compatibilizer, and the compatibility of PLA and PA11 was improved. The compatibilization, toughness mechanisms, and rheological behavior of PLA/PA11 blends were studied. Positron annihilation lifetime spectroscopy (PALS) was used to study the free volume and interfacial compatibility of the compatibilized blends. Moreover, the influence of free volume and void volume on the barrier properties of the blend films was discussed. The glass-transition temperature and storage modulus of PLA in the compatibilized PLA/PA11 blends decreased, and the rheological behavior in the blends changed from liquid-like to solid-like at low-frequency. This finding showed that the interfacial compatibility between PLA and PA11 improved, and the material properties underwent a rigid-to-tough transition. PALS analysis further showed the improved interfacial compatibility of the multifunctional epoxy reactive compatibilizer reduced the free-volume pores and increased the number of free-volume pores. The entanglement degree of the molecular-chain segment in the compatibilized blend system increased, and the volume of free-volume pore decreased. The reactively compatibilized PLA/PA11 blend had excellent oxygen and water barrier properties, and its oxygen transmissibility and water-vapor diffusion coefficient greatly decreased. Therefore the reactive compatible PLA/PA11 blends had potential application and research value as packaging-barrier film materials.

Effects of monomer rigidity on microstructures and properties of novel polyamide thin-film composite membranes prepared through interfacial polymerization for pervaporation dehydration

In this study, thin-film composite (TFC) membranes were produced through interfacial polymerization between diamine and trimesoyl chloride on a polyetherimide (PEI) support. The TFC membranes with different diamines, 4,4′-((propane-2,2-diylbis(4,1-phenylene))bis(oxy))dianiline (BAPP), 4,4′-((methylene bis(4,1-phenylene))bis(oxy))dianiline (MPDA), and 6,6′-bis(4-aminopheoxy)-4,4,4′,4′,7,7′-hexamethyl-2,2′-spirobichroman (SBC), were denoted as TFCPEI/B, TFCPEI/M, and TFCPEI/S, respectively. These three aromatic diamines have different central moieties that affect reactivity during the interfacial polymerization reaction. The crosslinking degree of the TFC membranes increased in the following order: TFCPEI/S < TFCPEI/M < TFCPEI/B. Positron annihilation lifetime spectroscopy analysis also unveils that TFCPEI/B had the lowest free volume. These results reveal that the appropriate steric structure of the diamine molecules can create less compact structure without impeding the formation of the crosslinked polyamide selective layer. Moreover, the TFCPEI/B membrane had a flux of approximately 705 ± 46 g∙m−2 h−1, and the water concentration in the permeate was maintained at approximately 99.8 wt% at 25°C during the 70 wt% isopropanol solution dehydration. Furthermore, the TFCPEI/B membrane can be operated under broad operating conditions and possesses high long-term stability.

Role of Zn on the rapid age-hardening in Mg-Ca-Zn alloys

Rapid age-hardening is critical for developing bake-hardenability in heat-treatable wrought magnesium alloys. This study investigates the role of Zn on the rapid age-hardening in Mg-0.3Ca-0.6Zn (at.%) alloy using positron annihilation lifetime spectroscopy (PALS), scanning transmission electron microscopy (STEM), and atom probe tomography (APT). Although trace Zn addition into the Mg-0.3Ca alloy accelerates the age-hardening response, PALS analysis indicates that it cannot be explained by excess quenched-in vacancies, which play a critical role in accelerating the kinetics in aluminum alloys. Instead, smaller trapping sites, i.e., open spaces, were detected in both samples. APT analysis reveals that the number density of Ca-Zn co-clusters in the Mg-0.3Ca-0.6Zn alloy increases in the early stage of aging, while that of Ca clusters tends to decrease in the Mg-0.3Ca alloy. Therefore, the rapid age-hardening in the Mg-0.3Ca-0.6Zn alloy is attributed to the formation of a large number of Ca-Zn co-clusters facilitated by open spaces.

Fabrication of analogous mixed matrix membranes via partially in-situ generation of rigid porous moieties without interfacial defects

Herein, a kind of a nalogous m ixed m atrix m embrane (AMMM) was constructed via partially in-situ generation of thermally rearranged polybenzimidazole (TR-PBI) moiety within the network PI matrix that contains ortho -amino group adjacent to imide ring. The role of highly rigid and permeable TR-PBI moieties was very similar to that of the porous fillers in traditional MMMs. By using this strategy, the issues of interfacial incompatibility and filler agglomeration were readily circumvented since the rigid porous fillers are, in fact, the rigid porous moieties that are totally belonged to the part of polymeric matrix itself. After the partially TR conversion, the average microporous diameter within membranes was increased according to the results of N 2 adsorption isotherms and positron annihilation lifetime spectroscopy (PALS) analyses. Gas transport tests revealed that the prepared PBI-PI AMMM exhibited a ∼28.2-fold increasing of in CO 2 permeability (up to 4234.9 Barrer), ∼25.8-fold increasing in O 2 permeability (up to 794 Barrer), and ∼36-fold increasing in N 2 permeability (up to 203.6 Barrer) relative to those of its network PI precursor, along with the decent selectivity of 3.9 for O 2 /N 2 and 20.8 for CO 2 /N 2 . As a result, the comprehensive gas transport properties of PBI-PI AMMM for gas pairs of O 2 /N 2 and CO 2 /N 2 exceeded or approached the 2008 Robeson upper bounds. We hope this proof-of-concept study can open a new avenue to design the advanced AMMMs, especially without the issues of interfacial incompatibility and filler agglomeration. • A novel spirobifluorene pentamine was designed using to form the nascent network PI matrix. • AMMM was constructed via partially in-situ generation of TR-polybenzimidazole moiety. • Mean microporous diameter within AMMM was increased based on the BET and PALS analyses. • Exceptional permeability enhancement in AMMM was observed via partially TR conversion.

Fabrication of zeolitic imidazolate frameworks based mixed matrix membranes and mass transfer properties of C4H6 and N2 in membrane separation

Abstract1,3‐Butadiene (BD) is a petrochemical‐based volatile organic compound, extensively used for the manufacture of synthetic rubber. There is no method reported for its recovery from nitrogen mixture. Herein, for the first time, BD is efficiently recovered by gas separation through facile and novel mixed‐metal ZIF‐8 based mixed matrix membranes (MMMs). Addition of Ni‐ZIF‐8 nanoparticles in PDMS matrix, significantly improved the penetrant‐membrane interactions and the solution‐diffusion properties of BD. Positron annihilation lifetime spectroscopy analysis showed that the well dispersion of Ni‐ZIF‐8 in PDMS enhanced the free volume of membrane and created efficient continuous paths for BD diffusion. Then, 15 wt% Ni‐ZIF‐8 MMM exhibited the BD permeance of 323 GPU and the BD/N2 ideal selectivity of 19.5, which were 60 and 81% higher than pure PDMS membrane, respectively. The simultaneous enhancement of BD permeance and BD/N2 ideal selectivity indicated that Ni‐ZIF‐8 was an effective filler applied in MMMs for efficient BD recovery.

Facile Preparation of a Laponite/PVA Mixed Matrix Membrane for Efficient and Sustainable Pervaporative Dehydration of C1-C3 Alcohols.

The exfoliation method was applied for the preparation of high-water selective mixed matrix membranes (MMMs), especially for the dehydration of C1–C3 alcohol–water solutions. Herein, a facile and easy method was employed to fabricate physically cross-linked Laponite nanosilicate clay–PVA MMMs without additional cross-linking by a one-step synthesis route for water dehydration from methanol, ethanol, and isopropanol aqueous solutions. The morphologies, chemical structures, thermal stabilities, and surface hydrophilicity of Laponite–PVA MMMs were investigated properly by different characterization techniques. The Laponite concentration has affected the fractional free volume of the membranes, as proven by positron annihilation lifetime spectroscopy analysis. The MMMs displayed both a significant improvement in the separation factor and remarkable enhancement in the permeation fluxes for the three alcohol systems. The influence of the operating temperature on the MMM performance was investigated for the methanol/water solution. The methanol permeability was 100-fold lower than that of the water, indicating that the membranes are more water selective. Particularly, the Laponite–PVA membrane with 5 mg/mL Laponite loading exhibits excellent separation efficiency for C1–C3 dehydration having water permeabilities higher than most other polymeric membranes from the other literature studies of 2.82, 2.08, and 1.56 mg m–1 h–1 kPa–1 for methanol, ethanol, and isopropanol/water systems, respectively. This membrane development allows a more efficient and sustainable separation of aqueous alcoholic mixtures.

The degradation investigation of biodegradable PLA/PBAT blend: Thermal stability, mechanical properties and PALS analysis

Polymer blends of polylactide (PLA) with poly (butylene adipate-co-terephthalate) (PBAT) to improve properties of PLA has been researched widely. But very few researches focus on the degradation of the blend, which is very important for biodegradable material. Herein, PLA and PBAT blends are prepared through solution casting, and the impact of degradation on thermal and mechanical properties of the blend are analyzed. Young’s modulus of the blend tends to keep steady, while tensile strain decreases drastically with degradation going on. Degradation also leads to poor thermal stability of the blend. Positron annihilation lifetime spectroscopy (PALS) is applied for the first time to investigate degradation process of PLA/PBAT blend, it shows that free volume holes have an increase in quantity and a decrease in size at the beginning of degradation, then show a decrease in quantity and an increase in size as the degradation going on. These findings give fundamental information for PLA/PBAT degradation process and the impact on properties, which helps the further development of PLA blend modification.

Free volume, thermal and morphological properties of photo-crosslinked thiol-Ene/ nanodiamond hybrid network

PurposeThe purpose of this research paper is to investigate the changes in free volume by adding acrylate modified nanodiamond particles. In this study, a cross-linked thiol-ene (T) network was obtained under ultraviole light. The changes in free volume were analyzed when acrylate-modified nanodiamond (M-ND) particles were added to the nanocomposites obtained. Positron annihilation lifetime spectroscopy (PALS), a well-established method, was used for this analysis. In addition, the effect of nanocomposites containing different ratios of acrylate M-ND particles (1, 2, 3 and 5 Wt. %) on the surface and the thermal properties were also examined.Design/methodology/approachThe impact of different quantities of acrylate M-ND on the free volume and surface morphological properties of thiol-ene polymer networks were studied by using scanning electron microscopy, differential scanning calorimetry, attenuated total reflection, Fourier transform infrared spectroscopy, PALS and thermogravimetric analysis measurements.FindingsThe thermal properties of T/M-ND were found to depend on the weight percentages of the M-ND content. For increasing weight percentages of M-ND added to thio-lene polymer networks, the glass transition temperature (Tg) increased from 103°C to 154°C. The ortho-positronium (o-Ps) lifetime (free volume) and free volume fraction characterization of T/M-ND nanocomposites were investigated using PALS. Increasing temperature caused both the o-Ps lifetime (free volume) to change with increasing saturation and to linearly increase the intensity; however, an increasing weight percentage of M-ND caused no change at all for the o-Ps lifetime (free volume) and the free volume fraction.Originality/valueAccording to published literature, and to the best of the authors’ knowledge, this is the first time a study examining the free volume properties in a thiol-ene system has been carried out.

Positron annihilation lifetime spectroscopy study of polyvinylpyrrolidone‐added polyvinylidene fluoride membranes: Investigation of free volume and permeation relationships

ABSTRACTPolyvinylidene fluoride (PVDF) membranes were prepared via the phase inversion method from casting solutions containing PVDF, dimethylformamide (DMF), and polyvinylpyrrolidone (PVP) as pore former. PVP was used in the casting solution in a range of 0–5 wt % and extracted. The effect on membranes of using PVP in the casting process was analyzed by X‐ray diffraction, differential scanning calorimetry, scanning electron microscopy, viscosity, and water permeability techniques. With an increase of PVP from 0 to 5 wt %, the PVDF casting solution viscosities increased from 858 to 1148 cP; the resulting PVDF membrane thickness increased; and the crystallinity of PVDF membranes decreased from 40.0 to 33.3%, which indicates that the addition of PVP inhibits the degree of crystallization in the PVDF membranes. SEM results revealed the shape and size of macropores in the membranes; these macropores changed after PVP addition to the casting solutions. The impact of structural changes on free‐volume properties was evaluated using positron annihilation lifetime spectroscopy (PALS) studies. PALS analysis indicated no effect on the average radius (~3.4 Å) of membrane free‐volume holes from the addition of PVP to the casting solution. However, the percentage of o‐Ps pick‐off annihilation intensity, I3, increased from 1.7 to 5.1% with increased PVP content. Further, increasing the PVP content from 0.5 to 5% resulted in an increased final pure water permeability flux. For instance, the 210 min flux for a 14% PVDF + 0.5% PVP membrane was found to be 3.3 times greater than a control membrane having the same PVDF concentration. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 589–598

Pore structure analysis of ionic liquid-templated porous silica using positron annihilation lifetime spectroscopy

Abstract Fundamental understanding of the pore structure of porous materials is essential for designing materials and controlling their properties to realize various applications. In this study, we quantified the structures of micropores as well as the mesopores in ionic liquid (IL)-templated porous silica using positron annihilation lifetime spectroscopy (PALS). Our PALS analyses distinguished three types of open spaces in IL-templated porous silica: (i) Vacancy clusters and/or microvoids, (ii) micropores between primary silica particles (1.0–1.4 nm in size), and (iii) mesopores (4–7 nm in size). Upon increasing the IL/SiO2 ratio, the size of the micropore between the primary particles decreased from 1.4 nm to 1.0 nm, implying that the sizes of the silica particles decreased because of the small volume of SiO2 compared with that of IL. In contrast, the sizes of the mesopores increased with the IL/SiO2 ratio, indicating that the open space expands according to the increase in the IL volume. In conclusion, the PALS method allowed comprehensive evaluation of the pore structure of the IL-templated porous SiO2. The relationship between pore structure and IL content will be used for optimization of the mechanical properties and chemical selectivity of porous SiO2.

Fatigue damage assessment of SUS316L using EBSD and PALS measurements

Kernel averaging misorientation (KAM) measurements and positron annihilation lifetime spectroscopy (PALS) were conducted to investigate the damage introduced by the tensile and fatigue testing of type 316L stainless steel. The fatigue tests were carried out at room temperature and at 550 °C under the strain controlled mode with total strain amounts, Δε of 0.4% and 1.5%. A number of different samples were prepared by interrupting the fatigue test at various ratios of fatigue cycle time to fatigue lifetime. Both KAM and PALS analyses indicated increasing damage as increasing misorientation average or number of vacancies with increasing strains in tensile- and fatigue-tested samples. Dislocations play an important role in the evolution of damage as they produce vacancies and form dislocation structures. In the fatigue test at high temperature, accelerated dislocation relaxation encourages formation of dislocation structures that result in an early increase in misorientation. Under the same conditions, the positron lifetime rather decreased because of the migration of defects at early stages of fatigue and rapidly increased at fracture. We observed different responses to mechanical straining that can be useful for evaluation of damage in 316L stainless steel.

Microwave treatment regulates the free volume of rice starch

The aim of this work was to investigate the role of microwave parameters and moisture content on the free volume (FV) changes of rice starch by positron annihilation lifetime spectroscopy analysis (PALS) and to explore the potential relationship between the changes of FV and physicochemical properties of rice starch. Microwave heating and water molecules lead to the increasing of FV of starch. However, this result is largely influenced by the plasticization of water molecule. The anti-plasticization caused by water evaporation resulting in a decrease in the size and concentration of FV during microwave heating. Significant decrease (p < 0.05) in the thickness of amorphous region of microwave-heated rice starch was found by small angle X-ray scattering (SAXS), and the glass transition temperature (Tg) and gelatinization temperature significantly increase (p < 0.05) after microwave heating. According to correlation analysis, the power intensity and heating time were correlated negatively with the lifetime of o-Ps. In addition, the changes of amorphous region and Tg of rice starch were strongly related to FV changes. These results provided a theoretical basis for further research on the directional regulation of FV and improvement the quality of starch-based food by using microwave treatment.