Impact testing of polymeric foam using Hopkinson bars and digital image analysis

The present investigation aims at testing polymeric foam under impact loading using large diameter nylon Hopkinson bars and optical field measurements. Accurate average stress-strain relations can be obtained when soft large diameter polymeric pressure bars and the appropriate data processing are used. However, as there are generally no homogeneous strain and stress fields for polymeric foams, an optical field observation is needed. In contrast to quasi-static tests where the digital image correlation (DIC) measurement is commonly used, technical difficulties still remain for the reliable use of DIC under impact conditions. In this paper, an accurate synchronization method based on the displacement measurement of the end of pressure bars (calculated by a robust DIC algorithm) is preferred to conventional MCDL box time synchronization. Also, the bar end displacement measurement offers a complementary calibration method for the tension/strain conversion coefficient. Strain fields are obtained for tests on foam sample at impact velocities up to 20 m/s. The localized strain fields permit better understanding of the observed stress plateau from SHPB results. The relevance of the present method for establishing mechanical response of polymeric foam is then demonstrated.     

Characterizing the constitutive response and energy absorption of rigid polymeric foams subjected to intermediate-velocity impact

As an optimum energy-absorbing material system, polymeric foams are needed to dissipate the kinetic energy of an impact, while maintaining the impact force transferred to the protected object at a low level. Therefore, it is crucial to accurately characterize the load bearing and energy dissipation performance of foams at high strain rate loading conditions. There are certain challenges faced in the accurate measurement of the deformation response of foams due to their low mechanical impedance. In the present work, a non-parametric method is successfully implemented to enable the accurate assessment of the compressive constitutive response of rigid polymeric foams subjected to impact loading conditions. The method is based on stereovision high speed photography in conjunction with 3D digital image correlation, and allows for accurate evaluation of inertia stresses developed within the specimen during deformation time. Full-field distributions of stress, strain and strain rate are used to extract the local constitutive response of the material at any given location along the specimen axis. In addition, the effective energy absorbed by the material is calculated. Finally, results obtained from the proposed non-parametric analysis are compared with data obtained from conventional test procedures.     

Effects of laser scanning speed on surface roughness and mechanical properties of aluminum/Polylactic Acid (Al/PLA) composites parts fabricated by fused deposition modeling

Although fused deposition modeling (FDM) has gradually become one of the popular additive manufacturing technologies in different industries, high surface roughness has always been an inevitable disadvantage of FDM parts. Laser polishing represents a recent and novel application of laser surface irradiation that can be used for precise, post-process smoothing of the rough surfaces commonly encountered on FDM parts. The influence of laser polishing on surface modification and mechanical properties of aluminum/Polylactic Acid (Al/PLA) composites has been investigated. Laser scanning speed was varied to evaluate its effect on the surface quality and mechanical properties of the experimental samples. The results indicated that laser polishing could enable reductions in surface roughness of over 86.6% (from 23.27 μm to 3.11 μm Sa). The tensile strength of specimen also increased from 41.01 MPa to 51.31 MPa with increasement of 25.1%. The dynamic mechanical analysis (DMA) results showed that there was a remarkable improvement in the storage modulus and glass transition temperature of Al/PLA composite specimens after laser polishing, which suggested that the laser polishing treatment could play a role in decreasing the porosity inside the FDM parts and improve interfacial adhesion between the PLA matrix and Al fibers. Moreover, the fracture morphologies were observed to investigate the possible strengthening mechanism. These results demonstrate how laser polishing can simultaneously smooth and modify the surface characteristics of a FDM part surface.     

Automated monitoring of the crack propagation in mode I testing of thermoplastic composites by means of digital image correlation

One of the main challenges of the mode I double cantilever beam (DCB) test is the simultaneous determination of the applied load and displacement with the developing delamination length. The present work addresses this issue by side-view tracking the crack propagation by means of digital image correlation (DIC). Two different reduction methods were developed to determine the crack length from the DIC data. On the one hand, the crack tip position was defined by the high strain concentration in the immediate vicinity of the crack tip, and on the other hand, by crack tip opening displacement (CTOD). The data obtained enabled the calculation of the energy release rate of carbon fibre reinforced thermoplastic specimens with either run-arrest or stable crack extension. For reasons of comparability, top surface analysis (TSA), as recently reported, was also carried out. Following this approach, the crack propagation was tracked applying DIC to the top specimen surface. The methods developed showed a good correlation with both the standardised procedure and TSA. It was shown that DIC can be used as an alternative to the conventional optical measuring tools to follow the crack propagation in the mode I DCB test.     

Mechanical behaviour analysis of the interface in single hemp yarn composites: DIC measurements and FEM calculations

The present work aims to investigate the local deformation mechanisms around a yarn in an eco-composite. Different hemp yarn orientations and two types of epoxy resin were tested. Full-field measurements were realised with the digital image correlation technique on specific single yarn composites, either on the face of the specimens, or on the edge. The tensile tests were performed under an optical microscope to give sufficient precision, and a numerical model was developed. The experimental results showed high heterogeneities in strain fields which increase with the applied stress level. The comparison with the underlying microstructure and the numerical model enabled us to study the influence of the yarn on the mechanical behaviour. The local constitutive behaviour of the different constituents of the specimens could be approached by these analyses. These results constitute a complete and original database on hemp/epoxy interface mechanical behaviour.     

Determination of creep compliance,recovery and Poisson's ratio of elastomers by means of digital image correlation (DIC)

This work aims to determine the creep compliance, creep recovery and Poisson's ratio of three common sealing elastomers by means of the digital image correlation (DIC). The tests were conducted by stressing specimens under three different constant stresses during short duration experiments (3 h) to see the prospective of DIC for this application. The strains were measured in x and y axes with time. Thus, the behavior of creep compliance, creep recovery, and the Poisson's ratio of each elastomer were obtained. The creep results exhibited repeatability, as well as, the mean Poisson's ratios estimated were close to reported values for elastomers. Finally, despite of some limitations from the DIC equipment, it was found that this procedure can be implemented as a suitable alternative for the characterization of creep compliance, creep recovery and Poisson's ratio of elastomers. Also, it may be enhanced by following some recommendations given.     

Oxaphosphetane versus betaine formation in epoxide ring opening by PPh3: a mechanistic probe by ab initio and DFT modeling

Ab initio and density functional investigations on the deoxygenation of cis-2,3-dimethylepoxide by PPh₃ reveal a two-step mechanism. Simultaneous ring-opening and C-C bond rotation facilitates oxaphosphetane formation thereby ruling out the formation of a betaine intermediate and is consistent with the inversion of stereochemistry observed in the reaction.     

A 3D structural and conformational study of procyanidin dimers in water and hydro-alcoholic media as viewed by NMR and molecular modeling

The three-dimensional structures of 5 procyanidin dimers have been determined in a hydro-alcoholic medium and in water using 2D NMR and molecular mechanics. They are made from monomers of catechin (CAT) and epicatechin (EPI)-B1: EPI-CAT, B2: EPI-EPI, B3: CAT-CAT, B4: CAT-EPI and B2g: EPI-EPI-3-O-gallate. These tannins exist in two conformations that are in slow exchange in the NMR timescale (s), one is compact and the other extended. The compact form is found to dominate (76-98%) when the dimer is made of at least one CAT monomer (B1, B3, B4). Both forms are found in even proportions only in the case of procyanidin B2. The latter tannin can be converted into a dominant compact form when the lower EPI unit is galloylated. The finding of a predominant compact form for procyanidin dimers is discussed in relation with tannin-saliva protein interactions that are of importance for the wine-tasting/making processes.     

Immersion by rotation‐based application of the matrix for fast and reproducible sample preparations and robust results in mass spectrometry imaging

Automated matrix deposition for matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) is crucial for producing reproducible analyte ion signals. Here we report an innovative method employing an automated immersion apparatus, which enables a robust matrix deposition within 5 minutes and with scalable throughput by using MAPS matrix and non‐polar solvents. MSI results received from mouse heart and rat brain tissues were qualitatively similar to those from nozzle sprayed samples with respect to peak number and quality of the ion images. Overall, the immersion‐method enables a fast and careful matrix deposition and has the future potential for implementation in clinical tissue diagnostics.     

原位光还原法制备高分散铂沉积多孔氮化碳复合材料及其降解水中4-氟苯酚的高效可见光光催化活性

作为一种新型水中有机污染物,有机氟化物中C–F共价键的键能较大,因而很难通过传统的可见光光催化剂降解.因此,开发高效可见光光催化剂是实现在可见光照射下成功降解水中有机氟化物的关键.作为一种非金属半导体光催化剂,石墨相氮化碳(g-C3N4)因具有可见光响应、环境友好及低成本等优点而广泛应用于水中有机污染物去除.然而,体相层状结构严重限制了g-C3N4的可见光活性.这是由于体相层状结构不利于光生电子的表面迁移,同时增加了光催化反应过程的传质阻力.为了开发一种可重复使用且具有优异可见光活性的光催化剂,进而实现在可见光照射下水中有机氟化物的高效降解及矿化,本文以氯铂酸和多孔氮化碳(pg-C3N4)为前驱体,运用简单的原位光还原法成功制备出一系列高分散铂沉积多孔氮化碳复合材料(Pt/pg-C3N4),而pg-C3N4则是以三聚氰胺为原料采用前驱体预处理法制备.与传统铂沉积石墨相氮化碳(Pt/g-C3N4)复合材料相比,由于多孔氮化碳前驱体具有暴露的几何内外表面,铂纳米粒子可高度分散于其上.因此,铂纳米粒子的电子捕获效应显著增强.另外,与其他传统还原法相比,原位光还原技术还可有效抑制铂纳米粒子的自凝聚.我们对制备的Pt/pg-C3N4复合材料的形貌、孔隙率、相结构、化学组成及光电性质进行了详细表征.结果显示,与传统Pt/g-C3N4复合材料相比,由于多孔微观结构的构建以及高度分散铂纳米粒子的沉积,制备的Pt/pg-C3N4复合材料的BET比表面积显著增大,光吸收能力明显增强,光催化量子效率显著提高.在可见光条件下,初步评价了该复合材料光催化降解水中偶氮染料甲基橙的活性,然后将其进一步应用于水中4-氟苯酚的降解及矿化.结果表明,由于多孔微观结构的构建以及高度分散铂纳米粒子的沉积,所制备Pt/pg-C3N4复合材料具有相当高的可见光光催化活性.结果还显示,所制复合材料具有很高的稳定性,连续使用4次均保持相似的活性.作为一种可见光催化剂,所制Pt/pg-C3N4复合材料有望广泛应用于水中持久性有机污染物的降解以及光催化劈裂水产氢、NO分解和CO2还原等领域.     

Ionomers based on copolymers of alkyl methacrylates with 2‐methacryloylamino‐3‐naphthalene carboxylic acid: Association in solutions studied by steady‐state and time‐resolved fluorescence

Methyl, butyl, and octadecyl methacrylate copolymers with 3‐methacryloylamino‐2‐naphthoic acid (MANA) carrying alkali counterions exhibit two emission bands in highly dilute dioxane, heptane, and toluene solutions. One band (α) has a maximum around 400 nm, and the other (β) has a maximum around 500 nm. The ratio of the intensity of the α band to the intensity of the β band depends on the counterion (Na⁺, Li⁺, and Cs⁺) and the solvent. Varying the MANA content of the copolymer with Na⁺ counterions increases the relative intensity of the α emission in proportion to the density of MANA residues in the ionomer chain, whereas in chains containing only 0.1% MANA residues, only a β emission can be seen. The α emission is due to associated ion pairs, and the β emission is due to unassociated ion pairs. The shorter the alkyl chain pendant is of the copolymer, the larger the fraction is of the associated ion pairs. The half‐bandwidth of the β emission is much larger than that of the α‐emission band in all cases. The half‐bandwidth decreases in the order Li⁺ > Na⁺ > Cs⁺. The fluorescence anisotropy decays for the α‐ and β‐emission bands are double‐exponential. The longer rotational correlation time and its fractional contribution to the β emission increase with an increasing content of the MANA monomer in the copolymer. The decay anisotropy data are consistent with the shell–core model of ionomers in nonpolar solvents. The fluorescence anisotropy decay of the copolymer of butyl methacrylate with a low content of the nonneutralized MANA (～ 0.1 mol %) is single‐exponential, and the rotational correlation time of the MANA fluorophore is eight times longer than that of 3‐acetyl‐2‐naphthoic acid methyl ester (0.3 ns) in the same solvent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1243–1254, 2004     

Rapid profiling of polymeric phenolic acids in Salvia miltiorrhiza by hybrid data‐dependent/targeted multistage mass spectrometry acquisition based on expected compounds prediction and fragment ion searching

Phenolic acids are the major water‐soluble components in Salvia miltiorrhiza (>5%). According to previous studies, many of them contribute to the cardiovascular effects and antioxidant effects of S. miltiorrhiza. Polymeric phenolic acids can be considered as the tanshinol derived metabolites, e.g., dimmers, trimers, and tetramers. A strategy combined with tanshinol‐based expected compounds prediction, total ion chromatogram filtering, fragment ion searching, and parent list‐based multistage mass spectrometry acquisition by linear trap quadropole‐orbitrap Velos mass spectrometry was proposed to rapid profile polymeric phenolic acids in S. miltiorrhiza. More than 480 potential polymeric phenolic acids could be screened out by this strategy. Based on the fragment information obtained by parent list‐activated data dependent multistage mass spectrometry acquisition, 190 polymeric phenolic acids were characterized by comparing their mass information with literature data, and 18 of them were firstly detected from S. miltiorrhiza. Seven potential compounds were tentatively characterized as new polymeric phenolic acids from S. miltiorrhiza. This strategy facilitates identification of polymeric phenolic acids in complex matrix with both selectivity and sensitivity, which could be expanded for rapid discovery and identification of compounds from complex matrix.     

Determination of the stoichiometry and the Yb2+/Yb3+ ratio in YbF x optical IAD films by RBS and in situ XPS analysis

Thin films of YbF₃ are interesting as a possible component in antireflection coatings matching the CO₂ laser radiation. Ion assisted deposition (IAD) techniques for producing high density films were applied to this material and proved to be most successful in optimising the figures of merit for this purpose (low absorption values, high damage thresholds). Our XPS and RBS measurements, however, reveal a deficiency of fluorine in these IAD films that becomes more pronounced with increasing ion bombardment. The deficiency correlates with an increasing Yb²⁺/Yb³⁺ ratio determined by XPS. It can be concluded that the fluorine deficiency is well compensated by a valence state transition of the Yb ion and the formation of a corresponding amount of YbF₂ in the film. This process appears to be essential for avoiding metallic precipitation and achieving good optical film properties. By applying an in situ XPS technique, results have been obtained that are representative for the bulk of the films as has been confirmed by RBS.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

基于SiO_(2)@Fe_(3)O_(4)的磁性纳米材料分离富集谷物中痕量黄曲霉毒素B_(1)北大核心CSCD

将SiO_(2)包覆的Fe_(3)O_(4)磁性纳米材料(SiO_(2)@Fe_(3)O_(4))表面偶联识别黄曲霉毒素B_(1)(AFB_(1))的抗体(Ab),用于特异性分离富集谷物中的AFB_(1),进而与高效液相色谱-串联质谱法(HPLC-MS/MS)结合,用于大米、玉米和小麦中AFB_(1)的高效准确检测。采用微波辅助水热合成法制备得到Fe_(3)O_(4)磁性纳米颗粒,并用100μL正硅酸乙酯(TEOS)对其进行SiO_(2)的包覆,得到SiO_(2)@Fe_(3)O_(4)磁性纳米材料,随后进行抗体的偶联得到Ab-SiO_(2)@Fe_(3)O_(4);以pH=7.4的磷酸盐缓冲液(PBS)作为富集缓冲液,加入8 mg Ab-SiO_(2)@Fe_(3)O_(4),在37℃下反应10 min进行AFB_(1)的分离富集,随后采用甘氨酸-盐酸(Gly-HCl)缓冲液对Ab-SiO_(2)@Fe_(3)O_(4)分离富集的AFB_(1)进行洗涤,将洗涤液氮吹后复溶,采用高效液相色谱-串联质谱法检测。在最佳条件下,方法检测AFB_(1)的线性范围为2~50μg/L,相关系数(R^(2))>0.99,检出限为0.04μg/kg,定量限为0.13μg/kg。在4个不同加标水平下,AFB_(1)在3种谷物基质中的加标回收率为76.21%~92.85%,RSD≤5.29%。大米、玉米和小麦等实际谷物样品中AFB_(1)的测定结果显示,在1个小麦样品和2个玉米样品中检出AFB1,其含量分别为0.38、0.13和0.47μg/kg,其他样品中并未发现AFB_(1)。方法将磁性纳米材料与HPLC-MS/MS相结合,实现了AFB_(1)的高效分离富集,富集材料成本低廉,储存性能好,在30 min内即可完成前处理过程,可在较短的时间内实现大批量样品的实际分析,在谷物中真菌毒素的检测方面具有良好的应用前景。     

Analysis of allergens in tubeimu saponin extracts by using rat basophilic leukemia 2H3 cell‐based affinity chromatography coupled to liquid chromatography and mass spectrometry

An affinity two‐dimensional chromatography method was developed for the recognition, separation, and identification of allergic components from tubeimu saponin extracts, a preparation often injected to treat various conditions as indicated by traditional Chinese medicine. Rat basophilic leukemia‐2H3 cell membranes were used as the stationary phase of a membrane affinity chromatography column to capture components with affinity for mast cells that could be involved in a degranulation reaction. The retained components were enriched and analyzed by membrane affinity chromatography with liquid chromatography and mass spectrometry via a port switch valve. Suitability and reliability of the method was investigated using appropriate standards, and then, the method was applied to identify components retained from tubeimu saponin extracts. Tubeimoside A was identified in this way as a potential allergen, and degranulation assays confirmed that tubeimoside A induces RBL‐2H3 cell degranulation in a dose‐dependent manner. An increase in Ca²⁺ influx indicated that degranulation induced by tubeimoside A is likely Ca²⁺ dependent. Coupled with the degranulation assay, RBL‐2H3 cell‐based affinity chromatography coupled with liquid chromatography and mass spectrometry is an effective method for screening and identifying allergic components from tubeimu saponin extracts.     

Detection of total microcystin in fish tissues based on lemieux oxidation and recovery of 2-methyl-3-methoxy-4-phenylbutanoic acid (MMPB) by solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC/MS)

Microcystins (MCs) are widespread cyanobacterial toxins in freshwater systems, and have been linked to both acute and chronic health effects. A growing number of studies suggest that MC can bioaccumulate in food webs. Although, several methods (i.e. ELISA, LC-MS) have been developed for analysis of MC in water, extraction (for subsequent analysis) of the toxin from biological matrices (i.e. animal tissues) is impeded owing to covalent binding of toxins and active sites of their cellular targets, i.e. protein phosphatases. As an alternative approach, chromatographic methods for analysis of a unique marker, 2-methyl-3-methoxy-4-phenylbutanoic acid (MMPB), the product of the Lemieux oxidation of MCs, have been previously developed, and shown to measure total (bound and unbound) MC. Application, however, has been limited by poor recovery of the analyte. An improved recovery method is proposed – specifically the use of solid-phase microextraction (SPME). The MMPB analogue, 4-phenylbutanoic acid (4PB), and oxidized MC, were used to develop methods, and we specifically investigated several SPME fibres, and post-oxidation steps. Specifically, a method employing post-oxidation methyl esterification, followed by headspace SPME recovery of MMPB, was developed, and subsequently applied to analysis of environmental samples (i.e. fish tissues) previously shown to contain MCs. The method shows high linearity for both water and tissues spiked with MC, and an improved limit of quantitation of approximately 140?ng?g^?1. Evaluation of field samples by SPME-GC/MS detected considerably higher levels of MC, than detected by conventional methods (i.e. ELISA), and it is proposed that this technique reveals MC (particularly in the bound form) that is not detected by these methods. These results indicate that the developed method provides improved detection capability for MC in biological matrices, and will enhance our ability to understand bioaccumulation in freshwater food webs, as well as monitor exposure.     

Solvent extraction of sodium perrhenate by 3m-crown-m ethers (m = 5, 6) and their mono-benzo-derivatives into 1,2-dichloroethane: Elucidation of an overall extraction equilibrium based on component equilibria containing an ion-pair formation in water

Equilibrium constants () for the ion-pair formation of a complex ion NaL⁺ with ReO₄⁻ in water were determined potentiometrically at 25 °C and the ionic strength (I) of 0 mol dm⁻³ using a Na⁺-selective electrode. Here, crown ethers, L, were 15-crown-5 ether (15C5), benzo-15C5, 18-crown-6 ether (18C6) and benzo-18C6. Also, NaReO₄ was extracted by the L into 1,2-dichloroethane and then extraction constants (K_ex/mol⁻² dm⁶) for the species, NaLReO₄, were determined at 25 °C by AAS. These K_ex values were resolved into four component equilibrium constants containing K_MLA calculated at given I values. Based on these data, extraction-abilities of the L against the perrhenate were discussed in comparison with those of sodium picrate-L systems reported previously.     

Magnetic solid‐phase extraction based on a polydopamine‐coated Fe3O4 nanoparticles absorbent for the determination of bisphenol A,tetrabromobisphenol A, 2,4,6‐tribromophenol,and (S)‐1,1’‐bi‐2‐naphthol in environmental waters by HPLC

Polydopamine‐coated Fe₃O₄ magnetic nanoparticles synthesized through a facile solvothermal reaction and the self‐polymerization of dopamine have been employed as a magnetic solid‐phase extraction sorbent to enrich four phenolic compounds, bisphenol A, tetrabromobisphenol A, (S)‐1,1′‐bi‐2‐naphthol and 2,4,6‐tribromophenol, from environmental waters followed by high‐performance liquid chromatographic detection. Various parameters of the extraction were optimized, including the pH of the sample matrix, the amount of polydopamine‐coated Fe₃O₄ sorbent, the adsorption time, the enrichment factor of analytes, the elution solvent, and the reusability of the nanoparticles sorbent. The recoveries of these phenols in spiked water samples were 62.0–112.0% with relative standard deviations of 0.8–7.7%, indicating the good reliability of the magnetic solid‐phase extraction with high‐performance liquid chromatography method. In addition, the extraction characteristics of the magnetic polydopamine‐coated Fe₃O₄ nanoparticles were elucidated comprehensively. It is found that there are hydrophobic, π–π stacking and hydrogen bonding interactions between phenols and more dispersible polydopamine‐coated Fe₃O₄ in water, among which hydrophobic interaction dominates the magnetic solid‐phase extraction performance.