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关键词： ionic liquids   molecular dynamics   physicochemical properties   Raman spectroscopy   viscosity  

摘要： The physicochemical properties of room temperature ionic liquids (RTILs) consisting of bis(trifluoromethanesulfonyl)amide (TFSA(-)) combined with 1-hexyl-1-methylpyrrolidinium (Pyr(1,6)(+)), 1-(butoxymethyl)-1-methylpyrrolidinium (Pyr(1,1O4)(+)), 1-(4-methoxybutyl)-1-methyl pyrrolidinium (Pyr(1,4O1)(+)), and 1-((2-methoxyethoxy)methyl)-1-methylpyrrolidinium (Pyr(1,1O2O1)(+)) were investigated using both experimental and computational approaches. Pyr(1,1O2O1)TFSA, which contains two ether oxygen atoms, showed the lowest viscosity, and the relationship between its physicochemical properties and the position and number of the ether oxygen atoms was discussed by a careful comparison with Pyr(1,1O4)TFSA and Pyr(1,4O1)TFSA. Ab initio calculations revealed the conformational flexibility of the side chain containing the ether oxygen atoms. In addition, molecular dynamics (MD) calculations suggested that the ion distributions have a significant impact on the transport properties. Furthermore, the coordination environments of the Li ions in the RTILs were evaluated using Raman spectroscopy, which was supported by MD calculations using 1000 ion pairs. The presented results will be valuable for the design of functionalized RTILs for various applications.

关键词： optical properties   humic substances   dissolved organic matter   fluorescence   charge transfer  

摘要： The reaction of dissolved organic matter (DOM) with sodium borohydride has been used to understand the geographic origin of DOM and investigate the photophysical model underlying DOMs optical properties. However, the physicochemical properties of DOM (e.g., molecular size and charge) that influence the kinetics and ultimate reducibility of DOM by borohydride remain poorly characterized. Herein, we studied the kinetics of DOM-borohydride reactions by recording absorbance and fluorescence spectra at a high temporal frequency (every similar to 10 min for 24 h) for a diverse set of DOM isolates of aquatic and soil origin. The reducibility of DOM by sodium borohydride (as judged by relative removal of initial absorbance) varied appreciably among the DOM samples studied, with soil humic substances being less reducible than aquatic humic substances and natural organic matter. While statistically significant correlations were found between the reducibility of DOM and descriptors of molecular size, these descriptors were not able to differentiate the reducibility of soil versus aquatic DOM isolates that had similar bulk properties. Thus, it appears that the extent of absorbance removal by borohydride is largely driven by the origin of the humic substance isolate (aquatic vs soil) instead of molecular size or charge. Borohydride reduction resulted in increased fluorescence emission across UV and visible excitation wavelengths. However, the enhanced emission at visible excitation decreased over a time period of hours to days, suggesting that reduction of an important subset of DOM chromophores is reversible. This reversibility in fluorescence emission is consistent with the small role of quinones in the absorbance of DOM but suggests a more important role for quinone-containing charge-transfer contacts in the fluorescence of DOM, particularly at visible excitation wavelengths.

关键词： Natural fibers, Diss fibers, thermal properties, mechanical properties, microstructural analysis  

摘要： The Ampelodesmos mauritanicus plant, Mauritanian grass or also called 'Diss', is a perennial abundant plant on the Mediterranean contour, having attractive characteristics for ecofriendly materials. This work aims to highlight the potential of the Diss fibers elements by assessing their use as reinforcement for polymer matrices (bio-composite). So, untreated and treated Diss fibers by chemical (soda, silane and acetic acid) and thermal treatment have been manually extracted and characterized to evaluate their surface condition as well as their chemical composition, their mechanical properties and their thermal stability. The obtained results have shown many advantages look promising for such an application, especially the fact that the Diss fiber bundles has small diameter (89 +/- 22 mu m), a rough surface with the presence of thorns, a low density of 0.93 g/cm3, and a tensile strength that can reach 270 MPa. Furthermore, all the treatments adopted have shown improvements regarding the fibrillation of fiber bundles (could reach -40% for the diameter), their surface state, their thermal stability and their mechanical behavior (could reach +60% for Young's modulus and +15% for tensile stress).

关键词： antibacterial properties   chitosan   mechanical properties   nano titanium dioxide   starch films  

摘要： Biodegradable composite films have been prepared from corn starch (CS) incorporating chitosan (CH) and nanoTiO(2) by a solution casting method and the mechanical, physicochemical and antimicrobial properties of the films were determined. Scanning electron microscopy (SEM) observations demonstrated that the appropriate proportion of components resulted in ideally homogeneous surface of films. Fourier transform infrared (FTIR) spectra analysis revealed that hydrogen bonds were formed between CH and CS and a covalent interaction existed between the nanoTiO(2) and the CS and CH. The addition of proper amounts of CH to a CS matrix produced an enhancement of mechanical and antimicrobial properties accompanied by lower water moisture resistance. Incorporation of nanoTiO(2) into the CS/CH film increased the tensile strength, moisture resistance and impermeability to oil and achieved significant antimicrobial properties. The tensile strength of the nanoTiO(2)/CH/CS composition film was 21.12 +/- 0.34 MPa which was 6.27 times that of a plasticized CS film, while the antibacterial activity for Escherichia coli reached 94 +/- 2%. The mechanical properties, moisture resistance and antimicrobial properties of the films were deteriorated by the incorporation of excessive nanoTiO(2) because of self-aggregation of the nanoparticles.

关键词： Elements   Chemical bonding   Quality management   Polarity   Electrical conductivity  

摘要： The use of the difference in electronegativity (EN) function is shown to be fundamentally untenable for differentiating ionic from covalent bonding in binary compounds. Also, the commonly used parameters of differences and averages of EN values do not provide a direct correlation with metallic, ionic, or covalent chemical bonding types. On the other hand, the cardinal coordinates of lower and higher EN values readily demonstrate such a correlation. Graphs and similar tables of these two parameters show how chemical bonding combines and separates a mixture of these three bonding types. The orthogonal axes of these two cardinal functions indicate that there are two separate contributors to bonding: a band-gap (conductive) and a polarity (insulative) component that together produce the variety of chemical bonding types. These characteristics arise from absolute and differential electronic potentials. This two-dimensional perspective provides the means for interpreting the nature of EN.

关键词： Surfactant   polyvinyl alcohol (PVA)   liquid crystallinity   mechanical strength  

摘要： Recently, new cleaning products based on polymer-surfactant platforms have captured the attention of the industry, thanks to their good mechanical strength and excellent solubility. In this study, surfactant-polyvinyl alcohol hydrogels using glycerin as a cross-linking agent were prepared to investigate which factors affect the mechanical properties of the dried films. The mixed gels were prepared and dried to approximately 15% moisture content through heat conduction using an aluminum alloy plate. The mechanical analysis was performed using a Material Testing System (MTS). Furthermore, X-ray diffraction (XRD) was used to obtain phase structure of the samples, and scanning electron microscopy (SEM) was used for microstructure analysis. The data from this study suggest that crystallinity of PVA affects the mechanical properties of the surfactant-PVA hydrogel. The liquid crystallinity is the main influencing factor of hydrogel flexibility and can be modified via surfactant compounding. Furthermore, a novel hypothesis for the adsorption of surfactant is also proposed, with the purpose of probing the interaction between polyvinyl alcohol and surfactant from a molecular perspective.

关键词： Water chestnut starch   Rice starch   Corn starch   Sodium alginate   Physicochemical properties   Thermal properties   Morphological properties  

摘要： Water chestnut (Trapa bispniosa), rice and corn starch were modified with sodium alginate and subjected to dry heating for 0,2 and 4 h for at 130 degrees C. The physicochemical, thermal and morphological properties of native as well as modified starches were determined. Thermal and morphological properties were studied using Differential Scanning Calorimeter (DSC) and Scanning Electron Microscopy (SEM). It was observed that the dry heating of starches with and without sodium alginate significantly reduce the swelling power, solubility, paste clarity whereas, water absorption and syneresis increased. The swelling power was higher for corn starch as compared to other starches while rice starch has higher syneresis. In the presence of sodium alginate the water absorption was increased in all starch samples upon heating. The onset temperature was found to be increased after dry heating of all starches. The maximum increased was noticed for rice starch. Morphological studies showed the damaging of granule surface with the accumulation of leached amylose and gum but total degradation was not observed. Peak viscosity, final viscosity, breakdown, and setback of RS- sodium alginate mixture were reduced on dry heating. Although pasting temperature of rice starch was not significantly changed.

关键词： 物理化学   石墨双炔   GDY   RDX   热分解   热重/红外/质谱(TG/IR/MS)   相容性  

摘要： 为探究石墨双炔(GDY)对RDX热分解性能的影响,采用液相法制备出GDY,对其进行扫描电镜(SEM)、透射电镜(TEM)、X光电子能谱(XPS)、热重(TG)、红外(IR)表征;采用物理混合法将不同质量分数的GDY与环三亚甲基三硝胺(RDX)复合,用差示扫描量热仪(DSC)测试其热行为,并用Kissinger和Ozawa法进行动力学计算;用热重/红外/质谱联用仪(TG/IR/MS)研究GDY质量分数为5%的复合样品的热分解机理;根据GJB772A-97,采用DSC法进行相容性分析;从热分解峰温和活化能角度,比较了不同炭材料对RDX热分解的影响。结果表明,升温速率10℃/min、GDY质量分数为5%时,RDX热分解峰温升高2.97℃,活化能降低10.75kJ/mol;TG/IR/MS研究表明,加入GDY后,主要气体产物种类没有发生改变,但是CH2O和N_(2)O气体产物在较低的温度下即会产生,表明GDY的加入能够促进C—N键的断裂,从而促进RDX的热分解;相容性测试表明GDY与RDX不相容;相比纯RDX,石墨烯和多壁碳纳米管(CNT)使RDX的热分解活化能分别降低59.76kJ/mol和25.6kJ/mol,降低程度高于GDY,而富勒烯(C60)则使RDX的活化能升高37.17kJ/mol。

关键词： Electrosorption   Modified activated carbon   Lanthanum   Fluoride removal  

摘要： This research reports the electrosorption of fluoride with a commercial bituminous activated carbon impregnated with Lanthanum(III), as this rare-earth element is an excellent fluoride adsorbent and has been associated with important electrochemical properties. Lanthanum was impregnated in a concentration of 0.45% w/w to promote a good dispersion of the formed La(III) clusters onto the carbon surface without blocking its micropores. For this, there were no significant differences in the textural and capacitive properties in both the pristine and the modified carbon. On the other hand, the surface chemistry of the modified carbon was changed abruptly, decreasing its point of zero charge (pHPZC) from 8.5 to 4.9, and increasing its potential of zero charge (EPZC) from 0.0 to 0.30 V. The electrosorption performance was evaluated by two polarization profiles: stepped-potential increases and single potentials applied from the beginning (0.4, 0.8 and 1.2 V vs. Ag/AgCl/3M NaCl). The modified carbon presented higher adsorption capacity and velocity and its subsequent anodic polarization increased its removal up to 5.93 mg g-1 (C0 = 20 ppm F, pH0 = 7), a 2.55 increase compared to its adsorption capacity (2.33 mg g-1). Desorption by depolarization was inefficient for the modified carbon, due to a chemisorption mechanism that took place at this matrix but was attained by reversing the polarization to -0.5 V. Surface charges, evaluated by the pHPZC and the EPZC, were the main parameters to explain and understand the obtained results. In addition, the analysis of the pHPZC during the cyclic performance, together with the open circuit potentials and electrochemical impedance spectroscopy analysis, confirmed that the surface of both carbons oxidized after their electrical polarization, although the modified carbon presented less oxidation, and a slight release of La(III) was also observed.