Surface free energy of films of alkali-treated cellulose microfibrils from banana rachis

Cellulose microfibrils extracted by various alkaline treatments of vascular bundles from banana rachis were used to elaborate films. The films were comparatively studied to determine changes in polarity induced by various treatments. Atomic force microscopy was used to characterize the surface morphology of the films and transmission electron microscopy was employed to characterize the microfibrils used to elaborate the films. Contact angles were measured to determine surface free energy (SFE) and thermogravimetric analyses were carried out to determine changes in composition of the films. The results showed that the films of cellulose microfibrils prepared by the peroxide alkaline (PA) and peroxide alkaline-hydrochloric acid (PA-HCl) treatments had lower content of non-cellulosic constituents like xylose and had lower SFE than films of microfibrils treated with KOH-5. Furthermore, specimens treated with the most concentrated KOH solution (18 wt%) and sodium chloride presented the highest SFE and polar component.     

First‐principles calculations of the stability and electronic properties of the PbTiO3 (110) polar surface

The structural and electronic properties of five terminations of cubic lead titanate (PbTiO₃) (110) polar surface were investigated by first‐principles total‐energy calculations using a periodic slab model. On the PbTiO termination, an anomalous filling of conduction band was observed, whereas on the O₂ termination, two surface oxygen atoms formed a peroxo group, demonstrating that the electronic structures of the two stoichiometric terminations undergo significant changes with respect to bulk materials. However, for the three nonstoichiometric TiO‐, Pb‐, and O‐terminated surfaces, their electronic structures are very similar to bulk. Charge redistribution results for the five terminations confirmed that electronic structure and surface composition changes are responsible for their polarity compensation. However, which mechanism actually dominates the stabilization process depends upon energetic considerations. A thermodynamic stability diagram suggested that the two stoichiometric terminations are unstable; however, the three nonstoichiometric terminations can be stabilized in some given regions. Furthermore, this study indicates that the very different stabilities and surface states filling behaviors of the PbTiO₃ (110) polar surface with respect to SrTiO₃ and BaTiO₃ ones seem to originate from the partially covalent characteristics of Pb O pairs. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009     

Preparation and characterization of copper(II) tetrasulfonated phthalocyanine nanoparticles formed by laser ablation in poor solvents

Laser irradiation of copper(II) tetrasulfonated phthalocyanine (CuTsPc) microcrystals in poor organic solvents such as methanol, 2-methyl-2-propanol, ethanol, tetrahydrofuran, and acetone has produced CuTsPc nanoparticles with 15–112 nm in diameter. Field emission scanning electron microscopy (FESEM) images have shown the formation of CuTsPc nanoparticles in poor organic solvents used in this work. The mean diameters of CuTsPc nanoparticles obtained from transmission electron microscopy (TEM) images in methanol, 2-methyl-2-propanol, ethanol, tetrahydrofuran, and acetone were determined to be 26, 36, 35, 86, and 78 nm, respectively. A correlation between the size of CuTsPc nanoparticles and a solvent polarity could be found in this work.     

Effect of solvent polarity on the Ultrasound Assisted extraction and antioxidant activity of phenolic compounds from habanero pepper leaves (Capsicum chinense) and its identification by UPLC-PDA-ESI-MS/MS

Phenolic compounds are secondary metabolites involved in plant adaptation processes. The development of extraction procedures, quantification, and identification of this compounds in habanero pepper (Capsicum chinense) leaves can provide information about their accumulation and possible biological function. The main objective of this work was to study the effect of the UAE method and the polarity of different extraction solvents on the recovery of phenolic compounds from C. chinense leaves. Quantification of the total phenolic content (TPC), antioxidant activity (AA) by ABTS⁺ and DPPH radical inhibition methods, and the relation between the dielectric constant (ε) as polarity parameter of the solvents and TPC using Weibull and Gaussian distribution models was analyzed. The major phenolic compounds in C. chinense leaves extracts were identified and quantified by UPLC-PDA-ESI-MS/MS. The highest recovery of TPC (24.39 ± 2.41 mg GAE g⁻¹ dry wt) was obtained using MeOH (50%) by UAE method. Correlations between TPC and AA of 0.89 and 0.91 were found for both radical inhibition methods (ABTS⁺ and DPPH). The Weibull and Gaussian models showed high regression values (0.93 to 0.95) suggesting that the highest phenolic compounds recovery is obtained using solvents with “ε” values between 35 and 52 by UAE. The major compounds were identified as N-caffeoyl putrescine, apigenin, luteolin and diosmetin derivatives. The models presented are proposed as a useful tool to predict the appropriate solvent composition for the extraction of phenolic compounds from C. chinense leaves by UAE based on the “ε” of the solvents for future metabolomic studies.     

Determination of polarity parameters for liquid crystals using solvatochromic method in anisotropic and isotropic phases

The use of liquid crystals (LCs) as anisotropic solvents is desired for various potential applications and usually for other organic and inorganic compounds. In this work, solvent polarity parameters are obtained using a spectroscopic method for four LCs with a range of high and low dielectric anisotropy (?ε). Solvatochromic polarity parameters for these LCs were defined via Kamlet–Abboud–Taft polarity functions characterizing different temperatures and phases, isotropic and anisotropic, and using the Reichardt’s dye and 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio) phenolate standard probe. The investigated polarity parameters reveal the effects of LC media on the photo-physical behaviour of solute molecules in isotropic and anisotropic media. Subsequently, a new LC polarity parameter (Z_o) is introduced as an overall matrix anisotropy polarity parameter to characterize variation between isotropic and anisotropic phases. The values of Z_o are sorted from higher to lower dielectric anisotropies (?ε).     

Polymerization kinetics of phosphonic acids and esters using an iodonium initiator

Phosphonic acids are known to be useful monomers in dental restorative materials because of their good potential to provide enhanced adhesion to hydroxyapatite and their high hydrolytic stability. In this study, the photopolymerization of phosphonic acid‐based monomer via the camphorquinone (CQ)/ethyl‐4‐(dimethylaminobenzoate) (EDAB) photoredox system is compared with a ternary system composed of iodonium hexafluorophosphate and CQ/EDAB. Photocalorimetry shows that the ternary system does not provide a significant acceleration of the polymerization with either acrylamide or methacrylate phosphonic acids. The complexation of the iodonium by the phosphonic moiety of the acidic monomers leads to a lowered iodonium reactivity and reduced polarizability of the medium and as a consequence limits the rate enhancement effect normally observed by phosphonic acids on the polymerization rate. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5046–5055     

Probing the Polarity of Sol-Gels and Ormosils via the Absorption of Nile Red

Conventional sol-gels are rather hydrophilic. A more hydrophobic material is obtained preparing organically modified siloxanes (ormosils). The polarity-sensitive probe Nile Red (NR) was doped in various sol-gels to probe their micro-polarity. The experiments show that the NR is an excellent probe and sensitive to the polarity of its microenvironment. Spectroscopic studies reveal remarkable changes in the absorption band positions and intensities as a function of the polarity of the sol-gel, which depends on the different precursors used. Furthermore, sol aging, gelation and temporal stability as a function of different ormosils have been investigated.     

基于K图的函数RM展开式在固定极性下的最小化

分析了K图的性质，发现在K图中过某格的所有聚合圈相应的各乘积项所含变量与该格对应的最小项均有相同的极性，在此基础上提出了得到基于K图函数RM展开式在固定极性下的最小化的图形方法，该方法可以从K图直接得到函数的最小化的RM展开式，从而省略了传统的把K图转变为bj图再求最小化的步骤，它具有直观、简单、易于掌握等特点。此外，文中还提出了该方法的改进算法。     

非退化扩散过程的极性与相交性

本文讨论非退化扩散过程的极性，得到了几个较好的充分条件，它可看作[1]的进一步深化，此外，我们将这些结果用来研究两个独立的非退化扩散过程的相交性，得到了一些有意思的结果。     

地球磁场的物理问题

地磁学的发展经历了两千多年的历史，文章回顾了这一漫长历史的四个主要阶段，对每一阶段研究的基本物理问题和主要进展做了简要概述．地磁场的空间分布、地磁场起源、地磁场长期变化和西向漂移、磁极移动和极性倒转、地磁场与人类生存环境等，是地磁学的基本物理问题．文章还从物理概念、研究现状和地磁学以及相关学科当前存在的问题等几个方面对地磁学未来的发展趋势做了简要的说明．