Synthesis of Discrete Alkyl‐Silica Hybrid Nanowires and Their Assembly into Nanostructured Superhydrophobic Membranes

We report the synthesis of highly flexible and mechanically robust hybrid silica nanowires (NWs) which can be used as novel building blocks to construct superhydrophobic functional materials with three‐dimensional macroporous networks. The hybrid silica NWs, with an average diameter of 80 nm and tunable length of up to 12 μm, are prepared by anisotropic deposition of the hydrolyzed tetraethylorthosilicate in water/n‐pentanol emulsions. A mechanistic investigation reveals that the trimethoxy(octadecyl)silane introduced to the water‐oil interface in the synthesis plays key roles in stabilizing the water droplets to sub‐100 nm and also growing a layer of octadecyl groups on the NW surface. This work opens a solution‐based route for the one‐pot preparation of monodisperse, hydrophobic silica NWs and represents an important step toward the bottom‐up construction of 3D superhydrophobic materials and macroporous membranes.     

Comparative Computational Studies of Gaseous Alkali Metal Amidoboranes MNH2BH3 and their Carbon Analogs MC2H5 (M = Li – Cs): Formation and Unimolecular Hydrogen Evolution

Comparative computational studies of reaction mechanisms of formation and unimolecular hydrogen evolution from alkali metal amidoboranes MNH₂BH₃ and their carbon analogs MC₂H₅ (M = Li – Cs) were performed at the B3LYP/def2‐TZVPPD level of theory. Transition states (TS) for the consecutive dehydrogenation reactions were optimized. In contrast to endergonic dehydrogenation of carbon analogs, dehydrogenation reactions of alkali metal amidoboranes are exergonic at room temperature. The nature of the alkali metal does not significantly affect the thermodynamic characteristics and activation energies of unimolecular gas phase dehydrogenation reactions. The influence of the alkali metal is qualitatively similar for amidoboranes and their carbon analogs.     

Three Inter‐Alkali Metal Acetylides: KNaC2, KRbC2, and NaRbC2: Syntheses,Crystal Structures,and Structural Systematics

Three alkali metal acetylides, namely KNaC₂, KRbC₂, and NaRbC₂, were synthesized and characterized by means of X‐ray powder diffraction. KNaC₂ and KRbC₂ crystallize as a variant of the anti‐PbCl₂‐type structure (Pnma, Z = 4), whereas NaRbC₂ crystallizes as a variant of the anti‐PbFCl‐type structure (Pmmn, Z = 2). Based on a simple systematic approach developed by Sabrowsky et al. for inter‐alkali metal chalcogenides all known inter‐alkali metal acetylides can be classified into two classes: variants of the anti‐PbCl₂ type structure and variants of the anti‐PbFCl type structure. Acetylides with Q(ABC₂) ≤ 1.45 crystallize in the anti‐PbCl₂‐type structure, whereas for Q(ABC₂) > 1.45 the anti‐PbFCl‐type structure is found (Q(ABC₂) = V_m(A₂C₂)/V_m(B₂C₂) with V_m(A₂C₂) > V_m(B₂C₂); V_m: molar volume, A, B = alkali metals).     

Synthesis and Characterization of the Rubidium Thiophosphate Rb6(PS5)(P2S10) and the Rubidium Silver Thiophosphates Rb2AgPS4, RbAg5(PS4)2 and Rb3Ag9(PS4)4

The metal thiophosphates Rb₂AgPS₄ ( 2 ), RbAg₅(PS₄)₂ ( 3 ), and Rb₃Ag₉(PS₄)₄ ( 4 ) were synthesized by stoichiometric reactions, whereas Rb₆(PS₅)(P₂S₁₀) ( 1 ) was prepared with excess amount of sulfur. The compounds crystallize as follows: 1 monoclinic, P2₁/c (no. 14), a = 17.0123(7) Å, b = 6.9102(2) Å, c = 23.179(1) Å, β = 94.399(4)°; 2 triclinic, P$\bar{1}$ (no. 2), a = 6.600(1) Å, b = 6.856(1) Å, c = 10.943(3) Å, α = 95.150(2)°, β = 107.338(2)°, γ = 111.383(2)°; 3 orthorhombic, Pbca (no. 61), a = 12.607(1) Å, b = 12.612(1) Å, c = 17.759(2) Å; 4 orthorhombic, Pbcm (no. 57), a = 6.3481(2) Å, b = 12.5782(4) Å, c = 35.975(1) Å. The crystal structures contain discrete units, chains, and 3D polyanionic frameworks composed of PS₄ tetrahedral units arranged and connected in different manner. Compounds 1 – 3 melt congruently, whereas incongruent melting behavior was observed for compound 4 . 1 – 4 are semiconductors with bandgaps between 2.3 and 2.6 eV and thermally stable up to 450 °C in an inert atmosphere.     

Films Consisting of Innumerable Tapered Nanopillars of Mesoporous Silica for Universal Antireflection Coatings

Films with a fine structure consisting of innumerable nanopillars of mesoporous silica (MPS) are formed by a reactive ion etching process with a fluorine‐containing gas. Each nanopillar has a tapered shape with a uniform height, which effectively suppresses reflection by the formation of an ideal graded refractive index structure. The nanopillars are spontaneously formed under low‐pressure conditions, wherein locally deposited Al?F compounds, originating from an alumina plate in the etching chamber, work as a fine etching mask. The high etching rate of the MPS film allows a very high aspect ratio of the nanopillars. The refractive index of the MPS nanopillars can be universally tuned by a controlled incorporation of TiO₂ into the mesopores, which results in effective reduction of reflectance on a given substrate. The outstanding antireflection performance is experimentally demonstrated for glass substrates with a wide refractive index range.     

Physicochemical and tensile properties of alkaline-treated new natural cellulosic Gossypium arboreum fiber

This article describes the characterization of novel natural lignocellulosic bark fibers extracted from the stem of the Gossypium arboreum (cotton) plant. The G. arboreum stem fibers were treated with 5% (w/v) aqueous NaOH solution for different soaking times, and the Fourier transform infrared spectroscopy analysis was conducted to examine the chemical compounds of the raw and treated fibers. The cellulose content improved from 70.06 to 83.91% after the treatment. The X-ray diffraction results indicate that the crystalline index and size were enhanced. Thermogravimetric analysis was performed to study the thermal properties and found that the thermal stability was higher for the treated fibers. The tensile strength and modulus were increased for the alkaline-treated fibers compared to the untreated fibers.     

New ICT probes: synthesis and photophysical studies of N-phenylaza-15-crown-5 aryl/heteroaryl oxadiazoles under acidic condition and in the presence of selected metal ions

Molecular probes 6 and 7, incorporating N-phenylaza-15-crown-5 and aryl/heteroaryl oxadiazole have been designed to function as the new intramolecular charge transfer (ICT) probes. Photophysical properties have been studied under acidic condition as well as in the presence of selected metal ions, Ca²⁺, Ba²⁺, Mg²⁺, Na⁺, K⁺, and Li⁺. The changes in the ICT character of the probes, following the addition of trifluoroacetic acid, were interpreted in terms of site and degree of protonations. Based on the cation affinity, the ICT bands in both UV-vis and emission spectra experienced varying degrees of blue shifts due to removal of the aza-crown ether nitrogen from conjugation. The cation-induced spectral shifts and the stability constants revealed binding strength in the order Ca²⁺>Ba²⁺?Li⁺>Na⁺>K⁺>Mg²⁺. Competitive experiments performed in a matrix of ions also indicated superior interaction of 6 and 7 with Ca²⁺. The excited state decay profiles remained largely unperturbed in the presence of metal ions. The studied probes displayed positive solvatochromism and the Stokes shifts and excited state lifetimes increased with increasing solvent polarity. These findings can be rationalized by invoking highly polar nature of the emittive states. The chemoionophores 6 and 7 constitute potentially interesting Ca²⁺ sensitive probes due to their relatively high binding interaction for Ca²⁺ (log K_s=3.55-3.10) vis-a-vis that of biologically interfering Mg²⁺ (log K_s=1.67-1.30).     

Influence of metal ions on the alkali-swelling behavior of carboxylated acrylic polymer latexes

The alkalization of carboxylated acrylic polymer latexes by sodium hydroxide gives rise to swelling of the particles. For a poly(n-butyl acrylate) latex copolymerized with 15 wt % methacrylic acid (MAA) and 7 wt % acrylonitrile the particle volume increases by a factor of 30. The alkali-swelling does not depend on the type of monovalent cation used in the base (LiOH, NaOH, KOH, NH₄OH). In contrast, when bivalent cation bases such as Ca(OH)₂ are employed no latex swelling is observed during neutralization because of ionic crosslinking of the copolymer chains. Crosslinking also takes place when the bivalent cations (Ca²⁺, Zn²⁺, Mg²⁺) are added as chlorides to dispersions with latexes previously swollen by sodium hydroxide. In these experiments the original size of the latexes is reached again at a molar ratio MAA: bivalent metal ion of 2:1, i.e. at charge compensation of the carboxyl groups. The shrinking behavior is almost independent of the type of bivalent metal ion used. On the other hand, it is more pronounced when trivalent cations such as Fe³⁺ are added. In general, the experiments demonstrate that the alkali swelling of acrylic latexes is dominated by electrostatic forces. Received: 18 August 1998 Accepted in revised form: 26 October 1998     

碱金属烯醇盐的从头算

在RHF／3－21GRHF／321G,RHF／6-31＋G,MP2／6－31＋G,RHF／lanl2dz,MP2／lanl2dz和MP2／6－31＋G水平上,对CH2＝CH（OM）（M＝Li,Na,K,Rb,C。）进行了研究．结果表明,所有化合物都有平面式和非平面桥式两种构型.结构参数、自然轨道布局分析和反应热均反映出碱金属对烯酸负离子的共振有很大程度的限制,不同的碱金属盐差别不十分明显．     

Valence p functions for alkali and alkaline-earth atoms

Contracted Gaussian-type function (CGTF) basis sets are reported for valence p orbitals of the six alkali and alkaline-earth atoms Li, Be, Na, Mg, K, and Ca for molecular applications. These sets are constructed by Roothaan–Hartree–Fock calculations for the ns → np excited states of atoms, in which both linear and nonlinear parameters of CGTFs are variationally optimized. The present CGTF sets reproduce well the numerical Hartree–Fock ns → np excitation energies: the largest error is 0.0009 hartrees for Li. New CGTFs are tested with diatomic Li₂, Na₂, K₂, and MH molecules, where M = Li, Be, Na, Mg, K, and Ca, by self-consistent-field (SCF) and multiconfiguration SCF calculations. The resultant spectroscopic constants compare well with those of more elaborate calculations and are sufficiently close to experimental values, supporting the efficiency of the present set for the valence p orbitals. Received: 9 July 1998 / Accepted: 17 September 1998 / Published online: 1 February 1999