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71.
72.
Principles of hierarchical meso- and macropore architectures by liquid crystalline and polymer colloid templating 总被引:1,自引:0,他引:1
Sel O Kuang D Thommes M Smarsly B 《Langmuir : the ACS journal of surfaces and colloids》2006,22(5):2311-2322
The generation of porous silica with hierarchically organized bimodal mesoporosity of adjustable size and well-defined shape was investigated by using surfactant mixtures and the nanocasting procedure (liquid crystalline templating). A systematic study of combinations of various block copolymers (Pluronics F127, KLE (poly(omega-hydroxypoly(ethylene-co-butylene)-co-poly(ethylene oxide))) and SE (PS-co-PEO)) with smaller surfactants (Pluronics P123, C16mimCl, and CTAB) revealed that hierarchical bimodal mesopore architectures could only be obtained by the usage of block copolymers with a strong hydrophilic-hydrophobic contrast, such as KLE and SE, giving rise to pores between 6 and 22 nm. Furthermore, the ionic liquid (IL) C16mimCl appeared to have advantageous templating properties, resulting in 2-3-nm pores being located between the block copolymer mesopores, whereas phase separation was observed for Pluronics and CTAB as small templates. Thereby, the study provided also general insights into the mixing and co-self-assembly behavior of block copolymers and ionic surfactants in water and confirmed the special templating properties of ILs, as recently proposed. In addition to the bimodal mesoporosity, additional tunable macroporosity was created by the presence of poly(styrene) or poly(methyl methacrylate) spheres, leading to well-defined trimodal hierarchical pore architectures with the small pores being located in the walls of the respective larger pores. As a major improvement, due to the pore hierarchy, these large-pore materials showed relatively large surface areas and pore volumes, and the size of densely packed macropores could even be decreased down to 90 nm. The materials were characterized by electron microscopy, small-angle X-ray scattering, and nitrogen sorption using a proper NLDFT (nonlocal density functional theory) approach for calculations of the pore size distribution in the entire range of micro- and mesopores. 相似文献
73.
We construct a physical model to study the effects of dimensional reduction that might have taken place during the inflationary
phase of the universe. The model we propose is a (1 + D)-dimensional (D > 3), nonsingular, spatially homogeneous and isotropic Friedmann model. We consider dimensional reduction to take place in
a stepwise manner and interpret each step as a phase transition. Independent of the details of the process of dimensional
reduction, we impose suitable boundary conditions across the transitions and trace the effects of dimensional reduction to
the currently observable parameters of the universe. In order to exhibit the cosmological features of the proposed model,
we construct a (1 + 4)-dimensional toy model for both closed and open cases of Friedmann geometries. It is shown that in these
models the universe makes transition into the lower dimension when the critical length parameter l
4,3, which signals dimensional reduction, reaches the Planck length in D = 3. The numerical models we present in this paper have the capability of making definite predictions about the cosmological
parameters of the universe such as the Hubble parameter, age and density. 相似文献
74.
Frequency-domain method based on the singular value decomposition for frequency-selective NMR spectroscopy 总被引:1,自引:0,他引:1
Stoica P Sandgren N Selén Y Vanhamme L Van Huffel S 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,165(1):80-88
In several applications of NMR spectroscopy the user is interested only in the components lying in a small frequency band of the spectrum. A frequency selective analysis deals precisely with this kind of NMR spectroscopy: parameter estimation of only those spectroscopic components that lie in a preselected frequency band of the NMR data spectrum, with as little interference as possible from the out-of-band components and in a computationally efficient way. In this paper we introduce a frequency-domain singular value decomposition (SVD)-based method for frequency selective spectroscopy that is computationally simple, statistically accurate, and which has a firm theoretical basis. To illustrate the good performance of the proposed method we present a number of numerical examples for both simulated and in vitro NMR data. 相似文献
75.
Merve Fırat Sezgin Bakırdere Sabriye Sel Dotse Selali Chormey Ömer Elkıran Fatih Erulaş 《International journal of environmental analytical chemistry》2017,97(7):684-693
A sensitive, reliable, simple and rapid analytical method was developed for the determination of arsenite [As(III)], arsenate [As(V)] and arsenobetaine (AsB) species using ion chromatography combined with inductively coupled plasma-mass spectrometry (IC-ICP-MS). Inorganic and organic arsenic species were separated with an anion exchange column (Dionex AS9) and a 50 mM sodium bicarbonate mobile phase (pH 10) at a flow rate of 1.0 mL min?1. %RSD values were found to be lower than 5.1% for all arsenic species. The limits of detection (LOD) obtained for As(III), As(V) and AsB were 16.5 ng L?1, 14.1 ng L?1 and 6.2 ng L?1, respectively. The developed analytical method was tested using AsB certified reference material (NMIJ CRM 7901-a), and spring water certified reference material (UME CRM 1201) for accuracy check. This method was applied for the quantitative determination of arsenic species in different water samples and chicken samples as a solid matrix. 相似文献
76.
A. G. Bazhenova A. V. Sel’kin A. Yu. Men’shikova N. N. Shevchenko 《Physics of the Solid State》2007,49(11):2109-2120
This paper reports on an experimental and theoretical study of the spectra of Bragg reflection of light from opal-like photonic crystals near the critical angle of incidence ? c , at which the Bragg reflection in the p polarization of reflected light disappears The objects studied were polymer photonic-crystal structures made up of polystyrene particles. It is shown that Bragg reflection for the electromagnetic TM mode becomes totally suppressed at an angle of incidence ? c , which depends on the geometric parameters and dielectric constants of the spatially periodic structure. 相似文献
77.
Selçuk Demir Günay Kaya Kantar Yıldıray Topcu Qiaowei Li 《Transition Metal Chemistry》2012,37(3):257-263
The complexes [Co(C4H4O4)]n (1) and [Zn(im)2(C4H4O4)]n
(2) (C4H4O4 = succinate dianion, suc; im = imidazole) have been synthesized solvothermally and characterized by elemental analysis, IR,
TG–DTA, and single-crystal X-ray diffraction techniques. Complex 1 is the first anhydrous member of the cobalt succinate family and has high thermal stability under a static air atmosphere,
up to 425 °C, and complex 2 is a 1D coordination polymer. In addition, a new synthesis method and some properties of the known [Co(HCOO)2·2H2O]n (3) complex are reported. After in situ synthesis of 3 via decomposition of DMF at 140 °C, it was found that complex 3 can adsorb some solvents repeatedly and is selective for H2O. 相似文献
78.
Dr. Ozlem Sel Dr. Thierry Azais Dr. Manuel Maréchal Dr. Gérard Gébel Prof. Christel Laberty‐Robert Prof. Clément Sanchez 《化学:亚洲杂志》2011,6(11):2992-3000
Hybrid organic–inorganic approaches are used for the synthesis of bifunctional proton exchange membrane fuel cell (PEMFC) membranes owing to their ability to combine the properties of a functionalized inorganic network and an organic thermostable polymer. We report the synthesis of both sulfonic and phosphonic acid functionalized mesostructured silica networks into a poly(vinylidenefluoride‐co‐hexafluoropropylene) (poly(VDF‐co‐HFP) copolymer. These membranes, containing different amounts of phosphonic acid and sulfonic acid groups, have been characterized using FTIR and NMR spectroscopy, SA‐XRD, SAXS, and electrochemical techniques. The proton conductivity of the bifunctional hybrid membranes depends strongly on hydration, increasing by two orders of magnitude over the relative humidity (RH) range of 20 to 100 %, up to a maximum of 0.031 S cm−1 at 60 °C and 100 % RH. This value is interesting as only half of the membrane conducts protons. This approach allows the synthesis of a porous SiO2 network with two different functions, having SO3H and PO3H2 embedded in a thermostable polymer matrix. 相似文献
79.
Pd-PEPPSI-IPent has proven to be an excellent catalyst for the Negishi cross-coupling reaction of secondary alkylzinc reagents with a wide variety of aryl/heteroaryl halides. Importantly, β-hydride elimination/migratory insertion of the organometallic leading to the production of isomeric coupling products has been significantly reduced using the highly-hindered Ipent ligand. 相似文献
80.
The mechanisms of formation of Bragg reflectance and transmittance spectra have been investigated for films of three-dimensional
opal-like photonic crystals. Attention has been drawn to the fact that the spectra exhibit an additional short-period interference
structure of the novel type due to the multiple Bragg diffraction of light. The spectra have been calculated in the framework
of the dynamical three-wave diffraction model taking into account strong spatial modulation of the dielectric function. It
has been found that short-period oscillations appear in the spectra due to the spatial quantization of additional modes with
a low group velocity. 相似文献