排序方式: 共有50条查询结果,搜索用时 15 毫秒
11.
Highly ordered SBA-15 nanoporous silica containing ethylene, phenylene bridges or/and amine, thiol, vinyl and phenyl surface
groups were synthesized by using amphiphilic block copolymer as the structure-directing agent. The XRD data shows high degree
of the order of the final structures. Obtained materials have well-developed porous structure—values of specific surface area
are in the range 700–1050 m2/g and the sizes of cylindrical mesopores are in the range 6.5–9.5 nm. It was determined that size of the mesopores strongly
depends even on small amounts of co-monomers co-condensing with TEOS. A new technique to introduce some amount of pendant
amine groups by co-condensation of proper monomers has been proposed. Tetragonal structure was obtained when small amount
of vinyl groups was introduced to the system. A new approach of determining pore size based only on the XRD measurements was
compared with KJS method, confirming full usefulness of the former for calculation of the size of mesopores in SBA-15 materials.
Dedicated to Professor Mietek Jaroniec on the occasion of his 60th birthday. 相似文献
12.
Anna Kultys Stanisław Pikus 《Journal of polymer science. Part A, Polymer chemistry》2001,39(10):1733-1742
Three series of new thermoplastic, high molecular weight, segmented thiopolyurethanes were synthesized by a one-step melt polymerization from newly obtained thiodiols, including bis[4-(2-hydroxyethyl)thiomethylphenyl]methane, bis[4-(3-hydroxypropyl)thiomethylphenyl]methane, and bis[4-(6-hydroxyhexyl)thiomethylphenyl]methane (BHHM), as chain extenders; hexamethylene diisocyanate; and 20–80 mol % poly(oxytetramethylene) glycol (PTMG; number-average molecular weight = 1000) as the soft segment. Solution polymerization with the chain extender BHHM gave considerably lower molecular weight polymers. The structures of all the polyurethanes were determined with Fourier transform infrared and X-ray diffraction analysis. The thermal properties of the polyurethanes were examined with differential scanning calorimetry and thermogravimetric analysis. Shore A/D hardness and tensile properties were also determined. All the polyurethanes showed partially crystalline structures; those obtained with 40–80 mol % PTMG were elastomers. An increase in the PTMG content decreased hardness, modulus of elasticity, and tensile strength, whereas elongation at break increased. BHHM-based polyurethanes obtained in the melt showed the best tensile properties. The polyurethanes exhibited definite glass transitions (−70 to −59 °C) that were nearly independent of the hard-segment content up to about 50 wt % (40–80 mol % PTMG), indicating the existence of mainly microphase-separated soft and hard segments. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1733–1742, 2001 相似文献
13.
Heating of controlled porous glass (CPG) in the temperature range 400–700°C leads not only to a dehydroxylation process of the surface but also brings about a diffusion of the boron atoms remaining in the silica network of CPG towards the glass surface. Some authors assume that a along thermal exposure can cause the formation of B2O3 crystals in the pores. In this paper the CPGs possessing different mean pore diameters before and after their thermal treatment were investigated by the SAXS (small angle X-ray scattering) method. The SAXS method is very useful in such cases because there are two sources of X-ray scattering: pores in glass and crystallites of the borate phase. The presence of these two sources is responsible for the change of the intensity of small angle X-ray scattering in comparison to X-ray scattering of the initial porous glass (without borate crystallites). In consequence, the pore size distribution function, calculated from the SAXS data, does not agree with the analogous one calculated from mercury porosimetric data. For the confirmation of the above artificial systems composed of silica gle with either deposited H3BO3 or Na2B4O7 were investigated. It appears from the presented data that there is a possibility to investigate the kinetics of the crystallization process of borate crystallites by means of the SAXS method. SAXS also allows one to control the process of the removal of the borate phase from the pores of CPG. It can be concluded from the obtained results that long time thermal heating causes the formation of borate crystallites in pores of CPG and that these crystallites are xNa2O·yB2O3 (where y ? x) rather than B2O3. 相似文献
14.
15.
Complexes of yttrium(III) and lanthanides(III) with 4-hydroxy-3,5-dimethoxybenzoic (syringic) acid were obtained as solids
with metal to ligand mole ratio of 1: 3. The compounds were characterized by elemental analysis, IR spectroscopy, X-ray diffraction
patterns, solubility, and thermal studies. The complexes are sparingly soluble in water and stable at room temperature. Compounds
of light lanthanides (from La to Nd) are hydrated and they crystallize in a triclinic system. When heated, they lose water
molecules in one step and in the next step they decompose to oxides. Complexes of yttrium and other lanthanides are anhydrous
and crystallize in a monoclinic system. They are stable up to 300°C and then decompose to oxides. As the coordination number
of lanthanide ions is usually equal to 9 or 8, one can suppose that hydroxy or methoxy groups take part in the coordination
of these metal ions. 相似文献
16.
Ordered mesoporous silicas (OMSs) such as SBA-15 (p6mm symmetry group) synthesized in the presence of block copolymers containing poly(ethylene oxide) blocks possess irregular complementary pores in the walls of ordered mesopores. The X-ray scattering caused by this complementary porosity contributes to the background of the SAXS patterns. This work shows the possibility of using the SAXS data for the study of intrawall channels interconnecting ordered cylinders in SBA-15. The proposed SAXS analysis was tested by using a series of SBA-15 samples obtained at different temperatures of hydrothermal treatment (from 60 to 180 °C). The structural modelling of the SAXS patterns recorded for a series of SBA-15 samples was performed by using the continuous density function (CDF) technique in combination with the derivative difference minimization (DDM) method of full-profile refinement. This method is well suited for extraction of the background curves from the SAXS patterns. The resulting smooth background curves were analyzed by the well-known method in the SAXS theory used for evaluation of heterogeneity distributions, which in this case characterize the intrawall complementary porosity. A relatively good agreement has been observed between the data obtained by SAXS and nitrogen adsorption analysis. The SAXS analysis is sufficiently sensitive for examination of heterogeneous microporosity in SBA-15 materials. The average diameter of intrawall pores for the SBA-15 sample obtained at 60 °C was only about 1.4 nm. However, this diameter increased with the increasing temperature of hydrothermal treatment; namely, it was 1.5, 1.8, 2.6, 2.6, 3.5 and 5.2 nm for the SBA-15 samples hydrothermally treated at 80, 100, 120, 140, 160 and 180 °C, respectively. 相似文献
17.
Adsorption and structural properties of periodic mesoporous organosilica with Im3m symmetry (SBA-16) and large heterocyclic bridging groups in cage-like mesopores are studied. The core of this bridging group is an isocyanurate ring integrated with three trimethoxysilyls through flexible propyl chains. 相似文献
18.
A short-time synthesis of SBA-15 is reported by using two different silica sources, sodium metasilicate (Na2SiO3(9)H2O) and tetraethyl orthosilicate (TEOS). The SBA-15 samples obtained from both silica sources were highly ordered as evidenced by SAXS spectra showing five reflection peaks characteristic for p6mm symmetry group. While the surface areas of these samples were similar, the pore volume of the sample prepared from TEOS was slightly larger than that from sodium metasilicate. However, the latter exhibited higher microporosity and thicker pore walls. It was shown that a significant reduction of time of the self-assembly step from 24 to 2 h had no detrimental influence on the quality of SBA-15 materials. 相似文献
19.
V.M. Asnin A.A. Bakun A.M. Danishevskii E.L. Ivchenko G.E. Pikus A.A. Rogachev 《Solid State Communications》1979,30(9):565-570
A novel photogalvanic effect induced by a circular polarized light in tellurium has been found. The absorption of light propagating along the C-axis of the crystal creates a fast e.m.f. which is proportional to the degree of the circular polarization and exhibits a sign dependence on the direction of the polarization. 相似文献
20.
We have demonstrated a surface plasmon polariton mediated optical Moiré effect by inserting a silver slab between two subwavelength gratings. Enhancement of the evanescent fields by the surface plasmon excitations on the silver slab leads to a remarkable contrast improvement in the Moiré fringes from two subwavelength gratings. Numerical calculations, which agree very well with the experimental observation of evanescent-wave Moiré fringes, elucidate the crucial role of the surface plasmon polaritons. The near-field Moiré effect has potential applications to extend the existing Moiré techniques to subwavelength characterization of nanostructures. 相似文献