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61.
Kuśmia S Kozak M Szcześniak E Domka L Jurga S 《Solid state nuclear magnetic resonance》2004,25(1-3):173-176
Penetration of water into low-density polyethylene-calcium lactate composite is studied with NMR techniques. The presence of filler speeds up the water uptake by the polymer matrix and facilitates polyethylene degradation. Spatial distribution of absorbed water molecules within the composite visualised with MRI corroborates differences in dynamical behaviour of the absorbed water molecules revealed by T2 measurements. 相似文献
62.
The molecular dynamics of tert-butyl chloride (TBC) confined to Controlled Pore Glass matrices of 25 and 7.5 nm were investigated by measuring NMR linewidths, lineshapes, and 1H and 2H spin--lattice relaxation times. The behaviour of confined TBC can be explained assuming that the guest molecules form two distinct phases; the surface-affected phase, composed of molecules located at the pore surface, and the bulk-like phase located at the centre of the pores. The bulk-like component of confined TBC, at the temperatures corresponding to the phase III, is characterized by two dynamically different subphases. 相似文献
63.
E R Andrew K Jurga J M Radomski E C Reynhardt 《Solid state nuclear magnetic resonance》1992,1(3):121-125
Polycrystalline progesterone (4-pregnene-3,20-dione, C21H30O2) has been investigated by proton NMR methods between 80 and 350 K. A reduction in dipolar second moment is ascribed to methyl group reorientation. Minima in the spin-lattice relaxation time found in measurements at five frequencies from 7 to 200 MHz are attributed to reorientation of two of the three methyl groups in each molecule, characterized by activation energy Ea = 10.9 +/- 0.8 kJ/mol and tau o = (2.3 +/- 0.2) x 10(-13) s. Additional relaxation at lower temperatures is attributed to reorientation of the third methyl group with Ea approximately 3.4 kJ/mol. Measurements were also made of relaxation in the rotating frame. 相似文献
64.
Studies in superconducting properties of NbN–SiO2 films are reported. The films were obtained through nitridation of sol–gel derived Nb2O5–SiO2 coatings at 1200 °C, a process leading to the formation of disordered structures with NbN metallic grains dispersed in the insulating SiO2 matrix. Electrical resistivity was measured with the conventional four-terminal method in the temperature range from 5 to 280 K. The samples’ superconducting properties, examined with magnetically modulated microwave absorption (MMMA), depend on the NbN/SiO2 molar ratio and the film’s thickness. 相似文献
65.
Ričardas Buividas Narges Fahim Jurga Juodkazytė Saulius Juodkazis 《Applied Physics A: Materials Science & Processing》2014,114(1):169-175
The actual surface area of a gold-coated conductive layer over the laser nano-textured surface of sapphire is determined using an electrochemical cyclic voltammetry. The method is down scaled to measure the sensing surface area of 200 × 200 μm2 on a laser-ablated ripple sensor used for surface-enhanced Raman spectroscopy/scattering (SERS). Ripple SERS sensors made on different substrates of high refractive index materials such as GaP, diamond, SiC, and Al2O3 make a versatile sensing platform with the detection of analyte (here a thiophenol) down to 10 nM concentrations. Direct measurement of the surface area provides a powerful tool to investigate roughness, porosity, and morphology of coatings used for SERS or other light harvesting surfaces such as solar cells. Novelty of the proposed method is in the use of cathodic peak of surface passivation–activation cycle for calculation of surface charge. The method enables high-accuracy surface area measurements from as small as 0.01 mm2 pads up to functional solar cells. 相似文献
66.
Baranowski M Woźniak-Braszak A Jurga K 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,208(1):163-166
This paper reports on design and construction of a double coil high-homogeneity ensuring Nuclear Magnetic Resonance Probe for off-resonance relaxation time measurements. NMR off-resonance experiments pose unique technical problems. Long irradiation can overheat the sample, dephase the spins because of B(1) field inhomogeneity and degrade the signal received by requiring the receiver bandwidth to be broader than that needed for normal experiment. The probe proposed solves these problems by introducing a separate off-resonance irradiation coil which is larger than the receiver coil and is wound up on the dewar tube that separates it from the receiver coil thus also thermally protects the sample from overheating. Large size of the irradiation coil also improves the field homogeneity because as a ratio of the sample diameter to the magnet (coil) diameter increases, the field inhomogeneity also increases (Blümich et al., 2008) [1]. The small receiver coil offers maximization of the filling factor and a high signal to the noise ratio. 相似文献
67.
Spin-lattice relaxation times T1 and T1d as well as NMR second moment were employed to study molecular dynamics of pyridoxine (vitamin B6) in the temperature range 10-350 K. The T1 minimum observed at low temperatures at 200 MHz is attributed to a motion of methyl group. The motion is interpreted in terms of Haupt's theory, which takes into account the tunneling assisted relaxation. At low temperatures, where T1 is temperature independent, occupation of the ground state only is assumed. A motion of proton of the hydroxyl groups or CH2OH groups probably provides additional mechanism of relaxation, in the high-temperature region. 相似文献
68.
Monika Makrocka-Rydzyk Stanislaw Glowinkowski Stefan Jurga Wolfang H. Meyer 《Solid state nuclear magnetic resonance》1995,4(6):353-360
Temperature dependences of proton and fluorine second moments and spin-lattice relaxation time T1 below glass transition were measured in glassy “I-Do,Pip-Me-BF4” ionene. The existence of motions of methyl groups and segments linking the cationic centers, namely piperidinium rings and trimethylene groups, for the polymeric part of ionene were established. Isotropic rotation of the counter-ion was evidenced and its limited diffusion suggested. To interpret the proton and fluorine relaxation data, a Davidson-Cole distribution of correlation times was assumed. 相似文献
69.
Isotactic polypropylene (iPP) modified by heterogeneous nucleation and molten state drawing was investigated using the DMTA and NMR methods. The nucleation was realized by specific α and β nucleating agents, 1,3,2,4-bis(3,4-dimetylobenzylideno) sorbitol (Millad 3988, Miliken) leading to the creation of the α phase, and N,N′-dicyklohexylo-2,6-naftaleno dikarboxy amid (NJ100) as the β phase promoter. The processing induced modification was performed by molten state drawing during an extrusion in the range between the die exit and the calibration unit. An increase of the glass transition temperature of iPP was found to be drawing independent for the β-nucleated samples, and dependent in the case of the α-iPP. Changes in the macromolecular mobility, depending on the α/β iPP structure and molten state drawing, was found by NMR lineshape and second moment measurements. 相似文献