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331.
A.?Sch?nhalsEmail author H.?Goering C.?Schick B.?Frick R.?Zorn 《Colloid and polymer science》2004,282(8):882-891
The glassy dynamics of poly(propylene glycol) (PPG) and poly(methyl phenyl siloxane) (PMPS) confined to nanoporous glasses (pore sizes 2.5–20 nm) investigated by dielectric spectroscopy, temperature modulated DSC and neutron scattering is compared. For both systems the relaxation rates estimated from dielectric spectroscopy and temperature modulated DSC agree quantitatively indicating that both experiments sense the glass transition.For PPG the glassy dynamics in nanopores is determined by a counterbalance of an adsorption and a confinement effect where the temperature dependence of the relaxation times obeys the Vogel/Fulcher/Tammann (VFT-) equation. The former effect results from an interaction of the confined macromolecules with the internal surfaces which in general slows down the molecular dynamics. A confinement effect leads to an acceleration of the segmental dynamics compared to the bulk state and points to an inherent length scale on which the glassy dynamics takes place. The step of the specific heat capacity cp at the glass transition vanishes at a finite length scale of 1.8 nm. This result supports further the conception that a characteristic length scale is relevant for glassy dynamics.For PMPS down to a pore size of 7.5 nm the temperature dependence of the relaxation times follows the VFT-dependence and a confinement effect is observed like for PPG. At a pore size of 5 nm this changes to an Arrhenius-like behavior with a low activation energy. At the same pore size cp vanishes for PMPS. This points to a dramatic change in the character of molecular motions responsible for glassy dynamics and supports further the relevance of a characteristic length scale on which it takes place.Quasielastic neutron scattering experiments on PMPS reveal that the microscopic dynamics characterized by the mean square displacement depends on confinement above the glass transition. The diffusive character of the relevant molecular motions seems to disappear at a length scale of about 1.6 nm. 相似文献
332.
Seong-Heun?Cho Jee-Hyun?Ryu Jung-Bae?Jun Kyung-Do?SuhEmail author 《Colloid and polymer science》2005,284(3):266-275
A flexible poly(dimethyl siloxane) diacrylate (PDMSDA) crosslinker was synthesized using different molecular weights of poly(dimethyl siloxane) (PDMS, M
n
=550, 1,700, 4,000 g/mol). The monodisperse polystyrene (PS) particles crosslinked with various contents of PDMSDA were prepared by dispersion polymerization, and applied as seed particles in the seeded polymerization. The crosslinking density of the PS particles was determined from the rate of transport of the monomer molecules to the crosslinked seed particles. It was confirmed that the monomer swelling capacity of seed particles and final morphological changes of polymer beads were determined significantly by the crosslinking density of the seed particles. In addition, the morphological change was not observed without the oligomer swelling step in the seeded polymerization due to the hydrophobic property of PDMS. When highly crosslinked seed particles were used in the seeded polymerization, peculiar morphology (doublet structure) of polymer beads appeared. 相似文献
333.
Lebrón-Aguilar R Quintanilla-López JE Tello AM Pérez-Parajón JM Santiuste JM 《Journal of chromatography. A》2005,1100(2):208-217
The method of solvation model has been applied to five poly (methyl-trifluoropropyl) siloxanes (TFPSXX) prepared in our laboratories, at five trifluoropropyl (TFP) group contents, XX = 0, 11.5, 26.3, 35.5 and 50.0%, at 80, 100, 120 and 140 degrees C. Previously, specific retention volumes of 60-odd solutes of varied polarities were measured upon each of these stationary phases within the above temperature range. Constant s prevails over all other constants, TFPSXX stationary phases showing strong dipole/induced dipole forces with the solutes, moderate acidity and no basicity at all. Constant e is zero in the stationary phase without TFP groups, but has negative low-medium values for the other fluorine contents, XX from 11.5 to 50.0%, hinting at repulsive forces, as expected. Normal values for constant l, decreasing from the less cohesive TFPS00 to the more cohesive TFPS50, were found. For each TFP content constants s, a and l show a negative temperature dependence, while constant e increases as temperature increases. Constant c also decreases with increasing temperature. At each temperature, constants s and a increase with increasing %TFP (or increasing stationary phase polarity), whereas constants e and l show the opposite trend, diminishing with increasing polarity of the stationary phase. Principal component analysis shows that the five stationary phases presented in this work conform a group with other earlier synthesized trifluoropropyl siloxanes and other fluorinated stationary phases taken from literature: VB-210, QF-1, DB-200, DB-210 and PFS6, showing the same selectivity which only the fluorine atom confers. A dendrogram of 38 stationary phases supports these results. 相似文献
334.
X. Andrew Guo Allen D. Hunter Jie Chen 《Journal of polymer science. Part A, Polymer chemistry》1994,32(15):2859-2866
The synthesis and characterization of five novel organonickel-organosilicon alternating copolymers having the repeating unit ? C6F4? Ni‘PBu3’2? C6F4? SiR2? [where SiR2 = ? SiMe2? , ? SiMe‘Hex’? , ? SiPh2? , ? SiMe2? O? SiMe2? , and ? SiMe2? ‘CH2’6? SiMe2? ] are reported. The model compounds Ni‘PR3’2‘1,4-C6F4SiMe3’2‘PR3 = PMePh2 or PBu3’ were prepared via reactions of Ni‘PR3’2‘1,4-C6F4Li’2 with 2 equiv of SiMe3Cl, and were characterized by conventional analytical and spectroscopic measurements. The Polymers were prepared from the reactions of Ni‘PBu3’2‘1,4-C6F4Li’2 with 1 equivalent of SiMe2Cl2 ‘polymer 1 , M w = 15,800’, SiMe ‘Hex’ Cl2 ‘polymer 2 , M w = 7300’, SiPh2Cl2 ‘polymer 3 , M w = 8600’, O‘SiMe2Cl’2 ‘polymer 4 , M w = 13,900’ and ‘CH2’6‘SiMe2Cl’2 ‘polymer 5 , M w = 19,700’. The molecular weights for each polymer were fully determined by both GPC and VPO. The multinuclear ‘1H-, 19F-, and 31P [1H]’-NMR, FTIR, and UV-Visible spectroscopic data for each polymer unambiguously establishes its repeating unit structure. The observations indicate that introduction of the silyl or siloxane units into the organonickel backbones has remarkably decreased the chain rigidity of the organonickel-organosilicon polymers compared to their rigid rod organonickel analogues ‘i.e., ? [? C6F4? Ni‘PR3’2? ]n? ’. © 1994 John Wiley & Sons, Inc. 相似文献
335.
V. M. Litvinov A. K. Whittaker A. Hagemeyer H. W. Spiess 《Colloid and polymer science》1989,267(8):681-686
Molecular motions in poly(diethyl siloxane) were studied by solid-state29Si-NMR in the temperature range 180–350 K. In this temperature range two solid phases
1 and
2, a mesophase
m, and an amorphous isotropic phase exist. The nature of the chain mobility in the different phases was deduced from the resulting changes in the NMR line-shape governed by anisotropic chemical shift. In the intermediate solid phase
2 its anisotropy is reduced by 25% compared with the low temperature phase
1 due to the onset of oscillations around the chain axis and conformational transitions. In the mesophase
m the polymer chain rotates about its long axis yielding an axially symmetric chemical shift tensor opposite in sign to that in the
1,
2 phases. The broad transition of the mesophase into the isotropic phase is accompanied by an increase in a narrow Lorentzian line arising from the amorphous phase. The results are compared with previous1H NMR, Raman-spectroscopy and x-ray measurements.After completion of this work we learnt that PDES has recently also been studied through13C-MAS and29Si-NMR by Möller et al. [13]. 相似文献
336.
Some slow potentiometric dyes, e.g., 3,3-dipropylthiacarbocyanine and tetramethylrhodamine methyl ester, exhibit fluorescence spectral changes on redistributing from aqueous medium to cells. This effect has been used for spectroscopic discrimination of the emissions from free and bound dyes in cells. Such a discrimination can, in principle, allow for the assessment of cell membrane potential in individual cells, using the Nernst equation applied to the ratio of free dye fluorescence intensities inside and outside of the cell. 相似文献
337.
用大束流加速器和透射电子显微镜研究了Zr-4合金在310 ℃和350 ℃下的质子辐照效应。当质子能量为2 MeV,在310 ℃和350 ℃下质子辐照产生原子离位损伤达5 dpa(注量率为8.5×1013 cm-2·s-1),辐照前后的明场像、高分辨相和电子衍射花样均表明:在310 ℃辐照产生原子损伤达到5 dpa,沉淀相Zr(Cr,Fe)2边缘5~10 nm的区域已经非晶化,而在350 ℃时质子辐照却没有非晶化发生。沉淀相Zr(Cr,Fe)2的元素分布图像和浓度分布表明,铁元素向基体扩散并且聚集在非晶化边界区域。 相似文献
338.
Maria Cazacu Carmen Racles Anton Airinei Mihaela Alexandru Angelica Vlad 《Journal of polymer science. Part A, Polymer chemistry》2009,47(21):5845-5852
A ferrocenyl‐siloxane polyamide, poly{1,1′‐ferrocene‐diamide‐[1,3‐bis(propylene)tetramethyldisiloxane]}, FAS, prepared by polycondensation in solution (methylene chloride) of 1,1′‐di(chlorocarbonyl)ferrocene with 1,3‐bis(aminopropyl)tetramethyldisiloxane has been dissolved in various concentrations in the range 0–1.5 g/dL in dimethylformamide. The solutions were investigated by tensiometry, viscometry, and UV–vis spectrophotometry at different temperatures. The results suggested the association occurrence, depending on the two parameters (concentration and temperature). The aggregates formation and their sizes were emphasized by dynamic light scattering and scanning electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5845–5852, 2009 相似文献
339.
Ecaterina Stela Dragan Maria Cazacu Alexandra Nistor 《Journal of polymer science. Part A, Polymer chemistry》2009,47(24):6801-6813
Ionic organic/siloxane networks containing quaternary ammonium salt (QAS) sequences in the cross‐linking bridges were obtained by the Menshutkin reaction of oligo(N,N‐dimethylaminoethylmethacrylate) (ODMAEM) with a telechelic chloroalkylated siloxane (CAS), such as 1,3‐bis‐(chloromethyl)‐1,1,3,3‐tetramethyldisiloxane, 1,3‐bis‐(chloropropyl)‐1,1,3,3‐tetramethyldisiloxane, and α,ω‐bis(chloromethyl) oligodimethylsiloxane. The resulted structures were investigated by Fourier transform infrared spectroscopy emphasizing the presence of both organic and siloxane moieties. The thermogravimetric analysis under inert atmosphere of the networks, besides the thermal stability, gave also information on the composition of hybrid hydrogels. The morphology of the lyophilized networks was evidenced by environmental scanning electron microscopy, as a function of CAS structure and CAS: ODMAEM feed molar ratio. The swelling response of the ionic networks in water as a function of pH and counterion nature and concentration as well as the water vapors sorption capacity in dynamic regime were evaluated. The properties of the ionic hybrid hydrogels were correlated with the reactants feed molar ratio and concentration of the reaction mixture, CAS type, and the presence of a catalyst. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 相似文献
340.
Houari Boumedine Khenous Patrick Laborde Yves Renard 《European Journal of Mechanics - A/Solids》2008,27(5):918-932
This paper is devoted to a new method dealing with the semi-discretized finite element unilateral contact problem in elastodynamics. This problem is ill-posed mainly because the nodes on the contact surface have their own inertia. We introduce a method based on an equivalent redistribution of the mass matrix such that there is no inertia on the contact boundary. This leads to a mathematically well-posed and energy conserving problem. Finally, some numerical tests are presented. 相似文献