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1.
H. Okabayashi K. Izawa T. Yamamoto H. Masuda E. Nishio C. J. O'Connor 《Colloid and polymer science》2002,280(2):135-145
Silica gel samples, modified with 3-mercaptopropyltriethoxysilane, and their S–S-bridged samples have been prepared. In order
to characterize the microstructure of the surface of these silica gel samples, Raman scattering and diffuse reflectance Fourier
transform IR spectra of these samples have been examined by comparison with Raman spectra of various n-alkyl disulfides and their related silane polymers. The S–S and C–S stretch modes characteristic of the CH2SSCH2 segment, in addition to the SH and C–S stretch modes of the CH2SH segment, have been assigned for these silica gel samples. It has been found that, even on the surface of the silica gel,
a specific conformer is stabilized about the CH2SSCH2 segment.
Received: 1 May 2001 Accepted: 16 June 2001 相似文献
2.
Three silica gel sample systems, modified with 3-amino-propyltriethoxy silane (APTS), were prepared by sequentially sampling
the reaction mixture at various time intervals. The concentrations of 3-aminopropylsilyl groups (APS) bound on the silica
surface were determined by elemental analysis. For the same sample systems, 29Si NMR intensities of an (–O)4Si species belonging only to the silica gel particles and corrected by a cross-polarization correction factor were also measured.
Both the APS-concentrations and the correc-ted 29Si NMR intensities depended upon reaction time, reflecting the rate of the APTS–silica gel reaction. Kinetic analysis of these
data was made by use of the Gauss–Newton method, and the overall reaction was found to consist of three reaction processes
(an initial fast reaction, a slower second reaction and a much slower third reaction). In particular, the conversion of (–O)3SiOH to (–O)4Si is predominant in the second reaction process and the pore size of a silica gel particle affects the reaction mechanism.
Received: 1 November 1996 Accepted: 24 January 1997 相似文献
3.
Hydroxylation of the silica in microfabricated thin layer chromatography plates as probed by time‐of‐flight secondary ion mass spectrometry and diffuse reflectance infrared Fourier transform spectroscopy 下载免费PDF全文
Supriya S. Kanyal Bhupinder Singh Cody V. Cushman Daniel T. Jankowski Matthew R. Linford 《Surface and interface analysis : SIA》2015,47(3):340-344
Microfabricated silica thin layer chromatography (TLC) plates have previously been prepared on patterned carbon nanotube forests. The high temperatures used in their fabrication reduce the number of hydroxyl groups on their surfaces. Fortunately, silica can be rehydroxylated. In diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), a silanol peak below 3740 cm?1 indicates a well‐hydroxylated silica surface that is fit for chromatography. Hydroxylations of our materials with HF are so effective that it is not possible to discern the position of this peak. In contrast, this signal is discernable when the plates are treated with NH4OH. To find a more convenient method for studying the surfaces of TLC plates, time‐of‐flight secondary ion mass spectroscopy (ToF‐SIMS) was considered. ToF‐SIMS is advantageous because multiple microfabricated TLC plates must be scraped to obtain enough silica for one DRIFT analysis, while static SIMS can be performed on very small regions (500 × 500 µm2 or less) of individual plates. Ratios of the SiOH+ and Si+ ToF‐SIMS signals for microfabricated TLC plates correlated well with ~3740 cm?1 silanol peaks from DRIFT. Thus, SIMS allows direct analysis of all of our treated and untreated plates, including those hydroxylated with HF. The best hydroxylation condition for HF, which was better than any studied for NH4OH, was around 150 ppm at room temperature. The best hydroxylation condition for NH4OH was 50 °C for 72 h. ToF‐SIMS versus DRIFT results of commercial TLC plates were also obtained and evaluated. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
4.
Pekka Savolahti 《Mikrochimica acta》1988,95(1-6):155-158
Diffuse reflectance infrared spectroscopy was used to study isothermal degradation of crude barley protein, that was obtained as a side product of alcohol production. The isothermal temperatures used were in the range 50–150° C. Before analysis the protein fraction was dried either by lyophilization or spray drying. The drying method did not have a major effect on the subsequent isothermal degradation of the material. The main reactions observed in the spectra were oxidation indicated by the appearance of a broad composite carbonyl band and degradation of both proteins and starch. The reactions were visible already in the spectra taken at 70° C and there rates gradually increased as the temperature was raised to 150° C. 相似文献
5.
Fourier transform infrared spectra in the wave number range 450–4500 cm-1 of poly (2-hydroxy-ethyl methacrylate) PHEMA have been studied as functions of water content in the range 38–2.6 wt% and
of temperature in the range 300–373 K. The results show changes in the intensities of the stretching frequencies of the carbonyl
band, H–O–H bending vibration and O–H stretching vibration with a change in water content and temperature. The results confirm
two types of water in the hydrogel polymer system, tightly bound water and loosely bound water. At low concentrations, water
is mainly hydrogen-bonded to the polymer and is described as tightly bound water. However, at water concentrations greater
than 18% by weight, part of the water exists in a different form and behaves as loosely bound water. For concentrations over
30%, there is some evidence that excess water behaves more loosely bound somewhat like bulk water. Infrared spectroscopic
results supplement those obtained by means of NMR by Smyth et al. and by dielectric spectroscopy. Our results also show that
some of the water continues to be hydrogen bonded to the polymer until at least a temperature of 373 K when the bulk water
should have evaporated. FTIR is found to yield greater site-specific insight into the local behaviour of water in hydrated
PHEMA.
Received: 22 August 1996 Accepted: 11 November 1996 相似文献
6.
Urbirajara Pereira Rodrigues Filho Yoshitaka Gushikem Fred Yukio Fujiwara Eduardo Stadler Valderez Drago 《Structural chemistry》1994,5(2):129-133
Pentacyanoferrate(II) absorbed on a silica gel surface previously modified with 3-aminopropyl and 3-imidazolylpropyl groups were characterized by13C MAS/NMR, FT-IR, Mössbauer spectroscopy, and cyclic voltammetry. FT-IR and13C MAS/NMR data indicated that the pentacyanoferrate(II) complex is bonded to the surface by the nitrogen atom of the functional group. The differences in the isomeric shifts, the quandrupole splittings and the midpoint potentials of the adsorbed complexes in comparison with the model complexes were attributed to the matrix polar effect—i.e., the interaction of the complex with polar groups on the silica surface. 相似文献
7.
Analytical methods find increasing use in the preservation of historical monuments. We have investigated the salt migration of lithium carbonate under the influence of water (rain, soil humidity). Diffuse reflectance infrared fourier transform spectroscopy (DRIFT) provides rapid information with less time consumption for sample preparation compared to transmission IR spectroscopy. Quantitative data about lithium migration have been obtained by flame photometry.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
8.
9.
The Raman scattering spectra for polyaminopropylsiloxane (poly-APS) samples in the solid state and in aqueous solution and
for the related compounds, γ-aminobutyric acid (GABA) and its hydrochloride salt (GABA ⋅ HCl), have been examined in the CH2 rock and skeletal stretch region. The Raman spectrum of the solid poly-APS sample may be accounted for by direct combination
of the Raman spectra for GABA and GABA ⋅ HCl, whose crystal structures have been elucidated by a single-crystal X-ray diffraction
study, suggesting that the APS segments of poly-APS in the solid state are in a conformationally ordered state. It has also
been found that the Raman spectra of the solid and aqueous poly-APS samples in this region are useful for diagnosing the conformations
of APS moieties bound onto the surface of silica gel.
Received: 18 September 1996 Accepted: 2 December 1996 相似文献
10.
D. V. Kazakov D. V. Mal’tsev G. Ya. Maistrenko S. L. Khursan M. Yu. Ovchinnikov V. P. Kazakov 《Russian Chemical Bulletin》2007,56(2):205-210
Decomposition of 1,4-dimethylnaphthalene endoperoxide supported on the silica gel and alumina surface is accompanied by chemiluminescence
(CL) in the IR and visible spectral regions. The CL emitter in the IR region is singlet oxygen. The 1O2 dimol contributes mainly to the emission at λmax = 630 and 700 nm. It was shown by the IR-CL method that endoperoxide decomposition on the sorbent surface follows the first-order
kinetics. The activation parameters of the process were determined. On the Al2O3 and silica gel surfaces a substantial acceleration of the decomposition of 1,4-dimethylnaphthalene endoperoxide is observed
compared to the solution.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 199–204, February, 2007. 相似文献
11.
J. Sonnefeld 《Colloid and polymer science》1996,274(12):1137-1144
The influence of an acid treatment on the pore structure as well as on the surface charge density of porous silica was investigated. It is shown that this treatment causes only small changes of the pore structure. Positive values of the surface charge density at pH>4 are interpreted in terms of surface impurities consisting of Na+ ions resulting from the synthesis of the gel from sodium silicate solution. This effect is strongly influenced by the acid treatment. The surface charge density parameters were evaluated on the basis of the triple-layer model for the electrical double layer. Here two different mechanisms of counterion attachment in the inner Helmholtz plane are discussed. 相似文献
12.
The B3LYP/6-311G(d) and CCSD(T)/6-311G(2df) (single-point) methods have been used to investigate the singlet potential energy
surface of C2NP, in which seven stationary isomers and seventeen interconversion transition states are involved. At the final CCSD(T)/6-311G(2df)//B3LYP6-311G(d)
level with zero-point vibrational energy correction the lowest-lying isomer is a linear NCCP followed by two linear CNCP isomers
at 23.9 and CCNP at 65.8 kcal mol−1, respectively. The three isomers are kinetically very stable towards both isomerization and dissociation, and CCNP is even
more kinetically stable than CNCP – by 14.3 kcal mol−1 despite its high energy. Further comparative calculations were performed at the QCISD and QCISD(T) levels with the 6-311G(d)
and 6-311G(2d) basis sets to obtain more reliable structures and spectroscopy for the three isomers. The calculated bond lengths,
rotational constant, and dipole moment for NCCP were in close agreement with the experimentally determined values. Finally,
similarities and discrepancies between the potential energy surface of C2NP and those of the analogous species C2N2 and C2P2 were compared. The results presented in this paper might be helpful for future identification of the two still unknown yet
kinetically very stable isomers CNCP and CCNP, both in the laboratory and in interstellar space.
Received: 3 January 2001 / Accepted: 6 June 2001 / Published online: 30 October 2001 相似文献
13.
The adsorption of poly-ethylene oxide (PEO) on modified colloidal silica and the stability of the aqueous suspension was
investigated. With octanol some silanol groups at the silica surface were replaced by octylgroups. The size of the modified
silica particles and the charge and chemical groups on the surface were charaterized by ultracentrifugation, photon correlation
spectrometry, polyelectrolyte titration and IR spectrometry. The adsorbed amounts of polyethylene oxides of different molar
mass were determined on the modified silica in water. With photon correlation spectrometry (PCS) the hydrodynamic layer thickness
of the PEO layers on the particles were measured. The dependences of the layer thicknesses on molar mass of the PEO, polymer
concentration and adsorption time were determined. The aggregation of the suspended PEO coated and uncoated modified silica
particles was examined with PCS by the time dependence of the diffusion coefficient at different salt concentrations. The
influence of molar mass and concentration of PEO as well as of the age of the dispersion was explored. The measured dependences
are discussed and compared with the behavior of unmodified silica- and latex-particles.
Received: 6 April 1998 Accepted: 27 May 1998 相似文献
14.
The diffusion coefficient of water into thin polymer layers of glutar aldehyde cross-linked atelocollagen type I matrix (sample
1, the typical layer thickness was about 0.065 × 10−3 m) at 23 °C was 1.142 × 10−10 m2 s−1. At twice the concentration of the cross-linking agent (sample 2) the diffusion coefficient was 2.795 × 10−10 m2 s−1. This increase was attributed to the more ordered morphology and the creation of ordered microvoids in the film. A larger
surface area is then available for the transport of diffusing molecules, allowing a higher penetration rate of the solvent.
Received: 11 January 2000/Accepted: 6 May 2000 相似文献
15.
S. F. Lascelles G. P. McCarthy M. D. Butterworth S. P. Armes 《Colloid and polymer science》1998,276(10):893-902
The effect of varying the oxidant, monomer and silica sol concentrations, silica sol diameter, polymerization temperature,
stirring rate and oxidant type, on the particle size, polypyrrole content and conductivity of the resulting polypyrrole– silica
colloidal nanocomposites has been studied. Surprisingly, nanocomposite formation appears to be relatively insensitive to most
of the above synthesis parameters. One synthesis parameter which does have a significant and reproducible effect is the stirring
rate: smaller, more monodisperse nanocomposite particles are obtained from rapidly stirred reaction solutions. However, this
effect is only observed for the (NH4)2S2O8 oxidant. An alternative oxidant, H2O2/Fe3+, was found to give nanocomposites of similar particle size, polypyrrole content and conductivity to those obtained using
the (NH4)2S2O8 oxidant. The colloid stability of these polypyrrole–silica nanocomposite particles depends on their silica content. The colloid
stability of a silica-rich nanocomposite prepared using the (NH4)2S2O8 oxidant in the presence of electrolyte was comparable to that of a silica sol, whereas a polypyrrole-rich nanocomposite prepared
using FeCl3 had markedly poorer colloid stability under these conditions. These observations are consistent with a charge stabilization
mechanism for these nanocomposite particles.
Received: 5 March 1998 Accepted: 27 April 1998 相似文献
16.
Y. Ohtsu O. Shirota T. Ogawa I. Tanaka T. Ohta O. Nakata Y. Fujiyama 《Chromatographia》1987,24(1):351-356
Summary A new type of column packing material designed for preparative liquid chromatography, silicone polymer-coated silica gel modified
with octadecyl group (S/S-C18), was applied to chromatographic purification of a lipophilic biotechnological product. Triglycerides containing γ-linolenic
acid were separated from the curde oil that consisted of triglycerides, diglycerides, free fatty acids, sterols and other
polar substances, using a S/S-C18 packed column (150 mm I.D. × 1000 mm). No column deterioration was observed after more than 1500 times of sample introductions. 相似文献
17.
Romain Dabre Achim Schwämmle Michael Lämmerhofer Wolfgang Lindner 《Journal of chromatography. A》2009,1216(16):3473-3479
Thiol-modified silica is often used as an intermediate product for further synthesis of modified stationary phases for chromatography or purification processes. Different conditions were used to synthesize such thiol-modified particles, but systematic optimizations remained scarce. In this study the reaction conditions for the synthesis of mercaptopropyl-modified silica were optimized. The general synthetic method consists in slurrying the silica gel in toluene before adding 3-mercaptopropyldimethoxymethylsilane together with a tertiary amine as catalyst (here dimethylaminopyridine). Reaction time and temperature were optimized using a full factorial design of experiment (DoE) from 3 to 25 h with temperature varying between 45 and 105 °C. The surface coverage of the silica with mercaptopropyl-groups was analyzed by two different ways (elemental analysis and chemical surface reaction with 2,2′-dipyridyl disulfide followed by HPLC-UV analysis of stoichiometrically liberated pyridyl-2-thione). We obtained a three-dimensional (3D) plot of the surface coverage as a function of reaction time and temperature. The arch-shaped hyperplane allowed us to determine an optimum with regard to time and temperature, which yields to the highest surface coverage possible. We also verified that the increase of the surface coverage does not lead to a decrease of the stability of the surface modification by subjecting the gels to treatment with high temperature and acidic conditions. The stability was monitored by different chromatographic methods. Moreover, 29Si cross-polarization-magic angle spinning (CP-MAS) NMR spectra of materials prepared by different conditions allowed to confirm that the Si species on the surface were essentially the same, while there was only a minute difference in signal intensities for the individual Si species for materials obtained by distinct temperatures. 相似文献
18.
T. Ogasawara A. Nara H. Okabayashi E. Nishio C. J. O'Connor 《Colloid and polymer science》2000,278(11):1070-1084
The polymerization behavior of 3-aminopropyltriethoxysilane, a process initiated by water molecules, has been examined using
time-resolved near-IR and 2D near-IR correlation spectra. By deconvolution of the time-resolved near-IR spectra, the existence
of the component bands at 5189, 5265 and 5300 cm−1, whose intensities decrease markedly as the reaction proceeds, has been confirmed in the 5000–5400 cm−1 region. The band at 5189 cm−1 has been assigned to water molecules, while those at 5265 and 5300 cm−1 have been assigned to the strongly and weakly associated silanol groups, respectively. The kinetics of the hydrolysis of
the ethoxy groups and of the formation of a siloxane bond have been analyzed using the time-dependent integral intensities
of these three bands and the mechanisms of the reactions have been discussed. Evidence for this polymerization process is
also clearly evident in the 2D near-IR correlation spectra.
Received: 14 March 2000/Accepted: 15 May 2000 相似文献
19.
The crystalline transformation in nylon 12 12 was monitored by variable-temperature wide-angle X-ray diffraction during heating,
isothermal and cooling processes. It could be found that the α phase of the sample transforms into a γ phase at about 130 °C
if the sample is heated from room temperature to a high temperature, which is the so-called Brill transition temperature.
In addition, nylon 12 12 was found to crystallize into the γ phase when isothermally crystallized at high temperature from
the melt. Upon further cooling from the crystallization temperature to room temperature, the reverse transition from the γ phase
to the α phase can be detected. Furthermore, in situ Fourier transform IR spectroscopy was also used to study the Brill transition
of nylon 12 12 samples on both heating and cooling. It is interesting that the hydrogen-bond strength in nylons decreases
dramatically and that some Brill bands of nylon 12 12 disappear abruptly during the Brill transition on heating.
Received: 3 April 2001 Accepted: 28 July 2001 相似文献
20.
Newton L. Dias Filho 《Mikrochimica acta》1999,130(4):233-240
The isotherms of adsorption of MeX2 (Me = Cu2+, Co2+; X = Cl–, Br–, ClO
4
–
) by silica gel chemically modified with 2-mercaptoimidazole (SiMI) were studied in acetone and ethanol solutions, at 25 °C. Covalently attached 2-mercaptoimidazole molecule to silica gel surface adsorbs MeX2 from solvent by forming a surface complex. The metal is bonded to the surface through the nitrogen atom of attached 2-mercaptoimidazole. At low loading, the electronic and ESR spectral parameters indicated that the Cu2+ complexes are in a distorted-tetragonal symmetry field. The d-d electronic transition spectra showed that for Cu(ClO4)2 complex, the peak of absorption did not change for any degree of metal loading and for Cl– and Br– complexes, the peak maxima shifted to higher energy with lower metal loading. The CoX2(X = Cl–, Br–, ClO
4
–
) analogues possess a distorted-tetrahedral field. 相似文献