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1.
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
2.
M. Jumaa F. El Saleh I. Hassan B. W. Müller P. Kleinebudde 《Colloid and polymer science》2000,278(7):597-607
The physicochemical properties of different types of powdered cellulose (PC) and microcrystalline cellulose (MCC) were studied
by examining the changes in particle size, viscosity and specific surface area after a homogenisation process. An additional
characterisation was carried out using X-ray diffractometry. A preliminary investigation using a type of MCC showed that increasing
the homogenisation pressure and the number of passage cycles led to a significant decrease in the particle size and simultaneously
to a remarkable increase in the specific surface area and viscosity. Most MCC types showed the same pattern during the homogenisation
process. “Colloidal” MCC displayed a higher viscosity than the others but without significant change in the viscosity after
different homogenisation cycles. In contrast to this behaviour of the MCCs, the PCs showed no remarkable change in the particle
size but did show a marked change in their viscosity. Furthermore, only MCC suspensions, with the exception of “colloidal”
MCC, agglomerated after the homogenisation process, whereas this was not seen in the PC suspensions. Hence, since the MCC
types as well as the PC types originally had the same chemical structure, this different behaviour among these types can only
be attributed to their different physical properties.
Received: 27 July 1999/Accepted: 15 December 1999 相似文献
3.
Crosslinking of cotton cellulose with succinic acid in the presence of titanium dioxide nano-catalyst under UV irradiation 总被引:1,自引:0,他引:1
The nanometer titanium dioxide (TiO2), succinic acid (SUA), and the mixture of nano- TiO2 and SUA were dispersed or dissolved in pure water, then irradiated with UV at the wavelength of 254 nm under stirring for
different time periods respectively. The pH and conductivity values and UV-vis spectra of those solutions were recorded immediately.
The powders obtained from the filtrated and vacuum dried from those solutions were examined with Fourier Transform Infrared
Spectroscopy and Wide Angle X-Ray Diffraction meter. It shows that the crystalline structure and IR and UV-vis spectra of
SUA adsorbed on nano-TiO2 particles are changed. The photo-reduced succinic acid in the presence of nanometer titanium dioxide under UV irradiation
can create aldehyde group on SUA and free radical of SUA to improve the catalytic effects of crosslinking reaction between
SUA and cotton cellulose. 相似文献
4.
A linear low-density polyethylene was gamma irradiated in presence of carbon dioxide under supercritical conditions. As already
reported, this process can be an interesting way to graft carboxylated functions to the polyethylene chains. In this work
a detailed analytical investigation of the carboxylation products grafted on LLDPE are presented. Derivatization procedures
with sulfur tetrafluoride and nitrogen monoxide, in order to selectively convert the carboxylated functions into groups more
easily identified and quantified by FTIR, were performed. The chemical nature of the grafted groups is very similar to that
obtained through gamma irradiation in air; furthermore, a significant degree of crosslinking is observed.
Received: 4 June 1996 Accepted: 15 October 1996 相似文献
5.
6.
Y. -K. Leong 《Colloid and polymer science》1997,275(9):869-875
The effect of pH on the flow behavior of ZrO2 suspensions containing polyacrylic and octanoic acids was evaluated. In the flocculated pH regime, the flow behavior is highly
shearthinning and can be described by a power-law model. The shear-thinning behavior increases with increasing degree of flocculation.
Maximum shearthinning was observed at the zero zeta potential condition. Hydrophobic interaction arising from adsorbed octanoic
acid was found to enhance the shear-thinning behavior. No such enhancement was observed for adsorbed polyacrylic acid. It
was also illustrated that the viscosity–pH behavior is a mirror image of the yield stress–pH behavior. A quantitative particle-pair
interactions model incorporating steric and hydrophobic interactions was proposed to explain the effects of polyacrylic and
octanoic acids on the maximum yield stress.
Received: 23 May 1997 Accepted: 4 June 1997 相似文献
7.
The photodegradation behaviour of ethylene-vinyl acetate copolymer (EVA)/low density polyethylene (LDPE) composite containing four different types of titanium dioxide (TiO2) was investigated through colour difference, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and mechanical tests. The results showed that the performance losses of composites were qualitatively correlated with the degradation degree. The vinyl acetate (VA) groups in EVA were sensitive to UV light and the photodegradation mainly occurred in the amorphous region. The chain scission and annealing effect facilitated the secondary crystallization of composites. The heterogeneous nucleation effect of TiO2 on the crystallization of composites was related to the particle size of TiO2. The micro rutile TiO2, micro anatase TiO2 and their mixture (rutile/anatase = 13/87) exhibited a photo-stabilising effect, while the nano mixed crystals TiO2 (rutile/anatase = 20/80) had an opposite effect. 相似文献
8.
Surface tension measure-ments in aqueous cetyltrimethyl ammonium bromide were performed in presence of various amounts of
9-(hydroxymethyl)anthracene (AM), 9-[1-(1-hydroxy)ethyl]anthracene (THAE), and 9-[1-(1-hydroxy-2,2,2-trifluoro)ethyl]anthracene
(TFAE). Free energies ΔG
⊖
m and ΔG
⊖
i of micellization and of adsorption to the air–water interface, respectively, were determined as well as the corresponding
enthalpies and entropies. ΔG
o−
m of micellization increased in the presence of AM and THAE, but became more negative when TFAE was added. In contrast to AM
and THAE, TFAE addition decreases ΔS
⊖
i. For this peculiarity of TFAE, its location and orientation in micellar solution was investigated by means of UV and 19F-NMR spectroscopy.
Received: 26 March 1997 Accepted: 16 May 1997 相似文献
9.
Zhou S Wang Y De Beer T Baeyens WR Fei GT Dilinuer M Ouyang J 《Electrophoresis》2008,29(11):2321-2329
The analysis is described for separating seven beta-adrenergic blocking agents (atenolol, celiprolol, clorprenaline, fenoterol, metoprolol, propranolol, terbutaline) and clenbuterol (sympathomimetic beta-2 receptor stimulating agonist, decongestant and bronchodilator, illicit anabolic used in athletics) by CE with UV detection. In order to simultaneously separate all analytes, Tris-H3PO4 solution was applied containing titanium dioxide nanoparticles (TiO2 NPs) as BGEs. The effects of important factors, such as concentration of TiO2 NPs, optimum pH, run buffer concentration, and separation voltage, were investigated so as to achieve best CE separation. The eight analytes could be well separated applying a separation voltage of 15 kV in 75 mM Tris-H3PO4 buffer at a pH of 2.40, containing 6.0 x 10(-6) g/mL TiO2 NPs. Under these optimal conditions, the RSDs for peak areas and for migration times were less than 2.7 and 2.3%, respectively. The detection limits were 0.1 microg/mL for celiprolol, 0.1 microg/mL for propranolol, 0.2 microg/mL for fenoterol, 1.0 microg/mL for atenolol, 1.0 microg/mL for clenbuterol, 1.0 microg/mL for clorprenaline, 1.0 microg/mL for metoprolol, and 1.0 microg/mL for terbutaline. The proposed method was successfully applied for the rapid CE determination of the frequently applied antihypertensive beta-blocking compounds atenolol, metoprolol, terbutaline, and propranolol in pharmaceutical tablets. 相似文献
10.
M. Sega Margherita Plassa Elena Amico di Meane 《Accreditation and quality assurance》2001,6(7):306-309
In routine chemical measurements traceability can be achieved by using analytical instruments calibrated against primary reference
materials. In the present work the calibration of a CO2 non-dispersive infrared (NDIR) analyzer with measuring range 0–2000 μmol/mol of CO2 and a resolution of 5 μmol/mol is reported. A procedure with working reference gas mixtures (WRMs) has been adopted, which
requires seven calibration points. Primary reference gas mixtures (PRMs) are used to validate WRMs in a narrower range around
the average atmospheric CO2 concentration value. In this range the relative uncertainty reached is of the order of some parts in 103 and the corrections are between 1 μmol/mol and 5 μmol/mol.
Received: 16 March 2000 Accepted: 27 November 2000 相似文献
11.
The current state of production, certification and use of standard samples of aluminium- and titanium-based alloys with specified
contents of gas impurities is described. A list of the certified standard samples with a specified gas impurity content which
are available in Russia is presented.
Received: 20 October 1998 / Accepted: 9 November 1998 相似文献
12.
Daniel Hork 《Journal of polymer science. Part A, Polymer chemistry》1999,37(20):3785-3792
Poly(2-hydroxyethyl methacrylate) particles in the micron size range were obtained by the dispersion polymerization. Cellulose acetate butyrate and dibenzoyl peroxide were used as steric stabilizer and initiator, respectively. The ultimate particle size could be adjusted by the selection of a suitable polymerization medium consisting of an alcohol added to toluene and by varying their relative amounts. The particle size increased with increasing solubility parameter of the mixture, i.e., by decreasing the toluene/2-methylpropan-1-ol, toluene/butan-2-ol, and toluene/3-methylbutan-1-ol ratio. The particle size decreased with increasing concentration of the stabilizer and/or initiator. At the same time, the particle size distribution became narrower. Particles prepared from polymerization mixtures purged with nitrogen before the start of polymerization were smaller, and of narrower distribution, than those prepared from nitrogen-non-purged mixtures. Equilibrium swelling of particles in toluene decreased with the decreasing content of toluene in the polymerization mixture. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3785–3792, 1999 相似文献
13.
Molecular dynamics thermodynamic integration (MDTI) method and quantum chemical calculations at the density functional theory
B3LYP 6-31+(d,p) level, which included the Tomasi model of the solvent reaction field, were applied to study the tautomeric
equilibrium of Mannich base in methanol solution. The values obtained for the free-energy difference are in good agreement
with experimental data. However, the results from quantum mechanical calculations were not as good as the results of MDTI
simulations owing to inappropriate treatment of intermolecular hydrogen bonds between the solute molecule and the first shell
of solvent molecules in the Tomasi model of the solvent reaction field. The radial distribution functions between solute atoms
and solvent atoms confirmed the formation of hydrogen bonds between the solute molecule and surrounding methanol molecules
and indicated that the zwitterionic form is associated more with an organized solvent structure at the level of the first
solvation shell than is the molecular form.
Received: 26 April 2002 / Accepted: 9 September 2002 /
Published online: 31 March 2003 相似文献
14.
Nano-sized rod-like titanium dioxide (TiO2) filled rigid poly(vinyl chloride) (PVC) nanocomposites were prepared by using injection-molding method. Vicat, Charpy impact and tensile tests as well as thermogravimetric and dynamic mechanical analyses were used to characterize the structure and properties of the nanocomposites. The results showed that nano-TiO2 could improve Vicat softening temperature and also improve thermal stability of PVC during the stages of dehydrochlorination and formation of carbonaceous conjugated polyene sequences, which can be ascribed to restriction of the nanoparticles on the segmental relaxation as being evidenced by raises in glass transition and β-relaxation temperatures of PVC upon filling TiO2. Addition of TiO2 nanoparticles less than 40 phr (parts per hundreds of resin) could significantly improve impact strength of the composites while the TiO2 agglomeration at high contents leads to a reduction in impact toughness. 相似文献
15.
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
16.
The packing behavior of benzoylterryleneimide was determined by X-ray powder and electron diffraction. The latter was applied to a material solidified from a solution after spreading it onto a water surface. By this procedure various nonequilibrium structures were prepared: crystalline lamellae are embedded in a structure of lower order, the texture of which looks similar to a texture seen in rigid liquid-crystalline polymers. The transition between both regimes is gradual. X-ray diffraction was applied to an annealed crystalline powder. The crystalline packing of the dark-blue compound can be described by a monoclinic unit cell with lattice parameters a?=?11.25?Å, b?=?10.93?Å, c?=?27.78?Å, β?=?91.0°, ρ?=?1.38?g/cm3 and Z?=?4?at ambient temperature. In order to enable optimum space-filling, the molecules are arranged parallel two by two with the planes of the aromatic ring systems 3.47?Å apart in centrosymmetrical relation and shifted longitudinally so that the diisopropylphenyl group of one molecule fits into the cavity at the carbonyl oxygen of the adjacent molecule. 相似文献
17.
Manuel Garcia‐Leiner John Song Alan J. Lesser 《Journal of Polymer Science.Polymer Physics》2003,41(12):1375-1383
The drawing behavior of ultrahigh molecular weight polyethylene fibers in supercritical carbon dioxide (scCO2) is compared to that in air at different temperatures. The temperature substantially influences the drawing properties in air, whereas in scCO2, a constant draw stress and tensile strength are observed. Differential scanning calorimetry shows an apparent development of a hexagonal phase along with a significant increase in the crystallinity of air‐drawn samples with increasing temperature. The existence of this phase is not confirmed by wide‐angle X‐ray scattering, which instead shows that air‐drawn samples crystallize in an internally constrained manner. In contrast, scCO2 allows crystals to grow without constraints through a possible crystal–crystal transformation, increasing the processing temperature to 110 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1375–1383, 2003 相似文献
18.
A theoretical consideration of the phase-inversion technique to prepare waterborne particles based on the experimental facts
of the phase inversion process given in part 1 of this series is presented. The deformation and breakup of the water droplets
dispersed in an epoxy resin phase under shear action are analyzed in terms of microrheology. The interaction and coalescence
dynamics among the water droplets stabilized by an interfacial layer formed by the emulsifier molecules are discussed in terms
of Derjaguin–Landau–Verwey–Overbeek theory and effective collision theory, respectively. A criterion for the completion of
phase-inversion is that the attraction among the water droplets exceeds the entropic repulsion. Thus, a physical model of
phase-inversion is proposed to predict the effects of some control variables on the phase-inversion process as well as the
structural features of the waterborne particles, by which the experimental results could be well interpreted. It is indicated
that the achievement of phase inversion is determined by the dynamic coalescence among the water droplets before the phase-inversion
point (PIP). If the dynamic coalescence among the water droplets is ignored, phase inversion is achieved completely and sub-
micron-sized particles are prepared. In comparison, if the dynamic coalescence is significant, phase inversion is achieved
incompletely and a large complex water-in-oil-in-water structure is prepared. In the case of complete phase inversion, it
is shown that the size of the waterborne particles is comparable with the size of the water droplets before the PIP.
Received: 15 March 2000/Accepted: 16 May 2000 相似文献
19.
We report the successful precipitation polymerization of 2‐hydroxyethyl methacrylate (HEMA) in supercritical carbon dioxide (scCO2) at pressures ranging from 15 to 27 MPa utilizing 2, 2′‐azobisisobutyronitrile (AIBN) as a free radical initiator. The effects of the reaction pressure, initiator concentration, monomer concentration, reaction temperature, and reaction time were investigated. Analyses by scanning electron microscopy (SEM) indicated that in all reaction conditions, polymerization in the absence of stabilizer led to the formation of large aggregates of partially coalesced particles, with diameters of approximate 1–10 µm. Analyses by gel permeation chromatography (GPC) indicated that for the reaction pressure, initiator concentration, monomer concentration, reaction temperature, and reaction time studied there are appreciable effect on product molecular weight. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
20.
Vivechana Dixit Jagdish C. TewariS. Kay Obendorf 《Journal of chromatography. A》2009,1216(36):6394-6399
Photocatalytic properties of fibers containing TiO2 nanoparticles were explored for use as a self-decontaminating material using degradation of the pesticide aldicarb as the model toxin. During the analysis of the aldicarb treated sample by liquid chromatography (LC) with diode array detector (DAD), an unidentified peak was found at relative retention time (RT) 3.9 min when compared to aldicarb and major metabolites, aldicarb sulfoxide, and aldicarb sulfone. An analytical method was developed to confirm and identify this degradation product. LC–APCI/MS techniques were used first to analyze molecular ions and major fragments comparing retention times and spectra with those of known standards. FTIR and LC–MS/MS techniques were used to confirm the identity of the degradation product as 2-propenal, 2-methyl-, O-[(methylamino)carbonyl]oxime. 相似文献