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1.
Production of soft core/hard shell composite polymer particles by the stepwise heterocoagulation method with heat treatment 总被引:1,自引:0,他引:1
Soft core/hard shell composite polymer particle was prepared by the stepwise heterocoagulation, which was proposed by authors
in 1990, of many cationic hard small polymer particles (SPs) onto an anionic soft large polymer particle (LP). The powder
was obtained by freeze-drying at 0 °C which was higher than glass transition temperature of LP (−7 °C) and lower than that of SP (90 °C).
Received: 9 December 1997 Accepted: 12 May 1998 相似文献
2.
The hydrolysis of SbCl3 in hydrochloric acid solution (2.0 mol dm-3 HCl) at 0 °C yields an amor-phous product consisting of uniform spherical particles (d∼0.5 μm), which on continuous aging at the same temperature transform to larger crystals, indicated by XRD to be Sb4O5Cl2. In contrast, in the same solution kept at 25 °C crystalline particles of the same composition form directly after an induction
period and then grow with time. The final products, obtained at 0 °C and 25 °C consist of aggregated subunits. These powders
on calcination in nitrogen are converted to Sb2O3 and in air to Sb2O4.
Received: 23 June 1997 Accepted: 1 July 1997 相似文献
3.
H. Kühne A. Fischer T. Morgenstern D. Grützmacher 《Journal of Solid State Electrochemistry》1998,2(4):273-280
The effect of boron incorporation during chemical vapor deposition of SiGe thin films from silane, germane, diborane, and
hydrogen gas mixtures is investigated. It is shown that boron incorporation during SiGe thin-film growth degrades the Ge profile
under certain growth conditions when the boron concentration is high enough (>1019 cm−3). In single-wafer atmospheric-pressure processes we find that no Ge concentration depression occurs at deposition temperatures
above 675 °C. In multi-wafer atmospheric-pressure processes we find an increasingly occurring depression of the Ge concentration
along the wafer stack, even at temperatures above 675 °C. In low-pressure processes, high-level in-situ doping of SiGe with
boron is possible at temperatures as low as 550 °C without any degradation of the Ge profile. Thus LPCVD is superior to APCVD
with respect to high-level in situ doping of SiGe with boron. The presence or absence of Ge profile degradation in boron-doped
SiGe thin films is explained by the discussion of growth rate enhancement phenomena.
Received: 15 September 1997 / Accepted: 7 November 1997 相似文献
4.
In this work, we studied the adsorption of butane, toluene and nitric oxide on NaMordenite exchanged with different amounts
of silver. The reactions that occurred when the adsorbed hydrocarbons interacted with NO and the effect of water adsorption
were also addressed. Different silver species were formed after ion exchange and they were detected by TPR analysis. Highly
dispersed Ag2O particles were reduced at temperatures lower than 300 °C whereas Ag+ exchanged ions showed two TPR peaks, which can be ascribed to species exchanged at different mordenite sites. The TPD experiments
after adsorption of NO at 25 °C showed that the only desorbed species was NO2 which was formed by the total reduction of Ag2O particles. When the adsorbed butane was exposed to NO (1000 ppm), isocyanate species were formed on Ag+ ionic sites as well as Ag+–(NOx)–CO species. Toluene adsorption was stronger than butane since adsorbed toluene molecules were held even at 400 °C.
The characteristic bands of the aromatic ring C=C bond was observed as well as that of methyl groups interacting with Ag+ and Na+ ions. However, the appearance of carboxylic groups at temperatures above 300 °C in inert flow indicated the partial oxidation
of toluene due to Ag2O species present in the samples. After contacting adsorbed toluene with NO, different FTIR bands correspond to organic nitro-compounds,
isocyanate, cyanide and isocyanide species adsorbed on Ag+ ions, were detected. The presence of water inhibited the formation of NO2 species and the hydrocarbon adsorption on Na+ sites but did not affect the toluene-Ag+ interaction. 相似文献
5.
Leonardo Soriano Petri P. Ahonen Esko I. Kauppinen Jorge Gómez-García Carmen Morant Francisco J. Palomares Marta Sánchez-Agudo Patrick R. Bressler José M. Sanz 《Monatshefte für Chemie / Chemical Monthly》2002,133(6):849-857
Summary. A complete characterization of nanostructures has to deal both with electronic structure and dimensions. Here we present
the characterization of TiO2 nanoparticles of controlled size prepared by aerosol methods. The electronic structure of these nanoparticles was probed
by X-ray absorption spectroscopy (XAS), the particle size by atomic force microscopy (AFM). XAS spectra show that the particles
crystallize in the anatase phase upon heating at 500°C, whereas further annealing at 700°C give crystallites of 70% anatase
and 30% rutile phases. Raising the temperature to 900°C results in a complete transformation of the particles to rutile. AFM
images reveal that the mean size of the anatase particles formed upon heating at 500°C is 30 nm, whereas for the rutile particles
formed upon annealing at 900°C 90 nm were found. The results obtained by these techniques agree with XRD data.
Received October 5, 2001. Accepted (revised) December 6, 2001 相似文献
6.
R. Farazandeh G. H. Rounaghi M. Ebrahimi S. Basafa 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2017,91(4):678-684
The complexation reaction of Cd2+ cation with 2-hydroxy-1,4-naphthoquinone (HNQ) was studied in acetonitrile (AN), 2-PrOH, ethyl acetate (EtOAc), EtOH, dimethylformamide (DMF) and in binary solutions AN–2-PrOH, AN–DMF, AN–EtOH, and AN–EtOAc using conductometric method at 15–45°C. The conductance data show that the stoichiometry of the Cd2+ complex with HNQ in all solvent systems is 1 : 1. In the pure solvents the stability of the complex changes in the order AN > 2-PrOH > EtOH > DMF. The stability of the complex at 25°C in the studied mixtures changes in the following order : AN?EtOAc > AN?2-PrOH > AN?EtOH > AN?DMF. These orders are affected by the nature and composition of the solvent systems and by the temperature. From the temperature dependence data, the thermodynamic functions values (ΔH° and ΔS°) for the complex formation were calculated. 相似文献
7.
Uniform particles of manganese compounds obtained by forced hydrolysis of manganese(II) acetate 总被引:1,自引:0,他引:1
M. Ocaña 《Colloid and polymer science》2000,278(5):443-449
Procedures for the preparation at low temperature (80 °C) of uniform colloids consisting of Mn3O4 nanoparticles (about 20 nm) or elongated α-MnOOH particles with length less than 2 μm and width 0.4 μm or less, based on
the forced hydrolysis of aqueous manganese(II) acetate solutions in the absence (Mn3O4) or the presence (α-MnOOH) of HCl are described. These solids are only produced under a very restrictive range of reagent
concentrations involving solutions of 0.2–0.4 mol dm−3 manganese(II) acetate for Mn3O4 and of 1.6–2 mol dm−3 Mn(II) and 0.2–0.3 mol dm−3 HCl for α-MnOOH. The role that the acetate anions play in the precipitation of these solids is analyzed. It seems that these
anions promote the oxidation of Mn(II) to Mn(III), which readily hydrolyze causing precipitation. The evolution of the characteristics
of the powders with temperature up to 900 °C is also reported. Thus, Mn3O4 particles transform to Mn2O3 upon calcination at 800 °C; this is accompained by a sintering process. The α-MnOOH sample also experiences several phase
transformations on heating. First, it is oxidized at low temperatures (250–450 °C) giving MnO2 (pyrolusite), which is further reduced to Mn2O3 at 800 °C. After this process the particles still retain their elongated shape.
Received: 19 October 1999 Accepted: 24 November 1999 相似文献
8.
A novel surfactant peptide consisting of an arginine cation with laurate anion has been synthesized, purified and characterized.
The critical micellar concentration (cmc) of peptide in aqueous solutions has been determined using spectroscopic techniques
and is found to increase from 0.06 to 0.11 mM with increasing temperature (15–45 °C). Cmc is also determined in the presence
of salts like NaCl, KCl and sodium acetate and it is found that these electrolytes hinder aggregation with a significant increase
in the case of sodium acetate. The aggregation number of the surfactant peptide has been determined using fluorescence quenching
measurements and is observed to decrease from 14 to 6 with increasing temperature (15–45 °C). The standard free energy change
(ΔG
0
m) and standard enthalpy change (ΔH
0
m) of the peptide aggregate are found to be negative with a small positive value for standard entropy change (ΔS
0
m). The peptide aggregate seems to undergo phase transition above 50 °C as observed from UV–vis and fluorescence spectroscopy.
From pyrene binding studies, it is shown that the interior dielectric constant increases from 5.08 at 34 °C to 8.77 at 50 °C
and further decreases with increase in temperature indicating a phase change at 50 °C. Also, the ratio of excimer intensity
to monomer intensity, which is a measure of microviscosity of the aggregate, decreases with increase in temperature with a
change at 50 °C indicating a phase change.
Received: 14 February 1997 Accepted: 13 August 1997 相似文献
9.
Latexes as dispersions of poly(methyl methacrylate-co-butyl methacrylate) copolymeric nanoparticles within water were produced by microemulsion polymerization of the respective
comonomers. Polymer yield, number-average and weight-average molecular weights, polydispersity index, and the glass-transition
temperature of the copolymer produced were 50%, 8.8 × 104, 2.54 × 105, 2.87, and 45 °C. Scanning tunneling microscopy (STM) images of the latex nanoparticles and film formation on highly oriented
pyrolitic graphite (HOPG) were obtained with a 2 V sample bias and a tunneling current of 20 pA. The STM pictures revealed
that the particle size was 18 ± 3 nm. There was no film formation in the case of dehydration at room temperature. There was
some coalesence of particles when the HOPG surface was preheated at 55 °C, while complete film formation was achieved when
the latexes were annealed at 55 °C in an oven for about 10 min.
Received: 23 August 1999 Accepted: 17 January 2000 相似文献
10.
Jie Cai Jia Guo Minglei Ji Wuli Yang Changchun Wang Shoukuan Fu 《Colloid and polymer science》2007,285(14):1607-1615
Fe3O4/SiO2/poly (N-isopropylacrylamide-co-N,N-dimethylaminoethyl methacrylate) [P(NIPAM-co-DMA)] multiresponsive composite microspheres with core–shell structure were synthesized by template precipitation polymerization.
First, the magnetite nanoparticles were coated with silica and then modified with 3-(trimethoxysilyl)-propyl methacrylate
(MPS). Subsequently, the Fe3O4/SiO2 particles grafted with MPS were used to seed the precipitation copolymerization of NIPAM and DMA. The composite microspheres
with core–shell structure were superparamagnetic, pH-sensitive, and thermoresponsive. The swelling ratio (D25 °C,
pH = 3/D50 °C,
pH = 9)3 coupling of pH and temperature increased up to 21.2, which was much higher than that without comonomer DMA. 相似文献
11.
S. Yamaguchi 《Colloid and polymer science》1998,276(8):715-722
Phase behavior of water/hexaethyleneglycol dodecyl ether (C12EO6)/propanol/heptane system was investigated in a composition–temperature space (25–30 °C) at atmospheric pressure. A cone-like three-phase body consisting of aqueous (W), surfactant (Dp), and oil (O) phases is
formed in the two-phase body of Wm (aqueous micellar phase)+O at 30.0 °C. With decreasing temperature the three-phase body becomes thinner and finally disappears at a critical double end point
(CDEP) where the two critical end points of W and Dp phases are merged. The CDEP exists at about 26.2 °C (T
CDEP). The hydrophile–lipophile balance (HLB) of the mixed amphiphile changes towards lipophilic on addition of propanol. As a
result, the Wm phase separates into two phases W+Dp above the T
CDEP. Further addition reduces the lipophobicity of aqueous media (or the solvophobicity of the mixed amphiphile), and the W and
Dp phases are merged again. Below T
CDEP, since C12EO6 becomes much hydrophilic, the change of HLB lurks and a middle phase (Dp) cannot be observed.
Received: 19 June 1997 Accepted: 20 March 1998 相似文献
12.
M. Fujiwara T. Okano T. -H. Nakashima A. A. Nakamura G. Sugihara 《Colloid and polymer science》1997,275(5):474-479
For a sodium salt of α-sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, critical micellization
concentration (CMC), solubility and degree of counterion binding (β) were determined by means of electrocon-ductivity measurements
at different temperatures (at every 5 °C) ranging from 15 to 50 °C. The phase diagram of 14SFNa in pure water was constructed
from the CMC- and solubility-temperature data, in which the Krafft temperature (critical solution temperature) was found around
0 °C. The changes in the Gibbs energy, ΔG
0
m, enthalpy, ΔH
0
m, and entropy, ΔS
0
m, upon micelle formation as a function of temperature were evaluated taking βvalues into calculation.
Received: 28 August 1996 Accepted: 5 November 1996 相似文献
13.
Monodispersed polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) composite particles having 9.4 μm in diameter were produced by seeded polymerization for the dispersion
of highly n-butyl methacrylate (BMA)-swollen PS particles, and their morphologies were examined. The highly BMA-swollen PS particles
(about 150 times the weight of the PS seed particles) were prepared by mixing monodispersed 1.8 μm-sized PS seed particles
and 0.7 μm sized BMA droplets prepared with an ultrasonic homogenizer in ethanol/water (1/2, w/w) medium at room temperature.
After NaNO2 aqueous solution as inhibitor was added in the dispersion, the seeded polymerization was carried out at 70 °C. In an optical
microscopic observation, one or two spherical high contrast regions which consisted mainly of PS were observed inside PS/PBMA
composite particles. In the PS domain, there were many fine spherical PBMA domains. Such morphologies were based on the phase
separation of PS and PBMA within the homogeneous swollen particles during the seeded polymerization.
Received: 04 June 1997 Accepted: 27 August 1997 相似文献
14.
P. Bermejo-Barrera Antonio Moreda-Piñeiro Jorge Moreda-Piñeiro Adela Bermejo-Barrera 《Analytical and bioanalytical chemistry》1997,358(7-8):844-847
Rapid methods were developed for the direct determination of Ag, Al, Cd and Mn in cocaine and heroin by ETAAS using programmes
omitting the charring step . Sample pretreatment was simple: dissolution in ultrapure water or in 35.0% (v/v) HNO3 for heroin or cocaine, respectively. Optimum drying temperatures were 250 °C for Ag, Al and Mn, and 300 °C for Cd. The run
cycles were 35 and 37 s, for Ag and Al respectively, and 36 s for Cd and Mn. The best results were obtained with Pd, Mg(NO3)2 and (NH4)2HPO4, as chemical modifiers. The limits of detection were 8.6, 55.9, 2.2 and 12.4 μg kg-1 for Ag, Al, Cd and Mn, respectively.
Received: 14 November 1996/Revised: 14 January 1997/Accepted: 18 January 1997 相似文献
15.
Mahmoud M. Khader Mahmoud M. Saleh Emad M. El-Naggar 《Journal of Solid State Electrochemistry》1998,2(3):170-175
Active ferric tungstate was prepared by fusing an equimolar mixture of tungsten oxide and ferric oxide at 1100 °C and annealing
at 800 °C for 20 h. Analysis of the electrode material by X-ray diffraction showed that its composition was Fe2WO6. When this material was illuminated by visible light in 0.1 M NaOH solution, an anodic photocurrent at a positive potential
of 0.5 V (SCE) was obtained. Therefore, this material is considered as an n-type semiconductor. The d.c. conductivity of this
material at 25 °C was 4 × 10−6 Ω−1 cm−1. In the dark, unexpectedly high anodic currents were observed at positive potentials of 0.8 V (SCE) in 0.1 M NaOH. These
currents are attributed to the existence of a high density of electron-hole recombination centers within the band-gap of ferric
tungstate. When dimethyl viologen (DMV) was used as an electroactive compound in the electrolyte, the anodic photocurrents
increased significantly. The oxidation of DMV is thus expected to compete with the electron-hole recombination process. Furthermore,
the process of electron-hole recombination was also predicted from the shape of the photocurrent transients under interrupted
illumination. These transients exhibited first-order relaxation effects in the region of the onset time of the photocurrents.
The band-gap energy of Fe2WO6 was found to be about 1.5 eV and its flat-band potential in 0.1 M NaOH was about −0.3 V (SCE). The photoelectrochemical properties
of ferric tungstate are explained according to the formalism of the band model of the semiconductor/electrolyte interface.
Received: 16 July 1997 / Accepted: 26 September 1997 相似文献
16.
Ultra-high-molecular-weight polyethylene (UHMWPE) – carbon black (CB) blends were prepared by gelation/ crystallization from
PE dilute solutions containing CB particles. The UHMWPE/CB composition chosen were 1/0.15, 1/0.25, 1/0.5, 1/0.75, 1/1, 1/3,
1/5, and 1/9, etc. The cross-linking of PE chains was performed by chemical reaction of dicumyl-peroxide at 160 °C. X-ray diffraction patterns indicate that the crystallinity of PE within the blends decreased drastically through the chemical
reaction at high temperature. The sample preparation method by gelation/crystallization provided the UHMWPE–CB system with
various CB contents up to 90% and the conductivities for the resultant specimens were in the range from 10-9 to 1 Ω-1 cm-1 corresponding to the electric conductivity range of semiconductors. The blends assured thermal stability of electric conductivity
by cross-linking of PE chains, although the mechanical property such as the storage and loss moduli were very sensitive to
temperature. The conductivity of the blends with CB content ≥20% were almost independent of temperature up to 220 °C and the values in the heating and cooling processes were almost the same. On the other hand, for the UHMWPE–CB blends with
13% CB content corresponding to the critical one, temperature dependence of electric resistivity showed positive temperature
coefficient (PTC) effect. The PTC intensities for non-cross-linked and cross-linked materials were lower than that of the
corresponding low-molecular-weight-polyethylene (LMWPE)–CB blend but the maximum peak appeared at 160 °C which is higher than the peak temperature of LMWPE–CB blend.
Received: 10 December 1997 Accepted: 9 April 1998 相似文献
17.
Qin Wang Yanbing Zhao Yajiang Yang Huibi Xu Xiangliang Yang 《Colloid and polymer science》2007,285(5):515-521
In situ gelable poly(N-isopropylacrylamide-co-acrylamide) microgels were prepared by precipitation polymerization in the presence of various amounts
of N,N′-methlenebisacrylamide as a crosslinker. The diameters of microgels were in the range of 200–300 nm with narrow distributions
as determined by photo correlation spectroscopy. The equilibrium swelling ratio and thermosensitive properties of the microgels
increased with decreasing crosslinker content. The volume phase transition of microgels dispersions at high concentrations
were investigated by phase diagrams. The microgels dispersions experienced four phases when the temperature was increased:
semitranslucent swollen gel, clear flowable suspension, cloud flowable suspension, and white shrunken gel. The related phase
transition temperatures were influenced by crosslinker content and the concentration of the microgel dispersions. Herein,
the gelation temperature was changed by more than 20 °C, shrinking temperatures were slightly changed by about 3 °C, and cloud
point temperatures showed almost no change. The three phase transition temperatures of microgels dispersed in phosphate-buffered
saline solutions were lower than that in water. As drug carriers, the release rates of bleomycin from bleomycin-loaded microgel
dispersions exhibited diffusion control at human body temperature. 相似文献
18.
Summary. The influence of reaction conditions (temperature, type of catalyst, time) on the base-catalyzed reaction of mono-, di-,
and trialkylphosphates (alkyl = methyl, ethyl, i-propyl, n-butyl) with Ca2+ ions and on the structure and composition of the reaction products was studied. The composition of the calcium phosphates
depends mainly on the reaction temperature. At temperatures below 100°C, a nanocrystalline solid product transforming into
dicalcium phosphate by heating (calcination) was found. Pure nanocrystalline hydroxyapatite was prepared by hydrothermal synthesis
at 160°C from mono- and dialkylphosphates. The size of hydroxyapatite crystallites was about 1 nm, the particle size about
150 nm. Agglomerated particles of hydroxyapatite larger than 2 μm were prepared at 200°C. Hydrothermal reaction of trialkylphosphates
with Ca2+ ions at 200°C produced CaHPO4. The experimental results were used to propose a reaction mechanism for base-catalyzed hydrothermal reactions of alkylphosphates
with Ca2+ ions.
Received October 4, 2001. Accepted (revised) November 19, 2001 相似文献
19.
The gel beads of N-normal-propylacrylamide are prepared by the radical copolymerization of N-normalpropylacrylamide and N,N′-methylene-bis-acrylamide in water. The optimum reaction conditions to obtain the gel beads are revealed from the phase diagram
of the reaction system together with the scanning electron microscopy of the reaction products. The scanning electron microscopy
of the reaction products also indicates the formation of the spherical gel beads of sub-micron size ranging from 250 to 500 nm
in diameter. The viscosity measurements of the suspension of the gel beads indicate that the concentration dependence of the
viscosity of the suspension is well described by Einstein’s theory of the viscosity of colloidal particles. The intrinsic
viscosity of the suspension of gel beads is then determined. The density of the gel beads, which was obtained from the intrinsic
viscosity of the suspension, indicates that the gel beads are in the swollen state at a temperature of 20 °C.
Received: 12 September 1997 Accepted: 17 December 1997 相似文献
20.
Characterization, Solution Behavior, and Microstructure of a Hydrophobically Associating Nonionic Copolymer 总被引:1,自引:0,他引:1
To obtain an oil-displacement polymer with good thermal stability and solution properties, self-assembling acrylamide (AM)/4-butylstyrene
(BST) copolymers (PSA) were synthesized by the micellar copolymerization technique. The resulting polymer was characterized
by elemental analysis and UV and FT-IR spectroscopy. Conventional DSC measurement was used successfully to characterize the
hydrophobic microblock structure of PSA, and two glass transition temperatures were found in the polymer: at 203 °C for the
AM segments and at 106 °C for the hydrophobic BST segments. The initial decomposition temperature (234 °C) of the polymer
is higher than that of polyacrylamide (210 °C). The DSC and TG results suggest that incorporation of BST into PSA enhances
the molecular rigidity and thermal stability of the polymer. The apparent viscosity of a PSA solution greatly depends on the
amount of BST in the polymer, and the polymer exhibits salt-thickening, temperature-thickening, thixotropy, pseudo-plastic
behavior, anti shearing, and good anti-aging properties at 80 °C. In addition, the apparent viscosities of PSA solutions are
increased remarkably by the addition of a small amount of surfactant. AFM measurements show that large block-like aggregates
and small compact aggregates are formed in aqueous solutions of 0.4 g⋅dL−1 PSA because of strong intermolecular hydrophobic associations, despite the low molecular weight, and their sizes increase
upon addition of a small amount of salt. 相似文献