共查询到20条相似文献,搜索用时 31 毫秒
1.
The analysis of the interaction of micelles formed by a blockcopolymer is given by means of small-angle X-ray (SAXS) and
small-angle neutron scattering (SANS). The blockcopolymer consists of poly(styrene) and poly(ethylene oxide) (molecular weight
of each block: 1000 g/mol) and forms well-defined micelles (weight-association number: 400, weight-average diameter: 15.4 nm)
in water. The internal structure has been studied previously (Macromolecules 29:4006 (1996)) by SAXS. There it has been shown
that the micelles are spherical objects. The structure factor S(q) as a function of the scattering vector q (q=(4π/λ) sin (θ/2); λ: wavelength of the radiation in the medium; θ: scattering angle) can be extracted from both sets of small-angle
scattering data (SANS: q≤0.4 nm-1; SAXS: q≤0.6 nm-1). It is shown that particle interaction in the present system can be described by assuming soft interaction which is modeled
by a square-step potential.
Received: 12 May 1997 Accepted: 9 July 1997 相似文献
2.
Isothermal equilibrium adsorption experiments were carried out to study the adsorption of concanavalin A (Con A) on dextran-modified
poly(methyl methacrylate) (PMMA) latex particles. Three PMMA particles with various levels of dextran modification were selected
for study: 0% (designated as D0), 1.24% (D20), and 2.45% (D75) based on total polymer weight. The Langmuir model is applicable
to both D0 and D20 systems, although the data for the D20 system are somewhat scattered. On the other hand, the amount of
Con A adsorbed per gram polymer particles (q*) versus the Con A concentration in water (c*) curve for the D75 system cannot be described by the Langmuir model. The deviation is attributed to the formation of a crosslinked
network structure, caused by specific binding of the dimeric Con A molecules onto two neighboring particles with grafted dextran.
The ratio of the initial number of Con A molecules to the initial number of active binding sites on the dextran-modified particle
surface plays an important role in determining the structure of flocs formed. The maximum amount of Con A adsorbed on the
particle surface (q
max) is of the order of 10−1 μmol per gram particles and q
max in decreasing order is D75 > D20 > D0. The dissociation constant of the Con A-D20 (or Con A-D75) pair is of the order of
10−1 μmol dm−3 which is 1 order of magnitude smaller than that of the Con A-D0 pair. Thus, the electrostatic interaction between Con A and
D0 is much weaker than the affinity interaction between Con A and D20 (or D75). An empirical model is proposed to qualitatively
explain the q* versus c* data.
Received: 18 June 1998 Accepted in revised form: 24 December 1998 相似文献
3.
M. D. Lechner Helmut Cölfen Vikas Mittal Antje Völkel Wendel Wohlleben 《Colloid and polymer science》2011,289(10):1145-1155
Analytical ultracentrifugation is one of the most powerful methods for the characterization of nanoparticles since the days
of its invention due to its high resolution and statistical significance. Latexes with different sizes and their mixtures
have been measured by sedimentation with the analytical ultracentrifuge (AUC) OPTIMA XL-I (Beckman Coulter, Palo Alto, CA,
USA) with interference optics at λ
0 = 675 nm and absorption optics at λ
0 = 546 and 263 nm. Additionally, a blue pigment with high absorption characteristic at visible light has been investigated.
A large influence of Mie scattering and Mie absorption on the particle size distribution with respect to absorption optics
and samples with moderate or broad size distribution is observed. Therefore, the consideration of the Mie scattering effect
is compulsory for most AUC measurements of nanoparticles with absorption optics. 相似文献
4.
The molecular order and phase transitions of two smectic poly(ester imide)s based on aminobenzoic acid trimellitimide (PEI
1) or aminocinnamic acid trimellitimide (PEI 2) and α,ω-dihydroxydodecane were investigated by X-ray scattering. During cooling,
the polymers pass through monotropic smectic liquid-crystalline (LC) phases (SA, SC), which transform into higher-ordered smectic-crystalline phases (SE, SH). The smectic layer structure of about 3 nm gives rise to a sharp reflection at 2θ ≅ 3°. Peak shape analysis and analysis
of the interface distribution function revealed long-range longitudinal correlation among the mesogens in the LC phase but
short-range lateral correlation. The development of a broad reflection in the small-angle X-ray scattering (SAXS, 2θ < 1°)
indicates the formation of a lamellar two-phase system. The long-period changes reversibly between 10 and 30 nm with increasing
temperature. The crystalline lamellae comprise a number of smectic-crystalline layers with packed mesogens, while the noncrystalline
interlamellar regions keep their smectic-LC order. In the metastable SB phase, formed during annealing of quenched PEI 1, the diffuse SAXS indicates a random distribution of small, probably fringed,
crystals with hexagonal-packed mesogens. In the lamellar SE and SH phases, tie molecules play an important role, but chain folding cannot be excluded.
Received: 16 July 1999/Accepted: 28 April 2000 相似文献
5.
6.
A turbidimetric analysis of particle interaction in latex suspensions is given. The turbidity measured at different wavelengths can be rendered by the product of an integrated form factorQ(2) and a suitably defined integrated structure factorZ(2,c). This factorization rests on the expansion of the form factor of the particlesP(q) and the structure factorS(q) [q=(4/)sin(/2); : scattering angle] of the system in even powers ofq. The accuracy of this approximation has been shown by calculating the turbidity for a system of hard spheres in terms of the Percus-Yevick structure factor by numerical integration. Also, the effect of polydispersity has been taken into account within the frame of Percus-Yevick-Vrij theory for non-uniform hard spheres. It is shown that the influence of small polydispersity (standard deviation below 8%) is within experimental uncertainty. The method is applied to precise UV-spectra (400800 nm) obtained from a polystyrene latex with a diameter of 77.4 nm. The integrated structure factorZ(2,c) obtained experimentally can be interpreted in terms of an effective diameter of interaction giving a measure for the strength of electrostatic interaction. 相似文献
7.
A small-angle x-ray scattering (SAXS) study of latex particles consisting of a polystyrene (PS) core and a polymethylmethacrylate (PMMA) shell in theq-range 0.037 nm–1q1.5 nm–1 (q=(4/) sin (/2); : scattering angle) is reported. The particle size distributions of the latices have been determined by ultracentrifugation and allow a quantitative comparison of the experimental scattering intensities with theoretical models. The data obtained for the PS/PMMA latex are shown to be consistent with the proposed core-shell morphology. Separate studies of the PS-core-latex demonstrate that the amount of surfactant being adsorbed on the surface of the particles can be monitored directly. All results show that SAXS is well-suited to study the structure of latex particles in great detail. 相似文献
8.
V. A. Mjagchenkov V. Y. Proskurina Y. Y. Gromova G. V. Bulidorova 《Colloid and polymer science》2001,279(5):468-478
The sedimentation kinetics of an ochre suspension in salt (NaCl)-containing aqueous media was studied in the presence of
ionogenic (anionic, A, and cationic, C) acrylamide copolymers with high molecular weight (M > 2 × 106) using a VT–0.5 torsion balance. The ionic strength of the dispersion medium varied in the wide range from 0.001 N to 0.4 N.
The flocculation proceeded predominantly by a `bridge' mechanism, and the fraction of macromolecules inactive in the acts
of floccule formation was significantly higher for C copolymer as compared with A copolymer. A drastic fall in the flocculating
activities of A and C copolymers when passing from salt-free to salt-containing media is caused mainly by two following events:
1. The change in the conformational state of macromolecules, primarily, in their effective dimensions
2. The participation of a certain part of electrolyte in the formation and modification of an electrical double layer around
disperse phase particles
After introducing binary compositions of A and C flocculants into salt-containing media their resultant flocculating effect
depends on the introduction mode of polymeric components. A strong difference in the magnitudes of the flocculating effect
for A and C copolymers is observed in water. In the region of high ionic strengths (0.1–0.4 N) this difference becomes far
less distinct. The flocculating activities of A and C copolymers were compared when introduced as the first (λA and λC) and the second (λA
′ and λC
′) additives. It was shown that λA/λA
′>1 and λC/λC
′>1.
Such relationship between λA and λA
′, λC and λC
′ indicates that selective interactions between A and C copolymers play an essential role in the flocculation processes. The
last statement was indirectly confirmed in the present work by the data of electrochemical and viscosimetric studies. When
using C copolymer as the second additive in the region of low ionic strengths its main function undergoes reversal, and the
copolymer begins to operate not as a flocculant, but as a stabilizer of disperse phase particles (λC < 0).
Received: 14 April 2000 Accepted: 4 August 2000 相似文献
9.
Atsushi Suzuki Motoyasu Fujiwara Masahiko Nishijima 《Colloid and polymer science》2008,286(5):525-534
We have studied the magnetic properties of an Fe(II) spin-crossover complex near its high spin/low spin (HS/LS) phase transition
in the emulsion polymerization of trifluoroethylmethacrylate (TFEMA) using poly(vinyl alcohol) (PVA) as a protective colloid,
in comparison with sodium lauryl sulfate (SLS). Morphological analysis was used to establish that the nanodispersed spin-crossover
complex was incorporated into the cores of polymer particles covered with PVA shells. The obvious bi-stability of the HS/LS
phase transition was considered by the identification of multiplet states such as the triplet (S = 1) and quintet (S = 2) states, and the paramagnetic state (S = 1/2), by noting a gradual shift of g-value anisotropy in the electron spin resonance (ESR) spectrum at 5 K. This was thought to have arisen from the exchange
interaction as a Jahn–Teller effect in the emulsion particles. Chemical modifications such as ligand substitution, and the
nature of the central metal atom in the emulsion particle, especially influenced the HS/LS phase transition. 相似文献
10.
Srabanti Ghosh S. C. Bhattacharya Abhijit Saha 《Analytical and bioanalytical chemistry》2010,397(4):1573-1582
The gamma irradiation method has provided a route for synthesis of highly water-soluble, good-quality luminescent CdS/dendrimer
nanocomposites with amino- or carboxyl-terminated PAMAM dendrimer. An attempt has been made to probe ascorbic acid with the
as-synthesized CdS/dendrimer nanocomposites (DNC). Ascorbic acid (AA) is an important biological antioxidant and marker for
different diseases in clinical chemistry as well as in quality control in the food industry. Micromolar concentrations of
AA significantly quenched the photoluminescence (PL) of both amino (–NH2) and carboxylic (–COOH) functionalized semiconductor nanocomposites. The quenching followed a linear Stern–Volmer equation
and time-resolved photoluminescence spectroscopy confirmed its static nature. A strong size dependence of the quenching pattern
was observed. The binding constants, and the corresponding thermodynamic parameters ΔG
θ, ΔH
θ, ΔS
θ at different temperatures were calculated. CdS DNC showed selectivity towards ascorbic acid even in the presence of possible
interfering molecules, such as uric acid, tartaric acid and citric acid. Nanocomposites-based assay techniques could override
the complications involved in multitudes of assay procedures, providing a simple and fast new strategy for the quantification
of Ascorbic acid in the range of 16.6 to 100 μM (R = 0.998, n = 9). The proposed method was applied to the detection of ascorbic acid in Vitamin C tablets with satisfactory results. 相似文献
11.
The temperature dependence of the dimensions of poly(N-isopropylacrylamide) (PNIPAM) adsorbed on two different colloidal silica particles was studied with dynamic light scattering.
The hydrodynamic diameter was measured when the temperature was varied stepwise from 10 to 60 °C. PNIPAM molecules free in
solution undergo a conformational transition at the θ temperature. We have found that PNIPAM adsorbed onto silica particles
also undergoes a transition below the θ temperature. When a small amount of polymer was adsorbed the coil-to-globule transition
at the θ temperature did not occur. Potentiometric titrations showed that the surface charge of the silica particles was not
affected by the polymer adsorption. Sodium dodecyl sulfate (SDS) (100–1200 mg/l) was added to improve the stability. The particles
with a higher zeta potential required a smaller addition of SDS to prevent coagulation compared to the particles with a smaller
surface potential. For low additions of SDS the transition curves of adsorbed PNIPAM were unaffected. For larger additions
of SDS the collapse of PNIPAM was shifted to higher temperatures. When as much as 1200 mg/l SDS was added, two regions with
weak transitions were observed before the collapse. It was also observed that the presence of SDS results in a smaller adsorption
of PNIPAM onto the particles. The addition of SDS strongly increased the magnitude of the electrophoretic mobility of the
polymer–particle unit. From the electrophoretic measurements an electrokinetic layer thickness was calculated and it was found
to be smaller than the corresponding hydrodynamic layer thickness, as obtained by dynamic light scattering.
Received: 14 December 1999/In revised form: 22 February 2000/Accepted: 6 March 2000 相似文献
12.
The reentrant behavior of Poly(vinyl alcohol) (PVA)–borax aqueous semidilute solutions with a PVA concentration of 20 g/l
and borax concentrations varies from 0.0 to 0.20 M was investigated using dynamic light scattering (DLS) and dynamic viscoelastic
measurements. Two (fast and slow modes) and three (fast, middle, and slow) relaxation modes of PVA semidilute aqueous solutions
without and with the presence of borax, respectively, were observed from DLS measurements. The fast and middle relaxation
modes were q
2-dependent (q is the scattering vector) characteristic of diffusive behavior; however, the slow modes were q
3-dependent, characteristic of intraparticle dynamics. The experimental results showed that the slow relaxation mode dominates
the DLS relaxation. The DLS slow mode relaxation time, τs, and the viscoelastic modulus G′(ω) and G′′(ω) data had a similar trend and demonstrated reentrant behavior as the borax concentration was increased from 0.0 to 0.20 M,
i.e. τs, G′(ω), and G′′(ω) fluctuated with increasing borax concentration. The excluded-volume effect of polymers, charge repulsion among borate
ions bound on PVA molecules, and intermolecular cross-linking didiol–borate complexation caused an expansion of the polymer
chain; however, the screening effect of free Na+ ions on the negative charge of the borate ions bound on PVA and intramolecular cross-linking didiol–borate complexation led
to a shrinkage of the polymer chain. The reentrant behavior was the consequence of the balance between expansion and shrinkage
of the PVA–borate complex.
Received: 26 March 1999/Accepted in revised form: 3 September 1999 相似文献
13.
N. Hattori H. Hirata H. Okabayashi M. Furusaka C. J. O'Connor R. Zana 《Colloid and polymer science》1999,277(1):95-100
The microstructure of the normal micelles formed by dimeric surfactants with long spacers, [Br−(CH3)2N+(C
m
H2
m
+1)-(CH2)
S
-(C
m
H2
m
+1)N+(CH3)2Br−, m = 10 and s = 8, 10 and 12], has been investigated by small-angle neutron scattering and compared with previously reported results for
micelles of the same dimeric surfactants with shorter spacers (m = 10 and s = 2, 3, 4 and 6). It was found that for dimeric surfactants with long spacers (s = 8 and 10), both micellar growth and variation in shape occur to only a small extent, if at all, compared with dimeric surfactants
with short spacers. However, for the dimeric surfactant with the longest spacer, s = 12, the extent of micellar growth and shape variation is also large. These results are due to the differences in conformation
of dimeric surfactants with short spacers (s = 2–6) compared with that of the surfactants with long spacers (s = 8–12).
Received: 15 June 1998 Accepted: 22 July 1998 相似文献
14.
A. I. Nekhaev 《Russian Journal of General Chemistry》2009,79(11):2317-2320
Approximate dependence of the refraction of sulfur atom (R
D) on its charge (q
S) is determined. On its basis R
D
S values in different sulfur compounds were calculated. Refraction of the unshared electron pair on sulfur atom was found to
be equal to 0.96. Refraction increments (Δ = MR
Dfound − MR
Dcalc) of sulfur-containing saturated heterocycles were calculated (thietanes Δ = −0.28, thiolanes Δ = −0.28, thianes Δ = −0.24)
as well as the refraction of deuterium atom bound with carbon (1.10). The values of q
S and R
D
S in sulfoxides (−0.1 and 6.5 respectively), in sulfones (0.72 and 3.73 respectively), q
S in dialkyl sulfides (−0.25), and also R
D of S4+ ion (0.77) were refined. 相似文献
15.
Coupled-cluster (CC) theory including single (S) and double (D) excitations and carried out with a spin-unrestricted Hartree–Fock
(UHF) reference wave function is free from S + 1 spin contamination as can be confirmed by an analysis of the expectation value of the spin operator, Ŝ
2. Contamination by the S + 2 contaminant can be projected out by an approximate procedure (APCCSD) with a projection operator, P^, represented by the product of the spin annihilation operators ?
s+
1 and ?s+2. The computational cost of such a projection scales with O(M
6) (M is the number of basis functions). The APCCSD energy obtained after annihilation of the S + 2 contaminant can be improved by adding triple (T) excitations in a perturbative way, thus leading to APCCSD(T) energies.
For the 17 examples studied, the deviation of the UHF-CCSD(T) energies from the corresponding full configuaration interaction
values is reduced from 4.0 to 2.3 mhartree on the average as a result of annihilating the S + 2 contaminant in an approximate way. In the case of single-bond cleavage, APCSSD leads to a significant improvement of
the energy in the region where the bonding electrons recouple from a closed shell to an open shell singlet electron pair.
Received: 13 April 2000 / Accepted: 12 July 2000 / Published online: 24 October 2000 相似文献
16.
Summary. The two new compounds Mn(dien)2[MoS4] (1) and Mn(dien)2[Mo2O2S6] (2) (dien = diethylenetriamine) were prepared under solvothermal conditions. Both compounds were obtained as phase-pure products. The
structures consist of new [Mn(dien)2]2+ cations and isolated tetrahedral [MoS4]2− (1) or [Mo2O2S6]2− (2) anions. Between the anions and the cations, hydrogen bonding is observed. Compound 1 crystallizes in the tetragonal space group I (a = 10.219(2), c = 9.259(2) ?, Z = 2), whereas 2 crystallizes in the monoclinic space group P21/c (a = 8.703(2), b = 18.390(4), c = 14.603(3) ?, β = 103.18(3)°, Z = 4). The thermal behaviour of the thiomolybdates was investigated using difference thermoanalysis (DTA) and thermogravimetry
(TG). Both compounds decompose under argon with a single endothermic signal in the DTA curve (peak maximum: 252 (1) and 242°C (2)).
Received November 5, 2001. Accepted December 27, 2001 相似文献
17.
The two new compounds Mn(dien)2[MoS4] (1) and Mn(dien)2[Mo2O2S6] (2) (dien = diethylenetriamine) were prepared under solvothermal conditions. Both compounds were obtained as phase-pure products. The structures consist of new [Mn(dien)2]2+ cations and isolated tetrahedral [MoS4]2− (1) or [Mo2O2S6]2− (2) anions. Between the anions and the cations, hydrogen bonding is observed. Compound 1 crystallizes in the tetragonal space group I (a = 10.219(2), c = 9.259(2) ?, Z = 2), whereas 2 crystallizes in the monoclinic space group P21/c (a = 8.703(2), b = 18.390(4), c = 14.603(3) ?, β = 103.18(3)°, Z = 4). The thermal behaviour of the thiomolybdates was investigated using difference thermoanalysis (DTA) and thermogravimetry (TG). Both compounds decompose under argon with a single endothermic signal in the DTA curve (peak maximum: 252 (1) and 242°C (2)). 相似文献
18.
Starting with Kirkwood's Fokker–Planck equation for the polymer configuration-space distribution function and using the Zwanzig–Mori projection operator technique we have calculated the scattering law S(q,w) for a freely jointed model polymer chain in a dilute solution. When memory effects are neglected, the theory predicts a Lorentzian for S(q,w) with a halfwidth Ω(q), which we have determined as a function of the momentum transfer q for all values of q. The results are compared with recent neutron scattering experiments on deuterated polytetrahydrofuran and polystyrene in dilute solution in CS2. It is found that the observed q dependence of Ω(q) is represented satisfactorily by the present theory with a bond length b of about 6.3 Å for polystyrene and 3.8 Å for polytetrahydrofuran, and a friction coefficient ζ = 4πη0b where η0 is the viscosity of the solvent. 相似文献
19.
Quasielastic light scattering measurements are reported for experiments performed on mixtures of gelatin and glutaraldehyde
(GA) in the aqueous phase, where the gelatin concentration was fixed at 5 (w/v) and the GA concentration was varied from 1×10−5 to 1×10−3 (w/v). The dynamic structure factor, S(q,t), was deduced from the measured intensity autocorrelation function, g
2(τ), with appropriate allowance for heterodyning detection in the gel phase. The S(q,t) data could be fitted to S(q,t)=Aexp(−D
f
q
2
t)+Bexp(−t/τc)β, both in the sol (50 and 60 ∘C) and gel states (25 and 40 ∘C). The fast-mode diffusion coefficient, D
f showed almost negligible dependence on the concentration of the crosslinker GA; however, the resultant mesh size, ξ, of the
crosslinked network exhibited strong temperature dependence, ξ∼(0.5−χ)1/5exp(−A/RT) implying shrinkage of the network as the gel phase was approached. The slow-mode relaxation was characterized by the stretched
exponential factor exp(−t/τc)β. β was found to be independent of GA concentration but strongly dependent on the temperature as β=β0+β1
T+β2
T
2. The slow-mode relaxation time, τc, exhibited a maximum GA concentration dependence in the gel phase and at a given temperature we found τc(c)=τ0+τ1
c+τ2
c
2. Our results agree with the predictions of the Zimm model in the gel case but differ significantly for the sol state.
Received: 25 May 1999 /Accepted in revised form: 27 July 1999 相似文献
20.
Comparison between Different Hydrolysis Processes of Vine-Trimming Waste to Obtain Hemicellulosic Sugars for Further Lactic Acid Conversion 总被引:1,自引:0,他引:1
Moldes AB Bustos G Torrado A Domínguez JM 《Applied biochemistry and biotechnology》2007,143(3):244-256
Trimming vine shoot samples were treated with water under selected operational conditions (autohydrolysis reaction) to obtain
a liquid phase containing hemicellulose-decomposition products. In a further acid-catalyzed step (posthydrolysis reaction),
xylooligosaccharides were converted into single sugars for the biotechnological production of lactic acid using Lactobacillus
pentosus. A wide range of temperatures, reaction times, and acid concentrations were tested during the autohydrolysis–posthydrolysis
process to investigate their influence on hemicellulose solubilization and reaction products. The maximum concentration of
hemicellulosic sugars was achieved using autohydrolysis at 210 °C followed by posthydrolysis with 1% H2SO4 during 2 h. Data from autohydrolysis–posthydrolysis were compared with the results obtained at the optima conditions assayed
for prehydrolysis (3% H2SO4 at 130 °C during 15 min) based on previous works. Prehydrolysis extracted more hemicellulosic sugars from trimming vine shoots;
however, the protein content in the hydrolysates from autohydrolysis–posthydrolysis was higher. The harsher conditions assayed
during the autohydrolysis process and the higher content of protein after this treatment could induce Maillard reactions decreasing
consequently the concentration of hemicellulosic sugars in the hydrolysates. Therefore, despite the several advantages of
autohydrolysis (less equipment caused by the absence of mineral acid, less generation of neutralized sludges, and low cost
of reagents) the poor results obtained in this work with no detoxified hydrolysates (Q
P = 0.36 g/L h, Q
S = 0.79 g/L h, Y
P/S = 0.45 g/g, Y
P/Sth = 61.5 %) or charcoal-treated hydrolysates (Q
P = 0.76 g/L h, Q
S = 1.47 g/L h, Y
P/S = 0.52 g/g, Y
P/Sth = 71.5 %) suggest that prehydrolysis of trimming vine shoots with diluted H2SO4 is more attractive than autohydrolysis-posthydrolysis for obtaining lactic acid through fermentation of hemicellulosic sugars
with L. pentosus. Besides the higher hemicellulosic sugars concentration achieved when using the prehydrolysis technology, no detoxification
steps are required to produce efficiently lactic acid (Q
P = 1.14 g/L h; Q
S = 1.64 g/L h; Y
P/S = 0.70 g/g; Y
P/Sth = 92.6 %), even when vinification lees are used as nutrients (Q
P = 0.89 g/L h; Q
S = 1.54 g/L h; Y
P/S = 0.58 g/g; Y
P/Sth = 76.1 %). 相似文献