共查询到20条相似文献,搜索用时 31 毫秒
1.
A. A. Zaman 《Colloid and polymer science》2000,278(12):1187-1197
In this study a systematic investigation on the adsorption of polyethylene oxide (PEO) onto the surface of silica particles
and the viscosity behavior of concentrated dispersions of silica particles with adsorbed PEO has been performed. The variation
of shear viscosity with the adsorbed layer density, concentration of free polymer in the solution (depletion forces), polymer
molecular weight, and adsorbed layer thickness at different salt concentrations (range of the electrostatic repulsion between
particles) is presented and discussed.
Adsorption and rheological studies were performed on suspensions of silica particles dispersed in solutions of 10−2 M and 10−4 M NaNO3 containing PEO of molecular weights 7,500 and 18,500 of different concentrations. Adsorption measurements gave evidence of
a primary plateau in the adsorption density of 7,500 MW PEO at an electrolyte concentration of 10−2 M NaNO3. Results indicate that the range of the electrostatic repulsion between the suspended particles affects both adsorption density
of the polymer onto the surface of the particles and the viscosity behavior of the system. The adsorbed layer thickness was
estimated from the values of zeta potential in the presence and absence of the polymer and was found to decrease with decreasing
the range of the electrostatic repulsive forces between the particles. Experimental results show that even though there is
a direct relation between the viscosity of the suspension and the adsorption density of the polymer onto the surface of the
particles, variation of viscosity with adsorption density, equilibrium concentration of the polymer, and range of the electrostatic
repulsion cannot be explained just in term of the effective volume fraction of the particles and needs to be further investigated.
Received: 15 February 2000/Accepted: 26 June 2000 相似文献
2.
J. Klein 《Advances in colloid and interface science》1982,16(1):101-115
The forces between mica surfaces a distance D apart immersed in cyclohexane, bearing adsorbed layers of polystyrene, have been measured at temperatures lower than the corresponding critical temperatures. Polymers of two different molecular weights were used. The results show that these forces are attractive for 3Rg > D >. Rg (where Rg is the polymer radius of gyration) and repulsive at lower D, and may be understood in terms of the phase equilibrium of the polystyrene-cyclohexane system. The adsorption of the polymer under these conditions appears to be effectively irreversible over the time of our experiments. The adsorbance of polymer and the thickness of the adsorbed layers are comparable with values measured in other studies using entirely different techniques. 相似文献
3.
The water desorption isotherms are determined in three cellulose acetate membranes with different acetyl content as a function
of p/p
0 at 10–40 °C. The partition coefficients (adsorbed water over water pressure) show a minimum at p/p
0=0.5–0.6. This indicates a two energy mechanism. The agreement of our results with the BET adsorption isotherms only till
p/p
0<0.3 shows that a two energy adsorption mechanism is valid only for small water contents, probably one hydrate layer and a
second more liquid-like water layer. At large p/p
0, the adsorbed water becomes more and more liquid like by polarization of the hydrogen bonds. The heat of desorption is larger
than the vaporization heat of water ΔH
vap(H2O). It decreases with increasing water content asymptotically to ΔH
vap(H2O). The cause may be a larger van der Waals interaction of the hydrate layer due to coordination numbers larger than 4.4 as
in liquid water. Additionally, we found a hole adsorption process by sorbing unpolar solvents. The water and methonal adsorption
are 100 times larger due to a swelling mechanism depending on the number of acetyl groups in the membranes. The amounts of
n-alcohols sorbed decrease with their chain length.
Received: 25 April 1997 Accepted: 10 June 1997 相似文献
4.
Ahmed A. El-Sherif 《Journal of solution chemistry》2010,39(1):131-150
The formation equilibria of copper(II) complexes and the ternary complexes Cu(HMI)L (HMI=4-Hydroxymethyl-imidazole, L=amino
acid, amides or DNA constituents) have been investigated. Ternary complexes are formed by a simultaneous mechanism. The results
showed the formation of Cu(HMI)L and Cu(HMI,H−1)(L) complexes. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in
terms of the parameters Δlog 10
K and log 10
X. The effect of the side chains of amino acid ligands (ΔR) on complex formation was discussed. The concentration distributions of various species formed in solution were also evaluated
as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants are investigated. The effects of dioxane as a solvent,
on the protonation constant of HMI and the formation constants of CuII–HMI complexes, were discussed. 相似文献
5.
Enthalpies of Dehydrations of Oxalate,Sulfate and Chloride Hydrates by Transpiration Method and DSC 总被引:2,自引:0,他引:2
Transpiration method was used to measure the equilibrium water vapor pressures of the dehydration of the respective hydrates,
such as oxalates, sulfates,chlorides and acetate, and the enthalpies of dehydrations (ΔH
Tr
0) of these hydrates were obtained. The heats of dehydrations (ΔH
DSC
0) were also determined by TG-DSC method. From the comparison with ΔH
Tr
0 of ΔH
DSC
0, the relation of ΔH
DSC
0/ΔH
Tr
0=R (=dehydration molar number determined by TG-DSC peak/stoichiometric dehydration molar number) was yielded. From these results,
the following relations were found: ΔH
DSC
0(corrected)=ΔH
DSC
0/R=ΔH
Tr
0
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
Heinz Gamsj?ger Wolfgang Preis Harald Wallner 《Monatshefte für Chemie / Chemical Monthly》2001,28(6):411-415
The solubility of hellyerite, NiCO3 · 6H2O, in water was studied at different temperatures. From the experimental data obtained, a preliminary set of the thermodynamic quantities Δf G ⊖, Δf H ⊖, and S ⊖ for hellyerite was derived using the ChemSage optimizer routine. 相似文献
7.
Heinz Gamsjäger Wolfgang Preis Harald Wallner 《Monatshefte für Chemie / Chemical Monthly》2001,132(3):411-415
Summary. The solubility of hellyerite, NiCO3 · 6H2O, in water was studied at different temperatures. From the experimental data obtained, a preliminary set of the thermodynamic
quantities Δf
G
⊖, Δf
H
⊖, and S
⊖ for hellyerite was derived using the ChemSage optimizer routine.
Received January 16, 2001. Accepted January 18, 2001 相似文献
8.
Muhammad A. Motin Tapan K. Biswas Entazul M. Huque 《Monatshefte für Chemie / Chemical Monthly》2003,134(4):475-487
Summary. Density and viscosity of NaNO3 and KNO3 in aqueous and in H2O-urea solutions were determined as a function of electrolyte concentrations at 308, 313, 318, 323, and 328 K, respectively.
The apparent molal volume (φ
v
) of the electrolytes were found to be linear functions of the square root of the solute molality (b). The φ
v
and data were fitted to the Masson equation [1] by the least square method to obtain the apparent molar volume at infinite dilution (φ
v
^), which is practically equal to the partial molar volume . The viscosity coefficients A and B were calculated on the basis of the viscosity of the solutions and the solvent concerned using the Jones–Dole [2] equation. The activation parameters for viscous flow (ΔG
≠, ΔS
≠, and ΔH
≠) were calculated according to Eyring [3]. The values of for the two systems were also calculated from B-coefficient data. The results were found to be of opposite nature in the two electrolyte systems. Where sodium nitrate showed
structure making behaviour both in aqueous and in H2O-urea solutions, KNO3 showed structure breaking behaviour in aqueous solutions and structure making behaviour in 5 molal H2O-urea solutions in the studied temperature range. The behaviour of these two electrolytes in aqueous binary and in aqueous-urea
ternary systems are discussed in terms of charge, size, and hydrogen bonding effects.
Corresponding author. E-mail: chemistry_ru@yahoo.com
Received January 24, 2002; accepted (revised) April 5, 2002 相似文献
9.
Excess Molar Volume and Viscosity of Isobutyric Acid + Water Binary Mixtures Near and Far Away from the Critical Temperature 总被引:1,自引:0,他引:1
The excess molar volume VE, shear viscosity deviation Δη and excess Gibbs energy of activation ΔG∗E of viscous flow have been investigated by using density (ρ) and shear viscosity (η) measurements for isobutyric acid + water (IBA+W) mixtures over the entire range of mole fractions at five different temperatures,
both near and close to the critical temperature (2.055K ≤ (T−Tc)≤ 13.055K). The results were also fitted with the Redlich–Kister equation. This system exhibited very large negative values
of VE and very large positive values of Δη due to increased hydrogen bonding interactions and correlation length between unlike molecules in the critical region and
to very large differences between the molar volumes of the pure components at low temperatures. The activation parameters
ΔH∗ and ΔS∗ have been also calculated and show that the critical region has an important effect on the volumetric properties. 相似文献
10.
X. Y. Feng X. P. Geng J. J. Peng H. Y. Hou Q. Bai 《Journal of Thermal Analysis and Calorimetry》2010,102(2):799-807
The displacement adsorption enthalpies (ΔH) of denatured α-Amylase (by 1.8 mol L−1 GuHCl) adsorbed onto a moderately hydrophobic surface (PEG-600, the end-group of polyethylene glycol) from solutions (x mol L−1 (NH4)2SO4, 0.05 mol L−1 KH2PO4, pH 7.0) at 298 K are determined by microcalorimeter. Further, entropies (ΔS), Gibbs free energies (ΔG) and the fractions of ΔH, ΔS, and ΔG for net adsorption of protein and net desorption of water are calculated in combination with adsorption isotherms of α-Amylase
based on the stoichiometric displacement theory for adsorption (SDT-A) and its thermodynamics. It is found that the displacement
adsorptions of denatured α-Amylase onto PEG-600 surface are exothermic and enthalpy driven processes, and the processes of
protein adsorption are accompanied with the hydration by which hydrogen bond form between the adsorbed protein molecules favor
formation of β-sheet and β-turn structures. The Fourier transformation infrared spectroscopy (FTIR) analysis shows that the
contents of ordered secondary structures of adsorbed α-Amylase increase with surface coverages and salt concentrations increment. 相似文献
11.
Summary. Single crystals of sodium dithiophosphate undecahydrate (Na3PO2S2 · 11H2O) and sodium trithiophosphate undecahydrate (Na3POS3 · 11H2O) were grown from aqueous solution. The crystal structures of Na3PO2S2 · 11H2O (P212121; a = 1248.1(1), b = 945.2(1), c = 1383.1(1) pm; R
1 = 0.0202, wR
2 = 0.0502) and Na3POS3 · 11H2O (Pna21; a = 1262.0(2), b = 947.6(2), c = 1431.5(2) pm; R
1 = 0.0720, wR
2 = 0.1371) are related to each other in a sense that all constituting units are arranged in similar positions and with similar
orientations. The geometries of the anions were determined with high accuracy; thus, the structural parameters of the POS3−
3 anion were measured for the first time.
Received September 25, 2001. Accepted January 21, 2002 相似文献
12.
E. Vessally M. Nikoorazm A. Esmaili H. Ghoudarzi Afshar 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(4):631-635
Thermal internal energy gaps, ΔE
s−t; enthalpy gaps, ΔH
s−t; Gibbs free energy gaps, ΔD
s−t, between singlet (s) and triplet (t) states of R2C4H2M (M = C, Si, and Ge) were calculated at B3LYP/6-311++G** level of theory. The ΔG
s−t of R2C4H2C was increased in the order (in kcal/mol): R = −CH3 (−10.51) > −H (−9.59) > i-Pr (−9.51) > t-Bu (−8.98). While, the ΔG
s−t of R2C4H2Si and R2C4H2Ge were increased in the order (in kcal/mol): −CH3 (17.01) > i-Pr (15.30) > −H (15.26) > t-Bu (14.35) and -H (22.79) > −CH3 (22.69) > i-Pr (21.66) > t-Bu (21.01), respectively. 相似文献
13.
Lutz Preu Wolfgang Kliegel Steven J. Rettig James Trotter 《Monatshefte für Chemie / Chemical Monthly》2001,132(10):1213-1224
Summary. The structure of the dehydrogenation product 1′,3a′-dihydro-3′-((1,3-dioxoindan-2-ylidene)-phenyl-methyl)-5′-phenyl-spiro-(indan-2,1′-pyrrolo[3,4-c]pyrrole)-1,3,4′,6′-(5′H, 6a′H)-tetrone derived from the cycloadducts (±)-(3a′S,6a′R)-1′,3a′-dihydro-3′-((R)-α-(1,3-dioxoindanyl)-benzyl)-5′-phenyl-spiro-(indan-2,1′-pyrrolo[3,4-c]pyrrole)-1,3,4′,6′(5H,6a′H)-tetrone and/or (±)-(3a′S,6a′R)-1′,3a′-dihydro-3′-((S)-α-(1,3-dioxoindanyl)-benzyl)-5′-phenyl-spiro-(indan-2,1′-pyrrolo[3,4-c]pyrrole)-1,3,4′,6′(5H,6a′H)-tetrone, which were synthesized by 1,3-dipolar cycloaddition of N-phenylmaleimide to 2-((2-(1,3-dioxoindan-2-yl)-2-phenyl-ethenyl)-imino)-indan-1,3-dione,
was determined by X-ray analysis. Crystal data (CCD, 180 K): rhombohedral, R&3macr;;, a = 34.0871(7), c = 13.9358(5) ?, Z = 18; the structure was solved by direct methods and refined by full-matrix least-squares procedures to R(F, I ≥ 3σ(I)) = 0.053. The molecule contains a central folded ring system of two cis-fused 5-membered heterocyclic rings; each ring is nearly planar, and the angle between the rings amounts to 59.0°. Dynamic
1H NMR spectroscopy of the product revealed an exchange process caused by restricted rotation of the double bonded 1,3-indandione
moiety and the phenyl group about the Csp2-Csp2 single-bonds. Molecular modeling and complete lineshape analysis indicated a four site exchange process for which free energies
of activation and free energies could be established. ΔG
‡ values for the barriers of rotation are in the range of 57–59 kJ · mol − 1 at 273 K, which is unusually high for an unsubstituted phenyl group.
Received May 3, 2001. Accepted (revised) June 8, 2001 相似文献
14.
Adsorption kinetic,thermodynamic and desorption studies of phosphate onto hydrous niobium oxide prepared by reverse microemulsion method 总被引:1,自引:0,他引:1
A type of Nb2O5⋅3H2O was synthesized and its phosphate removal potential was investigated in this study. The kinetic study, adsorption isotherm,
pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order
rate model very well. The phosphate adsorption tended to increase with a decrease of pH. The adsorption data fitted well to
the Langmuir model with which the maximum P adsorption capacity was estimated to be 18.36 mg-P g−1. The peak appearing at 1050 cm−1 in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The positive values of both
ΔH° and ΔS° suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. ΔG° values obtained were negative indicating a spontaneous adsorption process. A phosphate desorbability of approximately 68%
was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive
sites on the surface of the adsorbent. The immobilization of phosphate probably occurs by the mechanisms of ion exchange and
physicochemical attraction. Due to its high adsorption capacity, this type of hydrous niobium oxide has the potential for
application to control phosphorus pollution. 相似文献
15.
Yan Bai Gui-Ying Xu Hong-Yuan Sun Xiao-Deng Yang Ai-You Hao Jin-Yu Pang Hou-Jian Gong Ming-Qi Ao 《Colloid and polymer science》2010,288(4):415-421
The surface property of an amphiphilic cyclodextrin 2-O-(hydroxypropyl-N,N-dimethyl-N-dodecylammonio)-β-cyclodextrin (HPDMA-C12-CD) was investigated using oscillating bubble rheometer and electrical conductivity method at different temperatures. The
surface tension and dilational viscoelasticity of HPDMA-C12-CD were provided. The results showed that HPDMA-C12-CD could adsorb on the air–water interface, which decreased the surface tension of water efficiently. Critical micelle concentration
(cmc) can be clearly defined from the surface tension isotherm. pC20 and π
cmc were derived from the surface tension isotherms as well. The thermodynamic parameters (ΔG
0
m , ΔH
0
m , −TΔS
0
m) derived from electrical conductivity indicated that the micellization of HPDMA-C12-CD was entropy-driven at lower temperature, while it was enthalpy-driven at higher temperature. The dilational modulus appeared
a maximum value while the phase angle appeared two maxima as a function of HPDMA-C12-CD concentration. 相似文献
16.
Bile salt structural effect on the thermodynamic properties of a catanionic mixed adsorbed monolayer
Marcos D. Fernández-Leyes Paula V. Messina Pablo C. Schulz 《Colloid and polymer science》2011,289(2):179-191
The interfacial effects of two bile salts (sodium deoxycholate (NaDC) and sodium dehydrocholate (NaDHC)) in a catanionic mixed
adsorbed monolayer have been investigated at 25 °C. The surfactant interfacial composition, the interfacial orientation of
the molecules and the energy changes are analysed to show a thermodynamic evidence of the hydrophobic BSs effect during its
intercalation into interfacial adsorbed didodecyldimethyl ammonium bromide (DDAB) molecules. Both mixed systems (NaDC–DDAB
and NaDHC–DDAB) have analogous adsorption efficiencies, which are similar from a pure DDAB monolayer and superior to that
obtained for both bile salts molecules. Nevertheless, their adsorption effectiveness is different: NaDC causes an increment
of Γ while NaDHC produces the opposite effect. The adsorption efficiency in surface tension reduction is due to the existence
of interfacial synergistic interactions (confirmed by the analysis of β
γ
and ΔG
ad
0 values). Maximum synergistic interaction is seen for α
BSs = 0.4. The hydrophobic steroid backbone of NaDHC molecule presents a deep interfacial penetration than NaDC. This fact causes
a great disturbance of DDAB hydrocarbon tails and conduces to a large separation of molecules (high A
m values) which explains the reduction of adsorption effectiveness (low Γ
m values). 相似文献
17.
Wincel H 《Journal of the American Society for Mass Spectrometry》2011,22(9):1570-1576
The thermochemical properties ΔH
o
n
, ΔS
o
n
, and ΔG
o
n
for the hydration of sodiated and potassiated monosaccharides (Ara = arabinose, Xyl = xylose, Rib = ribose, Glc = glucose,
and Gal = galactose) have been experimentally studied in the gas phase at 10 mbar by equilibria measurements using an electrospray
high-pressure mass spectrometer equipped with a pulsed ion beam reaction chamber. The hydration enthalpies for sodiated complexes
were found to be between −46.4 and −57.7 kJ/mol for the first, and −42.7 and −52.3 kJ/mol for the second water molecule. For
potassiated complexes, the water binding enthalpies were similar for all studied systems and varied between −48.5 and −52.7
kJ/mol. The thermochemical values for each system correspond to a mixture of the α and β anomeric forms of monosaccharide
structures involved in their cationized complexes. 相似文献
18.
Hong-Lin Zhang Zhe Kong Yong-Mei Yan Gan-Zuo Li Li Yu Fei Geng 《Journal of solution chemistry》2008,37(12):1631-1644
The power-time curves for the micelle formation process were determined for two anionic surfactants, sodium laurate (SLA)
and sodium dodecyl sulfate (SDS), in mixed alcohol + N,N-dimethylacetamide (DMA) solvent using titration microcalorimetry.
From the data of the lowest point and the area of the power-time curves, their critical micelle concentration (CMC) and ΔH
mo were obtained. The other thermodynamic functions of the micellization process (ΔG
mo and ΔS
mo) were also calculated with thermodynamic equations. For both surfactants, the effects of the carbon number (chain length)
of the alcohol, the concentration of alcohol, and the temperature on the CMC and thermodynamic functions are discussed. For
systems containing identical concentrations of a different alcohol, values of the CMC, ΔH
mo and ΔS
mo increased whereas ΔG
mo decreased with increasing temperature. For systems containing an identical alcohol concentration at the same temperature,
values of the CMC, ΔH
mo,ΔG
mo and ΔS
mo decrease with increasing carbon number of alcohol. For systems containing the same alcohol at the same temperature, the CMC
and ΔG
mo values increase whereas ΔH
mo and ΔS
mo decrease with increasing alcohol concentration. 相似文献
19.
The fungicide triadimenol consists of a mixture of two diastereoisomers. Diastereoisomer A (1RS,2SR) could be obtained from the mixture by fractionated crystallization from ethanol/water and toluene, successively, whereas
diastereoisomer B (1RS,2RS) could be separated by column chromatography on a silica gel column using ethylacetate as eluent. Four different crystal
forms of diastereoisomer A could be derived. The modifications were characterized by means of thermal analysis (thermomicroscopy,
DSC), FTIR-spectroscopy, FT-Raman-spectroscopy and powder X-ray diffraction, as well as pycnometry. The thermodynamic relationships
are illustrated in a semischematic energy/temperature-diagram which provides information about the relative thermodynamic
stabilities and physical properties of the four crystal forms. Mod. II (m.p. 132 °C, ΔHf 33.1±0.2 kJ mol−1, density 1.271±0.001 g cm−3) was obtained from toluene after the separation of diastereoisomer A and is enantiotropically related to mod. I (m.p. 138 °C,
ΔHf 32.0 ± 0.2 kJ mol−1, density 1.243±0.001 g cm−3). The transition point of mod. II with mod. I was determined between 30 and 40 °C, which means that mod. II is thermodynamically
stable at ambient conditions. Mod. III (m.p. 112 °C, ΔHf 25.1±0.5 kJ mol−1) and mod. IV were obtained from the melt. Furthermore, the phase diagrams of the binary systems of diastereoisomer B and
the four modifications of diastereoisomer A were calculated by means of the experimentally obtained thermodynamical data.
Received September 30, 1999. Revision July 30, 2000. 相似文献
20.
Temperature dependences of the relative reactivity of substituted phenols RC6H4OH in the presence of potassium hydrogen carbonate and of potassium phenoxides RC6H4O−K+ toward 2,4-dinitrophenyl benzoate in dimethylformamide were studied using the competitive reactions technique. Correlation
analysis of the relative rate constants k
R/k
H and differences in the activation parameters (ΔΔH
≠ and ΔΔS
≠) of competitive reactions revealed the existence of two isokinetic series for each type of nucleophiles. The mechanism of
transesterification was interpreted in terms of an approach based on analysis of the effect of substituent in the nucleophile
on the activation parameters. 相似文献