Aluminum-27 NMR spectroscopy was used to characterize aqueous and methanolic alkaline solutions of tetramethylammonium (TMA) aluminosilicates. Aluminosilicate solutions have been prepared with different concentrations of silicon [0.577–1.24% (w/w)], aluminum [0.0022–0.239% (w/w)], methanol [0.0–0.70% (w/w)] and H2O [0.23–90% (w/w)]. All solutions contain the same ratio of Si/TMA = 1 and Si/Al molar ratios between 0.5 and 25.27Al NMR spectra of TMA aluminosilicate solutions are characterized by a variety of aluminosilicate species such as q1(Al1OSi), q2(Al2OSi), q3(Al3OSi) and q4(Al4OSi). Aluminum-27 NMR spectra of TMA aluminosilicate solutions indicate that considerable changes occurred by changing the Si/Al ratio. The distribution of aluminosilicate species was affected by the presence of the methanol and the method of mixing the silicate and aluminosilicate solutions. A methanolic aluminosilicate solution needs about twice the time required for an aqueous aluminosilicate solution to reach a steady state, i.e., the latter takes 36 h to reach steady state. Results with the same concentration of silicon and aluminum show that the formation and distribution of aluminosilicate species are strongly dependent on the solvent comprising the silicate and aluminate solutions. 相似文献
Summary: We developed a novel method of producing polymer gels in aqueous solution using UV irradiation. Persulfates were effective photosensitive initiators of polymerization and/or gelation of acryloyl‐type monomers/polymers. The gelation was confirmed by an abrupt increase in light scattering intensity, 〈I(q)〉T, at the gelation point. The gelation method entails significant advantages: it does not need any cross‐linkers, temperature control (heating), and additives except the persulfate.
The UV irradiation time dependence of light scattering intensity, 〈I(q)〉T, for pre‐gel solutions containing N‐isopropylacrylamide (NIPAm) and/or ammonium persulfate (APS). 相似文献
Time-resolved light scattering was employed to investigate kinetics of phase separation in mixtures of poly (ethylene glycol monomethylether) (PEGE)/poly (propylene glycol) (PPG) oligomers. Phase diagrams for PEGE/PPG of varying molecular weights were established by means of cold point measurements. The oligomer mixtures reveal an upper critical solution temperature (UCST). Several temperature quench experiments were carried out with a 60/40 PEGE/PPG blend by rapidly quenching from a single phase (69°C) to two-phase temperatures (66–61°C) at 1°C intervals. As is typical for oligomer mixtures, the early stage of spinodal decomposition (SD) was not detected. The kinetics of phase decomposition was found to be dominated by the late stage of SD. Time-evolution of scattering intensity was analyzed in accordance with nonlinear and dynamical scaling theories. The time dependence of the peak intensity Im and the corresponding peak wavenumber qm was found to follow the power-law {Im(t)? tα, qm(t)? t-β} with the values of α = 3 ± 0.3 and β = 1 ± 0.2, which are very close to the values predicted by Siggia. This process has been attributed to a coarsening mechanism driven by surface tension. In the temporal scaling analysis, the structure function reveals university with time, suggesting self-similarity. Phase separation dynamics in 60/40 PEGE/PPG resembles the behavior predicted for off-critical mixtures. 相似文献
Spruce sulphite cellulose (number average degree of polymerization 620) dissolved in an aqueous solution of 8% (w/w) LiOH*H2O and 12% (w/w) urea was methylated with dimethyl sulphate (DMS). By varying the reaction temperature between 22 and 50 °C, the molar ratio between 9 and 15 mol DMS per mol anhydroglucose unit, and the reaction time from 4 to 24 h, methyl cellulose (MC) with degree of substitution (DS) values in the range of 1.07 and 1.59 was prepared. The chemical structure of MC was analysed by FTIR and 1H NMR spectroscopy. The turbidity (given in nephelometric turbidity units, NTU) of the aqueous solution of MC reached an optimum of 10 NTU for a product obtained with 12 mol DMS/mol AGU at 50 °C. GPC measurements revealed polymer degradation to a certain extent. The intrinsic viscosity and the Huggins constant k of the MC samples increased with increasing DS value. The MC samples possess k values higher than 0.8, indicating association of the polymer chain. The zero-shear viscosity decreased with increase of both temperature and the amount of methylation agent due to the depolymerization. During the heating/cooling cycle (20-90 °C) of the aqueous solutions of MC, it was observed that samples synthesized at 22 °C with DS values lower than 1.3 did not undergo phase separation in aqueous solution. Phase separation hysteresis with a precipitation temperature up to 80 °C was obtained for aqueous solutions of MC with DS values between 1.07 and 1.66 synthesized at higher temperatures. The functionalization pattern determined by GLC of the corresponding partially methylated glucitol acetates is close to randomness and comparable with those of commercial MC samples. 相似文献
Rheological methods and small angle neutron scattering (SANS) were used in the characterization of dilute and semidilute aqueous solutions, both with and without added salt, of anionic poly(vinyl alcohol) (PVA−) and its hydrophobically modified analogue (HM-PVA−). The rheological measurements showed that the concentration induced viscosification effect and elastic responses are considerably stronger for solutions of HM-PVA− than in solutions of the unmodified polyelectrolyte. Over the considered polymer concentration domain, the solutions of PVA− exhibit virtually Newtonian behavior, whereas strong shear thinning effects are observed in the HM-PVA− solutions. The SANS results for HM-PVA− solutions reveal a pronounced peak in the plot of scattering intensity versus scattering wavevector q at intermediate q values and the position of the maximum scales with polymer concentration as qmax∼c0.28±0.02. This peak is suppressed in solutions of the unmodified polyelectrolyte and merely a shoulder in the scattering curve appears. Additionally, an “upturn” in the scattered intensity is observed at small q values and the magnitude of this effect depends on polymer concentration, hydrophobicity and salt addition. At large q values, the SANS results from HM-PVA− solutions suggest morphological changes, from rod-like chains to a network of semiflexible chains, as the polyelectrolyte concentration increases. 相似文献
We study the structure and dynamics of poly(N-isopropylacrylamide) (PNIPAm) core-shell nanogels dispersed in aqueous trimethylamine N-oxide (TMAO) solutions by means of small-angle X-ray scattering and X-ray photon correlation spectroscopy (XPCS). Upon increasing the temperature above the lower critical solution temperature of PNIPAm at 33 °C, a colloidal gel is formed as identified by an increase of I(q) at small q as well as a slowing down of sample dynamics by various orders of magnitude. With increasing TMAO concentration the gelation transition shifts linearly to lower temperatures. Above a TMAO concentration of approximately 0.40 mol/L corresponding to a 1 : 1 ratio of TMAO and NIPAm groups, collapsed PNIPAm states are found for all temperatures without any gelation transition. This suggests that reduction of PNIPAm-water hydrogen bonds due to the presence of TMAO results in a stabilisation of the collapsed PNIPAm state and suppresses gelation of the nanogel. 相似文献
We report the evidence for attractive interaction of latex particles which are covered by poly(ethylene oxide) chains. These
particles are suspended in aqueous solutions of ammonium sulfate. The interaction is probed by measurements of the turbidity
of the suspensions up to 70 g/l. Turbidity is insensitive to multiple scattering and allows the static structure factor, S(q) [q=(4πn0/λ0)sin(θ/2), where θ is the scattering angle, n0 is the refractive index of the medium and λ0 is the wavelength in vacuo], to be determined at small q values. The analysis of S(q) at small q values yields information about possible attraction of the particles. The analysis of the turbidity data furthermore shows
that no aggregation took place in these systems. A weak but long-range attractive interaction was found at ammonium sulfate
concentrations of 0.01 and 0.1 M. The relation of this attractive force to hydrophobic forces is discussed.
Received: 9 March 2000/Accepted: 28 June 2000 相似文献
Batch experiments aimed at the sorption of Pb(II) onto peat were performed from an aqueous solution in both the absence and
presence of common complexing agents (acetate or citrate). The influence of the initial pH of the solution, metal ion concentration
and contact time on the sorption efficiency of Pb(II) was examined at ambient temperature (18 ± 0.5) °C for each experiment.
The results showed that the presence of acetate improved the efficiency of the sorption process, while the presence of citrate
in the aqueous solution decreased the efficiency of the Pb(II) sorption onto peat. The equilibrium data fitted well with the
Langmuir isotherm model and confirmed the monolayer sorption of uncomplexed and complexed Pb(II) species onto peat. The values
of maximum sorption capacities (qmax) were 135.13 mg g−1 for Pb(II) complexed with acetate, q > 79.36 mg g−1 for uncomplexed Pb, q > 38.46 mg g−1 for Pb(II) complexed with citrate. The kinetics of Pb(II) sorption onto peat, in both the absence and presence of complexing
agents, indicated a pseudosecond order mechanism. Analysis of IR spectra showed that carboxylic and hydroxyl groups had an
important role in the binding process of Pb(II) species onto peat. 相似文献
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 q2-dependent (q is the scattering vector) characteristic of diffusive behavior; however, the slow modes were q3-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
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, g2(τ), with appropriate allowance for heterodyning detection in the gel phase. The S(q,t) data could be fitted to S(q,t)=Aexp(−Dfq2t)+Bexp(−t/τc)β, both in the sol (50 and 60 ∘C) and gel states (25 and 40 ∘C). The fast-mode diffusion coefficient, Df 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+β1T+β2T2. 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+τ1c+τ2c2. 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
The gelation process of polyethylene oxidea–polypropylene oxideb–polyethylene oxideacopolymer (poloxamer 407) aqueous solutions is studied by means of FTIR spectroscopy, rheology, and differential scanning calorimetry (DSC). The C–O–C stretching bands of infrared spectra were found to shift toward higher wavenumbers with sol–gel transition, indicating that hydrogen bonding is not the driving force for gelation. Linear viscoelastic data provide an alternative method for gel point determination of these thermoreversible gels. The results obtained with this method are found to coincide with those obtained using DSC. Gel point temperatures determined by these methods are close to 14°C for 25% (w/w) poloxamer 407 solutions and 10°C for 30% (w/w) solutions. In gel state, the elastic modulus (G′) and dynamic viscosity (η*) are found to be concentration and temperature independent for temperatures ranging from 20 to 35°C. In light of our results, we suggest a mechanism of gelation based on micelles packing and entanglements. 相似文献
In this report, we present a thermodynamic and kinetic study of the selective dissolution of calcite from low-grade phosphate
ores (Epirus area, Greece) by dilute acetic acid at isothermal conditions. A twin calorimeter with two identical membrane
vessels, for the acid dissolution process, and for the reference was used. The curves of rate vs. time of the phosphorite
dissolution for various temperatures show that the maximum (.qmax) was increased, whereas the time (tpeak) to achieve the corresponding .qmax values was decreased, as the experimental temperature was increased. The dissolution enthalpy was increased from 13.1 to
16.7 kJ mol−1, as the experimental temperature was increased from 10.0 to 28.0°C. The chemical analysis of the supernatant solutions shows
that the main process was the calcite dissolution. The reaction model with general form, ln(1/(1-X))=ktm, was found to fitted the experimental data regardless of the experimental temperature. These results were assigned in the
presence of two different kinds of particles in the phosphorite. The activation energy of the dissolution process was found
69.7 kJ mol−1. The SEM micrographs of acid dissolution samples showed two different textures after acid dissolution. 相似文献
The volume changes on mixing aqueous solutions of glycine-PEG and L-alanine-PEG were respectively measured with a vibration densimeter as functions of concentration and temperature. The volume changes (
m)V for the glucine-PEG-H2O system were positive, and these v(x,m) values of different total molality almost linearly decreased with an increase in temperature and converged around 110°C by extrapolation. On the other hand, those for the L-alanine-PEG-H2O system were almost zero and independent of temperature. It is considered that the influence of hydration cospheres on glycine-PEG interaction for the glycine-PEG-H2O system disappears around 110°C. 相似文献
The solubility of sildenafil citrate (SC) in aqueous mixtures of propylene glycol (PG) was investigated. This study was carried out at different mass fractions of PG ranging from 0.1 to 0.9 at T = 293.2–313.2 K. The solubility of SC in the mixed solutions increased with increasing temperature and PG mass fraction.
The solubility values were correlated by two co-solvency models (Jouyban–Acree model and van’t Hoff–Jouyban–Acree model). The mean relative deviations (MRD) were 5.7% and 5.5%, respectively. Density of the SC-saturated solutions over the entire solvent composition and temperature range was also measured and the results correlated with the Jouyban–Acree model. Furthermore, the apparent thermodynamic properties, dissolution enthalpy, dissolution entropy and Gibbs free energy change of dissolution process of SC in all the mixed solvents were calculated according to van’t Hoff and Gibbs equations. Dissolution of SC in these mixed solvents is an endothermic process. 相似文献