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21.
The properties of thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogel in tetrahydrofuran/H2O mixtures were studied. Scanning electron microscopic (SEM) images demonstrate that the hydrogel changes from homogeneous to heterogeneous microstructure upon the addition of tetrahydrofuran to water. This heterogeneous PNIPAAm hydrogel in the mixture solvent exhibits a very slow response rate at temperatures above its lower critical solution temperature. The decreased response rate is attributed to the formation of special ternary complexes including the polymer and the two solvents in the tetrahydrofuran/H2O mixture. Factors controlling the thermoresponse rate are discussed further and several suggestions are provided for designing and developing fast-response PNIPAAm hydrogels in the future. 相似文献
22.
An experimental mixture design was applied to a differential scanning calorimetry (DSC) study performed to evaluate naproxen
compatibility in tablet formulations consisting of four classic excipients (sorbitol, sodium carboxymethylcellulose, poly(ethylene
glycol) 20000 and Veegum) each in adequate concentration ranges accounting for the relevant values actually used in pharmaceutical
formulations. Twenty-seven different tablets were obtained from as many mixtures prepared according to the experimental design
plan and analyzed in a random order by DSC. Statistical evaluation of experimental data enabled correlation of both enthalpy
and onset temperature variations of drug melting endotherm (selected as responses indicative of the presence of drug-excipient
interactions) with the mixture composition. Variance analysis (Anova) confirmed the reliability of the postulated polynomial
model in providing adequate prediction of true system behaviour.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
23.
L. Ambrosone L. Costantino G. D’Errico V. Vitagliano 《Journal of solution chemistry》1997,26(7):735-748
The self-diffusion coefficients of HDO and some surfactants in aqueous mixtures at different concentrations, below the critical
micelle concentration, have been determined by means of the NMR, spin-echo pulsed field gradient method. The surfactant solutes
chosen were ethylene glycol-pentyl alcohol (diethylene glycolpentylalcohol, ethylene glycol-hexyalcohol, diethylene glycol-hexyl
alcohol, triethylene glycol-hexyl alcohol, tetraethylene glycol-hexyl alcohol, pentaethylene glycol-hexyl alcohol). The interactions
in solution are studied by analyzing the solute self-diffusion coefficients extrapolated to infinite dilution. These values
are compared with those of 1-alkanols. The slope of the self diffusion coefficientsvs. the solute concentration are correlated with the microscopic friction coefficients. A model for interpreting the experimental
data is suggested. 相似文献
24.
B. S. Narwade P. G. Gawali Rekha Pande G. M. Kalamse 《Journal of Chemical Sciences》2005,117(6):673-676
Dielectric constant (ε’) and dielectric loss (ε") of n-propyl alcohol (PA), ethylenediamine (EDA) and their binary mixtures,
for different mole fractions of ethylenediamine have been experimentally measured at 11.15 GHz microwave frequency. Values
of density (ρ), viscosity (η) and square refractive index (n
D
2
) of binary mixtures as well as those of pure liquids are reported. Excess square refractive index, viscosity and activation
energy of viscous flow have also been estimated. These parameters have been used to explain the formation of complexes in
the system. 相似文献
25.
ABSTRACT Novel chiral three-ring (R) enantiomers were synthesised using optically active (R)-(?)-2-octanol. Properties, such as the sequence of phases, the transition temperatures and enthalpies, were tested by a polarising optical microscope and differential scanning calorimeter. An antiferroelectric smectic phase (SmCA*) with a direct transition from the antiferroelectric to the isotropic phase (SmCA*-Iso) was observed for three esters with an achiral C3F7CH2O(CH2)3O– terminal chain. Bi- and multicomponent mixtures with a broad temperature range of the antiferroelectric phase and good electro-optical properties were formulated. Helical pitch of pure esters and mixtures was measured by spectrophotometry method. 相似文献
26.
将改进的基本度量理论与热力学微扰理论相结合,提出了胶体/高分子系统排空相互作用的IRDFT理论。该理论解释了在实际胶体系统中起重要作用的排斥体积效应和高分子链内相关性的竞争机制。应用该IRDFT,分别以线性链状和环状结构的高分子及其单体为排空元,计算了不同排空元条件下的胶体间排空相互作用。研究表明:对于絮凝破坏,自由环状高分子具有更大的优势。 相似文献
27.
S Katrych A Grytsiv A Bondar T Velikanova M Bohn 《Journal of solid state chemistry》2004,177(2):493-497
Phase equilibria in the Nb-Nb5Si3-NbB region were studied in the melting (crystallization) range by means of light microscopy, XRD, SEM and EMPA on alloys after arc-melting and annealing at 1800°C and at subsolidus temperatures. Phase transition and melting temperatures were determined by DTA and pyrometric Pirani-Alterthum technique resulting in a solidus projection and two isopleths, Nb77Si23-Nb77B23 and Nb99Si1-Nb5Si2B. The T2-phase Nb5Si3−xBx (0?x?2, Cr5B3-type) was found to form equilibria with (Nb), NbB, Nb3Si, and with the T1-phase (Mn5Si3 derivative type). The T2-phase melts incongruently (Nb5Si1.8B1.2 at 2245°C) and forms a quasibinary eutectic with the niobium solid solution on a minimum tie-line at ∼1880°C. 相似文献
28.
N. Bélaïd-Drira H. Zamali M. Jemal 《Journal of Thermal Analysis and Calorimetry》1996,46(5):1449-1458
Phase diagram of the binary system LiNO3-NaNO3 has been obtained by using direct and differential thermal analysis between 323 and 623 K. This system is characterized by an eutectic plateau at 467 K. The eutectic point is at 0.465 mole NaNO3. A peritectic appears at 550 K. There is no miscibility in the solid state. These findings associated with some other thermodynamic results have been used to calculate the activities of the constituents along the liquids curve and the excess thermodynamic functions at 618 K. The constituents seem not to have a symmetrical influence on the thermodynamic quantities. 相似文献
29.
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
30.
天然和人工培植红景天挥发油的对比研究 总被引:2,自引:0,他引:2
应用GC-MS和GC-IR两种联机法对比研究了天然和人工培植红景天挥发油、分别鉴定出27个和24个化合物。MS给出结构信息和IR给出官能团信息相结合,提高了分析测试复杂样品的可靠性。 相似文献