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排序方式: 共有154条查询结果,搜索用时 15 毫秒
61.
Liu J Han B Zhang J Li G Zhang X Wang J Dong B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(6):1356-1360
The solubility of Ls-54 surfactant in supercritical CO(2) was determined. It was found that the surfactant was highly soluble in SC CO(2) and the water-in-CO(2) microemulsions could be formed, despite it being a non-fluorous and non-siloxane nonionic surfactant. The main reasons for the high solubility and formation of the microemulsions may be that the surfactant has four CO(2)-philic groups (propylene oxide) and five hydrophilic groups (ethylene oxide) and its molecular weight are relatively low. The results of this work provide useful information for designing CO(2)-soluble non-fluorous and non-siloxane surfactants. The phase behavior of the CO(2)/Ls-54/H(2)O system, solvatochromic probe study, and the UV spectrum of lysozyme proved the existence of water domains in the SC CO(2) microemulsions. The method of synchrotron radiation small-angle X-ray scattering was used to obtain the structural information on the Ls-54 based water-in-CO(2) reverse micelles. By using the Guinier plot (ln I(q) versus q (2)) on the data sets in a defined small q range (0.022-0.040 A(-1)), the radii of the reverse micelles were obtained at different pressures and molar ratio of water to surfactant, W(0), which were in the range of 20.4-25.2 A. 相似文献
62.
New topic of supercritical fluids: local activity coefficients of supercritical solvent and cosolvent around solute 总被引:1,自引:0,他引:1
Hou M Zhang X Han B Song J Liu G Zhang Z Zhang J 《The Journal of chemical physics》2008,128(10):104510
The study of inhomogeneity in supercritical fluids (SCFs) is of great importance. In this work, we propose the concept of local activity coefficients in supercritical (SC) solutions, which link thermodynamics and inhomogeneity in SC systems. The local activity coefficients of CO(2)+acetonitrile+phenol blue and CO(2)+acetic acid+phenol blue systems are investigated at 308.15 K in critical region and outside critical region. To do this, the local compositions of CO(2)+acetonitrile and CO(2)+acetic acid mixed solvents around phenol blue are first estimated using UV-visible spectroscopy. Then it is considered that there exist bulk phase and local phase around phenol blue in the systems. The activity coefficients of CO(2) and the cosolvents (acetonitrile or acetic acid) in bulk phase are calculated using Peng-Robinson equation of state. The local activity coefficients of CO(2) and the cosolvents are then calculated on the basis of thermodynamic principles. It is demonstrated that in the critical region the local activity coefficients differ from bulk activity coefficients significantly and are sensitive to pressure. This can explain many unusual phenomena in SC systems in critical region thermodynamically. 相似文献
63.
Zhang C Zhang J Li W Feng X Hou M Han B 《Journal of colloid and interface science》2008,327(1):157-161
The formation of micelles of Pluronic block copolymers in poly(ethylene glycol) (PEG) was studied using fluorescence, solubilization measurements, and frozen fracture electron microscopy (FFEM) methods at 40 degrees C. It was discovered that surfactants L44 (EO(10)PO(23)EO(10)), P85 (EO(26)PO(40)EO(26)), and P105 (EO(37)PO(56)EO(37)) can form micelles in PEG 200 (PEG with a nominal molecular weight of 200), and the critical micellization concentration (CMC) decreases with increasing molecular weight of the surfactants. The size of the micelles formed by these Pluronic block copolymers is in the range of 6-35 nm. The CMC values in PEG 200 are higher than those in aqueous solutions. 相似文献
64.
群G的子群H称为半置换的,若对任意的K≤G,只要(|H|,|K|)=1.就有HK=KH,H称为s-半置换的,若对任意的p‖G|,只要(p,|H|)=1,就有PH=HP,其中P∈Sylp(G).本文利用Sylow子群的2-极大子群的s-半置换性得到有限群为p-幂零群的一些充分条件. 相似文献
65.
Wei Li Jianling Zhang Dr. Yueju Zhao Minqiang Hou Dr. Buxing Han Prof. Dr. Cailan Yu Jianping Ye 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(4):1296-1305
The study of the micelle‐to‐vesicle transition (MVT) is of great importance from both theoretical and practical points of view. Herein, we studied the effect of compressed CO2 on the aggregation behavior of dodecyltrimethylammonium bromide (DTAB)/sodium dodecyl sulfate (SDS) mixed surfactants in aqueous solution by means of direct observation, turbidity and conductivity measurements, steady‐state fluorescence, time‐resolved fluorescence quenching (TRFQ), fluorescence quantum yield, and template methods. Interestingly, all these approaches showed that compressed CO2 could induce the MVT in the surfactant system, and the vesicles returned to the micelles simply by depressurization; that is, CO2 can be used to switch the MVT reversibly by controlling pressure. Some other gases, such as methane, ethylene, and ethane, could also induce the MVT of the surfactant solution. A possible mechanism is proposed on the basis of the packing‐parameter theory and thermodynamic principles. It is shown that the mechanism of the MVT induced by a nonpolar gas is different from the MVT induced by polar and electrolyte additives. 相似文献
66.
67.
结合罚函数思想和广义梯度投影技术,提出求解非线性互补约束数学规划问题的一个广义梯度投影罚算法.首先,通过扰动技术和广义互补函数,将原问题转化为序列带参数的近似的标准非线性规划;其次,利用广义梯度投影矩阵构造搜索方向的显式表达式.一个特殊的罚函数作为效益函数,而且搜索方向能保证效益函数的下降性.在适当的假设条件下算法具有全局收敛性. 相似文献
68.
矩形网格上二元切触插值的表现公式 总被引:3,自引:0,他引:3
In this paper, we make use of the generalized Vandermonde matrix, and set up formula of bivariate contact interpolation over rectangular grids and a example is given. 相似文献
69.
70.
Haigang Yang Shoubin Xu Yuanqing Song Jianling Zhang Long Jiang 《Journal of Macromolecular Science: Physics》2014,53(6):1059-1073
The thermal decomposition behavior of poly(vinyl alcohol) (PVA) with NaHSO4 at 280~290°C as well as the optical characteristics and the thermal stability of the resulting thermally decomposed PVA were investigated by means of UV-Vis spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The results suggest that (1) the elimination reactions of side groups in PVA with NaHSO4 can occur under our conditions resulting in formation of carbon–carbon double and triple bonds; (2) most of the carbon–carbon double bonds were conjugated; (3) the PVA thermally treated with NaHSO4 could absorb light in the region of 190~600 nm; (4) the thermal stability of the resulting PVA was better than that of PVA without thermal treatment; and (5) compared with the thermal reaction of PVA without NaHSO4, the addition of NaHSO4 can promote the thermal elimination of side groups of PVA. 相似文献