An intermediate spherical model of a ferromagnet

A one-parameter family of partition functions is considered which for zero value of the parameter reduces to the spherical model of a ferromagnet. The model for > 0 is closer to the usual discrete lattice spin model of a ferromagnet than is the spherical model. The first four terms in of the limiting value of the partition function are calculated above and below the critical temperature for arbitrary interactions using the saddle point method to calculate certain correlation functions for the spherical model. These calculations indicate that the critical temperature is independent of for small and certain interactions.Part of this research appeared in the author's doctoral thesis.⁽³⁾     

The spherical limit forn-vector correlations

We investigate then limit of then-vector model single-spin and pairspin correlation functions. In this limit we show that the correlation functions become those of the corresponding spherical model.     

Optimization strategies in micellar electrokinetic capillary chromatography

Summary Computer-assisted procedures for the one-parameter optimization of the surfactant concentration and the concentration of urea or D-glucose as modifiers in micellar electrokinetic capillary chromatography have been developed. These procedures permit a rapid optimization of one parameter on the basis of only two experiments. Predicted values are compared to empirically obtained optimum values. The influence of the modifier concentration on the critical micelle concentration of sodium dodecyl sulfate was experimentally determined in buffers commonly employed in micellar electrokinetic chromatography. The alteration of retention factors of solutes caused by the influence of urea addition on the critical micelle concentration of sodium dodecyl sulfate was calculated under the assumption of constant distribution coefficients and compared to experimentally obtained values. It was demonstrated that the addition of urea or of D-glucose does not alter the phase ratio substantially.     

离子液体[BMim]BF4对SDS水溶液表面活性和聚集能力的促进

采用表面张力测定法和核磁共振谱等方法研究了阴离子表面活性剂十二烷基硫酸钠(SDS)在水溶性室温离子液体[BMim]BF4/水混合溶剂中的表面性质及聚集行为, 发现极少量[BMim]BF4的介入就可以显著降低SDS的临界胶束浓度, 提高体系的表面活性; 且[BMim]BF4在混合溶剂中所占的摩尔分数(x1)在一定范围内(0相似文献   

核糖核酸酶A在DAB-环乙烷溶液中的活性和构象

The activity and conformation of ribonuclerse A (RNaseA) solubilized in cyclohexane via dodecylammonium butyrate(DAB) reverse micelles were investigated. The activity of RNaseA was studied using the cytidine 2’,3’ -phosphate as the substrate, and it was found that kcat increases significantly with respect to that in water attended by an increased Km•FT-IR spectra of RNaseA in reverse micellar solution were investigated as a function of w0(= [H2O]/ [DAB]), and it was noted that the structure of RNaseA became losser in reverse micelles campared to that in aqueous solution. The relation between activity and conformation was discussed.     

A proton NMR study on aggregation of cationic surfactants in water: effects of the structure of the headgroup

 ¹H NMR chemical shifts of solutions of the following cationic surfactants in D₂O were determined as a function of their concentrations: cetyltrimethylammonium chloride, CTACl, a 1 : 1 molar mixture of CTACl and toluene, cetylpyridinium chloride, CPyCl, cetyldimethylphenylam-monium chloride, CDPhACl, cetyldimethylbenzylammonium chloride, CDBzACl, cetyldimethyl-2-phenylethylammonium chloride, CDPhEtACl, and cetyldimethyl-3-phenylpropylammonium chloride, CDPhPrACl. Plots of observed chemical shifts versus [surfactant] are sigmoidal, and were fitted to a model based on the mass-action law. Satisfactory fitting was obtained for the discrete protons of all surfactants. From these fits, we calculated the equilibrium constant for micelle formation, K, the critical micelle concentration, CMC and the chemical shifts of the monomer, δ_mon and the micelle δ_mic. ¹H NMR-based CMC values are in excellent agreement with those which we determined by surface tension measurements of surfactant solutions in H₂O, allowing for the difference in structure between D₂O and H₂O. Values of K increase as a function of increasing the size of the hydrophilic group, but the free energy of transfer per CH₂ group of the phenylalkyl moiety from bulk water to the micellar interface is approximately constant, 1.9±0.1 kJ mol^-1. Values of (δ_mic–δ_mon) for the surfactant groups at the interface, e.g., CH₃–(CH₂)₁₅–N+(CH₃)₂ and within the micellar core, e.g., CH₃–(CH₂)₁₅–N⁺ were used to probe the (average) conformation of the phenyl group in the interfacial region. The picture that emerges is that the aromatic ring is perpendicular to the interface in CDPhACl and is more or less parallel to it in CDBzACl, CDPhEtACl, and CDPhPrACl. Received: 23 February 1996 Accepted: 29 August 1996     

Temperature dependence of second critical micelle concentration of dodecyldimethylbenzylammonium bromide in aqueous solution

The specific conductivity of dodecyldimethylbenzylammonium bromide (C12BBr) in aqueous solutions, in the temperature range of 15 to 40 °C, has been measured as a function of molality. The two breaks which were found on the conductivity against molality plots were attributed to the critical micelle concentration, cmc, and second critical micelle concentration, 2^nd cmc, respectively. The ratio of the slopes, S, of the three linear fragments on the plots, S2/S1 and S3/S1, was attributed to the degree of ionization of the micelles at cmc and 2^nd cmc respectively. It was shown that the values of the 2^nd cmc estimated above 27 °C are only apparent due to thermal disintegration of the micelles. In the temperature range of 15 to 27 °C, the values of the 2^nd cmc increase gradually and the plot of the 2^nd cmc against temperature is concave. The ratio of 2^nd cmc/cmc for C12BBr at 25 °C amounts to 15 and appears to be high compared to the literature values for other surfactants. For comparative purposes the cmc and 2^nd cmc values were also estimated conductometrically for decyldimethylbenzylammonium bromide (C10BBr) at 25 °C. The 2^nd cmc value for this surfactant is higher compared to the value for the C12 homologue by a factor of 2.6.The standard Gibbs free energies of micellization at cmc and at the 2^nd cmc were estimated from the experimental data for both surfactants at 25 °C.     

无机盐对正负表面活性剂混合体系性质的影响

用滴体积法测定了四种离子强度下(μ=0.02, 0.05, 0.1, 0.2 mol·kg~(-1), 支持电解质为NaBr)C_(12)H_(25)SO_4Na/C_6H_(13)(NC_5H_5)Br混合体系在五种比例(10:1, 3:1, 1:1, 1:3, 1:10)时的临界胶团活度cma(25 ℃). 提出了无机盐对正负表面活性剂混合体系临界胶团活度的影响程度的计算式.     

The self-consistent mean spherical approximation for the one-component plasma

The consequences of choosing the adjustable hard-core diameter in the mean spherical approximation for the one-component plasma so as to achieve thermodynamic consistency between the energy and compressibility equations are investigated. Such a choice is found to be possible only for >8.5 and, although the resulting correlation functions are discontinuous, the height of the main peak in the static structure factor is remarkably accurate. Two especially noteworthy aspects of the thermodynamic results are that the compressibility equation is much more accurate than in any previous approximation free of input from computer simulations and that the nonstatic part of the internal energy has a ^1/4 dependence in the strong coupling limit in agreement with Monte Carlo data.     

N，N-二丁基癸酰胺萃取硝酸有机相结构研究

利用界面张力、电导、FT-IR等研究了不同硝酸浓度下萃取有机相的微结构。利用Gaussian曲线拟合处理N，N-二丁基癸酰胺(DBDEA)的羰基吸收峰，结果表明体系中存在多种以氢键结合的物种如DBDEA·HNO₃、(DBDEA)₂·HNO₃等。在较高酸度下有机相中萃取剂分子自组装成小的聚集体-反相胶团，极性核由水、硝酸和萃取剂高电荷密度的极性部分构成。