Thermodynamic Characteristics of Micellization in the Droplet Model of Surfactant Spherical Molecular Aggregate

The dependence of the work of the molecular aggregate formation on the aggregation number and surfactant monomer concentration in solution that has the key role for the theory of micellization was studied on the basis of a simple realistic droplet model of spherical aggregate composed of surfactant molecules (the o/w micelle type). Analytical formulas were derived for the coordinates of maximum and minimum of aggregate formation work on the aggregation number axis arising with an increase in the concentration of micellar solution. Model calculations of the thermodynamic characteristics of the kinetics of micellization were performed for premicellar and micellar regions of aggregate sizes within a wide range of solution concentration including the critical micellization concentration.     

Thermodynamic Characteristics of the Micellization in Droplet and Quasi-Droplet Models of Surfactant Molecular Aggregates with Account of Experimental Data on Equilibrium Micelle Distribution

Formuals for the thermodynamic characteristics of micellization in the droplet and quasi-droplet models of surfactant molecular aggregates are derived. These formulas account for the experimental data on the mean size of micelles and average statistical scatter of their sizes in the equilibrium state. These formulas cover critical micellization concentration corresponded to the onset of surfactant accumulation in micelles and higher (than CMC) concentrations at which micelles incorporate noticeable or even the largest portion of surfactant in micellar solution. Analytical dependence of thermodynamic characteristics of micellization on the initial parameters of droplet and quasi-droplet models of molecular aggregates at critical micellization concentration is disclosed.     

无盐聚电解质溶液的分子热力学模型

聚电解质在水处理和胶体领域应用广泛 ,在生物系统中 ,蛋白质和 DNA等均是聚电解质 .文献中已发表了不少聚电解质溶液的理论和模型 ,如基于柱型胞腔模型的 Poison- Boltzmann( PB)方程理论[1]及其改进型 ( MPB) [2 ] 、Manning反离子凝聚理论 [3 ] 、积分方程理论 [4] 及适合于工程应用的半经验模型 [5 ]等 ,但离工程实际应用的要求还相差较远 .最近 ,姜建文等 [6]建立的分子热力学模型 ,其预测结果与 MD模拟数据非常吻合 .本文在此基础上进一步考虑聚离子与反离子间的缔合作用 ,可以在中高浓度范围内很好地关联实验数据 .1　模　　型…     

电解质溶液的分子热力学模型研究进展

"本文从经典溶液理论及半经验模型、近代统计力学理论和分子模拟三大方面阐述了近年来国内外电解质溶液热力学的研究进展。指出电解质溶液的研究已逐渐从经典的溶液理论和半经验模型转向用统计力学理论进行研究, 从电解质的原始模型转向非原始模型。从分子和离子的微观参数出发建立高水平的热力学理论模型, 以预测电解质溶液体系的宏观热力学性质, 是发展的必然趋势。     

Thermodynamic Studies of Aqueous m-s-m Gemini Surfactant Systems

The specific conductance, surface tension, and apparent molar volume properties of aqueous solutions of two series of m-s-m gemini surfactants-one having a constant spacer s(=3) with m=8, 10, 12, and 16 and the other having a constant alkyl chain length m(=12) with variable spacer length 2相似文献   

Near-Contact Motion of Surfactant-Covered Spherical Drops: Ionic Surfactant

A lubrication analysis is presented for near-contact axisymmetric motion of spherical drops covered with an insoluble nondiffusing surfactant. The surfactant equation of state is arbitrary; detailed results are presented for ionic surfactants. The qualitative behavior of the system is determined by the dimensionless force parameter &Fcirc;, the external force normalized by the maximum resistance force generated by Marangoni stresses. For &Fcirc; > 1 drops coalesce on a time scale commensurate with the coalescence time tau0 for drops with clean interfaces. For &Fcirc; < 1, the system evolves on the time scale tau0 until Marangoni stresses approximately balance the external force; thereafter a slow evolution occurs on the Stokes time scale. In the long-time regime a self-similar surfactant concentration profile is attained that scales with the extent of the near-contact region. The gap width decreases exponentially with time but slower than for rigid particles because of surfactant backflow. For &Fcirc; < 1, drop coalescence does not occur without van der Waals attraction. Quantitative results depend only moderately on the surfactant equation of state. Copyright 1999 Academic Press.     

Thermodynamic Analysis of Trisiloxane Surfactant Adsorption and Aggregation Processes

The trisiloxane polyether surfactant (3-[3-(hydroxy)(polyethoxy)propyl]-1,1,1,3,5,5,5 -heptamethyltrisiloxane) (TS-EO12) was successfully synthesized by a hydrosilylation reaction in the presence of Karstedt catalyst. The structural analysis of the surfactant was done by ¹H-NMR, ¹³C-NMR, ²⁹Si-NMR and FT-IR analysis. In addition the thermal stability of TS-EO12 was studied by the thermogravimetric measurements. On the one hand the surface properties of TS-EO12 at the water-air interface were investigated by surfactant aqueous solutions surface tension measurements carried out at 293 K, 303 K and 313 K, and on the other the aggregation properties were analyzed based on the solubilization properties of TS-EO12 aggregates at different temperatures. On the basis of the obtained thermodynamic parameters of adsorption and micellization of studied surfactant the temperature impact on its surface and volume properties were deduced. It was proved that the tendency of the studied surfactant molecules to adsorb at the water-air interface and to form micelles weakens with decreasing temperature. It was also concluded that the structure of the adsorption layer changes with temperature. Optical microscopy measurements were used for the TS-EO12 micelle morphology determination.     

DPH-环糊精纳米管状聚集体的计算机模拟

1,6-二苯基－1,3,5-己三烯（1,6-diphenyl-1,3,5-hexatriene）（简称DPH）不能与α-环糊精，但可以分别与β-、γ-环糊精通过超分子自组装作用形成纳米管状结构的聚集体.该文采用分子力学和分子动力学模拟对这些聚集体在中性和碱性下条件的理论模型进行了预测，并分析了其主客体间的非键相互作用以及氢键的形成情况.计算结果表明，在碱性条件下，环糊精分子间氢键的消失导致了纳米管状结构的解离；而空腔过小是α-环糊精和DPH之间不能形成纳米管状结构的原因.     

锆-氚反应热力学特性

<正>利用金属氢化物可以方便地对氢同位素氕、氘、氚进行泵输、转移、固态吸附贮存、功能薄膜制造等。目前应用较成熟的有铀[1]、钛[2]、锆钴合金[3]等材料。锆与钛是属于同一族的金属元素,也是一种吸氢密度很高的功能材料,目前国内外已有较多关于氢在锆中固溶[4]、扩散[5-6]等方面的报道,但有关锆吸氚性能     

锆-氘反应热力学特性研究

The p-c-T curves and the relation between equilibrium pressure and temperature of deuterium absorption and desorption from zirconium were measured in the temperature range of 400～675 ℃. Equilibrium pressure of the absorption and desorption at different temperatures were given and then the thermodynamic parameters and the deuterium absorption capacity were determined according to Vant Hoff equation. There are different changes of enthalpy and entropy when zirconium changes to different phases. The change of enthalpy in the phase of α plus δ is -98.9 kJ·mol^-1 in the temperature range of 400～475 ℃. The changes of enthalpy in the first and second plateau are -75.1 kJ·mol^-1 and -161.7 kJ·mol^-1, respectively in the temperature range of 525～675 ℃. The corresponding changes of entropy are -66.5 J·K^-1·mol^-1, -32.4 J·K^-1·mol^-1 and -146.5 J·K^-1·mol^-1, respectively. There are obvious lagging effects when zirconium desorbs deuterium.     

An Insoluble Surfactant Model for a Vertical Draining Free Film

A mathematical model is constructed to study the evolution of a vertically oriented thin liquid film draining under gravity when there is an insoluble surfactant with finite surface viscosity on its free surface. Lubrication theory for this free film results in three coupled nonlinear partial differential equations describing the free surface shape, the surface velocity, and the surfactant transport at leading order. We will show that in the limit of large surface viscosity, the evolution of the free surface is that obtained for the tangentially immobile case. For mobile films with small surface viscosity, transition from a mobile to an essentially immobile film is observed for large Marangoni effects. It is verified that increasing surface viscosity and the Marangoni effect retard drainage, thereby enhancing film stability. The theoretical results are compared with experiment; the purpose of both is to act as a model problem to evaluate the effectiveness of surfactants for potential use in foam-fabrication processes. Copyright 2000 Academic Press.     

表面活性剂界面自组装的分子动力学模拟

主要介绍了表面活性剂在液／液、气／液和固／液界面的自组装,详细讨论了分子动力学模拟在表面活性剂界面自组装体系的应用,指出了近年来该领域的发展现状及应用前景。     

有序分子聚集体化学研究展望

本文对有序分子聚集体领域的最新进展作了评述, 并展望了有序分子聚集体化学的发展动向。     

Automated and Efficient Generation of General Molecular Aggregate Structures

Modeling intermolecular interactions of complex non-covalent structures is important in many areas of chemistry. To facilitate the generation of reasonable dimer, oligomer, and general aggregate geometries, we introduce an automated computational interaction site screening (aISS) workflow. This easy-to-use tool combines a genetic algorithm employing the intermolecular force-field xTB-IFF for initial search steps with the general force-field GFN-FF and the semi-empirical GFN2-xTB method for geometry optimizations. Compared with the alternative CREST program, aISS yields similar results but with computer time savings of 1–3 orders of magnitude. This allows for the treatment of systems with thousands of atoms composed of elements up to radon, e.g., metal-organic complexes, or even polyhedra and zeolite cut-outs which were not accessible before. Moreover, aISS can identify reactive sites and provides options like site-directed (user-guided) screening.     

The Effect of Simulation Cell Size on the Diffusion Coefficient of an Ionic Surfactant Aggregate

Results of all-atom molecular dynamics simulation have been presented for salt-free aqueous solutions of sodium dodecyl sulfate at its fixed total concentration in a simulation cell containing one to four preliminarily formed quasi-stable ionic aggregates with equal aggregation numbers n = 32. The obtained molecular dynamics trajectories have been used to study the structural and transport properties of the micellar solution. The value of the counterion diffusion coefficient obtained using the Green–Kubo relation has turned out to be somewhat higher than the corresponding value calculated by the Einstein equation. The diffusion coefficients of the aggregates in the systems containing from two to four aggregates have appeared to be higher than the diffusion coefficient of a single aggregate in a cell. The mean force potential obtained for the interaction between the aggregates having aggregation number n = 32 as a function the distance between the aggregate centers of mass has a local minimum in the system containing four such aggregates.     

Structural and Chemical Characteristics of Model Molecular Fragments of Petroleum Resins

Supramolecular, molecular and electronic structures of petroleum resins are studied. The experimental part includes isolation of resins by the eluent method and measuring electron and IR spectra. The structural parameters are calculated by molecular mechanics and DFT/B3LYP methods. The calculated data are in good agreement with the experiment. The nonplanar structure of petroleum resins is confirmed by the results of our structural study.     

Thermodynamic Limitations of the Reptation Model

Summary: The paper deals with the question whether the tube/reptation model of polymer chain dynamics is compatible with general laws of statistical physics. Based on a relation between the mean squared fluctuation of the number of segments in a given volume element and the isothermal compressibility of the polymer system, it follows straightforwardly that the tube/reptation model predicts fluctuations larger than permitted by thermodynamics on the time scale t ≳ τ_R, where τ_R is the Rouse relaxation time.     

Thermodynamic Insight into Protein Aggregation Using a Kinetic Ising Model

In this work, we present a kinetic analysis for protein aggregation using the kinetic Ising model, which serves as a new application of a previously proposed model [Liang et al., J. Chin. Chem. Soc.­ 2003 , 50, 335]. Considering protein as a single spin unit, we map two states of a unit to the aggregation‐prone (AP) and the fibril (F) states. This work shows that the model can successfully capture the nucleation‐growth features of protein aggregation from experiments, which offers thermodynamic interpretations of aggregation properties, such as lag‐time and fibril stability.