Determination of Interparticle Forces by Colloidal Particle Scattering: A Simulation Study

Preflocculated ferric hydroxide flocs were subjected to either a simple shear flow or a two-dimensional straining flow, and their motion was optically observed. Digital image analysis was applied to extract information on orientation and deformation from the digitized frames. It was found that the simple shear flow led to a rotation of the flocs whose motion can be understood from the behavior of a solid ellipsoid. In the extensional flow, no continuous rotation occurred and flocs were broken apart along the axis of straining. The rupture forces estimated from an ellipsoid model were found to be in the range of 0.1 N/m(2). Copyright 2000 Academic Press.     

Structural Interpretations of Static Light Scattering Patterns of Fractal Aggregates

A method based on static light scattering by fractal aggregates is introduced to extract structural information. In this study, we determine the scattered intensity by a fractal aggregate calculating the Structure and the Form factors noted, respectively, S(q) and F(q). We use the approximation of the mean field Mie scattering by fractal aggregates (R. Botet, P. Rannou, and M. Cabane, appl. opt. 36, 8791, 1997). This approximation is validated by a comparison of the scattering and extinction cross sections values calculated using, on the one hand, Mie theory with a mean optical index n) and, on the other hand, the mean field approximation. Scattering and extinction cross sections values differ by about 5%. We show that the mean environment of primary scatterers characterized by the optical index n(s) must be taken into account to interpret accurately the scattering pattern from fractal aggregates. Numerical simulations were done to evaluate the influence of the fractal dimension values (D(f)>2) and of the radius of gyration or the number of primary particles within the aggregates (N=50 to 250) on the scatterers' mean optical contrast (n(s)/n). This last parameter plays a major role in determining the Form factor F(q) which corresponds to the primary particles' scattering. In associating the mean optical index (n) to structural characteristics, this work provides a theoretical framework to be used to provide additional structural information from the scattering pattern of a fractal aggregate (cf. Part II). Copyright 2000 Academic Press.     

Near-Field Scattering Enhancement of Perylene Based Aggregates for Random Lasing

Strong near-field scattering enhancement (NFSE) of polyhedral oligomeric silsesquioxanes (POSS) nanoparticles (NPs) aggregates is found through physical simulation. An aggregation of begin{document}$N$end{document}, begin{document}$N'$end{document}-di-[3-(isobutyl polyhedral oligomeric silsesquioxanes) propyl] perylene diimide (DPP) which possesses POSS as scatteres experimentally performs strong NFSE, which confirms the physical simulation results. Moreover, coherent random laser is triggered from the DPP aggregates in carbon disulfide. It is the NFSE of POSS NPs connected to both ends of DPP through covalent bonds and the NFSE of their aggregation thanks to DPP's aggregation that is responsible for the coherent random laser. So, this work develops a method to improve weak scattering of system through construction of molecules, and opens a road to a variety of novel interdisciplinary investigations, involving molecular designing for disordered photonics.     

Computer Study of the Association Behavior of Gradient Copolymers: Analysis of Simulation Results Based on a New Algorithm for Recognition and Classification of Aggregates

We present a computer study of the association behavior of copolymer chains with a gradient part and soluble tail of variable length. As a simulation method we use dynamic Monte Carlo simulation on a simple cubic lattice with pair interaction parameters. The solvent quality and selectivity is modeled by the variation of pair interaction parameters between nearest neighbors on the lattice. The role of the length of soluble part in the self‐assembly and its effect on the structure of aggregates was the main goal of this work. The size and structure of aggregates were analyzed using an improved topological classification method which has been developed and tested in the present study. The structure and association numbers of aggregates were compared with those of linear diblock copolymers.

     

凝胶化反应中标度行为及凝胶化点关系

在苯乙烯(St)-二乙烯苯(DVB)自由基聚合的凝胶化反应过程中,定时取样,得到凝胶化点前后及直至反应终点的一系列溶胶样品,利用光散射技术研究了溶胶相的重均分子量M_w、尺寸均方旋转半径R_g的变化过程,建立了M_w、R_g和反应时间t的标度关系,并在此基础上提出一神新的准确求取凝胶化时间t_gel的方法.     

Measurement of Fractal Aggregates of Polydisperse Particles Using Small-Angle Light Scattering

The effect of primary particle polydispersity on the structure of fractal aggregates has been investigated through the salt-induced, diffusion-limited aggregation of mixtures of hematite. The fractal dimension was determined experimentally using three independent methods: q dependence of static light scattering, kinetic scaling, and correlation of aggregate mass and linear size both determined from Guinier scattering. The fractal dimensions D(f) obtained were 1.75+/-0.03, 1.76+/-0.03, and 1.70+/-0.05, respectively. The use of a previously derived fractal mean particle size was validated in allowing data collapse to master curves for the aggregation kinetics data. The fractal mean particle size is shown to have general utility by taking a number weighting to describe polydisperse aggregation kinetics and a mass weighting to describe small q scattering behavior. Copyright 2000 Academic Press.     

κ-卡拉胶热可逆凝胶的非遍历行为研究

采用散射斑纹(speckle)技术, 即散射光强涨落法, 研究了κ-卡拉胶(KC)热可逆凝胶的非遍历行为. 证明了非遍历性的存在, 并研究了浓度、温度等条件对该非遍历性的影响. 结果表明：该物理凝胶存在非遍历性, 并随KC浓度增加, 凝胶非遍历性增大；随温度升高, 凝胶非遍历性逐渐减小, 直至消失.     

高密度聚乙烯结晶行为的Rayleigh散射研究

研究了高密度聚乙烯在结晶成核剂──二苄叉山梨醇存在下的Ｒａｙｌｅｉｇｈ散射特征，证明了棒状结晶的存在。讨论了成核剂对结晶的影响，计算了棒晶的棒长和半径。     

κ-卡拉胶热可逆凝胶的非遍历行为研究

采用散射斑纹(speckle)技术,即散射光强涨落法,研究了κ-卡拉胶(KC)热可逆凝胶的非遍历行为.证明了非遍历性的存在,并研究了浓度、温度等条件对该非遍历性的影响.结果表明:该物理凝胶存在非遍历性,并随KC浓度增加,凝胶非遍历性增大;随温度升高,凝胶非遍历性逐渐减小,直至消失.     

小牛胸腺脱氧核糖核酸的共振散射光谱特性

1　引　　言脱氧核糖核酸 (ＤＮＡ)是生命的遗传物质。Ｘ 射线研究表明 ,ＤＮＡ呈双螺旋结构 ,双螺旋的直径约为 2ｎｍ ,长度约为5 0 0 0ｎｍ ,是一种特殊的纳米线。用共振散射技术研究ＤＮＡ与有机染料相互作用已有报道 ,但未见ＤＮＡ的共振散射、非线性共振散射光谱以及有关影响因素的研究报道。本文对ＤＮＡ的共振散射光谱及其影响因素进行了研究 ,发现ＣＴＭＡＢ使ＤＮＡ的共振散射强度增强 ,且使 3 1 0ｎｍ处的肩峰变成最强共振散射峰。2　实验部分2 .1　主要仪器和试剂　ＲＦ 5 4 0型荧光分光光度计 (日本岛津公司 ) ;ＵＶ 3 4 0 0型…     

Simulating Light Scattering Behavior of Branched Molecules

Monte Carlo simulations reveal long chain branching (LCB) topology based on kinetics of systems like low‐density polyethylene (ldPE). Examining the topologies computed shows the majority of branch arms to be short as compared to backbone length, while also a significant branch‐on‐branch fine structure is observed. Until now, predicting scattering function P ⁻¹(θ) from LCB has only been successful for structures like simple combs or stars. Topologies in graph theoretical form are used to predict scattering function P ⁻¹(θ) and by summating intramolecular distances, accounting for branching and excluded volume. Experimental size exclusion chromatography with multiangle light scattering can be brought in line with the predicted branching character. Branching is less than predicted due to a different fine structure in ldPE leading to stronger size contraction.     

Simulation of Colloidal Particle Scattering: Sensitivity to Attractive Forces

Colloidal particle scattering is a recently developed method for the determination of surface forces between micrometer-sized particles. In this paper we extend earlier simulation studies to interactions of the DLVO type including purely attractive potentials. We examine the criteria for capture and compare simulated results for a range of interaction parameters. We find that the scattering patterns can be represented in a simple way once a correction for angular distortion has been applied. This representation should aid the analysis and interpretation of experimental data. Copyright 2000 Academic Press.     

动态光散射研究盐对Gemini表面活性剂网状聚集体的影响

以动态光散射为主要手段研究了盐对羧酸盐Gemini表面活性剂O,O′-双(2-月桂酸钠)-p-二苯氧(记为C12φ2C12)自组织的影响.结果表明盐的加入很容易使C12φ2C12的网状聚集体转变为小(流体力学半径Rh,app约几纳米)和大(Rh,app100 nm)两种尺寸共存的聚集体,1,6-二苯基-1,3,5-己三烯(DPH)探针增溶实验证实小尺寸聚集体为核-壳结构的似球胶束,流变学测量说明大尺寸聚集体可能已经是线型的核-壳胶束.这种行为被归结为初始的网状聚集体不稳定,添加的反离子与C12φ2C12头基结合破坏了网状结构的亲水亲油平衡,促使了它们的转变.盐效应规律表现为MgCl2NaCl、Bu4NBrMe4NBrEt4NBrPr4NBr,这里Bu4NBr不遵循上述静电力顺序的原因是它提供了携带的丁基与C12φ2C12烷烃链疏水相互作用的附加力.     

Interfacial Composition of Surfactant Aggregates in the Presence of Fragrance: A Chemical Trapping Study

In recent years, there has been increasing interest in daily-use chemical products providing a pleasant scent. The added fragrance molecules may induce microstructural transitions of surfactant aggregates, which further affect the physical and chemical properties of the products. Here, the effects of four types of aromatic alcohols (cinnamyl alcohol, phenyl ethanol, phenyl methanol and anisyl alcohol) on cetyltrimethylammonium bromide (CTAB)/KBr aggregates were studied. The combined results from rheology, dynamic light scattering, and transmission electron microscopy measurements showed that cinnamyl alcohol induced significant micellar growth, while increases in micellar growth were less obvious for the other aromatic alcohols. The changes in the interfacial molarities of water, aromatic alcohol, and bromide ions during such transitions were studied using the chemical trapping method. Transitions resulting from added cinnamyl alcohol were accompanied by significant declines in interfacial water and bromide ion molarities, and a rise in interfacial alcohol molarity. The marked decrease in interfacial water molarity was not observed in previous studies of the octanol induced formation of wormlike micelles and vesicles, indicating that a different mechanism was presented in the current system. Nuclear magnetic resonance investigation showed that π–π stacking between cinnamyl alcohols, but not cation–π interactions between alcohols and CTAB headgroups, facilitated the tight packing of alcohol molecules in CTAB aggregates and the repulsion of water from the interfacial region. The current study may provide a theoretical basis for the morphological regulation of surfactant aggregates in the presence of additives.     

Annealing Behavior of Silica Gel Powders Modified with Silver Crystalline Aggregates

The annealing behaviour of silica powders added with silver, prepared by the sol-gel method, was studied using X-ray diffraction. Partial crystallization of amorphous SiO₂ samples as low as 600°C has been observed. For that, silver needed to be added to the precursor solution in such a way that it formed aggregates. Silica xerogel samples were prepared using a molar ratio ethanol/H₂O/TEOS of 4:11.6:1 and loaded with silver in three different ways: in the form of silver nitrate, silver chloride, or chemically synthesised silver fine particles. The microstructure of the silica xerogel powders was studied as a function of annealing temperature. Attention was paid to the evolution of the glass matrix as well as the silver aggregates in the SiO₂ matrix. Partial crystallization of the glass matrix was achieved at temperatures much lower than those specified by the phase diagram, independently of preparation method of the silver aggregates.     

An Effective Simulation of Aqueous Micellar Aggregates by Computational Models

Summary We have computationally studied the interaction modes, localization and orientation of a benzene (Bz) molecule on the surface of micelles formed by cetyltrimethylammonium salts CTAX. Experimental ¹H-NMR data on complexation shifts induced by Bz on the polar head hydrogens and on the adjacent methylene hydrogens of CTAX have been interpreted using a computational approach that combines an automatic molecular docking procedure with a calculation module that accounts for NMR complexation shifts due to ring current diamagnetic anisotropy. Three different models were used to reduce the complexity of the micellar system. Computational results, in good agreement with available experimental data, point to a preferential localization of the Bz molecule along the CTAX alkyl tail, about 3.9 Å away from the charged nitrogen. The Bz molecular plane is predicted perpendicular to the C-H bonds of the alkyl tail. The good results obtained with the simplest model suggest that it could be used to study more complex systems involving surfactants endowed with molecular recognition or catalytic abilities.     

Rheological Behavior and Scattering Studies of Acrylamide-Based Copolymer Solutions

Summary: In this paper the chemical structure of an acrylamide-N,N-dihexylacrylamide copolymer was established by IR and NMR. Static and dynamic light scattering in formamide were used in order to evaluate the polymer structural parameters, such as weight-average molecular weight (M_w), second virial coefficient (A₂), radius of gyration (R_G), the form factor P(q) and the hydrodynamic radius (R_H). Additionally to the classical characterization, those results indicated the presence of aggregation, showing that formamide is not a very good solvent, as stated in earlier investigations. The rheological behavior in aqueous solutions was evaluated as a function of the salt concentration. The solutions presented an important viscosity increase in the presence of NaCl and did not show any sensitivity to the presence of CaCl₂. This result is in favor of the oil recovery especially in high salinity reservoirs.     

表面单层组装多环芳烃荧光行为的Monte Carlo模拟

Recently,a series of sensing films based upon the supra-molecular behavior of aromatic compounds immobilized on substrate surfaces and its dependence to the composition of the medium have been successfully prepared. It is found that the properties and performances of the films depend upon various factors,including the nature of the sensing element,the way of immobilization,the nature of the substrate,and the density of the sensing element immobilized etc. To accelerate and deepen the studies,it was decided to carry out the theoretical simulation of the sensing films based upon the proposed principle. The fluorescence behavior of a functional plate,of which the surface is functionalized by single layer immobilization of aromatic compounds（sensing elements）,is simulated by Monte Carlo simulation method. The effects of the immobilization density of a sensing element,the excitation efficiency,and the association efficiency,P,which is a characteristic parameter of an aromatic compound,between the molecules of the sensing element on the ratio of the excimer emission to the monomer emission of the plate have been systematically examined. But the effects of the length and flexibility of a spacer are neglected,because in this simulation aromatic compounds are immobilized on a plate by the short stiff spacer. It is demonstrated that,for a functionalized plate of a short stiff spacer in a polar solvent（ in this case,the association tendency is strong,and P is close to 1）,aromatic compounds of middle excitation efficiency might be suitable as sensing elements. In addition,the immobilization density of the sensing element should be controlled. A recommended value is about 50%.