Nonelectrolyte-Induced Micellar Shape Changes in Aqueous Solutions of Silicone Surfactants

Dynamic light scattering, cloud point (CP), and surface tension studies have been carried out to examine the influence of six (including two acetates, two alkoxyethanols, and two sugars) nonelectrolyte additives on two silicone surfactants based on poly (dimethyl siloxane)—graft—polyethers in aqueous solutions. The results indicate that the presence of alkoxyethanols induced the oblate ellipsoidal to spherical micellar transition, while sugars increase the size of the ellipsoidal micelles. The effect of cosolvent or additives on critical micelle concentration (CMC) and CP is discussed on the basis of water structure making and breaking effect. The thermodynamic and surface active parameters were calculated from the surface tension isotherm curves.     

Surfactant-free coating of thiols on gold nanoparticles using sonochemistry: A study of competing processes

A method for the surfactant-free coating of gold nanoparticles with thiols using sonochemistry is presented. The gold nanoparticles were prepared by a modified Zsigmondy method, affording good control over the particle-size distribution, and the thiol coating was performed by the sonication of a biphasic system consisting of a nanoparticle suspension in water and thiols in toluene. The effects of two important reaction parameters on the particle morphology, viz. sonication time and thiol concentration, were investigated in detail using transmission electron microscopy. The effect of the thiol chain length was also studied. We show that the morphology of the coated particles is determined through a competition between two opposing effects: particle fusion, due to the sonication conditions, and digestive ripening, due to the action of the thiols. Additionally, we illustrate the utility of our technique for various applications, including surface-enhanced Raman scattering from bound molecules, and further functionalization using a thiol-exchange reaction. Our technique paves the way for an efficient synthesis of thiol-coated AuNPs of different shapes and sizes, suitable for a range of diverse applications.     

Preparation of a variety of fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide oligomer/silica nanocomposites possessing no weight loss characteristic at 800°C

A variety of fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide oligomer [R_F‐(DOBAA)_n‐ R_F]/silica nanocomposites, in which the oligomer contents are 18–96%, were prepared by reactions of the corresponding fluorinated oligomer with tetraethoxysilane and silica nanoparticles under alkaline conditions. Each fluorinated oligomer/silica composite thus obtained is nanometer size‐controlled very fine particles (22–68 nm) possessing a good dispersibility and stability in a variety of solvents including water. Interestingly, the weight loss of R_F‐(DOBAA)_n‐R_F/silica nanocomposites, in which the oligomer contents are 18–72%, were not observed at all even at 800°C, as well as the original silica nanoparticles, although the corresponding sub‐micrometer size‐controlled R_F‐ (DOBAA)_n‐R_F/silica composites (particle size: 359 nm) decomposed completely at 800°C to afford the weight loss in proportion to the content of R_F‐(DOBAA)_n‐R_F oligomer in composites. On the other hand, a slight weight loss of R_F‐(DOBAA)_n‐R_F/silica nanocomposites, in which the oligomer contents are 75–94%, was observed at 800°C compared to that of the original silica nanoparticles. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of gamma irradiation on synthesis and characterization of bio-nanocomposite SF/Ag nanoparticles

This study describes the synthesis of silver nanoparticles (AgNPs) using aqueous silk fibroin (SF) solution obtained from Bombyx mori silk under gamma radiation environment. The obtained AgNPs were characterized using UV–visible (UV–Vis) spectroscopy, X-ray diffraction (XRD) measurements, dynamic light scattering experiment (DLS) and transmission electron microscope (TEM) images. The UV–Vis absorption spectra of the samples confirmed the formation of AgNPs by showing surface plasmon resonance (SPR) band in the range of (= 428–435?nm. The XRD study revealed metal silver with the face-centered cubic (FCC) crystal structure. DLS measurements showed the dose-dependent average size of the AgNPs. TEM images showed formed AgNPs are nearly spherical in shape with smooth edges. From this study, it was found that the increasing radiation dose increases the rate of reduction and decreases the particle size. The size of the AgNPs can be tuned by controlling the radiation dose.     

Fluorescent probe for turn-on sensing of l-cysteine by ensemble of AuNCs and polymer protected AuNPs

A new fluorescent probe based on ensemble of gold nanoclusters (AuNCs) and polymer protected gold nanoparticles (AuNPs) for turn-on sensing of l-cysteine was designed and prepared. The AuNCs were protected by bovine serum albumin and had strong fluorescence. The polymer protected AuNPs were synthesized by a facile in situ strategy at room temperature and could quench the fluorescence of AuNCs due to the Förster resonance energy transfer. Interestingly, it has been observed that the quenched fluorescence of AuNCs was recovered by l-cysteine, which could induce the aggregation of polymer protected AuNPs by sulfur group. Then the prepared fluorescent probe was successfully used for determination of l-Cys in human urines, which would have an evolving aspect and promote the subsequent exploration.     

Micellization and interaction of anionic and nonionic mixed surfactant systems in water

Interaction between binary surfactant mixtures containing anionic surfactants viz. sodium dodecyl sulphates (NaDS) and magnesium dodecyl sulphates (Mg(DS)₂) and a nonionic surfactants viz. dodecyl dodecapolyethylene glycol ether (C₁₂E₁₂) and dodecyl pentadecapolyethylene glycol ether (C₁₂E₁₅) in water at different mole fractions (0–1) were studied by surface tension, viscometry and dynamic light scattering (DLS) methods. The composition of mixed micelles and the interaction parameter, β evaluated from the CMC data obtained by surface tension for different systems using Rubingh's theory were discussed. Activity coefficient (f₁ and f₂) of metal dodecyl sulphates (MDS)/C₁₂E_m (m = 12, 15) mixed surfactant systems were evaluated, which shows extent of ideality of individual surfactant in mixed system. The estimated interaction parameter indicates an overall attractive interaction in the mixed micelles, which is predominant for NaDS as compared to Mg(DS)₂. Counter ion valency has specific effect on the mixed micelles, as Mg(DS)₂ has less interaction with nonionic surfactants in comparison to NaDS due to strong condensation of counter ion. The stability factors for mixed micelles were also discussed by Maeda's approach, which was justified on the basis of steric factor due to difference in head group of nonionic surfactant. DLS measurements and viscosity data reveals the synergism in mixed micelles, showing typical viscosity trends and linearity in sizes were observed.     

Polymeric Nanoparticles Stabilized by Surfactants Investigated by Light Scattering,Small-Angle Neutron Scattering,and Cryo-TEM Methods

We have investigated self-organization of polymers with surfactants through solvent shifting process resulting in formation of stable and uniform nanoparticles. We studied polymeric nanoparticles made of poly(methylmethacrylate) and of polystyrene dispersed in water. The dispersion was prepared by a fast mixing of a solution of the polymers with a solution of several ionic and nonionic surfactants in pure water. We observed the formation of well defined nanoparticles by light scattering, small-angle neutron scattering (SANS), and cryogenic transmission electron microscopy (Cryo-TEM) methods. The study shows how nanoparticle properties are changed by the chemical composition of surfactants, molar mass of polymers, concentrations of both components and finally, by variations in method of nanoparticles preparation. Dynamic light scattering (DLS) and static light scattering (SLS) provide the hydrodynamic radii and radii of gyration for selected types of nanoparticles. Cryo-TEM experiments prove that the nanoparticles have good spherical shape. Analysis of SANS data and Cryo-TEM micrographs suggest that the prepared particles are composed of polymer and surfactant that are evenly distributed.     

Differences in self‐assembly features of thermoresponsive anionic triblock copolymers synthesized via one‐pot or two‐pot by atom transfer radical polymerization

The self‐assembly process in aqueous solutions of the methoxyl‐poly(ethylene glycol)‐block‐poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic sodium)‐block‐poly(N‐isopropyl acrylamide) (PNIPAAM) triblock copolymer, synthesized via two different atomic transfer radical polymerization methods, namely “one‐pot” (P3‐sample) and “two‐pot” (P2‐sample), was studied by various experimental techniques. The “one‐pot” procedure leads to a copolymer (P3) where the PNIPAAM block is contaminated with a minor quantity of 2‐acrylamido‐2‐methyl‐1‐propane sulfonate (AMPS) residuals and this sample does not form micelles over the considered temperature region, but unimers and temperature‐induced aggregates coexist in the presence of a small amount of salt. The P2 polymer forms micelles and intermicellar structures, but the former moieties disappear at high temperatures, whereas the latter species contract with increasing temperature. Small‐angle neutron scattering results revealed correlation peaks, both for P3 and P2, and no micelle formation for P3, but a pronounced upturn of the scattered intensity at low wavevector values at elevated temperatures for the P2 copolymer. The findings from this study clearly show that the spurious AMPS residuals have a drastic influence on the self‐assembly and micelle formation of the triblock copolymer. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 524–534     

萃金体系第三相的产生及其谱学研究

利用^198Au示踪法研究了十四烷基二甲基苄基氯化铵从碱性氰化液中萃取金第三相的产生过程，同时用傅里叶变换红外光谱（FTIR），核磁共振（NMR），激光光散射（DLS）等方法分析了第三相形成后上下两有机相的微观结构，结果表明，随着有机相中金浓度的增大，有机相中有纳米级的聚集体形成；当金浓度继续增大时，有机相分为上下两相，有机相中的金，磷酸三丁酯（TBP）和水主要集中在下层，下层有机相有明显的水特征吸收峰，TBP的P=O伸缩振动向低频移动，核磁共振（^31P-NMR)的化学位移明显移向高场；用激光光散射技术测定了两有机相中聚集体的大小。     

原子力显微镜与动态光散射研究疏水缔合聚丙烯酰胺微观结构

驱油用疏水缔合聚丙烯酰胺(HAP)性能优劣由其微观结构决定,优选研究HAP微观结构的方法,方便现场准确筛选功能良好的驱油聚合物。本文通过原子力显微镜(AFM)和扫描电镜(SEM)观察了不同浓度HAP溶液的微观结构,动态光散射(DLS)与AFM分析了粒径分布。结果表明,随着聚合物浓度的增加,DLS测得粒径增大,粒径分布由单峰变为双峰;SEM观察到由无空间网络结构,到相对松散、易被盐破坏空间网络结构,再到不易被盐破坏的完整、致密的网络结构;AFM可以同时得到一定空间结构以及与DLS相符的粒径大小,三种方法综合比较发现,结合三种不同的表征手段能够较好的、较全面的表示HAP在溶液中的微观结构。