Selective grafting of proteins on Janus particles: Adsorption and covalent coupling strategies

Janus particles have proven to be original particles to sense protein-cell interactions or to organize cell on a substrate. This work presents a covalent coupling strategy to graft fibronectin on a specific side of Au/PS or Au/SiO₂ 1 μm Janus particles. By studying several buffers that could limit adsorption of protein on plain particles of PS, SiO₂ and Au, fibronectin is covalently grafted on those particles. We demonstrate two ways of grafting proteins on one side of the Janus particles, either on the Au side functionalized with thiols or on the PS/SiO₂ side activated with carboxylate groups.     

Colloid straining within saturated heterogeneous porous media

The transport of 0.46 μm, 2.94 μm, 5.1 μm and 6.06 μm latex particles in heterogeneous porous media prepared from the mixing of 0.78 mm, 0.46 mm and 0.23 mm quartz sands was investigated through column transport experiments. It was observed that the 0.46 μm particles traveled conservatively within the heterogeneous porous media, suggesting that under the experimental conditions employed in this research the strong repulsive interactions between the negatively charged latex particles and the clean quartz sands led to minimal colloid immobilization due to physicochemical filtration. The immobilization of the 2.94 μm, 5.1 μm and 6.06 μm latex particles was thus attributed to colloid straining. Experimental results showed that the straining of colloidal particles within heterogeneous sand mixtures increased when the fraction of finer sands increased. The mathematical model that was developed and tested based on results obtained using uniform sands (Xu et al., 2006) was found to be able to describe colloid straining within heterogeneous porous media. Examination of the relationship between the best-fit values of the clean-bed straining rate coefficients (k₀) and the ratio of colloid diameter (d_p) and sand grain size (d_g) indicated that when number-average sizes were used to represent the size of the heterogeneous porous media, there existed a consistent relationship for both uniform sands and heterogeneous sand mixtures. Similarly, the use of the number-averaged sizes for the heterogeneous porous media produced a uniform relationship between the colloid straining capacity term (λ) and the ratio of d_p/d_g for all the sand treatments.     

Wafer-scale self-assembled plasmonic thin films

Plasmonic films have become important for many applications including photonics, energy conversion, and chemical sensing, but the fabrication of these films often requires special equipment, great care, and skill. Colloidal metal nanoparticles offer an alternative as they have been shown to self-assemble into highly-ordered monolayer films by the simple and inexpensive technique of drop casting. Using this technique, we fabricated wafer-scale films of highly-ordered 6 nm Au nanoparticles and evaluated them as candidates for plasmonic applications. These colloidal films were found to support uniform and high-quality plasmon modes over the entire area of the wafer. A combination of microscopy and spectroscopy was used to evaluate and correlate the structural and optical qualities of the films. Electron and atomic force microscopy showed that the nanoscale structure of the films was compact and highly ordered, with few defects or bilayers. Spectroscopic ellipsometry showed that the majority of the film was optically quite uniform with some bilayer patches and voids. These were subsequently confirmed by microscopy. Optical analysis of the thin film showed a prominent plasmon resonance band across the entire wafer. The plasmon frequency was quite insensitive to the presence of voids or bilayers. The width of the plasmon band was more sensitive to bilayers, however, and was found to be as much as 15% wider than in monolayer regions. These results indicate that self-assembled colloidal thin films should be suitable for large-scale plasmonic applications.     

Colloid‐Enhanced Ultrafiltration of Chlorophenols in Wastewater: Part V. Simultaneous Removal of a Chlorophenol and a Metal Ion

Abstract

Polyelectrolyte micellar‐enhanced ultrafiltration (PE‐MEUF) is a separation process to remove target solutes from water using a mixture of a surfactant and an oppositely charged polyelectrolyte as a colloid. An organic solute and a metal cation can simultaneously associate with the colloid, which is subsequently ultrafiltered from solution. An organic solute solubilizes in the surfactant micelle‐like aggregates whereas an inorganic cation binds onto the oppositely charged polyion chains. The solution is then passed through the membrane having pore sizes small enough to block the passage of the surfactant‐polymer aggregates. In this work, PE‐MEUF has been applied to mixtures containing dichlorophenol (DCP) and magnesium ion (Mg²⁺), using cetylpyridinium chloride (CPC) and sodium poly(styrenesulfonate) (PSS) mixtures. It was observed that the presence of Mg²⁺ does not affect DCP rejection. The [CPC] to [PSS] ratio and colloid concentration have a significant effect on both DCP and Mg²⁺ rejections. Increased ionic strength from added salt increases the gel point (colloid concentration at which flux is zero). The viscosity of the colloid solution is inversely related to the gel point.     

Colloidal Fouling during Ultrafiltration

Abstract

Colloidal fouling causes serious problems in many membrane plants. Two different kinds of flux-reducing phenomena occur when treating colloidal dispersions. When treating stable dispersions the flux is reversible and can be restored after changing the operating parameters, such as the transmembrane pressure or the cross flow velocity. The flux reduction experienced when treating unstable colloidal dispersions is irreversible. In this study the DLVO theory, well-known from colloid chemistry, has been used to illustrate the mechanisms underlying the difference in filtration characteristics between stable and unstable colloidal dispersions.     

氢氧化锌胶体与三磷酸腺苷二钠联用对狂犬病疫苗诱导小鼠体液免疫应答的增强作用

目的制备氢氧化锌[Zn(OH)2]胶体,并检测其单独或与三磷酸腺苷二钠(Disodium adenosine tripho-sphate,简称ATP)联用对狂犬病疫苗诱导小鼠体液免疫应答的增强作用。方法采用葡萄糖酸锌作为锌源,与NaOH反应制备Zn(OH)2胶体溶液,对其进行纯化及检测,并进行小鼠急性毒性试验;将不同剂量的Zn(OH)2胶体单独或与不同剂量的ATP联用,与狂犬病疫苗(0.25 IU)混合,免疫ICR小鼠,并设生理盐水对照组和抗原对照组,每组8只,Zn(OH)2和Zn(OH)2+ATP和生理盐水对照组采用单次免疫,抗原对照组分别免疫1、2、3、5次,分别于初次免疫后4、8、12、16周采血,分离血清,检测血清中抗狂犬病病毒特异性IgG抗体水平。结果所制备Zn(OH)2胶体溶液最大吸收波长为213 nm,可观察到明显的丁达尔现象,浓度为6 mg/ml,经光学色差显微镜及扫描电镜观察合格,小鼠急性毒性试验未观察到急性毒副作用。大部分佐剂组抗体水平高于抗原单次免疫组,但均未达到抗原5次免疫组水平;0.27和0.21 mg Zn(OH)2组在初次免疫后8周内有高水平抗体产生;0.27 mg Zn(OH)2组在初次免疫后16周出现抗体水平反弹性升高;0.18 mg Zn(OH)2+1.0 mg ATP组和0.18 mg Zn(OH)2+0.5 mg ATP组在初次免疫后4周内产生的抗体水平较高,之后逐渐下降;2次和3次免疫抗原对照组在初次免疫后8周内,其抗体水平不及佐剂组。结论所制备的Zn(OH)2胶体佐剂单独或与ATP联用均可增强狂犬病疫苗诱导小鼠特异性体液免疫应答,且安全性良好,有望应用于疫苗生产。     

A new method to evaluate polydisperse kaolinite clay particle removal in roughing filtration using colloid filtration theory

Previous application of colloid filtration theory to roughing filtration has not considered a reliable method for determining a representative attachment factor for a polydisperse suspension (of constant particle density). Establishment of such a method would broaden the application of trajectory modelling in roughing filtration, and progress the development of a comprehensive database of attachment factors and surface charge potentials for various particle and fluid types. This study establishes a methodology for the application of colloid filtration theory to roughing filtration and incorporates recent advancements in theoretical single-collector efficiency. A polydisperse kaolinite clay suspension was passed through a series of four gravel upflow roughing filters and removal efficiencies were calculated. Both the classical and Tufenkji and Elimelech's more recent correlation equations were used to calculate theoretical single-collector efficiencies and associated attachment factors for three different filter media sizes, flow rates, and suspended solids concentrations (0.137+/-0.023). The use of Tufenkji and Elimelech's modified correlation equation resulted in reduced variability in the estimation of theoretical single-collector efficiencies.     

Removal efficiencies and attachment coefficients for Cryptosporidium in sandy alluvial riverbank sediment

Riverbank filtration has been shown to be effective for removing viable Cryptosporidium parvum oocysts. Drinking water systems that employ riverbank filtration may receive additional treatment credits beyond that which they can obtain using traditional engineering approaches. In order to develop guidance for removal effectiveness, screening level predictive modeling by colloid filtration theory combined with advection and dispersion modeling is potentially useful. Currently, only few studies have measured basic effective colloid filtration parameters for Cryptosporidium oocysts with naturally occurring riverbank sediments. In the focus of this study we conducted flow column experiments in triplicate and measured effective attachment rate coefficients for sandy river sediments of the Southern Great Plains which are low in organic matter. We found that for sediment sampled from these high-energy rivers there was no apparent dependency of C. parvum removal with carbon content, bacterial colony forming units, or with gross texture properties of the sands. The differences in particle size distribution for the sediments suggested that straining did not play a role in removal efficiency. First-order colloid attachment rate coefficients followed lognormal distribution functions. The coefficients also appeared to be unrelated to the differences in particle size distributions of the sediments, bacterial counts, or levels of total carbon or total organic carbon. Using Monte Carlo analyses, the lowest observed 5th percentile was 8.0 × 10⁻⁶ min⁻¹ and the highest observed 95th percentile was 1.6 × 10⁻³. Total log₁₀ removals ranged from 23 to 200 m⁻¹. These results have application for screening level colloid filtration modeling of riverbank filtration in these systems.     

Competition between kaolinite flocculation and stabilization in divalent cation solutions dosed with anionic polyacrylamides

Divalent cations have been reported to develop bridges between anionic polyelectrolytes and negatively-charged colloidal particles, thereby enhancing particle flocculation. However, results from this study of kaolinite suspensions dosed with various anionic polyacrylamides (PAMs) reveal that Ca²⁺ and Mg²⁺ can lead to colloid stabilization under some conditions. To explain the opposite but coexisting processes of flocculation and stabilization with divalent cations, a conceptual flocculation model with (1) particle-binding divalent cationic bridges between PAM molecules and kaolinite particles and (2) polymer-binding divalent cationic bridges between PAM molecules is proposed. The particle-binding bridges enhanced flocculation and aggregated kaolinite particles in large, easily-settleable flocs whereas the polymer-binding bridges increased steric stabilization by developing polymer layers covering the kaolinite surface. Both the particle-binding and polymer-binding divalent cationic bridges coexist in anionic PAM- and kaolinite-containing suspensions and thus induce the counteracting processes of particle flocculation and stabilization. Therefore, anionic polyelectrolytes in divalent cation-enriched aqueous solutions can sometimes lead to the stabilization of colloidal particles due to the polymer-binding divalent cationic bridges.     

胶体磨在乳化炸药生产中的应用

简述了目前常用的立式胶体磨和卧式胶体磨两种胶体磨的结构特点和工作原理。主要讨论了立式胶体磨应用于乳化炸药生产所必须具备的前提 ;立式胶体磨成功应用于炸药生产的半连续式生产工艺、静态混合器作预乳器的连续生产工艺和连续乳化器作预乳器的连续生产工艺三种主要工艺流程设计、配套设备研制和选用原则 ;三种工艺流程的各自优缺点和主要控制要素等