环状高分子对胶体稳定性影响的理论研究

将改进的基本度量理论与热力学微扰理论相结合,提出了胶体/高分子系统排空相互作用的IRDFT理论。该理论解释了在实际胶体系统中起重要作用的排斥体积效应和高分子链内相关性的竞争机制。应用该IRDFT,分别以线性链状和环状结构的高分子及其单体为排空元,计算了不同排空元条件下的胶体间排空相互作用。研究表明:对于絮凝破坏,自由环状高分子具有更大的优势。     

Uniform Mesoporous Silica Hexagon and Its Two‐Dimensional Colloidal Crystal

Well‐ordered mesoporous silica nanoparticles with uniform hexagonal disk shapes are synthesized under dilute alkaline conditions with a two‐step process, separating the nucleation and growth process. The resulting monodisperse hexagons can be arranged in a 2‐dimensional (2D) ordered periodical super‐structure. The hexagonal symmetry is similar in both scales. A statistical mechanical cell model is applied to analyze consequences of the interesting packing structure, including osmotic bulk modulus, phase separation and defects.     

Scattering properties,stability analysis,and phase separation of polyelectrolyte mixtures

The conditions of stability for weakly charged polyelectrolyte mixtures are analyzed from a scattering theory developed previously. In the thermodynamic limit of zero wave vector q = 0, it is found that electrostatic interaction induces a compatibility enhancement which is discussed for various cases of charge distributions. The condition of microphase separation transition at the wave vector for which the scattering is a maximum is also discussed. © 1993 John Wiley & Sons, Inc.     

Low-Shear Viscosities of Dilute Dispersions of Colloidal Rodlike Silica Particles in Cyclohexane

Low-shear viscosities have been studied for isotropic dispersions of uncharged colloidal silica rods in cyclohexane as a function of volume fraction Φ and aspect ratior_p. Intrinsic viscosities in the limit Φ → 0 agree with theoretical results [Brenner, H.,Int. J. Multiphase Flow1,195 (1974)] for colloidal cylinders. The Φ²term in the low-shear viscosity, accounting for two-particle interactions, is considerably larger than predicted by D. H. Berry and W. B. Russel [J. Fluid Mech.180,475 (1987)] for dilute hard-rod dispersions. The discrepancy is very likely due to weak interparticle attractions, which also account for the novel observation of an isotropic–isotropic phase separation in the silica rod dispersions. Our results demonstrate that, in comparison to spheres, high aspect ratios markedly increase both the shear viscosity and its sensitivity to even minor attractions.     

浊度法表征温敏性微凝胶体积的相转变行为

以N-异丙基丙烯酰胺(NIPAM)、甲基丙烯酸(MAA)为单体,N,N-亚甲基双丙烯酰胺(MBA)为交联剂,制备了温敏性聚(N-异丙基丙烯酰胺)(PNIPAM)和具有温度、pH敏感性的聚(N-异丙基丙烯酰胺-co-甲基丙烯酸)(PNIPAM-MAA)微凝胶。通过测定不同温度和pH条件下微凝胶浊度变化,表征微凝胶的温度及pH敏感性,描述了NaCl浓度和pH对微凝胶体积相转变温度的影响。同时,测定了微凝胶的临界聚沉浓度及临界絮凝温度,表征了微凝胶的稳定性,讨论了影响微凝胶的稳定性因素。     

Colloidal stability of PVC primary particles in vinyl chloride

The electrostatic contribution to the colloidal stability of PVC primary particles (R=0.15 m) dispersed in vinyl chloride, was calculated using models based on the Coulombic interactions and the DLVO theory. The calculations were based on: a) the particle charge as obtained from literature data on the electrophoretic mobility of PVC primary particles in VCM and b) on estimates of the Debye length as obtained from measurements of the electrical conductivity of VCM and of solutions of Bu₄NBF₄ in VCM.The calculations showed that particle stability would decrease with particle size (experimentally-observed behaviour), only if the particle charge increased with size at a lower rate than in proportion to particle radius.The calculations also suggest that particle growth may be governed by a competitive growth mechanism of electrostatic origin. Particle growth is assumed to occur by absorption of many small, weakly charged basic particles from the monomer phase. According to the calculations, the electrostatic interaction between primary and basic particles may be such that the growth of the smaller primary particles is favoured over that of the larger ones.     

The Influence of Ion Pair Formation on the Phase Behavior of Polyelectrolyte Solutions

In this paper we calculate the phase diagrams of polyelectrolyte solutions taking into account the possibility of ion pair formation between counterions and ions on polymer chains with their subsequent aggregation in multiplets. Multiplets play a role of reversible physical crosslinks between different polymer chains. Furthermore, we assume that the dielectric constant, and hence the binding energy of ion pairs and multiplets, depends on the volume fraction of polymer in the solution. We have shown that ion pairing and multiplet formation leads to instability of the homogeneous phase, so that at some conditions the phase separation can proceed even in good solvent. Another qualitatively new feature of the behavior of polyelectrolyte solutions is the emergence of a triple point on the phase diagram. The effect of the solvent polarity and the polarity of the dry polymer on the general form of the phase diagram is studied in detail.     

Photoluminescence Stability of Colloidal CdTe Quantum Dots in Various Buffer Solutions

Mercaptoacetic acid-capped CdTe quantum dots (QDs) are potential luminescent markers for biological analysis. The photoluminescence (PL) stability of the QDs in buffer solutions determines their practicability as markers in electrophoresis. The stability of the QDs was thus investigated in electrophoresis buffers including tris–borate–ethylenediaminetetraacetic acid (TBE) and tris–acetate–ethylenediaminetetraacetic acid (TAE). The QDs were completely unstable in high-concentrated buffers (≥0.1×). In the case of low concentrations (≤0.07× for TAE, ≤0.035× for TBE), the PL intensity of the QDs in two kinds of buffers decreased with increasing buffer concentrations. A red-shifted PL peak wavelength and PL intensity fluctuation were observed after dispersing the QDs in diluted TAE buffer solutions with concentrations of ≤0.07× for long time. According to the Stern–Volmer plots of PL degradation, the factors leading to the degradation were complicated, which was attributed to the actions of the components including tris, borate or acetic acid, and ethylenediaminetetraacetic acid as well as their mutual effects.     

Stability of Na-montmorillonite suspension in the presence of different cations and valences

The aim of this study was to investigate the effects of inorganic cations (Na⁺, Ca²⁺, and Al³⁺) with different valences and concentrations on the stability of Na-montmorillonite (Na-MMT) suspension. The stability was studied by turbidity and zeta potential measurements and adsorption thermodynamics. The results showed that the Na-MMT particles coagulated at pH 3–4.8, the stability of which was much inhibited by cations with higher concentration and higher valence. This was caused by the adsorption of cations and the reduction of electrostatic repulsion. Adsorption of Ca²⁺ on Na-MMT surface fits the Freundlich curve model well. Furthermore, the adsorption reduced the zeta potential of Na-MMT and then the energy barrier between the particles which well obeyed the classic DLVO theory.     

The Rheology of Bimodal Mixtures of Colloidal Particles with Long-Range, Soft Repulsions

Osmotic pressure and elastic moduli of bimodal suspensions of particles experiencing long-range, soft repulsions were measured. At fixed osmotic pressure, the total suspension volume fraction, φ, varies linearly as the mixing ratio φ_l/φ is increased from 0 to 1. Here φ_lis the volume fraction of large particles based on total suspension volume. This result suggests the suspensions studied here are phase separated into domains containing primarily small and primarily large particles and is not expected for hard sphere suspensions where, at fixed osmotic pressure, φ passes through a maximum as φ_l/φ is increased. Elastic moduli are well described by a model based on a composite microstructure where the domains of pure large and small particles must have the same osmotic pressure which fixes the local particle volume fraction and hence the elastic modulus in each phase. The existence of phase separation is supported by electron micrographs taken on samples prepared by rapidly drying suspensions with volume fractions near 0.6.     

Dispersibility of Barium Titanate Suspension in the Presence of Polyelectrolytes: A Review

Dispersibility of colloidal barium titanate suspensions is reviewed with an emphasis on the use of various polyelectrolytes as dispersants. The fundamentals of colloidal stability are discussed followed by the colloidal properties of barium titanate powder. Dispersion behavior of BaTiO₃ in both nonaqueous and aqueous media has been reviewed. Several studies on the stabilization of micron and nano‐sized barium titanate using various polymeric dispersants and a rhamnolipid biosurfactant are presented and discussed. The article attempts to provide a comprehensive review of the current state‐of‐the‐art in the area of colloidal processing of barium titanate.     

Synthesis of raspberry‐like organic–inorganic hybrid nanocapsules via pickering miniemulsion polymerization: Colloidal stability and morphology

Raspberry‐like hybrid nanocapsules with a hydrophobic liquid core were successfully prepared via the copolymerization of styrene, divinylbenzene (DVB), and 4‐vinyl pyridine (4‐VP) in Pickering‐stabilized miniemulsions by using silica particles as the sole emulsifier and hexadecane (HD) as liquid template. When compared with conventional Pickering miniemulsions and Pickering suspensions, the colloidal stability of the current systems is much more sensitive to the variation of reaction parameters such as pH, size, amount of silica particles, and content of 4‐VP. The systems without coagulum were only obtained in a narrow pH range at around 9.5 and by using 12 nm silica particles as emulsifier. The formation of well‐defined raspberry‐like capsules was confirmed by transmission electron microscopy (TEM) and high‐resolution scanning electron microscopy (HRSEM). The stable attachment of silica particles on the surface of hybrid particles was verified by centrifugation and subsequent characterizations, such as Fourier transform infrared spectroscopy, TEM, and HRSEM. The influence of pH and weight content of HD, DVB, and 4‐VP on the particle morphology was extensively investigated. Interestingly, the particle morphology strongly depends on the particle size. When compared with the organic surface‐active surfactant, the formation of capsule morphology could be promoted by the application of silica particles taking advantage of their surface inactivity. The formation mechanisms of capsules/solid particles are discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Novel Azobenzene-Functionalized Polyelectrolytes of Different Substituted Head Groups 1: Synthesis,Characterization and Absorption Spectroscopy Studies

A new class of a series of amphiphilic polyelectrolytes functionalized with azobenzene chromophores have been synthesized and thoroughly characterized by various techniques. A facile two stage strategy is developed, and first involved the preparation of a precursor base polymer, designated as P(APEA), by the free-radical copolymerization of the monomers of acrylic acid (AA) and 2-(phenylethylamino)ethyl acrylate (PEA). In the second step, precursor PAPEA polymers are reacted and post-polymer modified with the diazonium salts to synthesize azobenzene polyelectrolyte, PAPEA-R with different substituted R-groups present on the para position of the aromatic ring of the azo chromophores. The PAPEA-R polyelectrolytes are same in their degree of polymerization and repeat unit compositions of AA and PEA monomers, and only differ from each other by the type of R-groups. The copolymers were classified on the basis of the characteristics of their R-groups into the hydrophilic-ionizeable smaller pair of ─SO₃H and ─COOH, the hydrophobic-non-ionizeable smaller pair of ─ H and ─OC₂H₅, and the hydrophobic-non-ionizeable larger octyl pair of ─C₈H₁₇ and ─ C₈F₁₇. The prepared copolymers are also characterized by NMR spectroscopy for structure, GPC for molecular weight, and UV-Visible spectroscopy for absorption determination. In DMF solvent, approximately similar absorption maxima, (λ_max) values were observed for azo chromophore-containing monomers and after incorporating these into their corresponding polymers structures. However, for the self-assembled multilayer thin films, λ_max moved to lower wavelengths to exhibit a blue shift with hydrophobic R-group of ─C₈H₁₇, while this behaviour was not observed for hydrophilic R-group of ─COOH. The shift in λ_max is found to be highly dependent on the type of substituted R-group, and attributed to aggregation of hydrophobic azo chromophores in DMF:H₂O mixture employed for self-assembly. The presence of the ionizeable AA and light-sensitive azo-chromophore functionalized PEA monomers in the PAPEA-R polyelectrolytes impart self-assembling and photoswitchable characteristics, respectively. Through understanding and controlling the solubility and complex solution aggregation behaviour of the different substituted R-groups of azo PEL, their adsorption, thickness, morphology, wetting, molecular-control, and photoresponsiveness can be tailored to enhance the capabilities of the self-assembled multilayer film process in diversified areas of microfluidics, sensing, and controlled release.     

Colloidal hydrolysis products of SbCl3 in acidic solutions

 The hydrolysis of SbCl₃ in hydrochloric acid solution (2.0 mol dm^-3 HCl) at 0 °C yields an amor-phous product consisting of uniform spherical particles (d∼0.5 μm), which on continuous aging at the same temperature transform to larger crystals, indicated by XRD to be Sb₄O₅Cl₂. In contrast, in the same solution kept at 25 °C crystalline particles of the same composition form directly after an induction period and then grow with time. The final products, obtained at 0 °C and 25 °C consist of aggregated subunits. These powders on calcination in nitrogen are converted to Sb₂O₃ and in air to Sb₂O₄. Received: 23 June 1997 Accepted: 1 July 1997     

A Simple Relation for the Concentration Dependence of Osmotic Pressure and Depletion Thickness in Polymer Solutions

We propose simple expressions and for the osmotic pressure Π and the depletion thickness δ as a function of the polymer concentration φ. Here, Π₀ and δ₀ correspond to the dilute limit, and φ_ex is an extrapolation concentration which is of the order of the overlap concentration φ_ov. The De Gennes exponent α describes the concentration dependence of the semidilute correlation length ; it is related to the Flory exponent ν through . The quantity φ_ex is experimentally accessible by extrapolating the semidilute limit towards Π = Π₀ or δ = δ₀. These expressions are exact in mean field, where the ratio φ_ex/φ_ov (0.49 for Π, 0.41 for δ) follows from established models. For excluded‐volume chains they describe simulation data excellently: in this case φ_ex/φ_ov is 0.69 for Π and again 0.41 for δ. We find also very good agreement with experimental data.

     

Influence of Temperature and Time on the Stability of Silver in Silica Sol-Gel Glasses

The darkening of silica sol-gel glasses doped with 0.05 mol% silver was studied. Six sols were prepared from TEOS and silver nitrate. Different additives were used, to influence the chemical and physical states of silver: oxidizing or reducing agents (H₂O₂, As₂O₅), colloid stabilizer (sodium citrate) and network modifiers (Li₂O, CaO). Sols were gelified at 60°C and densified at 600°C. The samples without additives and those prepared with H₂O₂ at room temperature even if they were protected from light. With increased temperature, the darkening became samples were heated above, 400°C, reversible bleaching took place. This darkening-bleaching is of thermal nature (“thermochromic effect”) and seems to be determined by a reversible aggregation-disaggregation of tiny silver particles. The presence of sodium citrate, as an additive delayed the darkening effect and the presence of CaO delayed it even further. Lithium oxide inhibited it totally.     

受限混合物溶剂中胶粒的耗尽势及吸附稳定性

基于密度泛函理论和Yvon-Born-Green方程得到了胶粒耗尽势的表达式.采用密度泛函理论计算了单壁附近和平行狭缝中的混合物溶剂中胶粒的耗尽势及其在单壁处的吸附稳定性.研究结果表明,不同溶剂组分的体积分数和粒子尺寸比等因素对胶粒耗尽势的强度、力程和周期均可产生显著影响,胶粒在单壁附近的吸附稳定性与溶剂粒子尺寸比和体积分数密切相关.此外,对受限于平行狭缝的胶体悬浮液,胶粒的耗尽势阱还可随粒子尺寸比和缝宽呈振荡趋势变化.     

Thermoresponsive Copolymers of Ethylene Oxide and N,N‐Diethyl Glycidyl Amine: Polyether Polyelectrolytes and PEGylated Gold Nanoparticle Formation

The synthesis of diblock as well as gradient copolymers of N,N‐diethyl glycidyl amine (DEGA) with ethylene oxide (EO) via anionic ring‐opening polymerization is presented. The polymers exhibit low polydispersities (≤1.13) and molecular weights in the range of 3300–10 200 g mol⁻¹. In PEG‐co‐PDEGA copolymers, incorporation of 4%–29% DEGA results in tailorable cloud point temperatures in aqueous solution and melting points depending on DEGA content. mPEG‐b‐PDEGA block copolymers can be quaternized to generate cationic double‐hydrophilic polyelectrolyte copolymers with polyether backbone. Furthermore, mPEG‐b‐PDEGA has been used as dual reducing and capping agent for gold nanoparticle synthesis.     

Recent Developments in Colloidal Synthesis of CuInSe2 Nanoparticles

Ternary semiconductor nanocrystals, such as CuInSe₂, are of high interest for photovoltaic application due to their relatively low toxicity and unique properties. During the last decades great success has been achieved in the colloidal synthesis of binary nanoparticles, but for ternary compounds this research is still in an early stage of development. These materials are a challenge for synthetic chemistry, because the interaction between the three components (copper, indium, and selenium) plays a major role for the production of high quality material. The purpose of this Minireview is to provide a summary of the achievements in colloidal synthesis of CuInSe₂ nanoparticles—in particular, details of reaction mechanism and its characterization possibilities, which might be useful also for the colloidal synthesis of other multicomponent systems.     

Some Observations on the Stability of Uric Acid in Alkaline Solutions

Abstract

The stability of uric acid in alkaline solutions has been studied by spectrophotometric, enzymic and chemical methods. Aqueous triethanolamine was shown to maintain stability of uric acid for a range of concentrations at around 2O°C and to considerably reduce the degradation loss at the higher temperature of 37°C.