Colloidal Properties of Polychlorotrifluoroethylene-Based Multicomponent Dispersions

A polychlorotrifluoroethylene-based multicomponent dispersion in dimethylformamide (DMF) was used to prepare protective polymer coatings by the electrodeposition method. The properties of the fluoroplastic coatings were modified by the addition of a cationic polyelectrolyte and pigments of different natures to the dispersion, the pigments being codeposited on a cathode together with the fluoroplastic particles. The optimal composition of the dispersion was determined. It was found that all dispersion components were wetted by DMF; the surface properties of the coatings depended on the concentration of the polyelectrolyte added to the dispersion. The polyelectrolyte adsorption on F-3 and pigment particles was estimated by the UV spectroscopy; the electrokinetic potential of the particles was measured. The charge on a particle surface increased the dispersion stability, thus facilitating the formation of a more uniform electrodeposited layer, i.e., the coating.     

Facile Assembly of 3D Binary Colloidal Crystals from Soft Microgel Spheres

It still remains a big challenge to fabricate binary colloidal crystals (binary CCs) from hard colloidal spheres, although a lot of efforts have been made. Here, for the first time, binary CCs are assembled from soft hydrogel spheres, PNIPAM microgels, instead of hard spheres. Different from hard spheres, microgel binary CCs can be facilely fabricated by simply heating binary microgel dispersions to 37 °C and then allowing them to cool back to room temperature. The formation of highly ordered structure is indicated by the appearance of an iridescent color and a sharp Bragg diffraction peak. Compared with hard sphere binary CCs, the assembly of PNIPAM microgel binary CCs is much simpler, faster and with a higher “atom” economy. The easy formation of PNIPAM microgel binary CC is attributed to the thermosensitivity and soft nature of the PNIPAM microgel spheres. In addition, PNIPAM microgel binary CCs can respond to temperature change, and their stop band can be tuned by changing the concentration of the dispersion.

     

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.     

C60溶液胶体性质的研究

The Tyndall effect, electrical conductivity and settleability of C(60) in benzene, toluene and toluene/ethanol were determined. The results show that the dispersed systems are in colloidal state in a range of concentrations and in suspension state at higher concentrations.     

Stokesian Dynamics Simulations of Ferromagnetic Colloidal Dispersions Subjected to a Sinusoidal Shear Flow

We have conducted Stokesian dynamics simulations to investigate the dynamic properties of ferromagnetic colloidal dispersions subjected to a sinusoidal shear flow. Thick chain-like cluster formation is significantly influenced by an oscillatory shear flow even if the amplitude is relatively small, since the internal structures of thick chain-like clusters are highly sensitive to the change in the direction of the shear flow. The motion of thick chain-like clusters is out of phase to a sinusoidal shear rate, and the phase difference is strongly correlated with that of the viscosity and normal stress coefficients. The viscoelastic properties become more apparent with decreasing frequency of the oscillatory shear flow, since such properties have a strong relationship with the thick chain-like cluster formation. In other words, since thick chain-like clusters are more stable for the case of a smaller frequency shear flow, such stable clusters induce significant viscoelastic properties of ferromagnetic colloidal dispersions in a strong, applied magnetic field. Copyright 2000 Academic Press.     

Physical and Chemical Properties of Magnetite and Magnetite-Polymer Nanoparticles and Their Colloidal Dispersions

The properties of polymer-coated magnetite nanoparticles, which have the potential to be used as effective magnetic resonance contrast agents, have been studied. The magnetite particles were synthesized by using continuous synthesis in an aqueous solution. The polymer-coated magnetite nanoparticles were synthesized by seed precipitation polymerization of methacrylic acid and hydroxyethyl methacrylate in the presence of the magnetite nanoparticles. The particle size was measured by laser light scattering. It was shown that the particle size, variance, magnetic properties, and stability of aqueous magnetite colloidal dispersion strictly depend on the nature of the stabilizing agent. The average hydrodynamic radius of the magnetite particles was found to be 5.7 nm in the stable aqueous colloidal dispersion. An inclusion of the magnetite particle into a hydrophilic polymeric shell increases the stability of the dispersion and decreases the influence of the stabilizing agent on the magnetic and structural properties of the magnetite particles as was shown by X-ray diffraction and M?ssbauer and IR spectroscopy, as well as by vibrating sample magnetometry. The variation in the polymeric shell size and the polymer net density can be useful tools for evaluation of the polymer-coated magnetite particles as effective contrast agents. Copyright 1999 Academic Press.     

液化膜对胶体悬浮液粘度的影响

Viscosity is one of the most important properties of colloids in mixing, transportation, stabilization, energy consumption, and so on. According to Einstein‘s viscosity equation, the viscosity of a colloidal dispersion increases with the increase of particle concentration. And the equation can be applicable to all micro-particle dispersions, because the effect of solvation films coated on particles can be neglectable in that case. But with the decrease of particle size to nano-scale, the formation of solvation films on nano-particles can greatly affect the viscosity of a dispersion, and Einstein‘s equation may not be applicable to this case. In this work, one kind of micro-size silica particle and two kinds of nano-size silica particles were used to investigate the effect of solvation films on dispersion viscosity, dispersed in water and ethyl alcohol solvents, respectively. The results of theoretical calculation and experimental investigation show that the increase of viscosity is contributed from solvation films by more than 95 percent for nano-particle dispersions, while less than 10 percent for micro-particle dispersions.     

丙烯酸酯共聚物无皂水溶胶稳定性的研究

用溶液聚合法合成了四种AA含量不同的丙烯酸酯共聚物(MMA/BA/HEMA/AA)，通过中和AA使共聚物带有—COO~-能起自乳化作用分散于水中而成为无皂水溶胶．TEM观察表明水溶胶粒子呈球状，单分散性好，粒径随AA含量增加而变小，在30～90 nm范围．用电导滴定法测定水溶胶粒子中—COOH和—COO~-的分布，表明绝大部分—COO~-处于粒子表面，并且随AA含量增加，粒子表面的—COO~-增多，Zeta电位增大，这是导致水溶胶的抗电解质稳定性(以C.C.C.值反映)和贮存稳定性(以表现粘度反映)随AA含量增加而提高的主要原因。     

Modeling and Scaling of Food Dispersions

Scaling laws, determined by dimensional analysis, have been used to make experimental predictions of constitutive shear-flow rheology. This study aimed to scale and model the flow curves of various suspensions consisting of xanthan gum (0.5, 1 wt%) and WPI (2, 4 wt%), and to determine the best-scaling law and rheological model. The scaling methods were relative viscosity, Péclet number, and Reynolds number. When the apparent viscosity is reduced relative to the viscosity of the medium at zero-shear rate, a distinct reduced flow curve is obtained, regardless of xanthan and WPI concentrations. This study tough to develop a technique of simplifying complex non-Newtonian flow curves and, therefore, predicting the rheological flow curves and fluid mechanics when different modifiers are added to food suspensions. The flow behavior of all samples was successfully modeled with the power law, Ellis, and Cross models; the power law model best described the flow behavior of dispersions. Results showed that both G′ and G″ increased with xanthan and WPI. However, viscoelastic behavior was mainly governed by the xanthan gum content.     

Cross‐Linking Density and Temperature Effects on the Self‐Assembly of SiO2—PNIPAAm Core–Shell Particles at Interfaces

SiO₂–PNIPAAm core–shell microgels (PNIPAAm=poly(N‐isopropylacrylamide)) with various internal cross‐linking densities and different degrees of polymerization were prepared in order to investigate the effects of stability, packing, and temperature responsiveness at polar–apolar interfaces. The effects were investigated using interfacial tensiometry, and the particles were visualized by cryo‐scanning electron microscopy (SEM) and scanning force microscopy (SFM). The core–shell particles display different interfacial behaviors depending on the polymer shell thickness and degree of internal cross‐linking. A thicker polymer shell and reduced internal cross‐linking density are more favorable for the stabilization and packing of the particles at oil–water (o/w) interfaces. This was shown qualitatively by SFM of deposited, stabilized emulsion droplets and quantitatively by SFM of particles adsorbed onto a hydrophobic planar silicon dioxide surface, which acted as a model interface system. The temperature responsiveness, which also influences particle–interface interactions, was investigated by dynamic temperature protocols with varied heating rates. These measurements not only showed that the particles had an unusual but very regular and reversible interface stabilization behavior, but also made it possible to assess the nonlinear response of PNIPAAm microgels to external thermal stimuli.     

高浓度丙烯酸酯类微凝胶分散液的制备及性质

用微乳液聚合方法合成了浓度高达30wt%的丙烯酸酯类微凝胶,研究了乳化剂用量和微乳液浓度对微凝胶粒径及分布的影响,以及交联剂用量对微凝胶二甲苯分散液的流变行为的影响。利用制备的微凝胶对高固体份羟基丙烯酸树脂进行了改性。实验结果表明,微凝胶改性的树脂具有显著的切力变稀现象。     

Efficient Simulations of Charged Colloidal Dispersions: A Density Functional Approach

Summary: A numerical method is presented for simulating charged colloidal dispersions in electrolyte solutions. Utilizing a smoothed profile for colloid‐solvent boundaries, efficient mesoscopic simulations are enabled for modeling dispersions of many colloidal particles exhibiting many‐body electrostatic interactions. The validity of the method was examined for simple colloid geometries, and the efficiency was demonstrated by calculating stable structures of two‐dimensional dispersions, which resulted in the formation of colloidal crystals.

Formation of a charged colloidal crystal.     

Obtaining the Osmotic Pressure of Electrostatically Stabilized Colloidal Dispersions from Frontal Ultrafiltration Experiments

A new method for determining the osmotic pressure of electrostatically stabilized colloidal particles from frontal ultrafiltration experiments has been developed. The method is based on a reverse calculation utilizing a previously developed analysis of frontal ultrafiltration (W. R. Bowen and F. Jenner, Chem. Eng. Sci. 50, 1707, 1995; W. R. Bowen and P. M. Williams, Biotechnol. Bioeng. 50, 125, 1996). The method has the following advantages over conventional membrane osmometer measurements: (i) only very simple apparatus is required, (ii) results are obtained quickly, (iii) only small sample quantities are required, and (iv) only dilute initial samples are needed, as the ultrafiltration process creates a concentrated solution at the membrane, making sample preparation a simple task. A comparison of the osmotic pressure determined by this new method with previously measured osmotic pressure data shows excellent agreement. The approach demonstrates how analysis of process data may provide quantitative information on the interactions of concentrated colloidal systems. Copyright 2001 Academic Press.     

Formulation of Cannabidiol in Colloidal Lipid Carriers

In this study, the general processability of cannabidiol (CBD) in colloidal lipid carriers was investigated. Due to its many pharmacological effects, the pharmaceutical use of this poorly water-soluble drug is currently under intensive research and colloidal lipid emulsions are a well-established formulation option for such lipophilic substances. To obtain a better understanding of the formulability of CBD in lipid emulsions, different aspects of CBD loading and its interaction with the emulsion droplets were investigated. Very high drug loads (>40% related to lipid content) could be achieved in emulsions of medium chain triglycerides, rapeseed oil, soybean oil and trimyristin. The maximum CBD load depended on the type of lipid matrix. CBD loading increased the particle size and the density of the lipid matrix. The loading capacity of a trimyristin emulsion for CBD was superior to that of a suspension of solid lipid nanoparticles based on trimyristin (69% vs. 30% related to the lipid matrix). In addition to its localization within the lipid core of the emulsion droplets, cannabidiol was associated with the droplet interface to a remarkable extent. According to a stress test, CBD destabilized the emulsions, with phospholipid-stabilized emulsions being more stable than poloxamer-stabilized ones. Furthermore, it was possible to produce emulsions with pure CBD as the dispersed phase, since CBD demonstrated such a pronounced supercooling tendency that it did not recrystallize, even if cooled to −60 °C.     

Stabile,Thermoresponsive Colloidal Clusters: An Unusual Morphology of Polymer Dispersions

A new class of colloidal polymeric particles consisting of polystyrene spheres grown in a poly(N‐isopropyl acrylamide) precursor scaffold is synthesized via redox‐initiated heterophase polymerization. The morphology and thermoresponsiveness of these assemblies is proven by electron microscopy investigations and temperature‐dependent measurements of the change of both the speed of sound travelling through the dispersion and the hydrodynamic particle size. Electron microscopy (EM) micrographs (transmission and scanning EM as well cryo‐scanning EM) prove the existence of colloidal clusters when the freeze‐dried copolymer is redispersed in pure water. The clusters have a size of several micrometers, contain about 800 polystyrene particles with diameter below 100 nm, and show a highly reproducible thermoresponsive behavior with a lower critical solution temperature corresponding to that of pure poly(N‐isopropyl acrylamide).

     

Influence of Reactive Compatibilization on the Melt Flow Properties and Morphology of Polyamide 6/Styrene-Acrylonitrile Blends

Summary: In this study, we investigate the influence of reactive compatibilization on the rheological properties of polyamide 6/styrene-acrylonitrile (PA 6/SAN) blends in the melt. Linear viscoelastic shear oscillations, simple elongation to a large stretch ratio and subsequent recovery experiments were performed. The morphology of the blends was examined by atomic force microscopy. We prepared three PA 6/SAN blends with different composition ratios of PA 6 and SAN (70/30, 50/50, 30/70) and a constant concentration of the reactive agent. Our experiments revealed that reactive compatibilization significantly increases the complex modulus of PA 6/SAN blends at low frequencies. In particular, the data of the PA 6/SAN 50/50 blend and the PA 6/SAN 30/70 blend indicated that an elastic network between neighbouring PA 6 domains was formed. In simple elongation, the transient elongational viscosity of the blends exceeded the values of the single components. In recovery, the recovered stretch of all blends was larger than the recovered stretch of the pure components. The differences of the blend morphology and of the linear viscoelastic behaviour were qualitatively explained by the asymmetric properties of the reactively compatibilized interface.     

纳米沸石胶体化学性质的研究

主要考察了MFI和BEA结构纳米沸石的胶体化学性质，对与纳米组装过程直接相 关的纳米沸石的电动性质体现为ξ电势）和自聚集性质进行了研究．考察了pH值、 离子强度和硅铝比对沸石ξ电势的影响．发现纳米沸石表的变化取决于其骨架结构 和组成，而电解质浓度的增大可使沸石胶粒的ξ电势减小；州增大可使ξ电势向负 电性增方向变化．较高的ξ电势是维持沸石胶液稳定的基本条件；而过小的ξ电势 则将导致纳米沸石的聚集或沉降，在毛细作用下纳米沸石可以自组装成沸石纤维， 沸石的粒径是影响该组装的关键因素，沸石粒径越小，越容易组装成致密透明的沸 石纤维．     

Colloidal Systems on the Basis of Novel Reactive Surfmers

Summary: New anion surfmers of the family of maleic acid asymmetrical esters have been synthesized. Some of its features in the process of emulsion copolymerization with styrene have been studied. The characteristics of covering, obtained on the basis of such latexes of new generation have been investigated as well.