Structure Of Colloidal Particles Research Articles

Structural Insight into Stabilization of Pickering Emulsions with Fe3O4@SiO2 Nanoparticles for Enzyme Catalysis in Organic Media

Encapsulation of enzymes with enhanced activity and recyclability in water‐in‐oil Pickering emulsions is a simple and efficient method for their immobilization; however, the effect produced by the structure of colloidal particles on the stabilization of the Pickering emulsion for enzyme catalysis has not been investigated in detail. In this study, four types of hydrophobic Fe3O4@SiO2 nanoparticles (NPs) with similar chemical compositions, particle diameters, but different surface characteristics have been prepared and utilized for enzyme encapsulation in various water‐in‐oil magnetic Pickering emulsions, after which the relationship between NPs structure, size of emulsions droplets, and enzyme activity is examined. The obtained results indicate that (i) the more hydrophobic Fe3O4@SiO2 NPs cause the higher enzyme activity; (ii) the higher hydrophobicity of oil phase also increases the enzyme activity, especially for Fe3O4@w‐SiO2 NPs which form in the solvent of water. The results are mainly attributed to the higher specific surface area of emulsion droplets and interfacial mass transfer of substrates through the interfaces of droplets. The reported data provide new insights into the mechanism of stabilization of Pickering emulsions for enhancing enzyme activity and demonstrate efficient theoretical references for enzyme immobilization and synthesis of stable and active biocatalysts with high recyclability.

移流集積法を用いた周期的コロイド堆積膜の構造制御

移流集積法を用いた周期的コロイド堆積膜の構造制御

Influence of host rocks on composition of colloid particles in groundwater at the Karachai Lake site

AbstractThe radioactive contaminant plume in groundwater at the Karachai Lake site has been examined further. The source of pollution is the Karachai Lake which was used as a reservoir for liquid radioactive waste (LRW) from the Radiochemical Production Association “Mayak” (South Urals, Russia). Taking into account that colloid-facilitated transport of radionuclides can substantially increase the contaminant migration velocity, the composition and structure of colloid particles from the groundwater within the contaminant plume were studied. Sampling of groundwater was carried out in the observation well within the contaminant plume. Different fractions of colloid particles were extracted from the groundwater samples by sequential filtration through membranes with decreasing pore size. Chemical and mineralogical compositions of the colloid particles were determined by X-ray photoelectron spectroscopy in combination with ion etching of the particle surfaces. The host rocks were studied using characteristic samples from the surface outcrop nearest to the observation well. The analysis showed that the colloid particles consisted of an inorganic core with a discontinuous organic cover. The inorganic core was close in composition to the host rocks along the flow path with a predominance of layered hydrosilicates.

Structure of colloid particles in groundwaters on the territory of the Mayak production association and its impact on the colloid transport of radionuclides in subsoil environments

Colloid particles were examined in groundwaters sampled at the large contamination area of the subsoil environment at the Mayak production association in the Southern Urals. Colloid particles were separated from groundwater samples by ultrafiltration, and their composition and structure were analyzed by X-ray photoelectron spectroscopy (XPS) and Auger spectroscopy (AS). Our results indicate that the chemical composition of the particles significantly varies at their surface and along their radii, from the peripheries to the cores of the particles. The data are used to estimate the possibility of utilizing properties of colloid particles contained in groundwaters (the composition, structure, and zeta potential of such particles) to numerically simulate the spreading of radioactive contamination with groundwaters with regard to the colloid mode of radionuclide transport. It is demonstrated that, along with transmitting electron spectroscopy (TEM) coupled with X-ray microprobe analysis and electron diffraction, the XPS and AS techniques make it possible to obtain information on heterogeneity in the distribution and modes of occurrence of various elements in colloid particles.

Quantitative Analysis of Polymer Colloids by Cryo-Transmission Electron Microscopy

The structure of colloidal latex particles in dilute suspension at room temperature is investigated by cryogenic transmission electron microscopy (cryo-TEM). Two types of particles are analyzed: (i) core particles made of polystyrene with a thin layer of poly(N-isopropylacrylamide) (PNIPAM) and (ii) core-shell particles consisting of core particles onto which a network of cross-linked PNIPAM is affixed. Both systems are also studied by small-angle X-ray scattering (SAXS). The radial density profile of both types of particles have been derived from the cryo-TEM micrographs by image processing and compared to the results obtained by SAXS. Full agreement is found for the core particles. There is a discrepancy between the two methods in case of the core-shell particles. The discrepancy is due to the buckling of the network affixed to the surface. The buckling is clearly visible in the cryo-TEM pictures. The overall dimensions derived from cryo-TEM agree well with the hydrodynamic radius of the particles. The comparison of these data with the analysis by SAXS shows that SAXS is only sensitive to the average radial structure as expected. All data show that cryo-TEM micrographs can be evaluated to yield quantitative information about the structure of colloidal particles.

Liquid Crystal Emulsions

ABSTRACT We review recent findings about the behavior of emulsions made of droplets suspended in liquid crystalline materials. By contrast to classical emulsions, which are usually made of isotropic oils and water, liquid crystal emulsions exhibit a variety of structures result in the ordering of the continuous phase. The droplets induce the formation of topological defects and distortions that lead to strong and anisotropic elastic forces between the particles. These elastic forces govern the stability and the ordering of the particles. This is observed in aqueous emulsions as well as in non-aqueous emulsions obtained from phase separation phenomena. It is shown that phase separations in liquid crystals can lead to the formation of highly ordered arrays of uniformly sized droplets. More generally, ordered structures seen in liquid crystal emulsions are of interest as examples of topologicallv-controlled organizations; they are also of potential practical importance as a novel way to control both the stability and the structures of colloidal particles.

Solving the generalized indirect Fourier transformation (GIFT) by Boltzmann simplex simulated annealing (BSSA)

The structure of colloidal particles can be studied with small-angle X-ray and neutron scattering (SAXS and SANS). In the case of randomly oriented systems, the indirect Fourier transformation (IFT) is a well established technique for the calculation of model-free real-space information. Interaction leads to an overlap of inter- and intraparticle scattering effects, preventing most detailed interpretations. The recently developed generalized indirect Fourier transformation (GIFT) technique allows these effects to be separated by assuming various models for the interaction,i.e.the so-called structure factors. The different analytical behaviour of these structure factors from that of the form factors, describing the intraparticle scattering, allows this separation. The mean-deviation surface is defined by the quality of the fit for different parameter sets of the structure factor. Its global minimum represents the solution. The former non-linear least-squares approach has proved to be inefficient and not very reliable. In this paper, the incorporation of the completely different Boltzmann simplex simulated annealing (BSSA) algorithm for finding the global minimum of the hypersurface is presented. This new method increases not only the calculation speed but also the reliability of the evaluation.

Study of Structure of Colloidal Particles of Fullerenes in Water Solution

The formation in water of highly stable cluster/crystallite structures from fullerene C60 is theoretically predicted and experimentally confirmed.

Preparation of textured alumina films by the sol-gel route

Alumina films were fabricated by the sol-gel route under various preparation conditions. The peptization rate and the structure of colloidal particles depend on these conditions. In particular, the peptization of a dried boehmite precipitate prepared from aluminum alkoxide was achieved within a few seconds without heating. The resulting sol is made of highly dispersed crystallites; this allows the formation of well-textured xerogel films as evidenced by the Weissenberg x-ray method.

Structure of colloidal particles of petroleum resins and asphaltenes

Structure of colloidal particles of petroleum resins and asphaltenes

Structure of colloidal particles in water oil mixtures stabilized by polymeric emulsifiers: 1. Phase diagrams and electron microscope studies

The phase diagrams of toluene/water mixtures, stabilized by amphiphilic graft copolymers in the presence of an alcohol, show two domains in which these systems are optically clear. The composition of the continuous phase of the polymeric microemulsions was determined by dialysis experiments. The results indicate a preferential solvation of the copolymer sequences by the ternary solvent mixture. The micellar particles were observed by electron microscopy on carbon replicas of freeze-fractured samples. Depending on the copolymer composition and the location of the system in the phase diagram, the micrographs reveal either individual particles ( 50 A ̊ < radius < 250 A ̊ ), well-dispersed in the continuous medium, or inter-particle clusters.

Structure of colloidal particles in water-oil mixtures stabilized by polymeric emulsifiers. 3. Hydrodynamic properties

The micellar properties of water-oil mixtures stabilized by polystyrene-poly(ethyleneoxide) graft copolymers, in the presence of an alcohol, have been investigated by quasielastic scattering of laser light and viscometry. The mean size, aggregation number, polydispersity and swelling degree of the polymeric micelles have been deduced for a series of copolymers as a function of the solvent composition. Both size and aggregation number are strongly dependent on the toluene/water ratio. The swelling degree of particles is primarily controlled by the weight ratio polystyrene/poly(ethyleneoxide).

Structure of colloidal particles in water-oil mixtures stabilized by polymeric emulsifiers: 2. Small angle neutron scattering investigation

Small-angle neutron coherent scattering techniques have been used to characterize the conformation of amphiphilic macromolecules in polymeric microemulsions. The radius of gyration, the molecular weight and the aggregation number of the macromolecules within the micelles have been measured using a dilution procedure in conjunction with an adjustment of the contrast factor between polymer and solvents. Additional information on the internal structure of the micelles has been obtained from the asymptotic behaviour of the scattering form factor P( q). From considerations of the respective affinities between the two copolymer sequences and the solvent mixture, plausible models are proposed for the micellar structure.

Small Angles and Small Particles

The structure of matter is an ancient mystery which continues to provide fruitful ground for study. Strangely enough, we possess more reliable information on the structure of atoms and small molecules than on the structure of colloidal particles and macromolecules which are very many times larger. Partly this is so because such particles are of greater complexity and occur in greater diversity than their atomic constituents, but it is also owing to the lack of adequate techniques for examining and measuring these particles. Among the tools for such study is the scattering of radiation by a substance.

Isoprene and Rubber. Part 34. Molecules or Micelles in a Rubber Solution

Abstract Measurements of the Viscosity of Rubber Solutions In the literature may be found numerous measurements of the viscosity of rubber solutions, the object of which was to throw light on the nature of colloidal solutions and changes in these solutions by various operations. These investigations give no insight into the structure of colloid particles and the reason for changes in rubber solutions because they are based on false assumptions, particularly the assumption that rubber has a micellar structure. Often highly viscous solutions were studied, and though these appeared to be of special interest to the colloid chemist, they were unsuited for such investigations, for they are gel solutions in which the structure of the colloid particles is much more difficult to explain than is that in dilute solutions (sol solutions), where the molecules have freedom of movement and do not disturb one another. The earlier works also contain references to the sensitivity of rubber to oxygen, though no special precautions were ever taken in the measurements to exclude oxygen; in fact this was unnecessary as a rule, for crude rubber solutions are much more stable, because of anticatalysts present, than solutions of pure rubber in which these have been removed. Pure rubber was prepared by the method of Pummerer and Pahl and, as described in the following work, was separated by fractional extraction into portions of different average molecular weights. Viscosity measurements of the individual fractions were then carried out under various conditions. The study of the rubber solution, like that of the balata solution, must be carried out with complete exclusion of air, and the solvent (tetralin or benzene) must be distilled in an atmosphere of pure nitrogen and be freed of oxygen. The filtration of the rubber solution, the filling of the viscosimeter, as well as the measurements themselves, are likewise made in an atmosphere of pure nitrogen. Measurements were taken in the Ubbelohde viscosimeter at different pressures, as a rule at 10.30 and 60 cm. mercury pressure. Very dilute solutions were also measured in the Ostwald viscosimeter, since the deviations from the Hagen-Poiseuille law are of no great importance at low concentration. Finally, it should be mentioned that these special precautions during the viscosity measurements, above all the careful exclusion of air, are necessary only in the case of rubber, not with the saturated hydrocarbons, polystyrene, and hydrorubber.