Preparation and properties of uniform amorphous and crystalline colloidal nickel sulfide

 Amorphous spherical particles of nickel sulfide of 10 nm in diameter were synthesized by the controlled double-jet precipitation (CDJP) technique using nickel sulfate and sodium sulfide. Cubic crystalline particles of ∼200 nm were obtained by aging dispersions of amorphous particles at 80 °C for more than a week, as long as the pH was kept between 3 and 3.5. Electrokinetic mobilities of these particles are reported, as well as color properties of their dispersions in liquids and in poly(vinyl alcohol) films are described. Received: 20 January 1997 Accepted: 21 January 1997     

Preparation of monodispersed plate-like particles of tungstic acid

 To understand the properties of colloidal dispersions it is often vital to prepare model materials with particles that have a small polydispersity in order to make experimental tests of theories or models. However few preparations have been developed that yield anisotropic particles with a narrow size distribution and precise shape. In this paper the preparation of a dispersion of charge stabilized, tungstic acid particles is described. The particles are rectangular and have a length of 7.0 μm, a width of 2.8 μm and a thickness of 0.2 μm. The polydispersity is 8% in length and 10% in width, making it one of the most monodisperse dispersions of anisotropic particles. Each particle is monocrystalline and the crystal orientation is fixed with respect to the particle morphology. Some interesting behavior is observed: these particles aggregate perpendicular and parallel to each other to give flat, ordered flocs when the stability is reduced. Received: 22 January 1998 Accepted: 4 February 1998     

Preparation of uniform colloidal cadmium and lead selenide particles

Colloidal cadmium selenide and lead selenide particles of narrow size distribution were prepared by decomposition of selenourea in solutions of corresponding metal salts. While both salts were crystalline, CdSe powders showed nearly spherical morphology whereas PbSe consisted of particles of cubic symmetry. In the latter case greater uniformity was achieved if homogeneous precipitation was carried out in methanol-water mixtures.     

Preparation and properties of uniform coated colloidal particles. VII. Silica on hematite

Spindle-type hematite particles of narrow size distribution were coated with uniform layers of silica by hydrolysis of tetraethylorthosilicate (TEOS) in 2-propanol. The effects of the reaction time and initial concentrations of ammonia and water on the thickness of the silica shell were investigated and the rate of the coating process, in terms of the TEOS concentration, was evaluated.     

Effects of dopant concentration and aging on the electrical properties of Y-doped ceria electrolytes

High purity cerium oxide and yttrium oxide were used to form ceria-based solid solution (Ce_1−xY_xO_2−δ, 0.05x0.4) via a conventional mixed-oxide method. All the samples used were aged at 1000 °C in air for 8 days. Crystal structure and microstructure were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ionic conductivity (i.e., grain interior (GI) grain boundary (GB) and total conductivities) in this system were systematically studied as a function of dopant content over the temperature range of 250–850 °C in air using an impedance spectroscopy. The lattice parameter decreased with increasing the Y content, but it did not obey Vegard's law. The Y doping had no significant effect on densification behavior and final sintered density, but leading to a significant decrease in grain size as compared to the undoped ceria. The composition x0.1 had a maximum GI conductivity, while a maximum total conductivity was observed at x0.15. A significant high-temperature aging effect was also found for the samples with higher Y doping levels. 10% and 15% decreases in the GI and GB conductivities, respectively, were detected in the aged Ce_0.7Y_0.3O_2−δ ceramic.     

Capabilities of polymer-modified monodisperse colloidal silica particles as biomaterial carrier

 Polymer modification of monodispersed colloidal silica (0.5 μm) with poly(maleic anhydride-co-styrene) (P(MA-ST)) and poly (maleic anhydride-co-methyl methacrylate) (P(MA-MMA)) and application of the composite particles to biomaterial carriers were investigated. The reaction of bovine serum albumin(BSA)-immobilized P(MA-MMA)/SiO₂ with the anti-BSA antibody showed higher sensitivity in immunological agglutination test than BSA–P(MA-ST)/SiO₂, though immobilization efficiency of BSA on P(MA-MMA)/SiO₂ was lower than that on P(MA-ST)/SiO₂. Alkaline phosphatase and glucose oxidase immobilized on the composite particles exhibited extremely low activities, but α-chymotrypsin immobilized on P(MA-MMA)/SiO₂ and its derivative particles showed the relative activity of 12.5% and 16.1% to the native enzyme, respectively. Grafting of a hydrophilic polymer of poly(acrylic acid) to P(MA-ST)/SiO₂ let to an increase of the immobilized α-chymotrypsin activity to give the maximum relative activity of 55.5%. Received: 23 August 1996 Accepted: 16 October 1996     

Coil-to-globule-type transition of poly(N-isopropylacrylamide) adsorbed on colloidal silica particles

 The temperature dependence of the dimensions of poly(N-isopropylacrylamide) (PNIPAM) adsorbed on two different colloidal silica particles was studied with dynamic light scattering. The hydrodynamic diameter was measured when the temperature was varied stepwise from 10 to 60 °C. PNIPAM molecules free in solution undergo a conformational transition at the θ temperature. We have found that PNIPAM adsorbed onto silica particles also undergoes a transition below the θ temperature. When a small amount of polymer was adsorbed the coil-to-globule transition at the θ temperature did not occur. Potentiometric titrations showed that the surface charge of the silica particles was not affected by the polymer adsorption. Sodium dodecyl sulfate (SDS) (100–1200 mg/l) was added to improve the stability. The particles with a higher zeta potential required a smaller addition of SDS to prevent coagulation compared to the particles with a smaller surface potential. For low additions of SDS the transition curves of adsorbed PNIPAM were unaffected. For larger additions of SDS the collapse of PNIPAM was shifted to higher temperatures. When as much as 1200 mg/l SDS was added, two regions with weak transitions were observed before the collapse. It was also observed that the presence of SDS results in a smaller adsorption of PNIPAM onto the particles. The addition of SDS strongly increased the magnitude of the electrophoretic mobility of the polymer–particle unit. From the electrophoretic measurements an electrokinetic layer thickness was calculated and it was found to be smaller than the corresponding hydrodynamic layer thickness, as obtained by dynamic light scattering. Received: 14 December 1999/In revised form: 22 February 2000/Accepted: 6 March 2000     

Interaction between small colloidal particles and polymer chains in a semidilute solution: Monte Carlo simulation

 Interaction between flexible-chain polymers and small (nanometric) colloidal particles is studied by Monte Carlo simulation using two-dimensional and three-dimensional lattice models. Spatial distribution of colloidal particles and conformational characteristics of chains in a semidilute solution are considered as a function of the segment adsorption energy, ɛ. When adsorption is sufficiently strong, it induces effective attraction of polymer segments, which results in contraction of macromolecular coils. The strongly adsorbing polymer chains affect the equilibrium spatial distribution of the colloidal particles. The average size of colloidal aggregates <m> exhibits a nontrivial behavior: with ɛ increasing, the value of <m> first decreases and then begins to grow. The adsorption polycomplex formed at strong adsorption exhibits a mesoscopic scale of structural heterogeneity. The results of computer simulations are in a good agreement with predictions of the analytic theory [P.G. Khalatur, L.V. Zherenkova and A.R. Khokhlov (1997) J Phys II (France) 7:543] based on the integral RISM equation technique. Received: 4 August 1997 Accepted: 16 April 1998     

Preparation and characterization of well-defined sterically stabilized latex particles with narrow size distribution

 The synthesis and comprehensive characterization of a purely sterically stabilized latex with narrow size distribution is reported. By use of non-ionic initiators no chemically bound surface charges are generated. Stabilization of the particles is achieved through use of a non-ionic surfactant having a double bond in the hydrophobic part which is chemically bound to the surface. Analysis of the latex particles thus generated by transmission electron microscopy, disc centrifugation, and small-angle X-ray scattering (SAXS) reveals that the size distribution is narrow (standard deviation between 6 and 10%). SAXS furthermore demonstrates that the surfactant is located in a thin layer on the surface. The interaction of the particles is purely repulsive as shown by the analysis of the turbidity of the latex. The systems obtained herein may serve as model systems of water-borne purely sterically stabilized colloid particles. Received: 23 December 1997 Accepted: 18 May 1998     

Cationic amino-containing N-isopropyl- acrylamide-styrene copolymer particles: 2-surface and colloidal characteristics

 In a previous paper [1], the synthesis of various polystyrene– poly[NIPAM] core–shell latexes bearing cationic amidino and/or amino charges has been described. Several colloidal properties of these cationic latexes have been charac-terized such as: particle size, surface charge density, electrophoretic mobility and finally colloidal stability. Due to the poly[NIPAM]-rich layer in the shell, it was found that temperature played a significant role on all these properties, a LCST around 33 °C being exhibited. In addition, ionic strength was also found to affect the colloidal behavior of these latexes, the largest effect being observed with latexes having both amidino and amino surface charges. The critical coagulation concentra-tions (CCC) of the various latexes above and below the LCST were determined, highlighting the contribution of electrostatic and steric repulsive forces to the stability of these particles. Received: 20 January 1998 Accepted: 8 June 1998     

Cobalt nanoparticles in block copolymer micelles: Preparation and properties

 The preparation and properties of Co nanoparticles in polystyrene(PS)-poly-4-vinyl-py-ridine(PVP) micelles were studied. Elementary Co was generated by two methods: (i) by reduction of micelles loaded with CoCl₂, and (ii) by thermal decomposition of Co₂(CO)₈ in micel-lar solutions of such block copolymers. Co particles formed by both processes are effectively stabilized by the block copolymer matrix and do not aggregate. For CoCl₂ as a Co-source, the formed particles have a size less than 1 nm. Thermal treatment of such dried polymers at 200 ^°C for 2 h leads to spherical particles of 3–5 nm in size. The polymeric hybrid materials prepared in this way display remarkably high values of magnetization at rather low Co contents in the polymer, i.e., we obtain a tenfold increase of the specific magnetization density. Co₂(CO)₈ as a Co source, results in a more complex behavior. Co₂(CO)₈ dissolves in the solvent as well as in the micelle core where it is converted to an cationic–anionic complex involving the 4-VP units. The shape and size of the Co nanoparticles formed by thermolysis can be controlled by the balance of 4-VP/Co and can be varied from spherical particles in the limit of lower Co loads being mainly attached to the micelle core to a star-like and cubic morphology in case of excess of Co₂(CO)₈. Both superparamagnetic and ferromagnetic materials can be prepared. For ferromagnetic samples coercive force varies from 250 to 475 Oe depending on Co content and polymer sample. Received : 27 September 1996 Accepted: 22 November 1996     

Synergistic effect of dealumination and ceria impregnation to the catalytic properties of MOR zeolite

MOR zeolite has been extensively employed as a catalyst in industries. However, high Brønsted acidity in MOR leads to rapid deactivation due to coke deposition on the pore mouths; thus, the surface acidity of MOR needs to be moderated. Herein, we report a modification of MOR chemical composition via acid treatment and deposition of ceria nanoparticles using a wet impregnation method. The acid treatment successfully increases the Si/Al ratio of MOR from 8.39 to 11.58 and reduces the total acid site concentration of MOR from 990 μmol/g to 752 μmol/g. The acidity of MOR is decreased when the Si/Al ratio is increased since the quantity of Brønsted acid sites is proportional to the number of Al framework. In addition, the acid treatment also improves the external surface area of MOR. Furthermore, ceria particles were successfully deposited on the MOR surface using wet impregnation method. The ceria content of parent MOR sample is lower compared to that of preceded by the acid treatment, which may be attributed to the formation of more terminal silanol groups. Finally, catalytic test on Friedel–Crafts alkylation of toluene with benzyl alcohol shows that the synergy between dealumination and the impregnation of ceria significantly improves the activity of MOR zeolite.     

Collapse transitions of a supersized neutral chain due to irreversibly adsorbed small colloidal particles

 We performed Monte Carlo simulations to study the destabilization processes of large neutral and flexible polymer chains due to irreversibly adsorbed colloidal particles attached to the chains like beads on a necklace. The particles are modeled as charged spherical units which interact with each other via repulsive electrostatic and attractive van der Waals (vdW) potentials. The usual Monte Carlo search procedure is extended and carefully checked to completely sample the chain conformational space and achieve dense conformations in the limit of both strong attractive and repulsive interaction potentials. Configurational properties, such as the radius of gyration, the end-to-end length, and the Kuhn length, are calculated as a function of the intensity of the vdW interactions and ionic strength values. It is observed that chains exhibit a new range of possible conformations compared to the classical random walk and self avoiding walk chains or polyelectrolytes. In the limit of low salt concentration, by gradually increasing vdW interactions, chains undergo a cascade of transitions from extended structures to dumbbells, from dumbbells to pearl necklaces, and from pearl necklaces to collapsed coils. Because of strong competition between the vdW and electrostatic forces, the distance along the chain between the interacting particles, and the sampling limitations, these transitions are found to sample metastable domains and to depend on the initial conformations. To gain insight into the spatial organization of the collapsed conformations, the pair correlation functions of both monomers and particles are calculated. It is shown that collapsed conformations which are the result of strong particle–particle interactions exhibit two distinct parts: a hard core mainly composed of particles and a surrounding polymeric shell composed of loops and tails. Possible effects of such a collapsed transition on the kinetics of flocculation of a mixture containing large flexible chains and small adsorbing colloidal particles are discussed. Received: 26 July 1999 Accepted in revised form: 9 November 1999     

An effective cross-linking of polymer layer on monodisperse, poly(maleic anhydride-styrene)-modified colloidal silica particles and properties of the composite

Summary  The cross-linkings of the surface polymer layer on mono disperse, poly(maleic anhydride-styrene)-modified silica particles by the reaction with diisocyanate were studied. The extent of cross-linking was estimated by the weight decrease by immersing the particles in the buffer solution of pH 2.0, 4.0 and 9.0 at a room temperature for 24 h. The reaction of the polymer-modified silica with 1,6-diisocyanatohexane afforded relatively stable composite particles which lost less than 5 wt% of the polymer in aqueous solution in the pH range 2.0–9.0. The diisocyanate was a preferable cross-linker to 2,4-diisocyanatotoluene in terms of stability in acidic or basic aqueous solution. The flexibility of the cross-linker molecule possibly plays an important role in the cross-linking reaction. The carboxyl and amino groups were formed by treating the cross-linked composite particles with diluted HCl solution; 5–6 and 0.5–1.1 μmol g^-1, respectively. The cross-linked composite particles exhibited the characteristic property of ζ-potential, −44 to −47 mV and −102 to −107 mV in a neutral aqueous solution and ethanol, respectively. Received: 26 May 1997 Accepted: 4 August 1997     

Preparation of styrene/acrylonitrile copolymer microspheres and their composites with metal particles

 Monodispersed poly(styrene-co-acrylonitrile) [P(St-co-AN)] microspheres were prepared by emulsifier-free emulsion copolymerization of St with AN. Fourier transform IR spectroscopy and elemental analysis were used to measure the content of AN in the poly(St-co-AN) microspheres. X-ray photoelectron spectroscopy (XPS) measurements indicated the presence of an AN unit on the surface of the microspheres. The combined results of the elemental analysis and the XPS measurements showed that the copolymer on the surface of the P(St-co-AN) particles was rich in AN compared with that in the interior of the particles. P(St-co-AN)–metal composite particles were prepared by chemical metal deposition. The addition of nickel could improve the distribution of cobalt on surface of the polymer microspheres. The preparation of polymer–bimetal composite particles was tried. Transmission electron microscopy and XRD were used to study the distribution and structure of the deposited metal particles. Received: 30 June 1999/Accepted in revised form: 16 September 1999     

Uniform particles of manganese compounds obtained by forced hydrolysis of manganese(II) acetate

 Procedures for the preparation at low temperature (80 °C) of uniform colloids consisting of Mn₃O₄ nanoparticles (about 20 nm) or elongated α-MnOOH particles with length less than 2 μm and width 0.4 μm or less, based on the forced hydrolysis of aqueous manganese(II) acetate solutions in the absence (Mn₃O₄) or the presence (α-MnOOH) of HCl are described. These solids are only produced under a very restrictive range of reagent concentrations involving solutions of 0.2–0.4 mol dm⁻³ manganese(II) acetate for Mn₃O₄ and of 1.6–2 mol dm⁻³ Mn(II) and 0.2–0.3 mol dm⁻³ HCl for α-MnOOH. The role that the acetate anions play in the precipitation of these solids is analyzed. It seems that these anions promote the oxidation of Mn(II) to Mn(III), which readily hydrolyze causing precipitation. The evolution of the characteristics of the powders with temperature up to 900 °C is also reported. Thus, Mn₃O₄ particles transform to Mn₂O₃ upon calcination at 800 °C; this is accompained by a sintering process. The α-MnOOH sample also experiences several phase transformations on heating. First, it is oxidized at low temperatures (250–450 °C) giving MnO₂ (pyrolusite), which is further reduced to Mn₂O₃ at 800 °C. After this process the particles still retain their elongated shape. Received: 19 October 1999 Accepted: 24 November 1999     

Preparation of core-shell polymer colloid particles by encapsulation

 By means of heterocoagulation anionic poly-[styrene] particles were coated with smaller electrosterically stabilised cationic particles of poly-[butyl methacrylate]. On heating the heterocoagulated units 45 °C above the glass transition temperature of poly-[butyl methacrylate], as predicted theoretically, the latter polymer spread over the surface of the poly-[styrene] particle to give a composite particle with a core-shell structure. It was found that the extent of packing of the small particles on the larger core particle was a critical feature of the coating process. Received: 12 September 1996 Accepted: 18 September 1996     

Preparation of micron-sized, monodispersed, anomalous polymer particles by utilizing the solvent-absorbing/releasing method

 About 2-μm-sized polystyrene (PS) particles having uneven surfaces were prepared by a posttreatment in which toluene-swollen PS particles were thrown into a methanol bath to release toluene therefrom rapidly. The posttreatment was named the “solvent-absorbing/releasing method”. The PS particle had large dents at the surface. The size of the dents was changed by the conditions of the posttreatment. Received: 3 August 1999/Accepted: 1 March 2000     

Preparation and characterization of crosslinked PMMA latex particles stabilized by grafted copolymer

 The preparation of polymethyl methacrylate lattices stabilized by polyhydroxystearic acid and crosslinked with ethylene glycol dimethylmethacrylate (EGDM) has been studied. Crosslinking is a new development in the synthesis of PMMA latex. The particles are monodisperse when the concentration of EGDM ranges from 0.33 to 1.44%. The lattices are stable in aromatic and aliphatic solvents. Swelling occurs due to penetration of solvent molecules into the latex. The degree of swelling is calculated by viscosity and by dynamic light scattering measurements. Received: 30 January 1997 Accepted: 2 June 1997