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In this work, a novel route to synthesize polymer/metal composite nanospheres has been proposed. This method combines the advantages that the polymer chains collapse and entangle in the presence of compressed CO(2), which acts as antisolvent, and the metal nanoparticles and polymers can be precipitated simultaneously from micellar solutions by the easy control of CO(2) pressure. Ag/polystyrene (PS) nanocomposites have been successfully prepared using this method. The transmission electronic micrographs (TEM) of the obtained nanocomposites show that the smaller Ag nanoparticles are immobilized by PS nanospheres of about 50 nm; the phase structure was characterized by X-ray diffraction (XRD). The Ag/PS nanocomposites show absorption properties at a wavelength of approximately 417 nm. The results of X-ray photoelectron spectra (XPS) and FT-IR spectra indicate that there is no chemical linkage or strong interaction between PS and Ag nanoparticles in the resultant products. This method has many potential advantages for applications and may easily be applied to the preparation of a range of inorganic/ polymer composite nanoparticles.
Fairly uniform poly(styrene)-poly(methyl methacrylate) (PST-PMMA) composite microspheres were prepared by employing an SPG (Shirasu Porous Glass) membrane emulsification technique. A mixture of PST, PMMA, and cosurfactant [lauryl alcohol (LOH)] dissolved in dichloromethane (DCM) was used as the dispersed phase, and an aqueous phase containing poly(vinyl alcohol) and sodium lauryl sulfate was used as the continuous phase. It is necessary to add LOH to obtain uniform particles with the SPG emulsification technique. The effects of the volume of LOH on the morphology of the final particles were investigated by varying the volume of LOH from 0 to 2 ml (per 1.2 g polymer). A three-component model was developed for different PMMA/PST ratios and LOH/polymer ratios, based on Sundberg's theory; and the calculation on morphology was carried out by using the three-component model. Agreement was obtained between experimental and calculated results. When 2 ml of LOH was added, it was found that LOH can engulf the polymer particles completely; a hemicore (HCP1P2P3) morphology, where PST and PMMA formed a hemisphere core inside a LOH shell, was observed when the PMMA/PST ratio was high, while core-shell-shell (CSP1P2P3) morphology, where PMMA formed a core and PST and LOH formed an inner shell and an outer shell, respectively, was observed when the PMMA/PST ratio was low. When the volume of LOH was below 1 ml (per 1.2 g polymer), however, LOH could not always engulf the inner polymer particles completely; cored hemisphere (CHSP3P2P1), core-shell-shell (CSP2P1P3), and hemicore (HCP1P2P3) morphologies were observed, depending on the PMMA/PST ratio and volume of LOH. Copyright 1999 Academic Press.
An experimental desorption study of Triton X-100 from latices with different functionality is presented. Two different strategies to follow the desorption experiment have been used: first, a discontinuous method based on the wash step (centrifugation-removal-redispersion); and second, a continuous method based on the replacement of the disperse media. The desorption results show that in all cases a residual amount of Triton X-100 remains adsorbed, indicating irreversibility of the surfactant adsorption. Finally, the effect of desorption on the colloidal stability of one type of latex-surfactant complex has been analyzed. Copyright 2000 Academic Press.
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Improved performance with the latex agglutination immunoassay, PACIA, is possible when the F(ab')2 fragments of antibody are chemically coupled at their hinge region to a protein-coated latex using a new coupling reagent, N epsilon-chloroacetyl lysine N-carboxyanhydride. This reagent, whether by orientating the complete antibody molecule or its F(ab')2 fragment or by preventing antibody denaturation, increased the sensitivity of the PACIA method. The use of F(ab')2 fragments eliminated most serum interference with the test.
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In this work we analyze the dielectric properties of dilute colloidal suspensions of nonconducting spherical particles with a thin electrical double layer from experimental data obtained by performing impedance spectroscopy experiments over a broad frequency range, from 20 Hz to 1 GHz. The electrode polarization correction was made by fitting a circuit model in the complex impedance plane (impedance spectrum) using a constant phase angle (CPA) element to fit the electrode polarization in series with the sample impedance. This simple procedure is found to be effective in eliminating the electrode contribution. The dielectric response shows two different dispersions, the alpha relaxation (counterion relaxation) that occurs at low kilohertz frequencies, and the delta relaxation (Maxwell-Wagner effect) found in the MHz range. These are reasonably well fitted over a broad frequency range by the theoretical expressions given by a simplified standard model (not including anomalous conduction) and a generalized model (including anomalous conduction) for the low-frequency dispersion, plus Maxwell-Wagner-O'Konski theory for the delta relaxation in the mid-frequency range. An analysis was also made of the need to include, for these latices, the effects of ion mobility in the Stern layer in order for the values of the zeta-potential obtained from electrophoretic and dielectric data to be compatible with each other.
A soap-free emulsion polymerization method with the use of an amphoteric initiator, currently proposed by the authors for producing highly monodisperse, micrometer-sized polymer particles, was examined in the polymerization of styrene with a 2,2'-azobis [N-(2-carboxyethyl)-2-2-methylpropionamidine] hydrate initiator and an NH(4)OH/NH(4)Cl pH buffer. The pH buffer was used to control the electric surface potential of particles to maintain a stable dispersion of particles and to prevent generation of new particles during the polymerization. Addition of monomer to the reaction system during polymerization could enlarge the average size of polymer particles to 5.7 microm with a coefficient of variation of 1.5%, which is much less than the standard criteria of monodispersity, 10%.
Visible polyaniline-latex particles 13 microm in diameter were used for obtaining a quantitative relationship between the adsorption force and the electroactivity at a platinum electrode. An optical cell equipped with wire electrodes was filled with the suspension in hydrochloric acid. When electrode potential was switched between the oxidized and the reduced domains, some adsorbed particles showed color change owing to the electroactivity. The numbers of electroactive and the inactive particles in the suspension were counted, including poly(N-vinylpyrrolidone) (PVP). The ratio of the numbers was proportional to the concentration of PVP, as it was in equilibrium. The adsorbed particles were desorbed mechanically by forced flow. The numbers of the desorbed particles did not decrease with an increase in the flow velocity until threshold values. The threshold value for the electroactive particle was 10 times larger than that for the inactive ones, corresponding to 10 times larger adsorption energy of the electroactive particles than of the inactive ones. The adsorption stress was evaluated from the removal of the electropolymerized polyaniline film from the electrode. Then the adsorption area of the particle was estimated.
Hydrophobic polymer (PS) nanoparticles preformed through an emulsifier-free emulsion polymerization method were successfully incorporated into a gallery of pristine sodium montmorillonite via interfacial cation exchange. The polymer beads confined between clay nanosheets were capable of (1) preventing the silicate layers from restacking and (2) maintaining the exfoliated state of clay. The increase in the abundance of surface groups promoted adsorption of the nanobeads onto the silicate surface and eventually led to the establishment of strong polymer-clay interactions. These findings suggest that, on the basis of the obtained pre-exfoliated clay masterbatch, the presence of strong polymer-clay interactions could improve the mechanical performance of nanocomposites.
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