Ferenc Csempesz

Enhanced flocculation of colloidal dispersions by polymer mixtures

Abstract Bridging flocculation and electrolyte coagulation of negatively charged colloidal dispersions in the presence and absence, respectively, of uncharged polymers and polymer mixtures were studied. The relative coagulation and flocculation rates of particles in the presence of electrolyte and small polymer amounts were measured and the stability ratios have been calculated at various ionic strengths. Also, the structure of polymer layers formed in individual adsorption of polymers and in simultaneous competitive adsorption from binary polymer mixtures at particle/solution interfaces was investigated. The electrophoretic mobility and the diffusion coefficient of particles with and without adsorbed polymer were measured by laser Doppler-electrophoresis and photon correlation spectroscopy, respectively, and the electrophoretic and the hydrodynamic thickness of adsorbed polymer layers have been calculated. It was found that the adsorbed polymers may enhance or diminish the rate of successsful encounters between particles, even at low surface coverages, depending on the magnitude of the interparticle electrostatic repulsion. In addition, competitive adsorption of chemically different polymers for particle surfaces may result in considerable alteration in the conformation of macromolecules in the mixed adsorption layer. Close correlation was found between the effectiveness of polymers as flocculants and the thickness of adsorbed polymer layers formed at optimum polymer dosages on the particle surfaces. Binary mixtures of suitable polymers proved to be very efficient flocculants for the dispersions. The enhanced flocculating effect of some mixtures can be ascribed to extended polymer layers formed in competitive adsorption of chemically different macromolecules at particle/solution interfaces. These findings have relevance in many environmental technologies and offer a way of improving the effectiveness of solid–liquid separation processes.

Effect of pH of aqueous ceramic suspensions on colloidal stability and precision of analytical measurements using slurry nebulization inductively coupled plasma atomic emission spectrometry

Abstract Colloidal stability of silicon nitride, silicon carbide and boron carbide aqueous slurries used for slurry nebulization inductively coupled plasma atomic emission spectrometry has been investigated in the pH range 2–10 by electrophoretic mobility and particle size measurements, together with sedimentation tests. The mean particle size of silicon nitride and silicon carbide suspensions change with increasing pH showing a maximum at the isoelectric points (pH 7.5 and 5.5 respectively). The particle size distribution of boron carbide slurries remains practically constant and the zeta potential of suspended boron carbide particles shows a small change in the pH range investigated. The silicon nitride and silicon carbide slurries have good stability at pH below 5 and above 8, respectively. Boron carbide slurries show excellent stability in the whole pH range investigated. The time demand for stabilization of the emission line intensities from the start of nebulization strongly depends on the colloidal stability of slurries. Consequently, it is advantageous to nebulize aqueous suspensions with a pH as far from the isoelectric point of the solid as possible and with the ionic strength of the dispersion medium as low as possible. The RSD values of the line intensity measurements determined after 3 min stabilization time decrease with increasing stability of the aqueous slurries.

The effect of polymer bridging on the flocculation kinetics of colloidal dispersions

Abstract Relative coagulation and flocculation rates of negatively charged colloidal dispersions (silver iodide sol, arsenic trisulphide sol, polystyrene latex) in the presence of electrolyte and small amounts of methylcellulose (MC), polyvinyl pyrrolidone (PVP) or 1:1 (w/w) MC-PVP mixture, have been determined by measuring the change in optical density of the dispersion with time. It was found that the adsorbed polymer may enhance or diminish the rate of successful encounters between particles, even at low surface coverages, depending on the magnitude of the interparticle electrostatic repulsion. In addition, it was shown that the use of an appropriate mixture of two unchanged polymers offers an effective way of increasing the rate of bridging flocculation. Polymer bridging resulted in considerable enhancement of flocculation rate only at low ionic strengths for the dispersions. Its contribution to the flocculation rate was maximal even when considerable double-layer repulsion prevented adhesion between particles in the absence of polymer. At these electrolyte concentrations, synergism in flocculation of the silver iodide sol and of the arsenic trisulphide sol by the MC-PVP mixture was observed. When the interparticle electrostatic repulsion was eliminated, any amount of adsorbed polymer reduced the rate of successful encounters relative to the coagulation rate of the polymer-free dispersion.

Simultaneous competitive adsorption of polymers from ternary solutions at solid/liquid interfaces

Abstract Individual adsorption and simultaneous competitive adsorption from ternary solutions of uncharged polymers on aqueous dispersions of polystyrene lattices with different particle sizes were studied. The effects of the ratio of the polymers competing in simultaneous adsorption for the particle surfaces, and of the extent of the surface area available for the molecules, respectively, on the adsorption preference were investigated. Based on the experimental results, preferential adsorption parameters for polymers in pairs were established and used as a measure of the affinity of the macromolecules competing for the solid surfaces.

Interfacial behaviour of binary polymer mixtures I. Effect of uncharged polymers and of their mixtures on the stability of silver iodide sol

Abstract The adsorption from aqueous solutions of methylcellulose (MC), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), adsorption of their binary mixtures on silver iodide sol, and the effect of these polymers and polymer mixtures on the stability of silver iodide sol, have been studied. All these polymers show high affinity-type adsorption isotherms and the adsorption is only partially reversible upon dilution. The order of preferential adsorption for the polymers is as follows; PVP &>; PVA &>; MC. The weakly adsorbed polymers, at high surface coverage, can be displaced from the interface by the preferentially adsorbed polymers. Synergism has been found in the flocculating effect of the MC—PVP and the PVA—PVP mixtures. At the onset of the stabilizing region, some increase in the effectiveness of the above two mixtures has also been observed. Non-additivity can be observed when the difference in the segment affinity of the two polymers for the particle surfaces is high enough. When synergism occurs, the conformation of the weakly adsorbed polymer appears to be distorted at the solid/liquid interface by the preferentially absorbed polymer. This “irregularly” extended polymer conformation is especially favourable for bridging flocculation.

Interfacial behaviour of binary polymer mixtures II. Competitive polymer adsorption and its effect on the stability of colloidal dispersions

Abstract This paper describes the adsorption of methylcellulose (MC), polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) and of their binary mixtures on arsenic trisulphide sol and polystyrene latex, respectively, and the effect of these polymers and polymer mixtures on the stability of the dispersions. The conditions for binary polymer mixtures resulting in a synergistic effect and the relation of this phenomenon to competitive adsorption of the polymers were studied. Each polymer itself shows high-affinity type adsorption isotherm on both solid surfaces. Upon simultaneous adsorption from binary mixtures, the order of preferential adsorption for the polymers is as follows: PVP>MC>PVA on the arsenic trisulphide sol, and MC>;PVP>PVA on the polystyrene latex. At high surface coverage, the weakly adsorbed polymers can be displaced from either interface by the preferentially adsorbed polymers. The effectiveness of the polymer mixtures, both as flocculants and stabilizers, closely correlates with the order of preferential adsorption for the polymers. Synergism in the flocculating effect of MC-PVP mixtures with components of different molecular mass, on arsenic trisulphide sol was found. At the onset of the stabilizing region, some increase in the effectiveness of MC-PVP and PVA-PVP mixtures on arsenic trisulphide sol was also observed. These phenomena are attributed to irregularly extended adsorption layers formed by the competitive adsorption of the polymers. Synergism can be observed when considerable difference exists in the segment affinity of the competing polymers for the particle surfaces and when the weakly adsorbed polymer itself is a more effective flocculant or stabilizer than the preferentially adsorbed polymer.

Comparison of the physicochemical properties of MCT-containing fat emulsions in total nutrient admixtures

The physical stability of two types of MCT-emulsions made by different technologies - physical mixture vs. structured lipids - was studied as a function of storage time and temperature. Particle size analysis, zeta potential and dynamic surface tension measurements were carried out to evaluate the possible changes in the kinetic stability of the emulsions. Our results indicate that the physical mixture technology of MCT-emulsions resulted in impaired physicochemical stability compared to the ones containing structured triglycerides. In the case of structured lipids, both medium and long chain fatty acids can be found in one triglyceride molecule, leading to a favorable interfacial location of structured triglycerides. Besides the advantageous metabolic effects of structured triglycerides, their application is recommended to improve the physical stability of TPN admixtures.

Colloidal stability of electrostatically stabilized sol particles. Part I: The role of hydration in coagulation and repeptization of ferric hydroxide sol

FeO(OH)·0.5 H2O powders were prepared by drying portions of a FeO(OH)·0.5 H2O sol at different relative vapor pressures, and the adsorption of water on the powders was determined. The magnitude of electrostatic potential barrier for the sol is of about 9 mJ·m−2. The reduction in the immersion enthalpy and in the surface free-energy in a range of the relative vapor pressures of 0.0–0.9 is as high as 140 mJ·m−2 and 130 mJ·m−2, respectively.It follows from the foregoing that two potential barriers may form. The electrostatic barrier presumably regulates the rate of flocculation and the “hydration barrier” (at closer separations) regulates the rate of particle coalescence or sintering.Peptizability of the FeO(OH)·0.5 H2O powders dried at relative vapor pressures between 0.4 and 0.9 was found to be fairly high, presumably because the adsorbed water prevented the formation of close contacts between the primer particles. Lowering the vapor pressure, however, resulted in a notable decrease in the peptizable amount, and also a considerable increase in the particle size of the peptized sol.

Kinetic stability of all-in-one parenteral nutrition admixtures in the presence of high dose Ca2+ additive under clinical application circumstances

BackgroundTPN infusions are usually administered during a treatment period of 10–24 hours per day due to the metabolic capacity of the liver. During this time interval physicochemically stable TPN solution (emulsion) is needed for the treatment. The purpose of the present study was to examine how the kinetic stability features of ready-made total parenteral nutrition admixtures containing olive oil and soybean oil will change under the usage-modeling 24-hour application with and without overdose Ca2+.MethodsParticle size analysis and zeta potential measurements were carried out to evaluate the possible changes in the kinetic stability of the emulsions.ResultsOur results indicate that in two of the four mixtures bimodal droplet-size distribution figures were detected and appearance of fat particles over 5 μm can not be disclosed. The tendency for separation of large diameter droplets in the two types of oil-based emulsion systems was different. In case of soybean containing emulsion second peak of droplets appeared in the bottom of the container in contrast to the olive oil containing emulsions where the second peak appeared in the surface layer. Interestingly this phenomenon is independent of calcium-content.ConclusionsFrom therapeutic point the emulsions of the bigger droplets containing upper layer are safer because the potentially dangerous big droplets could remain in the infusion bag after the administration.

Complexation of Statins with β-Cyclodextrin in Solutions of Small Molecular Additives and Macromolecular Colloids

The solubility of lovastatin and simvastatin (inevitable drugs in the management of cardiovascular diseases) was studied by phase-solubility measurements in multicomponent colloidal and non-colloidal media. Complexation in aqueous solutions of the highly lipophilic statins with β-cyclodextrin (β-CD) in the absence and the presence of dissolved polyvinyl pyrrolidone, its monomeric compound, tartaric acid and urea, respectively, were investigated. For the characterization of the CD-statin inclusion complexes, stability constants for the associates have been calculated.