PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Flocculation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,045 records · Page 58Linked to original sources
PubMed2006

Clay and oxide destabilization induced by mixed alum/macromolecular flocculation aids.

The review points out typical differences and analogies of the bulk characteristics of aluminum ion complexed polyelectrolytes and of their adsorption behaviors when such systems were supplied to inorganic colloids such as oxides and clays. It reports some particular investigations that were carried out in aqueous media to determine (i) the nature of the interactions existing between clay or oxides, aluminum ions and polyelectrolytes and (ii) the effects on the interfacial characteristics and the colloid stability related to the relative concentrations of these different constituents. The investigations concerned the synthetic alumina/polyacrylic acid systems and the natural kaolinite/humic acid systems, as well as partly the mixed alumina/humic acid systems. Different adsorption features and destabilization kinetics were determined to develop within these systems. One of the main constraints of the investigation arose from the presence of three interacting components which developed amphoteric and amphipatic interactions, the latter being generated by the hydrophobic moieties induced by the aluminum ions/carboxylic acid groups ion-pairing. The investigations concerned the extent and the rate of transfer of hydrogen, aluminum ions and polyelectrolytes from the bulk solution to the solid surface. Electrical surface charge characteristics were expressed in terms of the zeta potential of the colloid/polymer complexes. The colloid stability of the systems was determined as a function of time at short and long terms. The variation as a function of time of the number and weight average masses was correlated with the variation with time of the zeta potential. All these systems were determined to reach the kinetic and thermodynamic equilibrium only slowly. Despite the fact that the supply of mixed coagulants provoked the initial aggregation and the subsequent fragmentation processes for both systems, the mechanisms responsible for the two processes were found to be different as revealed by comparatively investigating the synthetic and the natural systems. The fragmentation originated from the slow segregation process of positively and negatively charged groups for the natural kaolinite/humic acid systems, while the segregation process affected hydrophobic and hydrophilic moieties for the synthetic alumina/polyacrylic acid systems.

Journal Article↗
PubMed2006

Solvent entrainment in and flocculation of asphaltenic aggregates probed by small-angle neutron scattering.

While small-angle neutron scattering (SANS) has proven to be very useful for deducing the sizes and masses of asphaltenic aggregates in solution, care must be taken to account for solvation effects within the aggregates so as to not err in the characterization of these important systems. SANS measurements were performed on solutions of asphaltenes dispersed in deuterated solvents in which a broad spectrum of solute and solvent chemical compositions was represented. Fits to the scattering intensity curves were performed using the Guinier approximation, the Ornstein-Zernike (or Zimm) model, a mass-fractal model, and a polydisperse cylinder model. The mass-fractal model provided apparent fractal dimensions (2.2-3) for the aggregates that generally decreased with increasing aggregate size, indicating increased surface roughness for larger aggregates. The polydisperse cylinder model provided typical values of the particle thicknesses from 5 to 32 angstroms, the average particle radius from 25 to 125 angstroms, and approximately 30% radius polydispersity. Subsequent calculation of average aggregate molar masses suggested a range of solvent entrainment from 30 to 50% (v/v) within the aggregates that were consistent with previous viscosity measurements. Additional calculations were performed to estimate the proportion of microparticle to nanoparticle aggregates in the solutions. The results indicate that the inclusion of solvation effects is essential for the accurate determination of aggregate molecular weights and fractal dimensions.

Journal Article↗
PubMed1993

The effect of phenol on the electrolyte flocculation of certain polymeric dispersions to thixotropic gels.

Aqueous dispersions of an acrylate-methacrylate, a water-insoluble copolymer, were prepared by a coacervation technique. Addition of sodium chloride (0.2 M) to the dispersion (10%, w/v) converted the system to a thixotropic gel which turns fluid on shaking and reverts to gel on standing. Phenol (0.03 M) inhibited the gelling effect of the electrolyte. Among the various phenolic compounds tested, phenol displayed the strongest and chlorocresol the weakest antigelling property. Sodium chloride reduced the electropotentials (index of particle-particle repulsiveness) of the polymer dispersions, while phenol increased the potentials. It is thought that the phenol solution acted as a dielectric which increased the interparticle repulsive potential, hence its antiflocculant effect.

Electrochemistry↗