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The initial-stage dynamics of flocculation of positively charged latex particles induced by polyelectrolytes (PEs) and polyelectrolyte complexes (PECs), composed of linear polyacrylic acid (PAA) and a PAA-based hydrophilic microgel (PAA#) with a small amount of a linear polycation, was comparatively analyzed by applying the standardized colloidal mixing procedure. Based on the rate of flocculation, this method allows us to investigate the dynamics of flocculation immediately after the onset. In addition to confirming the prediction made regarding the initial rate of flocculation with linear polyanions-which was mostly similar to that observed in negatively charged colloids with positively charged PEs-we have confirmed two important new results regarding the microgel: (1) the increase of the initial rate is less markedly affected by the microgel concentration than by the linear polymer concentration, which can be explained by the fact that the three-dimensional (3D) cross-linked structure of the microgel that does not deform as easily as the linear structure upon touching the colloidal surface; and (2) there is a remarkable increase of the initial rate due to the contribution of instant aggregation of the negatively charged microgel induced by the polycation adsorption. These results suggest the significance of state and formation dynamics of PECs prior to reaching the surface of targeted colloidal particles for the intension of effective flocculation. These aspects are not treated so far in the dynamic process of flocculation.

Wide usage of clay-based materials in industry requires investigations concerning efficient modification techniques to control their mechanical behavior in aqueous media. The challenging problem in this field involves minimization of the modifying agent content to provide marked changes in the operating characteristics of the material. In this work, the physicochemical, mechanical and structural aspects of the interaction of capillary water-saturated kaolinite with polyelectrolytes were studied. Modification of kaolinite with a negligible amount (0.1 wt.%) of hydrophilic and amphiphilic polyelectrolytes provides the control for rheological parameters of kaolinite suspensions such as storage and loss modulus in the range of three orders of magnitude. The results obtained reveal the wide possibilities for the production of a spectrum of clay materials using minor amounts of polymer modifying agents.

A synthetic procedure is described for preparation of magneto-sensitive nanocomposites from maghemite nanoparticles and a natural polysaccharide, sodium alginate cross-linked with calcium ions. With this procedure, a series of nanocomposites was synthesized and characterized by spectrophotometry, transmission electron microscopy, X-ray diffraction, Mössbauer spectroscopy, Fourier transform IR-spectroscopy and magnetometry with the following main conclusions: (a) The nanocomposites retain their solubility in water unless the iron content exceeds 18.1±0.2 wt%. (b) Only γ-Fe2O3 nanoparticles are included in the nanocomposite. (c) Size of nanoparticles lies within a 4–20 nm range with a dominant diameter of 7±1 nm. (d) Maghemite nanoparticles bind to the alginate matrix via formation of electrostatic and coordination contacts between the surface Fe3+ maghemite ions and functional alginate groups. (e) The nanocomposites exhibit properties which are characteristic for soft magnetic materials since they have a low coercive force. (f) Magnetic characteristics of the nanocomposites, saturation magnetization and residual magnetization, are effectively controlled by the maghemite content. (g) An external magnetic field causes the nanocomposites to move in an aqueous dispersion.