Yu. M. Chernoberezhskii

Stability of Aqueous Crystalline Quartz Dispersions in the Acidic pH Region: The Role of the Structural Component of the Particle Interaction Energy

On the basis of the data obtained by studying the sols of crystalline quartz in aqueous KCl solutions at pH 2.0, 3.0, and 6.2, the domains of the parameters of structural forces for SiO2 particles are estimated using the method of flow ultramicroscopy and their dependence on the pH value of the dispersion medium is demonstrated.

Aggregate stability of the sol prepared from crystalline quartz in aqueous solutions of potassium chloride

The aggregate stability of the sol prepared from crystalline quartz is investigated by the direct method of flow ultramicroscopy. It is demonstrated that the boundary layers of water and the structural component of the particle interaction energy affect the stability of the sol and depend on the pH value. The parameters of the structural component of the energy of the interaction between quartz particles are estimated.

Electrosurface properties and aggregation kinetics of natural diamond sol in LiCl solutions

Electrosurface properties and aggregation stability of natural diamond sol in aqueous LiCl solutions at pH 6.0 and 9.0 are studied. It is shown that the aggregation of particles occurs according to the barrierless mechanism in the potential minimum, the depth of which is determined by the radius of structural forces. The ranges of the parameters of the structural forces of natural diamond in these solutions are determined. It is revealed that the extension of the water boundary layers on natural diamond decreases with an increase LiCl concentration and pH.

Effect of the Concentration of Sulfate Lignin on the Aggregation Stability of Its Aqueous Dispersions

The dependence of the aggregation stability of an aqueous dispersion of sulfate lignin on its concentration in the system is investigated by spectrophotometry within the wide range of pH values. It is shown that an increase in the concentration of sulfate lignin shifts the onset of its coagulation separation into the region of higher pH values.

The effect of pH on aggregation kinetics of monodisperse silica sol in naCl solutions

The aggregation kinetics of monodisperse silica sols with a particle size of 220 nm in aqueous NaCl solutions is studied by flow ultramicroscopy in a pH range of 2.0–10.2. Slow coagulation of the sols is found to occur via the barrierless mechanism in the secondary potential minimum resulting from the summation of dispersion attractive and structural repulsive forces. The influence of pH and NaCl concentration on the parameters of the structural component of the energy of the interaction between SiO2 particles is demonstrated.

Electrosurface properties of microcrystalline cellulose dispersions in aqueous solutions of aluminum chloride, nitrate, and sulfate

The method of microelectrophoresis is employed to study the dependence of the ζ-potential of microcrystalline cellulose particles on the concentration (10−6–10−3 M) and pH (2–11) of aqueous aluminum chloride, nitrate, and sulfate solutions. It is shown that, in the absence of aluminum salts, the isoelectric point (IEP) of the particles is independent on the nature of acid anions and is observed at pH 3.2. The addition of aluminum salts in concentrations as low as 2 × 10 −6 M for chloride and nitrate and 1 × 10−5 M for sulfate causes a shift of IEP to a less acidic region (pH 3.8), the value of which is virtually independent of the nature of the salt. As the concentration of salts is increased, the ζ-potential becomes positive, rises with an increase in pH to a maximum magnitude at pH 5.0–6.0, and decreases further until the second IEP (pH ∼ 6.5–7.0) is reached. At higher pH values, the ζ-potential becomes negative again. The observed ζ(pH) dependences are explained by the formation of hydrolyzed aluminum species exhibiting different adsorbabilities on microcrystalline cellulose particles. It is shown that positively charged hydroxocomplexes formed in aluminum sulfate solutions are characterized by a lower adsorbability than hydroxocomplexes formed in chloride and nitrate solutions.

Histograms of the size distribution of kraft lignin particles in aqueous solutions at various pH values

The size distribution of kraft lignin particles in aqueous solutions in a wide pH range (9.5−2.0) was studied by filtration through track membranes.

Influence of NaOH, HCl, NaCl, and CaCl2 electrolytes on aggregation stability of aqueous craft lignin dispersion according to data of filtration through track membranes

The method of filtration through track membranes with different capillary diameters (50–2500 nm) is used to study the aggregation stability of dilute (10 mg/l) aqueous dispersions of craft lignin in NaCl and CaCl2 solutions (0–10−1 mol/l) at pH 9.5–2.0. It is shown that, in the absence of salts, the isolation of craft lignin on filters increases at decreasing pH, i.e., upon approaching the isoelectric point of craft lignin (pH 2.0). The addition of the salts enhances the efficiency of craft lignin rejection, which is higher in the case of CaCl2. The sizes of craft lignin aggregates in solutions of different compositions are determined from the obtained data.

Study of the dependences of particle sizes in aqueous dispersions of sulfate lignin on pH by the filtration through track-etched membranes

Aggregation stability of low concentrations (10 mg/l) of aqueous dispersions of sulfate lignin is studied in a wide pH range (9.40–2.15) by filtration through track-etched membranes with pore sizes of 30–200 nm. It is shown that at all of the studied pH values, the solution of sulfate lignin is a polydisperse system. As pH decreases, the size of sulfate lignin particles increases, whereas the polydispersity of a system in the studied range of particles sizes (30–200 nm) decreases.

Conductivity and Electrokinetic Potential of Microcrystalline Cellulose Particles in Aqueous HCl and NaOH Solutions

The conductivity of microcrystalline cellulose (MCC) dispersions in aqueous 10–5–10–2 M HCl and NaOH solutions was measured as a function of the particle volume fraction by the conductometry. The dependence of the relative conductivity of MCC particles on pH of equilibrium solutions was determined using the Wagner equation. The electrophoretic mobility of MCC particles in the aforementioned solutions was measured by the microelectrophoresis, and corresponding dependences of the particle ζ potentials on pH of aqueous HCl and NaOH solutions (pH 2–11) were calculated using the Smoluchowski and Henry equations of the electrophoresis theory. It was shown that, in the case of MCC, the Henry equation, which allows for the significant conductivity of the dispersed particles, as compared with the dispersion medium, makes it possible to calculate more accurate ζ potential values and, consequently, to derive the ζ(pH) dependence, which is satisfactorily consistent with the effect of the surface charge and solution ionic strength on the ζ potential in a wide pH range.