Decrease In Ζ-potential Research Articles

Instantaneous interaction of mucin with pectin- and carrageenan-coated nanoemulsions

The efficiency of drug delivery and sensory perception is intertwined with mucoadhesive systems. The physiochemical characteristics of mucus induce flocculation of emulsion droplets, which could significantly influence their sensory perception. In this study, we investigated the interactions between pectin- and carrageenan-coated nanoemulsions with mucin. The size and ζ-potential changes in the nanoemulsions were investigated at pHs 3.0–5.0. The results showed no significant differences (p > 0.05) in size without the addition of gums; however, the ζ-potential decreases from 2.92 mV to −2.51 mV as pH increased. The stability of nanoemulsions over the extended time (15 days) and at elevated temperature (60 °C) resulted in minimal degree of phase separation observed. The mucin particle size method was employed to characterize mucin-nanoemulsion interactions. Results confirmed that mucin-emulsion complexes were formed instantaneously mostly due to electrostatic interactions. The contact angle analysis and UV–Vis spectroscopy confirmed contribution of wetting and absorption mechanisms in the mucin interactions.

Intensification of the contact clarifiers work during the drinking water preparation

Abstract In this paper we studied the intensification of the water clarification process on contact clarifiers with quartz sand filtering bed, which was modified with a solution of aluminum sulphate coagulant. The modification of the quartz sand filtering bed was carried out by applying to the surface of grains of quartz sand solution of coagulant aluminum sulphate with different doses. Investigation of the electrokinetic potential of the filtering material (quartz sand) was carried out by the percolation potential method. The influence of electrical properties (size and sign of the charge) of the filtering bed itself and suspended solids in the water on the filtration process was studied. The filter material – quartz sand used in contact clarifiers has a negative electric charge. When the electric charge of the particles decreases, that is, as the ζ-potential decreases, the repulsive forces decrease and it the adhesion of particles becomes possible. This is the process of coagulation of the colloid. The forces of mutual gravity between the colloidal particles begin to predominate over the electric repulsive forces at the ζ-potential of the system less than 0.03 V. Modification of quarts filtering bed with a solution of coagulant aluminum sulphate recommended for the purification of surface water allows: to intensify the process of water clarification, to reduce the consumption of reagents by 25–30%, with the obtaining purified water of the required quality, to reduce the production areas necessary for reagent management of treatment facilities, and to reduce the cost of water treatment by 20–25%.

Thermo-/pH-responsive behaviours of base-rich diblock polyampholytes in aqueous solution: experiment and simulation

We report on the thermo-responsive and pH-responsive behaviours exhibited by two poly(acrylic acid)-poly(2-(dimethylamino)ethyl methacrylate) diblock copolymers with unbalanced acid–base compositions, PAA40-PDMAEMA120 and PAA40-PDMAEMA285, in water, a selective solvent. Using a combination of ultraviolet–visible (UV–vis) spectroscopy and dynamic light scattering, the dual-stimuli responsive behaviours can be clearly detected. The ζ-potential decreases sharply for a symmetrical counterpart PAA60-PDMAEMA70 solution, while it changes evenly for PAA40-PDMAEMA120 and PAA40-PDMAEMA285 solutions because of the asymmetrical compositions. The lower critical solution temperature of the PAA40-PDMAEMA285 solution is always less than that of the PAA40-PDMAEMA120 solution at the same solution concentration and pH values. The molecular dynamics simulation is used to explore the molecular mechanism of the responsive behaviour. The simulation also evidences the presence of dual-stimuli responsive behaviour of the copolymer with respect to changes in temperature and pH in aqueous solutions. The radius of gyration Rg and the end-to-end distance Re of the asymmetric polyampholyte A20-B60 are smaller than those of the symmetric one A40-B40 at all simulated temperatures, which indicates increased aggregation behaviour and the compact aggregates of asymmetric polyampholyte chains. The effect of polymer molecular mass MW on the aggregation behaviour seems to be more profound than that of polymer composition, which may be attributed to the fact that increasing the molecular weight of the copolymer increases the variability of the micelle sizes. Additionally, hydrophobic interaction plays a key role in the aggregation process.

Proton–arsenic adsorption ratios and zeta potential measurements: Implications for protonation of hydroxyls on the goethite surface

Successfully modeling the surface charge of goethite and anion adsorption on goethite using a surface complexation model (SCM) alone cannot verify the assumptions of this model. In this study, the assumptions of 2-p K triple layer model (TLM) and two-site 1-p K basic stern model (BSM) were assessed with respect to their ability to interpret both the proton–anion adsorption ratios of dimethylarsinate (DMA), monomethylarsonate (MMA), and arsenate and their effect on the ζ-potential. The proton–DMA adsorption ratio is around 0.9 at pH 4.25 and 1.1 at pH 6.75 at DMA surface coverage ranging from 0 to 2 μmol m −2, and the ζ-potential is independent of DMA adsorption at these two pH values. The proton–MMA adsorption ratio increases to 1.5 at pH 4 and 2.1 at pH 6.75 as the MMA surface coverage decreases to 0.5 μmol m −2. The ζ-potential is less dependent on MMA adsorption at a surface coverage range of 0 to 1.8 μmol m −2, and it then decreases with a further increase in the MMA surface coverage at pH 4 and 6.75. The proton–arsenate adsorption ratio decreases to 2 as the arsenate surface coverage approaches zero, and the ζ-potential decreases linearly with the increasing arsenate surface coverage at pH 4 and 6.75. Neither the 2-p K TLM nor the 1-p K BSM give a consistent interpretation of both the proton–arsenic adsorption ratio and the effect of arsenic on the ζ-potential. The results suggest that the 1-p K MUSIC model in which each type of surface hydroxyls has its own intrinsic proton-affinity constant and only one type of surface hydroxyls is involved in DMA, MMA, and arsenate adsorption is preferably pursued. The protonation degree of reactive hydroxyls estimated from proton–arsenic adsorption ratios is 0.2 at pH 4 and 0 at pH 6.75 in 0.001 M NaNO 3.

Properties of Aqueous Suspensions of Highly Dispersed Silica in the Presence of Polyvinylpyrrolidone

The effect of polyvinylpyrrolidone (PVP) on stability, rheological, electrokinetic and electrophysical properties of aqueous dispersions of A-300 pyrogenic silica was studied. The suspensions were shown to be most stable at PVP concentrations in the range from 0.12 to 0.24 wt % that was provided by structure-related mechanical factors. In the presence of PVP, the value of ζ-potential decreases, the ac conductivity increases, and rheological properties vary similarly to variations of oxide dispersity.

The dynamic and static electrophoretic mobility of paraffin particles dispersed in water

The surface electrical properties of paraffin particles have been investigated by electrophoretic light scattering and ESA (using the ESA-8000 and the AcoustoSizer). Potentiometric titrations have also been performed. The results show that anomalous surface conductance (also known as Stern layer conductance) is unimportant in this system, despite the fact that the bare surface charge density is of the order of 1 C m −2 and about 90% of the counterions are residing in the Stern layer. The magnitude of the ζ-potential decreases monotonously with increasing ionic strength, and the good agreement between the ζ-potentials obtained with different electrokinetic techniques further supports the relative unimportance of anomalous surface conductance in this system. We have, however, observed that the magnitude of the ζ-potential does decrease with time, and this effect needs to be further investigated.

Pentachlorophenol-induced change of ζ-potential and gel-to-fluid transition temperature in model lecithin membranes

We have determined ζ-potentials for dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) membranes by measuring the electrophoretic mobility of multilayered vesicles and the temperatures of the gel-to-ripple-to-fluid phase transitions of sonicated vesicles by a photometric method. Some conclusions are: (1) The ζ-potentials of DMPC and DPPC vesicles become negative due to adsorption of ionized pentachlorophenol (PCP), (2) their magnitude changes, step-like, on gel-to-fluid transition and (3) the temperature of the step-like change in ζ-potential decreases with an increase in PCP concentration. (4) PCP exhibits a large effect on membrane structure: It induces an isothermal phase change from the ordered to disordered state, which is enhanced by monovalent salt in the aqueous phase. (5) Both ionized and unionized PCP decrease the melting phase transition temperature and abolish the pretransition, (6) the unionized species increases the melting transition width and (7) the ionized species is more potent in abolishing the pretransition. (8) The shorter chain lipid (DMPC) is more sensitive to the presence of PCP; the maximum decrease in ΔT t is 13 K (DMPC) and 7 K (DPPC) in the presence of ionized PCP. We have shown experimentally, by comparing the ΔT t from photometric studies with the density of adsorbed PCP derived from ζ-potential isotherms, that (9) the shift of the melting phase transition temperature increases linearly with the density of adsorbed PCP. (10) In contrast to membranes made of negatively charged lipids, the transition temperature of DMPC and DPPC membranes in the presence of PCP further decreases in the presence of monovalent salt. The salt effect is due to screening of the membrane surface leading to enhanced adsorption of ionized PCP and a depression in transition temperature. (11) It is shown that both the adsorption and the changes of gel-to-fluid phase transition temperature can be described in terms of the Langmuir-Stern-Grahame model and (12) proposed that future studies of membrane toxicity of PCP should be focused on its pH dependence.

THE INFLUENCE OF METAL SALTS ON THE ζ-POTENTIAL OF DEGUMMED SILK FIBRE

The ζ-potential at the interfaces between degummed silk fibre and the aqueous solutions containing a number of trivalent metal nitrates was measured by means of the streaming potential method. The trivalent metals used were Al, Ga, In, Cr, Fe, Rh, Sc, Y, La, Sm, Tb, Er and Yb.At pH 5.0, generally, the negative ζ-potential decreases with increasing concentration of metal salt. In the cases of Al, Ga, In, Cr, Fe, Rh and Sc, it reverses its sign at concentrations in the region of 10-6-10-4M and then approaches a limiting positive value which differs for each metal salt: the sequence for the reversal of charge concentrations is Fe Ga>Rh. In the cases of Al, In, Cr and Sc, with increasing concentration of metal salt, the ζ-potential decreases and nearly becomes zero at concentrations in the region of 10-6-10-5M. At higher concentrations it rises slightly. In other cases, the ζ-potential decreases with increasing concentration of metal salt and reaches a negative value. The decrease in the ζ-potential is due to the adsorption of nitrate ions: this was discussed by measuring the ζ-potential for potassium nitrate.