We describe an improved method for determining the electroosmotic mobility and zeta potential of surfaces based on a current‐monitoring method. This technique eliminates the requirement for ...measurements of channel dimensions and sample conductivities, leading to a simple high precision measurement. The zeta potential of PDMS is measured for native surfaces and surfaces treated with a nonionic surfactant in low‐conductivity electrolytes.
In this investigation, we aimed to fabricate easy separable composite microbeads for efficient adsorption of tetracycline (TC) drug. MIL-125(Ti)/MIL-53(Fe) binary metal organic framework (MOF) was ...synthetized and incorporated with carbon nanotube (CNT) into alginate (Alg) microbeads to form MIL-125(Ti)/MIL-53(Fe)/CNT@Alg composite microbeads. Various tools including FTIR, XRD, SEM, BET, Zeta potential and XPS were applied to characterize the composite microbeads. It was found that the specific surface area of MIL-125(Ti)/MIL-53(Fe)/CNT@Alg microbeads was 273.77 m
/g. The results revealed that the adsorption of TC augmented with rising CNT proportion up to 15 wt% in the microbeads matrix. In addition, the adsorption process followed the pseudo-second-order and well-fitted to Freundlich and Langmuir models with a maximum adsorption capacity of 294.12 mg/g at 25 ◦C and pH 6. Furthermore, thermodynamic study clarified that the TC adsorption process was endothermic, random and spontaneous. Besides, reusability test signified that MIL-125(Ti)/MIL-53(Fe)/CNT@Alg composite microbeads retained superb adsorption properties for six consecutive cycles, emphasizing its potentiality for removing of pharmaceutical residues.
Summary
The objective of this study was to evaluate the influence of pH on rheological and viscoelastic properties of solutions based on blends of type A (GeA) or type B (GeB) gelatin and chitosan ...(CH). Solutions of GeA, GeB, CH, GeA:CH, and GeB:CH were prepared in several pH (3.5–6.0) and analyzed for determination of zeta‐potential. Rheological analyses (stationary and dynamic essays) were carried out with blends allowing to study the effect of pH on shear stress, apparent viscosity, loss (G”) and storage (G’) moduli, and angle phase (Tanδ). Zeta potential of all biopolymers decreased linearly as a function of pH. CH presented higher values, and GeB, the lowest one, being the only having negative values at pH > 5. Overall, the pH influenced the rheological and viscoelastic properties of the colloidal solutions: shear stress and apparent viscosity increased as a function of pH. Other assays were carried out at 3% and 5% strain, for GeA:CH and GeB:CH, respectively. In the sol domain, G’ and G” (1 Hz) increased linearly for GeA:CH. But for GeB:CH, they increased in two linear different regions: one function between pH 3.5 and 5.0 and another one between 5.0 and 6.0, being a more important effect was visible in this last domain probably due to the negative net charge of gelatin, above it pI. An effect in two domains was also visible for Tanδ, explained in the same manner as previously. The GeB:CH blends behaved like diluted solutions, and transition temperatures increased as a function of pH.
Rheological and viscoelastic properties of colloidal solutions based on gelatins and chitosan as affected by pH.
The existence of bulk nanobubbles has long been regarded with scepticism, due to the limitations of experimental techniques and the widespread assumption that spherical bubbles cannot achieve stable ...equilibrium. We develop a model for the stability of bulk nanobubbles based on the experimental observation that the zeta potential of spherical bubbles abruptly diverges from the planar value below 10 μm. Our calculations recover three persistently reported-but disputed-properties of bulk nanobubbles: that they stabilize at a typical radius of ∼100 nm, that this radius is bounded below 1 μm, and that it increases with ionic concentration.
This study investigates the impact of cellulose-derived polymers, anionic carboxymethylcellulose (CMC), and cationic cellulose (CC) on the colloidal and thermal stability of zeolite Na-X materials. ...By exploring polymer adsorption onto Na-X surfaces and characterising the resultant materials, using FT-IR, XPS, SEM, PSD, CHN, and zeta potential, the research unveils how CMC and CC modify zeolite properties. This investigation elucidates the potential roles of these polymers in colloidal systems with zeolites, revealing their promise for crafting organic-inorganic materials. Additional insight was also provided by careful examination of the thermal stability (TGA-DSC) of the obtained cellulose/zeolite materials. Furthermore, the study distinguishes the different adsorption mechanisms of CMC and CC, with CMC relying on some weak interactions (H-bonding and van der Waals forces), while CC interacts mainly via electrostatic forces. Both CMC and CC can act as stabilizing agents, with CMC being more efficient and using both electrosteric and depletion stabilizations. Importantly, the concentration of CC plays a role in bridging flocculation, highlighting the concentration-dependent nature of the stabilization mechanism.
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Phosphoric-acid-activated metakaolin-based geopolymers (PGPs) have been investigated as promising options for the disposal of radionuclides. However, a lack of understanding of the surface chemical ...properties of PGPs has hindered further research into them and their application. This study explored the structure-related electrostatic properties and anion immobilisation potentials of PGPs via zeta potential measurements, structural characterisation, and leaching experiments. These findings suggest that acid activation triggers the geopolymerisation of metakaolin, resulting in new Alx-PO units (x = IV, VI representing VI- and V-coordination), the ratio of which controls the surface charge of PGPs. PGPs possess a positive charge in the equilibrium pH range of approximately 2–5 and exhibit a maximum positive zeta potential at approximately pH 4. Under acidic conditions, the AlVI-PO unit within the surface structure is released, decreasing the zeta potential as the pH decreases. In contrast, in alkaline environments, the AlVI/Si-OH hydroxyl group loses protons, causing a decrease in the zeta potential with increasing pH. Furthermore, PGPs can effectively immobilise SeO32−, SeO42−, I−, and IO3− anions through stabilisation/solidification (S/S). This immobilisation is primarily facilitated by electrostatic attraction between the anions and the positively charged surface of the PGPs. Importantly, the immobilisation process does not cause significant alterations to the matrix structure of the PGPs, even after solidification or subsequent leaching.
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•Charge characteristics of NF membranes were clarified by surface charge and zeta potential.•Effects of charge characteristics were systematically evaluated for salt rejection ...behavior.•The variation in the salt rejection behavior was better described by the zeta potential results.•Zeta potential values were affected by both electrophoretic and electroosmotic flows.•Electrophoresis method is a promising tool for predicting the electrostatic transport of ions.
The charge characteristics (i.e., surface charge and zeta potential) of two different nanofiltration (NF) membranes were characterized by the potentiometric titration and electrophoresis methods under various experimental conditions, i.e., pH, ionic strength, ionic species, and organic fouled membranes to clarify the salt rejection mechanism of the NF membranes. The both charge characteristics of the NF membranes clearly represented the variation in the salt rejection behavior at different ionic strengths and for electrostatically fouled membranes. However, the surface charge of the NF membranes was independent of the ionic species and with the neutrally fouled membrane, whereas the zeta potential changed substantially with changes in the ionic species and the neutrally fouled membrane. Therefore, the variation in salt rejection behavior for different ionic species and with a neutrally fouled membrane was better described by the zeta potential values, which reflected the ion transport properties (i.e., ion valency and diffusivity) affecting the electrophoretic and electroosmotic flows at the shear plane of the membranes. These results indicate the electrophoresis method is considered as a promising tool for predicting the electrostatic transport of various ions at the shear plane of the membrane surfaces, intimately associated with the salt rejection behavior in the NF membrane processes.
Nucleation effects of seeds in reactive magnesia cement (RMC) systems have been reported, but this process has never been directly observed. In this study, different types and contents of seeds were ...introduced in RMC formulations. Results show that seeded RMC samples revealed accelerated hydration/carbonation that led to their more rapid strength development, and the use of magnesite outperformed other seeds given their overall performances, as explained by their more homogenous microstructures. Further, in the model solution, the amount of Mg2+ ions adsorbed onto seeds particles continuously increased with the increment of Mg2+ concentrations, confirming the nucleation effects of seeds in RMC formulations directly, and seeds surfaces revealed a much higher affinity for Mg2+ ions than other ions due to their acid‐base interactions. Therefore, the use of seeds could act as accelerators that shorten the curing period of RMC‐based concrete products on a large scale.
Three peppermint oil emulsions using polyglycerol esters of fatty acids‐casein (PGFE‐CN), polyglycerol esters of fatty acids‐sodium caseinate (PGFE‐NaCN), and polyglycerol esters of fatty acids‐whey ...protein isolate (PGFE‐WPI) as emulsifiers were fabricated, and the droplet size, zeta potential, viscosity, and stability of emulsions were determined. The experimental results showed that the emulsion containing PGFE‐CN has relatively smaller droplet size of 231.77 ± 0.49 nm. No significant changes were observed on the average particle size, polydispersity index and zeta potential during 4‐week of storage, indicating that the emulsions kept stable against pH, salt ion, freeze‐thaw, and storage. Fourier transform infrared spectrometer (FTIR) results showed that the electrostatic interaction occurs between CN and PGFE in the emulsion. The confocal laser scanning microscope (CLSM) was used to observe the microstructure of the emulsion, proving that droplets were evenly distributed throughout the aqueous phase by PGFE‐CN emulsifier. The protein‐stabilized emulsions can be used as potential carriers for the delivery of the lipophilic nutrients such as peppermint oil.
Practical Application
PGFE‐CN emulsifier can be directly added to the beverage systems containing oil or protein, such as coconut milk, peanut milk, and walnut milk. It can enhance the stability of beverage, prevent the precipitation, stratification, and oil floating, improve the homogeneity of the system and therefore extend the shelf life.
Stability of nanobubbles in different salts solutions Hewage, Shaini Aluthgun; Kewalramani, Jitendra; Meegoda, Jay N.
Colloids and surfaces. A, Physicochemical and engineering aspects,
01/2021, Volume:
609
Journal Article
Peer reviewed
Open access
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The stability of nanobubbles in electrolyte solutions under different ion valence values was studied using deionized water, NaCl, Na2SO4, Na3PO4, CaCl2, and FeCl3. Nanobubbles were ...generated using hydrodynamic cavitation, and bubbles were tested for size and zeta potential. All the samples were stable for one week with no significant deviation in either bubble size or zeta potential values. The variation of size and zeta potential among six samples can be attributed to the solution properties and was mainly dependent on solution pH and the cation valency. The ion profiles revealed that the cation concentration at the bubble surface was higher than that of bulk, confirming that the bubbles were negatively charged for neutral and high pH values (≥4) under low valency cation adsorption. The high valency cations have the potential to neutralize or completely reverse the bubble charge. Anions or co-ions have minimal effect on the surface potential or the surface charge. The calculated internal pressures of bubble were unrealistically high, suggesting that the surface tension should be lower than that of water for nanobubble solutions. The interaction energy profile shows no significant energy barrier that overcomes the attractive van der Waals forces for all the solutions, except NaCl which had a 1.87 × 10−20 J barrier at a 5 nm separation distance. However, with the recorded stable bubbles, the calculation of the attractive van der Waals forces produced unrealistic values indicating that the Hamaker constant used for the calculation may not be valid at the nanobubble gas-liquid interface. This revealed that nanobubbles should contain exceptional interfacial properties that need to be carefully investigated and evaluated.
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