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.
Exosomes are nanometer-sized lipid vesicles present in liquid biopsies and used as biomarkers for several diseases including cancer, Alzheimer's, and central nervous system diseases. Purification and ...subsequent size and surface characterization are essential to exosome-based diagnostics. Sample purification is, however, time consuming and potentially damaging, and no current method gives the size and zeta potential from a single measurement. Here, we concentrate exosomes from a dilute solution and measure their size and zeta potential in a one-step measurement with a salt gradient in a capillary channel. The salt gradient causes oppositely directed particle and fluid transport that trap particles. Within minutes, the particle concentration increases more than two orders of magnitude. A fit to the spatial distribution of a single or an ensemble of exosomes returns both their size and surface charge. Our method is applicable for other types of nanoparticles. The capillary is fabricated in a low-cost polymer device.
•Polymers induce large variations in zeta potential of hematite particles below iep.•Aggregation shown to result from interactions between oppositely charged particles.•Broad zeta potential ...distributions characteristic of aggregating hematite particles.•Narrow zeta potential distributions characteristic of dispersed hematite particles.•Width of zeta potential distribution as indicator of steric redispersion of hematite.
The effect of adsorption of two carboxymethyl celluloses and sodium lignosulfonate on the zeta potential distributions and the aggregation/dispersion behavior of hematite (isoelectric point at pH 6.7) was investigated at pH 5.5 and 10.5. At pH 5.5, all three polymers caused hematite aggregation at lower dosages followed by steric re-dispersion at higher concentrations. It was found that the width of the zeta potential distribution at pH 5.5 gradually increased with polymer adsorption and reached a maximum value at polymer concentrations that led to strongest aggregation of hematite. The results indicated that the main role of the polymers in hematite aggregation at pH 5.5 was to generate large variations in the zeta potential characteristics between individual hematite particles, producing populations of oppositely charged particles that readily underwent aggregation. In the absence of such polymer-induced variations (e.g., at pH 10.5), adsorption of the polymers resulted in strong dispersion of hematite. The width of the zeta potential distribution, rather than the adsorption density of the polymers, was found to be a common factor determining the onset of steric re-dispersion by the tested polymers regardless of the polymer type. Using the width of the zeta potential distribution as a measure of zeta potential variations among the particles, it was shown that steric dispersion at pH 5.5 started to occur when the hematite particles acquired very similar zeta potential characteristics as a result of polymer adsorption. The onset of steric dispersion coincided with a well-defined transition from broad to narrow zeta potential distributions. It was also shown that zeta potential distributions offered additional insights into the mechanism of the aggregating/dispersing action of the tested polymers, compared to the average zeta potential value alone.
Surface potential of biomaterials is a key factor regulating cell responses, driving their adhesion and signaling in tissue regeneration. In this study we compared the surface and zeta potential of ...smooth and porous electrospun polycaprolactone (PCL) fibers, as well as PCL films, to evaluate their significance in bone regeneration. The ’ surface potential of the fibers was controlled by applying positive and negative voltage polarities during the electrospinning. The surface properties of the different PCL fibers and films were measured using X-ray photoelectron spectroscopy (XPS) and Kelvin probe force microscopy (KPFM), and the zeta potential was measured using the electrokinetic technique. The effect of surface potential on the morphology of bone cells was examined using advanced microcopy, including 3D reconstruction based on a scanning electron microscope with a focused ion beam (FIB-SEM). Initial cell adhesion and collagen formation were studied using fluorescence microscopy and Sirius Red assay respectively, while calcium mineralization was confirmed with energy-dispersive x-ray (EDX) and Alzarin Red staining. These studies revealed that cell adhesion is driven by both the surface potential and morphology of PCL fibers. Furthermore, the ability to tune the surface potential of electrospun PCL scaffolds provides an essential electrostatic handle to enhance cell-material interaction and cellular activity, leading to controllable morphological changes.
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•Applied voltage polarity in electrospinning tailors surface chemistry and potential of PCL fibers.•Surface potential was analyzed by KPFM and compared with zeta potential in liquid.•Cell adhesion, collagen formation and mineralization are controlled with surface potential.•Surface potential on PCL fibers can enhance the bone regeneration process.
It is important to predict the thermophysical properties of nanofluids, which have higher heat transfer performance compared to the base fluid, without the need for experimental studies. In this ...study, two different artificial neural networks were created to predict the thermal conductivity and zeta potential of Fe3O4/water nanofluid. The thermal conductivity and zeta potential of the Fe3O4/water nanofluid prepared at three different concentrations were experimentally measured. An innovative mathematical correlation is proposed to calculate thermal conductivity based on temperature and concentration using the obtained experimental data. Considering that the correlations in the literature can generally be calculated according to concentration, the novelty of the proposed model stands out. The calculated values for thermal conductivity and zeta potential of the created artificial neural network and the new mathematical correlation were compared with the results of the experiments. In addition, a comprehensive performance analysis was made by calculating different performance parameters. The R values of the neural network models were above 0.99 and mean squared error values were obtained as 1.47E-05 and 1.58E-06, respectively. In addition, the mean deviation values calculated for the thermal conductivity of the network model were 0.03%, while it was 0.05% for the new mathematical correlation. The study results showed that ANN models can predict the thermal conductivity and zeta potential of Fe3O4/water nanofluid with high accuracy. The proposed new mathematical correlation was also found to have higher error rates compared to the ANN model, although it was able to calculate thermal conductivity values with high accuracy.
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•Fe3O4/water nanofluid prepared in three different concentrations.•Thermal conductivity and zeta potential values were experimentally measured.•Two different artificial neural networks were created.•Thermal conductivity and zeta potential values were predicted.•Experimental values are found compatible with ANN outputs.
Laboratory experiments and field trials have shown that oil recovery from carbonate reservoirs can be increased by modifying the brine composition injected during recovery in a process termed ...controlled salinity water-flooding (CSW). However, CSW remains poorly understood and there is no method to predict the optimum CSW composition. This work demonstrates for the first time that improved oil recovery (IOR) during CSW is strongly correlated to changes in zeta potential at both the mineral-water and oil-water interfaces. We report experiments in which IOR during CSW occurs only when the change in brine composition induces a repulsive electrostatic force between the oil-brine and mineral-brine interfaces. The polarity of the zeta potential at both interfaces must be determined when designing the optimum CSW composition. A new experimental method is presented that allows this. Results also show for the first time that the zeta potential at the oil-water interface may be positive at conditions relevant to carbonate reservoirs. A key challenge for any model of CSW is to explain why IOR is not always observed. Here we suggest that failures using the conventional (dilution) approach to CSW may have been caused by a positively charged oil-water interface that had not been identified.
•Heat transfer for mixed electroosmotic and pressure-driven flow in a microchannel is studied.•Closed form expressions for the velocity and temperature profiles, and Nusselt number are ...presented.•Influence of slip dependent surface potential on thermal transport is examined.•Effects of Joule heating, pressure-gradient, Debye length, slip length and viscous dissipation are studied.•Comparative assessment of slip independent and slip dependent surface potential on heat transfer is reported.
The use of hydrophobic surfaces in electrokinetic flows results in an intricate analysis due to the coupling of surface potential and interfacial slip which challenges their independent measurement. Thus, it becomes significant to consider the slip-dependent surface potential which can decouple the interfacial slip from the zeta potential. In this article, we develop an analytical model to investigate the heat transfer characteristics for combined electroosmotic and pressure-driven flow through a plane microchannel considering the slip-dependent zeta potential. We solve analytically the Poisson–Boltzmann (PB) equation, the mass, momentum and energy conservation equations for hydrodynamically and thermally fully developed flow with appropriate boundary conditions to obtain closed form expressions for the induced potential within the electrical double layer (EDL), the velocity and temperature profiles and the Nusselt number in terms of different physico-chemical parameters. The results reveal that interfacial slip-dependent surface potential has a strong influence on the thermal transport phenomenon along with other parameters, like Joule heating, applied pressure-gradient, electrokinetic parameter, slip length and viscous dissipation. The velocity in the core region is always under-predicted considering the slip-independent surface potential and the under-prediction is amplified for thinner EDL and pure electroosmotic flow. Beyond the critical values of the slip length, the consideration of the slip-independent surface potential in the paradigm of thermal transport dynamics for electrokinetic flows, over-predicts the Nusselt number and the over-prediction is amplified for thinner EDL. Moreover, a critical Brinkman number, Brk is also identified such that for Br < Brk, Nusselt number increases with Debye parameter, while the opposite effect is observed for Br > Brk. The relative enhancement in Nusselt number due to the interfacial slip increases with the applied pressure-gradient and slip length at smaller values of Brinkman number. Furthermore, the sensitivity of Nusselt number on slip is highly dependent on the Debye parameter, Brinkman number and applied pressure-gradient.
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Carbon-driven advanced oxidation processes are appealing in wastewater purification because of the metal-free feature of the carbocatalysts. However, the regime of the emerging nonradical pathway is ...ambiguous because of the intricate carbon structure. To this end, this study was dedicated to unveil the intrinsic structure-performance relationship of peroxydisulfate (PDS) activation by carbon nanotubes (CNTs) toward nonradical oxidation of organics such as phenol (PE) via electron transfer. Eighteen analogical CNTs were synthesized and functionalized with different categories and contents of oxygen species. The quenching tests and chronopotentiometry suggest that an improved reactivity of surface-regulated CNTs was attributed to the reinforced electron-transfer regime without generation of free radicals and singlet oxygen. The quantitative structure–activity relationships were established and correlated to the Tafel equation, which unveils the nature of the nonradical oxidation by CNT-activated PDS complexes (CNT-PDS*). First, a decline in the concentration of oxygen groups in CNTs will make the zeta potential of the CNT become less negative in neutral solutions, which facilitated the adsorption of PDS because of weaker electrostatic repulsion. Then, the metastable CNT-PDS* was formed, which elevated the oxidation capacity of the CNT. Finally, PE would be oxidized over CNT-PDS* via electron transfer to fulfill the redox cycle. Moreover, the nonradical oxidation rate was uncovered to be exponentially related with the potential of the complexes, suggesting that the nonradical oxidation by the CNT-PDS* undergoes a mechanism analogous to anodic oxidation.
The importance of the isoelectric point for the preparation and characterization of functional materials to understand their behavior and optimize their performance is highlighted, with especial ...focus on industrial catalysts. In different liquid-phase steps involved in materials synthesis, the knowledge of the surface charge as a function of the pH of the medium is fundamental, since it is the dynamizing agent of processes such as gelation, peptization, coagulation and agglomeration to form solid particles. Therefore, zeta potential (ζ) measurements, often based on electrophoretic migration techniques, are a powerful source of information. The basic principles are introduced to explain through relevant examples the possibilities for materials design. Regarding materials preparation, the measurement of the zeta potential to control the synthesis and coating of supports is reviewed, with special attention to shaped supports. Aspects as the influence of the binders on the supports properties depending on their mutual interaction are analyzed, with example systems based on TiO2 or Al2O3 and natural silicates such as sepiolite. Also, how the knowledge of ζ as a function of pH allows, by choosing the appropriate pH, the preferential impregnation of noble metals on porous supports, as well as the washcoating of dense ceramic monoliths with porous supports. Special attention has been paid to surfaces characterization based on the use of zeta potential measurements to estimate the formation and relative location of species, the apparent surface coverage, or the adsorption and reactivity, to establish synthesis strategies to achieve specific properties.
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•Zeta potential measurements help defining synthesis and coating strategies.•Explanation of the relative distribution and apparent surface coverage of active species in shaped supports.•Estimation of active phase dispersion on a support until multilayers or agglomerated crystals start to form.•Prediction of nanomaterials reactivity in the human body and the environment for grouping and a safe and sustainable design.
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