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Sharma H, Nirmalkar N, Zhang W. Nanobubbles produced by nanopores to probe gas-liquid mass transfer characteristics. J Colloid Interface Sci 2024; 665:274-285. [PMID: 38531273 DOI: 10.1016/j.jcis.2024.03.080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Revised: 02/27/2024] [Accepted: 03/11/2024] [Indexed: 03/28/2024]
Abstract
HYPOTHESIS This study tested the hypothesis of how the nanopore size of membranes and how the surface charge of nanobubbles responds to its pinch-off from the nanopore. This study also tested the hypothesis that nanobubbles that remain in solution after production may increase the dissolved oxygen content in water. EXPERIMENTS The effect of membrane pore size, hydrodynamic conditions (gas and liquid flow rates), and physicochemical parameters (pH and temperature) on volumetric mass transfer coefficient (kLa) for oxygen nanobubbles formed by the nanopore diffusion technique was investigated. This study experimentally determined the kLa by carefully removing the dissolved oxygen by nitrogen purging from nanobubble suspension to examine the sole contribution of nanobubble dissolution in water to the reaeration. RESULTS Scaling estimates indicate that the nanobubble pinch-off radius and nanopore radius have a power-law correlation and that nanobubble size declines with the nanopore size. This is in line with our experimental results. The surface charge of nanobubbles delays its pinch-off at the gas-liquid interface. Nanobubbles offered 3-4 times higher kLa than microbubbles. Standard oxygen transfer efficiency in water was found to be 78%, significantly higher than that in microbubbles. However, dissolving stable nanobubbles in water does not considerably increase dissolved oxygen levels.
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Affiliation(s)
- Harsh Sharma
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar-140001, India
| | - Neelkanth Nirmalkar
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar-140001, India.
| | - Wen Zhang
- John A. Reif, Jr. Department of Civil and Environmental Engineering, New Jersey Institute of Technology, Newark, NJ 07102, USA
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2
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Yadav G, Nirmalkar N, Ohl CD. Electrochemically reactive colloidal nanobubbles by water splitting. J Colloid Interface Sci 2024; 663:518-531. [PMID: 38422977 DOI: 10.1016/j.jcis.2024.02.148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Revised: 02/07/2024] [Accepted: 02/19/2024] [Indexed: 03/02/2024]
Abstract
HYPOTHESIS The existing literature reports have conflicting views on reactive oxygen species (ROS) generation by bulk nanobubbles. Consequently, we propose the hypothesis that (i) ROS may be generated during the process of nanobubble generation through water splitting, and (ii) bulk nanobubbles possess electrochemical reactivity, which could potentially lead to continuous ROS generation even after the cessation of nanobubble production. EXPERIMENTS A comprehensive set of experiments was conducted to generate nanobubbles in pure water using the water-splitting method. The primary aims of this study are as follows: (i) nanobubble generation by electrolysis and its characterization; (ii) to provide conclusive evidence that the nano-entities are indeed nanobubbles; (iii) to quantify the production of reactive oxygen species during the process of nanobubble generation and (iv) to establish evidence for the presence of electrochemically reactive nanobubbles. The findings of our experiment suggest that bulk nanobubbles possess the ability to generate reactive oxygen species (ROS) during the process of nanobubble nucleation. Additionally, our results indicate that bulk nanobubbles are electrochemically reactive after the cessation of nanobubble production. The electron spin spectroscopy (ESR) response and degradation of the dye compound over time confirm the electrochemical reactivity of bulk nanobubbles.
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Affiliation(s)
- Gaurav Yadav
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar, 140001, Punjab, India
| | - Neelkanth Nirmalkar
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar, 140001, Punjab, India.
| | - Claus-Dieter Ohl
- Otto von Guerricke University, Institute for Physics, Universitätsplatz, Magdeburg, 39106, Germany
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3
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Dutta N, Mitra S, Nirmalkar N. Understanding the Role of Surface Charge on Nanobubble Capillary Bridging during Particle-Particle Interaction. Langmuir 2024; 40:4475-4488. [PMID: 38356240 DOI: 10.1021/acs.langmuir.3c03963] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2024]
Abstract
The interactions between particles due to long-range hydrophobic forces have been extensively investigated. The hydrophobic force is likely a capillary force that arises from the formation of capillary bridges due to the merging of nanobubbles. In this study, we aim to investigate the impact of the nanobubble surface charge on the capillary bridge and, subsequently, the interaction between particles. The surface charge of the nanobubbles was altered in the presence of various surfactants (cationic, anionic, and nonionic) and salts (mono-, di-, and trivalent). The particle-particle interaction was quantified by measuring the aggregate size of the hydrophobized glass particles. Both experimental and theoretical findings confirm that the interaction between particles was enhanced when the surface potential of the nanobubble was around the neutral regime. This is probably because, when the surface potential was close to neutral, the interaction between two surface-deposited nanobubbles dominated over electrostatic repulsion, which was more conducive to the formation of the nanobubble capillary bridge. The estimation of the constrained Gibbs potential also showed the capillary bridge to be more stable when surface charge density along the bridge gas-liquid interface was minimal.
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Affiliation(s)
- Nilanjan Dutta
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Punjab 140001, India
| | - Subhasish Mitra
- ARC Center of Excellence for Enabling Eco-efficient Beneficiation of Minerals, School of Engineering, The University of Newcastle, New South Wales 2308, Australia
| | - Neelkanth Nirmalkar
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Punjab 140001, India
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4
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Sharma H, Trivedi M, Nirmalkar N. Do Nanobubbles Exist in Pure Alcohol? Langmuir 2024; 40:1534-1543. [PMID: 38176064 DOI: 10.1021/acs.langmuir.3c03592] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2024]
Abstract
The existence of nanobubbles in pure water has been extensively debated in recent years, and it is speculated that nanobubbles may be ion-stabilized. However, nanobubbles in the alcohol-water mixture and pure alcohols are still controversial due to the lack of ions present in the alcohol system. This work tested the hypothesis that stable nanobubbles exist in pure alcohol. The ultrasound and oscillatory pressure fields are used to generate nanobubbles in pure alcohol. The size distribution, concentration, diameter, and scattering intensity of the nanobubbles were measured by nanoparticle tracking analysis. The light scattering method measures the zeta potential. The Mie scattering theory and electromagnetic wave simulation are utilized to estimate the refractive index (RI) of nanobubbles from the experimentally measured scattering light intensity. The average RI of the nanobubbles in pure alcohols produced by ultrasound and oscillating pressure fields was estimated to be 1.17 ± 0.03. Degassing the nanobubble sample reduces its concentration and increases its size. The average zeta potential of the nanobubbles in pure alcohol was measured to be -5 ± 0.9 mV. The mechanical stability model, which depends on force balance around a single nanobubble, also predicts the presence of nanobubbles in pure alcohol. The nanobubbles in higher-order alcohols were found to be marginally colloidally stable. In summary, both experimental and theoretical results suggest the existence of nanobubbles in pure alcohol.
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Affiliation(s)
- Harsh Sharma
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar 140001, India
| | - Mohit Trivedi
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar 140001, India
| | - Neelkanth Nirmalkar
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar 140001, India
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Agarwal K, Trivedi M, Ohl CD, Nirmalkar N. On Nanobubble Dynamics under an Oscillating Pressure Field during Salting-out Effects and Its DLVO Potential. Langmuir 2023; 39:5250-5262. [PMID: 37014662 DOI: 10.1021/acs.langmuir.2c03085] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
We have investigated the origin, stability, and nanobubble dynamics under an oscillating pressure field followed by the salting-out effects. The higher solubility ratio (salting-out parameter) of the dissolved gases and pure solvent nucleates nanobubbles during the salting-out effect, and the oscillating pressure field enhances the nanobubble density further as solubility varies linearly with gas pressure by Henry's law. A novel method for refractive index estimation is developed to differentiate nanobubbles and nanoparticles based on the scattering intensity of light. The electromagnetic wave equations have been numerically solved and compared with the Mie scattering theory. The scattering cross-section of the nanobubbles was estimated to be smaller than the nanoparticles. The DLVO potentials of the nanobubbles predict the stable colloidal system. The zeta potential of nanobubbles varied by generating nanobubbles in different salt solutions, and it is characterized by particle tracking, dynamic light scattering, and cryo-TEM. The size of nanobubbles in salt solutions was reported to be higher than that in pure water. The novel mechanical stability model is proposed by considering both ionic cloud and electrostatic pressure at the charged interface. The ionic cloud pressure is derived by electric flux balance, and it is found to be twice the electrostatic pressure. The mechanical stability model for a single nanobubble predicts the existence of stable nanobubbles in the stability map.
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Affiliation(s)
- Kalyani Agarwal
- Department of Chemical Engineering, Indian Institute of Technology, Ropar 140001, India
| | - Mohit Trivedi
- Department of Chemical Engineering, Indian Institute of Technology, Ropar 140001, India
| | - Claus-Dieter Ohl
- Otto-von-Guericke University Magdeburg, Faculty of Natural Sciences, Institute for Physics, Department Soft Matter, Universitaetsplatz 2, Magdeburg 39106, Germany
| | - Neelkanth Nirmalkar
- Department of Chemical Engineering, Indian Institute of Technology, Ropar 140001, India
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Vara Prasad GVVS, Sharma H, Nirmalkar N, Dhar P, Samanta D. Augmenting the Leidenfrost Temperature of Droplets via Nanobubble Dispersion. Langmuir 2022; 38:15925-15936. [PMID: 36508708 DOI: 10.1021/acs.langmuir.2c01891] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Droplets may rebound/levitate when deposited over a hot substrate (beyond a critical temperature) due to the formation of a stable vapor microcushion between the droplet and the substrate. This is known as the Leidenfrost phenomenon. In this article, we experimentally allow droplets to impact the hot surface with a certain velocity, and the temperature at which droplets show the onset of rebound with minimal spraying is known as the dynamic Leidenfrost temperature (TDL). Here we propose and validate a novel paradigm of augmenting the TDL by employing droplets with stable nanobubbles dispersed in the fluid. In this first-of-its-kind report, we show that the TDL can be delayed significantly by the aid of nanobubble-dispersed droplets. We explore the influence of the impact Weber number (We), the Ohnesorge number (Oh), and the role of nanobubble concentration on the TDL. At a fixed impact velocity, the TDL was noted to increase with the increase in nanobubble concentration and decrease with an increase in impact velocity for a particular nanobubble concentration. Finally, we elucidated the overall boiling behaviors of nanobubble-dispersed fluid droplets with the substrate temperature in the range of 150-400 °C against varied impact We through a detailed phase map. These findings may be useful for further exploration of the use of nanobubble-dispersed fluids in high heat flux and high-temperature-related problems and devices.
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Affiliation(s)
| | - Harsh Sharma
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Punjab140001, India
| | - Neelkanth Nirmalkar
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Punjab140001, India
| | - Purbarun Dhar
- Hydrodynamics and Thermal Multiphysics Lab (HTML), Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, West Bengal721302, India
| | - Devranjan Samanta
- Department of Mechanical Engineering, Indian Institute of Technology Ropar, Punjab140001, India
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7
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Trivedi M, Gupta R, Nirmalkar N. Electroosmotic transport and current rectification of viscoelastic electrolyte in a conical pore nanomembrane. J Memb Sci 2022. [DOI: 10.1016/j.memsci.2022.120755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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8
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Alam MJ, Nirmalkar N, Gupta AK. Stability criteria and convective mass transfer from the falling spherical drops, part
II
:
Herschel‐Bulkley
fluids. CAN J CHEM ENG 2022. [DOI: 10.1002/cjce.24372] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Md J. Alam
- Department of Chemical Engineering Indian Institute of Technology Ropar India
| | - N. Nirmalkar
- Department of Chemical Engineering Indian Institute of Technology Ropar India
| | - A. K. Gupta
- Department of Chemical and Biochemical Engineering Indian Institute of Technology Patna India
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9
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Agarwal K, Trivedi M, Nirmalkar N. Does salting-out effect nucleate nanobubbles in water: Spontaneous nucleation? Ultrason Sonochem 2022; 82:105860. [PMID: 34915251 PMCID: PMC8683758 DOI: 10.1016/j.ultsonch.2021.105860] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 11/30/2021] [Accepted: 12/04/2021] [Indexed: 05/05/2023]
Abstract
The solubility of gases in aqueous salt solution decreases with the salt concentration, often termed the "salting-out effect." The dissolution of salt in water is followed by dissociation of salt and further solvation of ions with water molecules. The solvation weakens the affinity of gaseous molecules, and thus it releases the excess dissolved gas. Now it is interesting to know that what happens to the excess gas released during salting-out? Since it is imperative to note that the transfer of the dissolved gas in the bulk liquid may often occur in the form of nanobubbles. In this work, we have answered this question by investigating the nano-entities nucleation during the salting-out effect. The solubility of gases in aqueous salt solution decreases with the salt concentration, and it is often termed as the "salting-out effects." The dissolution of salt in water undergoes dissociation of salt and further solvation of ions with water molecules. The solvation weakens the affinity of gaseous molecules, and thus it releases the excess dissolved gas. Now it is interesting to know that what happens to the excess gas released during salting-out? While it is also imperative to note that the gas transfer in the bulk liquid often occurs in the form of bubbles. With this hypothesis, we have experimentally investigated that whether the salting-out effect nucleates nanobubble or not. What is the strong scientific evidence to prove that they are nanobubbles? Does the salting-out parameter affect the number density? The answers to such questions are essential for the fundamental understanding of the origin and driving force for nanobubble generation. We have provided three distinct proofs for the nano-entities to be the nanobubbles, namely, (1) by freezing and thawing experiments, (2) by destroying the nanobubbles under ultrasound field, and (3) we also proposed a novel method for refractive index estimation of nanobubbles to differentiate them from nano drops and nanoparticles. The refractive index (RI) of nanobubbles was estimated to be 1.012 for mono- and di-valent salts and 1.305 for trivalent salt. The value of RI closer to 1 provides strong evidence of gas-filled nanobubbles. Both positive and negative charged nanobubbles nucleate during the salting-out effect depending upon the valency of salt. The nanobubbles during the salting-out effect are stable only for up to three days. This shorter stability could plausibly be due to reduced colloidal stability at a low surface charge.
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Affiliation(s)
- Kalyani Agarwal
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar 140001, Punjab, India
| | - Mohit Trivedi
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar 140001, Punjab, India
| | - Neelkanth Nirmalkar
- Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar 140001, Punjab, India.
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10
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Dutta N, Kopparthi P, Mukherjee AK, Nirmalkar N, Boczkaj G. Novel strategies to enhance hydrodynamic cavitation in a circular venturi using RANS numerical simulations. Water Res 2021; 204:117559. [PMID: 34496315 DOI: 10.1016/j.watres.2021.117559] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Revised: 07/21/2021] [Accepted: 08/09/2021] [Indexed: 06/13/2023]
Abstract
Hydrodynamic cavitation is a popular advanced oxidation technique and it has received wide range of applications from waste water treatment to the nanoparticles synthesis in recent years. The enhancement of the intensity of the hydrodynamic cavitation is always been an emerging field of research. Within this framework, we have proposed and investigated three distinct strategies to enhance the intensity of cavitation in a circular venturi, namely, (1) by introducing the surface roughness on the wall (2) single or multiple circular hurdles in the diverging section (3) By modifying the diverging section from planer to the trumpet shape. RANS (Reynolds Averaged Navier-Stokes) based numerical simulations are carried out the over wide range of conditions: 2≤PR≤6 (pressure ratio), 6.2∘≤β≤10∘ (half divergent angle), 15∘≤α≤20∘ (half convergent angle), and 1≤l/d≤3 (throat length). An extensive numerical and experimental validation with the literature have been presented to ensure the reliability and accuracy of present work. Detailed results on velocity fields, local and average volume fraction, pressure loss coefficients, cavitation number, discharge coefficient and pressure distribution are reported as function of dimensionless parameters. Five designs of various combinations of surface roughness, circular hurdles, and trumpet diverging section have been compared. The effect of surface roughness on trumpet diverging wall has been observed to be more pronounced than the other designs. Trumpet diverging wall with surface roughness is found to be optimum for the practical applications.
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Affiliation(s)
- Nilanjan Dutta
- Department of Chemical Engineering, Indian Institute of Technology, Ropar 140001, India
| | - Prasad Kopparthi
- R&D and Scientific Services Division, TATA Steel Limited, Jamshedpur, 831007, India
| | - Asim Kumar Mukherjee
- R&D and Scientific Services Division, TATA Steel Limited, Jamshedpur, 831007, India
| | - Neelkanth Nirmalkar
- Department of Chemical Engineering, Indian Institute of Technology, Ropar 140001, India.
| | - Grzegorz Boczkaj
- Department of Process Engineering and Chemical Technology, Faculty of Chemistry, Gdansk University of Technology, G. Narutowicza 11/12 Str., 80-233 Gdansk, Poland.
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11
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Nirmalkar N, Alam MJ, Gupta AK. Stability criteria and convective mass transfer from the falling spherical drops, part I: Bingham plastic fluids. CAN J CHEM ENG 2021. [DOI: 10.1002/cjce.24218] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Neelkanth Nirmalkar
- Department of Chemical Engineering Indian Institute of Technology Ropar India
| | - Md J. Alam
- Department of Chemical Engineering Indian Institute of Technology Ropar India
| | - Anoop K. Gupta
- Department of Chemical and Biochemical Engineering Indian Institute of Technology Patna India
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12
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Abstract
We investigate the existence and stability of bulk nanobubbles in various aqueous organic solvent mixtures. Bulk nanobubble suspensions generated via acoustic cavitation are characterized in terms of their bubble size distribution, bubble number density, and zeta potential. We show that bulk nanobubbles exist in pure water but do not exist in pure organic solvents, and they disappear at some organic solvent-water ratio. We monitor the nanobubble suspensions over a period of a few months and propose interpretations for the differences behind their long-term stability in pure water versus their long-term stability in aqueous organic solvent solutions. Bulk nanobubbles in pure water are stabilized by their substantial surface charge arising from the adsorption of hydroxyl ions produced by self-ionization of water. Pure organic solvents do not autoionize, and therefore, nanobubbles cannot exist in concentrated aqueous organic solvent solutions. Because of preferential adsorption of organic solvent molecules at the nanobubble interfaces, the surface charge of the nanobubbles decreases with the solvent content, but the strong hydrogen bonding near their interfaces ensures their stability. The mean bubble size increases monotonically with the solvent content, whereas the surface tension of the mixture is sharply reduced. This is in agreement with literature results on macro- and microbubbles in aqueous organic solutions, but it stands in stark contrast to the behavior of macro- and microbubbles in aqueous surfactant solutions.
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Affiliation(s)
- N Nirmalkar
- School of Chemical Engineering , University of Birmingham , Edgbaston , Birmingham B15 2TT , U.K
| | - A W Pacek
- School of Chemical Engineering , University of Birmingham , Edgbaston , Birmingham B15 2TT , U.K
| | - M Barigou
- School of Chemical Engineering , University of Birmingham , Edgbaston , Birmingham B15 2TT , U.K
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Abstract
This paper elucidates parts of the mystery behind the interfacial and colloidal stability of the novel bubble system of bulk nanobubbles. Stable bulk nanobubble suspensions have been generated in pure water using hydrodynamic cavitation in a high-pressure microfluidic device. The effects of pH adjustment, addition of different types of surfactant molecules and salts on the nanobubble suspensions have been studied. Results show that nanobubble interfaces in pure water are negatively charged, suggesting the formation of an electric double layer around the nanobubbles. It is presumed that the external electrostatic pressure created by the charged nanobubble interface, balances the internal Laplace pressure; therefore, no net diffusion of gas occurs at equilibrium and the nanobubbles are stable. Such stability increases with increasing alkalinity of the suspending medium. The addition of mono- and multi-valent salts leads to the screening of the electric double layer, hence, destabilizing the nanobubbles. Different surfactant molecules (non-ionic, anionic, cationic) affect the stability of bulk nanobubbles in different ways. Calculations based on the DLVO theory predict a stable colloidal system for bulk nanobubbles in pure water and this could be a further reason for their observed longevity. All in all, in pure water, the long-term stability of bulk nanobubbles seems to be caused by a combination of ion-stabilisation of their interface against dissolution and colloidal stability of the suspension.
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Affiliation(s)
- N Nirmalkar
- School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
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14
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Abstract
Bulk nanobubbles are a novel type of nanoscale bubble system. Because of their extraordinary behavior, however, their existence is not widely accepted. In this paper, we shed light on the hypothesis that bulk nanobubbles do exist, they are filled with gas, and they survive for long periods of time, challenging present theories. An acoustic cavitation technique has been used to produce bulk nanobubbles in pure water in relatively large numbers approaching 109 bubble·mL-1 with a typical diameter of 100-120 nm. We provide multiple evidence that the nanoentities observed in suspension are nanobubbles given that they disappear after freezing and thawing of the suspensions, their nucleation rate depends strongly on the amount of air dissolved in water, and they gradually disappear over time. The bulk nanobubble suspensions were stable over periods of many months during which time the mean diameter remained unchanged, suggesting the absence of significant bubble coalescence, bubble breakage, or Ostwald ripening effects. Measurements suggest that these nanobubbles are negatively charged and their zeta potential does not vary over time. The presence of such a constant charge on the nanobubble surfaces is probably responsible for their stability. The effects of pH, salt, and surfactant addition on their colloidal stability are similar to those reported in the literature for solid nanoparticle suspensions, that is, nanobubbles are more stable in an alkaline medium than in an acidic one; the addition of salt to a nanobubble suspension drives the negative zeta potential toward zero, thus reducing the repulsive electrostatic forces between nanobubbles; and the addition of an anionic surfactant increases the magnitude of the negative zeta potential, thus improving nanobubble electrostatic stabilization.
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Affiliation(s)
- N Nirmalkar
- School of Chemical Engineering , University of Birmingham , Edgbaston , Birmingham B15 2TT , U.K
| | - A W Pacek
- School of Chemical Engineering , University of Birmingham , Edgbaston , Birmingham B15 2TT , U.K
| | - M Barigou
- School of Chemical Engineering , University of Birmingham , Edgbaston , Birmingham B15 2TT , U.K
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16
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Nirmalkar N, Chhabra R. Corrigendum to “Mixed convection from a heated sphere in power-law fluids” [Chem. Eng. Sci. 89 (2013) 49–71]. Chem Eng Sci 2016. [DOI: 10.1016/j.ces.2015.10.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Affiliation(s)
- N. Nirmalkar
- Department
of Chemical Engineering, Indian Institute of Technology, Kanpur-208016, India
| | - A. K Gupta
- Department
of Chemical Engineering, Indian Institute of Technology, Kanpur-208016, India
| | - R. P. Chhabra
- Department
of Chemical Engineering, Indian Institute of Technology, Kanpur-208016, India
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18
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Affiliation(s)
- N. Nirmalkar
- Department
of Chemical Engineering, Indian Institute of Technology, Kanpur, India 208016
| | - R. P. Chhabra
- Department
of Chemical Engineering, Indian Institute of Technology, Kanpur, India 208016
| | - R. J. Poole
- School
of Engineering, University of Liverpool, Liverpool, L69 3GH, United Kingdom
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19
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Nirmalkar N, Chhabra RP, Poole RJ. Numerical Predictions of Momentum and Heat Transfer Characteristics from a Heated Sphere in Yield-Stress Fluids. Ind Eng Chem Res 2013. [DOI: 10.1021/ie400703t] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- N. Nirmalkar
- Department of Chemical Engineering,
Indian Institute of Technology, Kanpur, India 208016
| | - R. P. Chhabra
- Department of Chemical Engineering,
Indian Institute of Technology, Kanpur, India 208016
| | - R. J. Poole
- School of Engineering, University of Liverpool,
Liverpool, L69 3GH, United Kingdom
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20
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