Subscriber access provided by CORNELL UNIVERSITY LIBRARY
Article
A microfluidic method for investigating ionspecific bubble coalescence in salt solutions Jianlong Wang, Say Hwa Tan, Anh V. Nguyen, Geoffrey M. Evans, and Nam-Trung Nguyen Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b03266 • Publication Date (Web): 18 Oct 2016 Downloaded from http://pubs.acs.org on October 24, 2016
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
1 2 3 4 5 6
A microfluidic method for investigating ion-specific bubble coalescence in salt solutions Jianlong Wang,a Say Hwa Tan,b Anh V. Nguyen,a Geoffrey M. Evans,c and Nam-Trung Nguyen*b a.
School of Chemical Engineering, University of Queensland, Brisbane, QLD 4072, Australia
b.
Queensland Micro- and Nanotechnology Centre, Griffith University, Brisbane, QLD 4111, Australia.
c.
School of Engineering, University of Newcastle, Callaghan, NSW 2308, Australia.
7 8
ABSTRACT
9
This paper reports the direct and precise measurement of bubble coalescence in salt solutions using
10
microfluidics. We directly visualised the bubble coalescence process in a microchannel using high-
11
speed imaging and evaluated the shortest coalescence time to determine the transition concentration of
12
sodium halide solutions. We found the transition concentration is ion-specific and the capacity of
13
sodium halide salts to inhibit bubble coalescence follows the order of NaF > NaCl > NaBr > NaI. The
14
microfluidic method overcomes the inherent uncertainties in conventional large-scale devices and
15
methods.
16
INTRODUCTION
17
Bubble coalescence in different salt solutions governs many interesting but unexpected phenomena.
18
These processes are found in nature and industrial applications. Examples include the formation of
19
white foam as waves break in seawater.1 Industrially, purification of mined coal from clays using air
20
bubbles is possible in seawater and other saline waters.2 Fine bubbles were often generated in saline
21
waters without the use of conventional surfactants. Unlike surfactants, salts are supposed to promote
22
bubble coalescence by increasing the surface tension. Ironically, both surface-active compound
23
(surfactants) and surface-inactive compound (inorganic salts) inhibit bubble coalescence. More
24
interestingly, these compounds can only fully or partially inhibit bubble coalescence above a critical
25
concentration referred to as the critical coalescence concentration (CCC), or increase the bubble
26
coalescence time above a transition concentration (TC).3, 4, 5, 6, 7, 8, 9, 10, 11, 12
27
Despite of the inconsistent definitions of CCC and TC in the literature, different techniques have
28
been developed to determine these values.3 Briefly, the techniques can be categorised into: (i) bubble
29
swarm experiments; (ii) bubble pair method and (iii) film balance technique. All these techniques
30
have not been satisfactory due to their inherent shortcomings and uncertainties. Values of CCC or TC
31
obtained via different techniques have shown significant discrepancy.3
32
Bubble swarm experiment studies the population of bubbles in a swarm..The CCC in this
33
experiment is defined either as the concentration corresponding to 50% bubble coalescence13 or as the
34
concentration above which a constant bubble size is reached.7, 14 The bubble swarm experiment is 1 ACS Paragon Plus Environment
Langmuir
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 10
1
useful for studying the effects of flow conditions on bubble coalescence. However, the measurements
2
of CCC are significantly influenced by hydrodynamic conditions, such as turbulence.15 Therefore, the
3
uncertainties of these measurements are significant by nature. For example, the CCC of NaCl varies
4
from 0.31 M to 0.778 M in different measurements of bubble size distribution in a bubble column.3
5
Obtaining the average bubble size by measuring the whole bubble population is also time-consuming.
6
In the bubble pair method, two bubbles are generated from adjacent capillaries placed either side
7
by side or facing each other. The CCC is now defined as the concentration at which 50% of the
8
contacted bubbles coalesce. Compared with bubble swarm experiments, the relative uncertainties
9
decrease due to the relatively stable environment. However, the bubble pairs are only labelled as
10
“coalescence” or “non-coalescence”. Therefore, important information representing the efficiency of
11
inhabitation, such as bubble coalescence time or lifetime of liquid film between bubbles, is missing.
12
The film balance technique, unlike the previous techniques, can provide important information to
13
understand the bubble coalescence process. For example, both the drainage time and thickness of the
14
liquid film can be measured. However, the exposure of the liquid film to the air results in many
15
uncertainties, such as the contamination, evaporation, and thermal or mechanical fluctuations from the
16
environment. Since no real bubble is generated, the film balance technique still cannot provide key
17
information such as bubble deformation and post-coalescence oscillation.16
18
The present paper demonstrates that microfluidics is a powerful tool to understand the complex
19
bubble dynamics. The design of the experiments in a microchannel eliminates the effects of long-
20
range inertial forces, therefore allowing for the investigation of only short-range effects (e.g. colloidal
21
forces) on the bubble coalescence process. This tool also circumvents many limitations mentioned
22
above. For example, the laminar flow behaviour allows the generation of extremely well-controlled
23
bubble size.17,
24
transport of microbubbles. Therefore, microfluidic devices have been utilised to study bubble
25
coalescence behaviours.19, 20 However, past studies on bubble coalescence in microfluidic devices
26
were limited mainly to the effect of hydrodynamics. We aim to report a different perspective where
27
the transition concentration of salt solutions is determined in a microfluidic flow-focusing device. The
28
well-controlled bubble dynamics in the microfluidic device allows for a more reliable and precise
29
determination of the transition concentration as compared to existing conventional techniques.
18
Furthermore, the confinement of a microchannel guarantees the well-controlled
30 31 32 33 2 ACS Paragon Plus Environment
Page 3 of 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
1
EXPERIMENTS
2
Air bubbles were generated in four sodium halide solutions (NaF, NaCl, NaBr and NaI) using the
3
flow-focusing geometry, Fig. 1. The flow rates of salt solution and air were 500 µL/h and 100 µL/h,
4
respectively. The frequency of bubble generation was about 52±5 Hz. Coalescence of air bubbles was
5
observed at the expansion of the microfluidic channels, Fig. 1 (a). It should be noted that only
6
coalescence events between two bubbles with the same initial bubble size were chosen to calculate the
7
coalescence time. A big bubble that is formed by the coalescence of two smaller bubbles does not
8
count in order to eliminate the effects of Ostwald ripening of bubbles on the coalescence process.
9
Standard soft lithography technique was used to fabricate microfluidic device in poly-
10
dimethylsiloxane (PDMS). PDMS has good chemical stability, and most molecules do not react with
11
the surface of PDMS.17, 21 The PDMS device was bonded to a glass slide using air plasma. The width
12
of the main channels and the orifice are 100 µm and 50 µm, respectively. Figure 1(a) shows the
13
detailed geometry of the microchannel that has a height of about 30 µm. Fig. 1(b) shows a
14
representative snapshot of the bubble generation process at the flow-focusing junction. The
15
subsequent bubble coalescence occurs at the expansion, Fig. 1(c). A high-speed camera (Miro 3,
16
Vision Research) mounted on an inverted microscope (Nikon Ti-E, Japan) recorded the bubble
17
images.
18
19 20
Fig. 1 (a) Schematic diagram of the flow-focusing microfluidic device; (b) Image of the bubble
21
generation and (c) coalescence in 0.5 M NaCl solution with a total NaCl solution flow rate of
22
500 µL/h and an air flow rate 100 µL/h. The depth of the channel is about 30 µm. The scale bar
23
represents 100 µm.
3 ACS Paragon Plus Environment
Langmuir
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 10
1
Sequential layer-by-layer deposition of polyelectrolytes (poly (allylamine hydrochloride) i.e. PAH
2
(98% Sigma–Aldrich, USA) and poly (sodium 4-styrenesulfonate) i.e. PSS (98% Sigma–Aldrich,
3
USA) was used to yield stable hydrophilic surface in the PDMS microfluidic devices.22 Briefly, the
4
PAH and PSS solutions (both 0.1% w/v in 0.5 M aqueous NaCl solution) and NaCl washing solution
5
(0.1 M) were alternately injected to fill the microchannel. The first positively charged PAH layer was
6
deposited onto the negatively charged PDMS surface treated by air plasma. Then the negatively
7
charged PSS layer was deposited onto the PAH layer. After 8 deposition cycles, a (PAH/PSS)8
8
polyelectrolyte multilayer was coated on the channel wall. Sufficiently long adsorption time of
9
approximately 5 minutes was taken for the deposition of each layer.23 The structure of the PAH/PSS
10
multilayer is very compact due to the high degree of complexation between the polyelectrolytes as
11
well as hydrogen bonds between the amines in PAH and oxygen in PSS.24, 25, 26 The stability of the
12
polyelectrolyte multilayer is independent of the salt type that we used because there is no interaction
13
between the outermost PSS layer (negtively charged) and the anions, and the only cation is Na+. The
14
water content of the PAH/PSS multilayer remained unchanged with a high concentration of NaCl in
15
the external solution up to 1.2 M.25 Considering the range of salt concentration in our study of 0 – 0.5
16
M, we can safely eliminate the influence of salt concentration on the stability of the polyelectrolyte
17
multilayer. The final washing step was performed with deionised water to remove traces of
18
contaminations in the micro-channels. Because the channel volume in a microfluidic device is
19
extremely small, applying a relatively large amount of deionised water (~20 mL, about 50,000 times
20
of the space in the microfluidic device) can thoroughly wash away the trace contaminants in the
21
microchannels. Subsequently, the equilibrium surface tension of water-air interface for the last 5 mL
22
washing water was measured, to check the cleanliness of the microchannel. The value of the
23
equilibrium surface tension was measued as 72.35 ± 0.14 mN/m (standard deviation of the mean) at
24
23 ˚C using the Wilhelmy plate method and matches the reported value of 72.3 mN/m.27 It should be
25
noted that the oxidation of the PDMS surface by plasma cleaning only leads to a temporarily
26
hydrophilic surface. The PDMS surface regains its orginal hydrophobicity after exposing to a low-
27
surface-energy medium such as air as used in our experiments to generate the bubbles.22, 28, 29
28
Deionised (DI) water was utilized to make the salt solutions, i.e. solutions of NaF (99% Sigma–
29
Aldrich, USA), NaCl (99.5 % Sigma–Aldrich, USA), NaBr (99% Sigma–Aldrich, Israel) and NaI
30
(99% Merck, Germany). Air and salt solutions were loaded in gas tight glass syringes and delivered
31
into the microfluidic device by a syringe pump (SPM 100 S-FLUIDPUMP, Singapore). Videos of
32
bubble coalescence were recorded at a frame rate of 13,000 frames per second (fps) and subsequently
33
processed with ImageJ (V1.48, NIH, USA). The coalescence time was calculated as the time interval
34
from the contact of two air bubble interfaces to the first frame of bubble coalescence. The uncertainty
35
for the measurement of coalescence time is the interval between two frames, i.e. 76.92 µs. Four to ten
36
measurements were taken to obtain the average coalescence time for each solution. Some 4 ACS Paragon Plus Environment
Page 5 of 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
1
measurements were repeated on another day (four, three and four measurements for 0.01, 0.05 and
2
0.075 M NaCl solutions and six measurements each for 0.05 and 0.1 M NaBr solutions) to ensure the
3
repeatability of the results. Fig. 2 shows image sequences of the coalescence process of two bubbles
4
in a 0.75 M NaF solution. We identified four consecutive stages of the coalescence process:
5
approaching (Fig. 2a), contact (Fig. 2b), liquid film draining (Fig. 2c) and coalescence (Fig. 2d). The
6
average diameter and the collision speed of the bubbles were 255±4 µm and 0.022±0.004 m/s,
7
respectively. The bubble size in this study is at least one order of magnitude smaller than the one
8
measured in all existing conventional techniques.3 The bubble approaching speed in this study is in
9
the “instant coalescence” regime (0.0012 – 0.14 m/s), i.e. bubble coalescence time is smaller than
10
0.01 s.30 Our measured bubble coalescence times of smaller than 0.001 s validate the existence of this
11
regime.
12 13
Fig. 2 Image sequences of air bubble coalescence in the 0.75 M NaF solution in different stages: (a)
14
approaching; (b) contact ( ݐൌ ݐ ); (c) liquid film draining and (d) First frame of coalescence ( ݐൌ
15
்ݐ ). The scale bar represents 100 µm.
16
RESULTS AND DISCUSSION
17
Fig. 3a shows the coalescence time of a colliding bubble pairs in sodium halide solutions for
18
different concentrations up to 0.5 M. The transition salt concentration (TC) was found at the shortest
19
bubble coalescence time. At TC, the bubble dynamics moves from coalescence to inhibition and the
20
bubbles can merge most efficiently. The TCs are found at 0.070 ± 0.010 M, 0.0850 ± 0.010 M, 0.175
21
± 0.025 M and 0.325 ± 0.025 M for NaF, NaCl, NaBr and NaI solutions, respectively. It is important
22
to note that our measured results of TC are within the range of previously published results that were
23
determined via the film balance technique, i.e. 0.080 M, 0.115 M, 0.195 M and 0.345 M for NaF,
24
NaCl, NaBr and NaI solutions, respectively.31, 32 However, the uncertainty of bubble coalescence time
25
using our microfluidic method (< 6%) is much smaller than that of the film balance technique (as high
26
as 20%).32 Despite of the consistency of our TC measurements, the measured bubble coalescence 5 ACS Paragon Plus Environment
Langmuir
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 10
1
times ranging from 100 to 500 µs are much shorter than the reported values of 0.1 to 30 s using liquid
2
film balance technique.3,
3
discrepancy. The approaching speed of 22 mm/s in this study is much greater than the one that drives
4
film drainage in the film balance technique (10 – 300 µm/s). A critical approach speed of
5
approximately 35 µm/s was reported previously. Above this critical speed, the bubbles coalesce
6
almost instantly within less than 0.1 s, and the transition concentration of salts is independent of the
7
approaching speed.32 Our microfluidic method with the high-speed camera makes the observation of
8
that instant coalescence possible. Furthermore, the time scale of the bubble coalescence process in our
9
study of few hundreds of microseconds is more relevant to the practical systems such as bubble
10
columns and flotation separation where the bubble contact time in solutions is shorter than 1 s, as
11
compared with the time scale (as long as 20 s) of the film balance experiments.32 The laminar flow in
12
a microchannel also eliminates the uncertainties of bubble coalescence due to the turbulence in the
13
bubble swarm experiment. Finally, the microfluidic method provides a reliable and precise bubble
14
coalescence time rather than qualitative description as “coalescence” or “non-coalescence” in the
15
bubble pair method.
32
The difference in the interface approaching speeds may lead to this
16
Fig. 3a shows that the measured TCs for the monovalent anions increase with the anion size. The
17
ion-specific effect on bubble coalescence in sodium halide salt solutions follows the order of
18
inhibition capability: NaF > NaCl > NaBr > NaI. At concentrations lower than TC, the curves for
19
bubble coalescence time almost overlap. However, at concentrations higher than TC, the curves
20
deviate from each another significantly. In the regimes of low salt concentration, the bubble
21
coalescence is controlled by the repulsion between the electric double layers at the bubble surfaces,
22
which becomes weak with increasing salt concentration due to the compression of the double layers.
23
The inhibition of bubble coalescence at high salt concentration is still not well understood.35, 36 Gibbs
24
elasticity of the liquid film caused by the surface tension gradient, and hydrophobic forces between
25
bubble interfaces due to dissolved gases in salt solutions are believed to be related to the ion-specific
26
effect on bubble coalescence inhibition at high salt concentration.3
27
We also plot the coalescence time against Ohnesorge number (ܱℎ ൌ ߤ/ඥߩߪ ܦwhere ߤ , ߩ, ߪ, and ܦ
28
are viscosity, density, surface tension and bubble diameter, respectively), which is the ratio of viscous
29
force to inertial and surface tension force, in Fig. 3b. The coalescence of bubbles and drops in an outer
30
fluid is related to this dimensionless number, and a phase diagram can be created to identify the
31
different regimes of the coalescence process.37 However, Fig. 3b shows that the change of Ohnesorge
32
number in current study is very small (0.0065 – 0.0068). Therefore, we can safely neglect the effects
33
of physical properties of salt solutions on the bubble coalescence process.
34
Nearly 130 years on since the ion-specific effect on protein precipitation had been found by
35
Hofmeister38, its satisfactory explanation is still a challenge for classic theories, including the Debye6 ACS Paragon Plus Environment
Page 7 of 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
1
Hückel and DLVO theories. Only phenomenological set of rules, such as the law of matching water
2
affinities 39 and combining rules of ions to inhibit bubble coalescence13 could successfully explain the
3
effect. Nevertheless, microfluidic technology proves here to be a useful tool for investigating the ion-
4
specific effect on bubble coalescence.
(a)
(b)
5 6
Fig. 3 Bubble coalescence time versus different salt concentrations (Fig. 3a) and Ohnesorge number
7
(Fig. 3b). Values of surface tension, viscosity and density for the salt solutions can be found in
8
literature.31, 33, 34 The symbols represent the different types of salts: NaF, NaCl, NaBr and NaI. The
9
lines are only for eyes guide. The error bars represent the standard error (n = 4-10). The transition
10
concentration refers to the shortest coalescence time as indicated with the arrows.
7 ACS Paragon Plus Environment
Langmuir
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 8 of 10
1
CONCLUSIONS
2
In summary, we report a microfluidic method to investigate the ion-specific effect on bubble
3
coalescence. We directly visualised the bubble coalescence in a microchannel using high-speed
4
imaging and evaluated the bubble coalescence time to determine the transition concentrations of
5
sodium halide solutions. We found the capacity of sodium halide salts to inhibit bubble coalescence
6
follows the order of NaF > NaCl > NaBr > NaI. Compared with conventional techniques, the
7
microfluidic method overcomes their inherent uncertainties and provides a promising tool for the
8
future studies on ion-specific effect.
9
AUTHOR INFORMATION
10
Corresponding Author
11
*E-mail:
[email protected] 12
Notes
13
The authors declare no competing finacial intersts.
14
ACKNOWLEDGEMENTS
15
The authors acknowledge the Australia Research Council (ARC) for financial support (project
16
number DP140101089). S. H. Tan and N. T. Nguyen gratefully acknowledges the support of the
17
Griffith University Post-doctoral fellowship, New Researcher grant, ARC linkage grant
18
(LP150100153) and Griffith University-Peking University collaboration grant.
19 20
REFERENCES
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
1. Craig, V. S. J.; Henry, C. L. Specific ion effects at the air-water interface: experimental studies. In Specific ion effects, Kunz, W., Ed.; World Scientific: London 2010. 2. Nguyen, A. V.; Schulze, H. J. Colloidal science of flotation; Marcel Dekker: New York, 2004; Vol. 118. 3. Firouzi, M.; Howes, T.; Nguyen, A. V. A quantitative review of the transition salt concentration for inhibiting bubble coalescence. Advances in Colloid and Interface Science 2015, 222, 305-318. 4. Marrucci, G.; Nicodemo, L. Coalescence of gas bubbles in aqueous solutions of inorganic electrolytes. Chemical Engineering Science 1967, 22 (9), 1257-1265. 5. Prince, M. J.; Blanch, H. W. Transition electrolyte concentrations for bubble coalescence. AIChE Journal 1990, 36 (9), 1425-1429. 6. Lessard, R. R.; Zieminski, S. A. Bubble Coalescence and Gas Transfer in Aqueous Electrolytic Solutions. Industrial & Engineering Chemistry Fundamentals 1971, 10 (2), 260-269. 7. Cho, Y. S.; Laskowski, J. S. Bubble coalescence and its effect on dynamic foam stability. The Canadian Journal of Chemical Engineering 2002, 80 (2), 299-305. 8. Laskowski, J. S.; Tlhone, T.; Williams, P.; Ding, K. Fundamental properties of the polyoxypropylene alkyl ether flotation frothers. International Journal of Mineral Processing 2003, 72 (1–4), 289-299. 8 ACS Paragon Plus Environment
Page 9 of 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
Langmuir
9. Grau, R. A.; Laskowski, J. S. Role of Frothers in Bubble Generation and Coalescence in a Mechanical Flotation Cell. The Canadian Journal of Chemical Engineering 2006, 84 (2), 170-182. 10. Kracht, W.; Finch, J. A. Bubble break-up and the role of frother and salt. International Journal of Mineral Processing 2009, 92 (3–4), 153-161. 11. Nassif, M.; Finch, J. A.; Waters, K. E. Developing critical coalescence concentration curves for industrial process waters using dilution. Minerals Engineering 2013, 50–51, 64-68. 12. Henry, C. L.; Dalton, C. N.; Scruton, L.; Craig, V. S. J. Ion-Specific Coalescence of Bubbles in Mixed Electrolyte Solutions. The Journal of Physical Chemistry C 2007, 111 (2), 1015-1023. 13. Craig, V. S. J.; Ninham, B. W.; Pashley, R. M. The effect of electrolytes on bubble coalescence in water. Journal of Physical Chemistry 1993, 97 (39), 10192-7. 14. Quinn, J. J.; Sovechles, J. M.; Finch, J. A.; Waters, K. E. Critical coalescence concentration of inorganic salt solutions. Minerals Engineering 2014, 58, 1-6. 15. Kracht, W.; Rebolledo, H. Study of the local critical coalescence concentration (l-CCC) of alcohols and salts at bubble formation in two-phase systems. Minerals Engineering 2013, 50–51 (0), 77-82. 16. Bournival, G.; Ata, S.; Karakashev, S. I.; Jameson, G. J. An investigation of bubble coalescence and post-rupture oscillation in non-ionic surfactant solutions using high-speed cinematography. Journal of Colloid and Interface Science 2014, 414, 50-58. 17. Nguyen, N.-T.; Wereley, S. T. Fundamentals and Applications of Microfluidics; Artech House: Boston London, 2002. 18. Chong, Z. Z.; Tor, S. B.; Loh, N. H.; Wong, T. N.; Ganan-Calvo, A. M.; Tan, S. H.; Nguyen, N.-T. Acoustofluidic control of bubble size in microfluidic flow-focusing configuration. Lab on a Chip 2015, 15 (4), 996-999. 19. Yang, L.; Wang, K.; Tan, J.; Lu, Y.; Luo, G. Experimental study of microbubble coalescence in a T-junction microfluidic device. Microfluidics and Nanofluidics 2012, 12 (5), 715-722. 20. Wu, Y.; Fu, T.; Zhu, C.; Ma, Y.; Li, H. Z. Bubble coalescence at a microfluidic T-junction convergence: from colliding to squeezing. Microfluidics and Nanofluidics 2014, 16 (1), 275-286. 21. and, Y. X.; Whitesides, G. M. SOFT LITHOGRAPHY. Annual Review of Materials Science 1998, 28 (1), 153-184. 22. Bauer, W.-A. C.; Fischlechner, M.; Abell, C.; Huck, W. T. S. Hydrophilic PDMS microchannels for high-throughput formation of oil-in-water microdroplets and water-in-oil-in-water double emulsions. Lab on a Chip 2010, 10 (14), 1814-1819. 23. Decher, G. Layer-by-Layer Assembly (Putting Molecules to Work). In Multilayer Thin Films; Wiley-VCH Verlag GmbH & Co. KGaA, 2012, pp 1-21. 24. Feldötö, Z.; Varga, I.; Blomberg, E. Influence of Salt and Rinsing Protocol on the Structure of PAH/PSS Polyelectrolyte Multilayers. Langmuir 2010, 26 (22), 17048-17057. 25. Jaber, J. A.; Schlenoff, J. B. Counterions and Water in Polyelectrolyte Multilayers: A Tale of Two Polycations. Langmuir 2007, 23 (2), 896-901. 26. Estrela-Lopis, I.; Iturri Ramos, J. J.; Donath, E.; Moya, S. E. Spectroscopic Studies on the Competitive Interaction between Polystyrene Sodium Sulfonate with Polycations and the NTetradecyl Trimethyl Ammonium Bromide Surfactant. The Journal of Physical Chemistry B 2010, 114 (1), 84-91. 27. Pallas, N. R.; Harrison, Y. An automated drop shape apparatus and the surface tension of pure water. Colloids and Surfaces 1990, 43 (2), 169-194. 28. Kim, J.; Chaudhury, M. K.; Owen, M. J. Hydrophobic Recovery of Polydimethylsiloxane Elastomer Exposed to Partial Electrical Discharge. Journal of Colloid and Interface Science 2000, 226 (2), 231-236. 29. Morra, M.; Occhiello, E.; Marola, R.; Garbassi, F.; Humphrey, P.; Johnson, D. On the aging of oxygen plasma-treated polydimethylsiloxane surfaces. Journal of Colloid and Interface Science 1990, 137 (1), 11-24. 30. Del Castillo, L. A.; Ohnishi, S.; Horn, R. G. Inhibition of bubble coalescence: Effects of salt concentration and speed of approach. Journal of Colloid and Interface Science 2011, 356 (1), 316-324. 31. Firouzi, M. Drainage and Stability of Foam Films during Bubble Coalescence in Aqueous Salt Solutions. Doctorate Degree, University of Queensland2014.
9 ACS Paragon Plus Environment
Langmuir
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Page 10 of 10
32. Firouzi, M.; Nguyen, A. V. Effects of monovalent anions and cations on drainage and lifetime of foam films at different interface approach speeds. Advanced Powder Technology 2014, 25 (4), 1212-1219. 33. Desnoyers, J. E.; Perron, G. The viscosity of aqueous solutions of alkali and tetraalkylammonium halides at 25°C. Journal of Solution Chemistry 1972, 1 (3), 199-212. 34. Novotny, P.; Sohnel, O. Densities of binary aqueous solutions of 306 inorganic substances. Journal of Chemical & Engineering Data 1988, 33 (1), 49-55. 35. Nguyen, P. T.; Hampton, M. A.; Nguyen, A. V.; Birkett, G. R. The influence of gas velocity, salt type and concentration on transition concentration for bubble coalescence inhibition and gas holdup. Chemical Engineering Research and Design 2012, 90 (1), 33-39. 36. Henry, C. L.; Craig, V. S. J. The link between ion specific bubble coalescence and Hofmeister effects is the partinioning of ions within the interface. Langmuir 2010, 26 (9), 6478-6483. 37. Paulsen, J. D.; Carmigniani, R.; Kannan, A.; Burton, J. C.; Nagel, S. R. Coalescence of bubbles and drops in an outer fluid. Nature Communications 2014, 5, 3182. 38. Hofmeister, F. Zur Lehre von der Wirkung der Salze. Archiv für experimentelle Pathologie und Pharmakologie 1888, 24 (4), 247-260. 39. Collins, K. D. Charge density-dependent strength of hydration and biological structure. Biophysical Journal 1997, 72 (1), 65-76.
19 20 21 22 23 24
TOC
25 26
100 µm
(a)
(b)
(c)
(d)
10 ACS Paragon Plus Environment
