scholarly journals HYDROPHOBIZATION OF SILICA PARTICLES WITH VARIOUS CATIONIC SURFACTANTS

2021 ◽  
Vol 64 (3) ◽  
pp. 41-45
Author(s):  
Alla V. Nushtaeva ◽  
Natalia G. Vilkova
Keyword(s):  
Contact Angle ◽  
Aqueous Phase ◽  
Volume Fraction ◽  
Saturated Hydrocarbon ◽  
Vertical Surface ◽  
Contact Angles ◽  
Silica Particles ◽  
Sessile Droplet ◽  
Phase Volume Fraction ◽  
Oil In Water

Silica particles with a radius of 3-7 nm (Ludox and Aerosil) and 270 nm (synthesized by the Stöber method), modified with cetyltrimethylammonium bromide (CTAB) and hexylamine, were used to stabilize emulsions. The hysteresis angles θ of the particle selective wetting were measured by the sessile droplet method on the vertical surface or by the pulling a ball method at using a glass substrate modified by contact coagulation of silica. The contact angle at the boundary between the aqueous phase and the saturated hydrocarbon (octane, decane) reached the values θrec = 53 ± 2 ° and θadv = 116 ± 4 ° (the aqueous phase receding and advancing angle, respectively) with an increase in the initial concentration of long-chain CTAB to (1.4–9.5)·10–2 mmol/g of silica. With a further increase in CTAB concentration, a second reoriented layer was formed, which lowered the contact angle. Accordingly, using CTAB, only oil-in-water emulsions were obtained with the oil phase volume fraction Øoil = 0.5. The amount of short-chain hexylamine required to start stabilizing the emulsions turned out to be 2-3 orders of magnitude higher than the amount of CTAB. At using hexylamine, it was possible to increase the contact angle up to the values θrec ≈ θadv = 163 ± 12 ° at a concentration of 7-21 mmol/g. This is due to the fact that hexylamine is not characterized by formation of micelle or reoriented layers. Apparently, the adsorption of hexylamine is possible not only on dissociated silanol groups Si–OH, but also on siloxane groups Si–O–Si≡, which makes it possible to make the silica surface superhydrophobic. The measured contact angles were correlated with the region of stable oil-in-water and water-in-oil emulsions.

scholarly journals Effects of Bentonite Nanoclay and Cetyltrimethyl Ammonium Bromide Modified Bentonite Nanoclay on Phase Inversion of Water-in-Oil Emulsions

2020 ◽  
Vol 4 (1) ◽  
pp. 2
Author(s):  
Sileola B. Ogunlaja ◽  
Rajinder Pal
Keyword(s):  
Contact Angle ◽  
Aqueous Phase ◽  
Phase Inversion ◽  
Volume Fraction ◽  
Critical Volume ◽  
Ammonium Bromide ◽  
Cetyltrimethyl Ammonium Bromide ◽  
Modified Bentonite ◽  
Critical Volume Fraction ◽  
Cetyltrimethyl Ammonium

The effects of unmodified and modified bentonite nanoclays (with various degrees of surfactant modification) on the catastrophic phase inversion from water-in-oil (W/O) emulsion to oil-in-water (O/W) emulsion were determined experimentally. The bentonite nanoclay (NC-Bt) was suspended in the aqueous phase, and the critical volume fraction of water where phase inversion from W/O to O/W emulsion took place was determined through conductivity measurements. Cetyltrimethyl ammonium bromide (CTAB) was used as a surfactant to modify the nanoclay. The adsorption of CTAB onto nanoclay had a strong influence on the contact angle and the critical volume fraction of water where phase inversion took place. The modification of the nanoclay brought about by the adsorption of CTAB increased the three-phase contact angle (measured through the aqueous phase), thereby making it more hydrophobic, and prolonged the phase inversion point. CTAB alone and CTAB-modified nanoclay delayed the phase inversion process in a similar manner, showing a strong dependence on the CTAB concentration.

Ring-Shaped Sessile Droplet

2011 ◽  
Author(s):  
Svyatoslav S. Chugunov ◽  
Douglas L. Schulz ◽  
Iskander S. Akhatov
Keyword(s):  
Contact Angle ◽  
Liquid Droplet ◽  
Liquid Structure ◽  
Solid Substrate ◽  
Contact Angles ◽  
Equilibrium Contact Angle ◽  
Sessile Droplet ◽  
System Equilibrium ◽  
Energy Consideration ◽  
External Forces

It is recognized that small liquid droplet placed on the solid substrate forms equilibrium contact angle that can be obtained from well-known Young’s law. Previously, deviations from Young’s law were demonstrated for the droplets exposed to external fields (gravity, electric, etc) and for the droplets on non-homogeneous substrates. This work reveals that the Young’s equilibrium contact angle can be altered by geometrical reasons only. We consider a ring-shaped droplet on a solid substrate as a test structure for our discussion. We use the global energy consideration for analysis of system equilibrium for the case of freely deposited liquid with no external forces applied. The theoretical analysis shows that steady ring-shaped liquid structure on a solid substrate does exist with contact angles on both contact lines to be different from the Young’s equilibrium contact angle.

scholarly journals Dependency of Contact Angles on Three-Phase Contact Line: A Review

2021 ◽  
Vol 5 (1) ◽  
pp. 8
Author(s):  
H. Yildirim Erbil
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Contact Radius ◽  
Phase Contact ◽  
Sessile Droplet ◽  
Line Energy ◽  
Three Phase ◽  
Tension Term

The wetted area of a sessile droplet on a practical substrate is limited by the three-phase contact line and characterized by contact angle, contact radius and drop height. Although, contact angles of droplets have been studied for more than two hundred years, there are still some unanswered questions. In the last two decades, it was experimentally proven that the advancing and receding contact angles, and the contact angle hysteresis of rough and chemically heterogeneous surfaces, are determined by interactions of the liquid and the solid at the three-phase contact line alone, and the interfacial area within the contact perimeter is irrelevant. However, confusion and misunderstanding still exist in this field regarding the relationship between contact angle and surface roughness and chemical heterogeneity. An extensive review was published on the debate for the dependence of apparent contact angles on drop contact area or the three-phase contact line in 2014. Following this old review, several new articles were published on the same subject. This article presents a review of the novel articles (mostly published after 2014 to present) on the dependency of contact angles on the three-phase contact line, after a short summary is given for this long-lasting debate. Recently, some improvements have been made; for example, a relationship of the apparent contact angle with the properties of the three-phase line was obtained by replacing the solid–vapor interfacial tension term, γSV, with a string tension term containing the edge energy, γSLV, and curvature of the triple contact line, km, terms. In addition, a novel Gibbsian thermodynamics composite system was developed for a liquid drop resting on a heterogeneous multiphase and also on a homogeneous rough solid substrate at equilibrium conditions, and this approach led to the same conclusions given above. Moreover, some publications on the line energy concept along the three-phase contact line, and on the “modified” Cassie equations were also examined in this review.

scholarly journals Encapsulation of Lactobacillus casei (ATCC 393) by Pickering-Stabilized Antibubbles as a New Method to Protect Bacteria against Low pH

2020 ◽  
Vol 4 (3) ◽  
pp. 40
Author(s):  
Vida Mardani Ghahfarokhi ◽  
Paolo P. Pescarmona ◽  
Gert-Jan W. Euverink ◽  
Albert T. Poortinga
Keyword(s):  
Aqueous Phase ◽  
Lactobacillus Casei ◽  
Silica Particles ◽  
Low Ph ◽  
New Method ◽  
Liquid Droplets ◽  
Freeze Dried ◽  
Oil In Water

Pickering-stabilized antibubbles were used as a new method to encapsulate Lactobacillus casei. Antibubbles consist of one or more liquid droplets within a shell of gas. The antibubbles were prepared from a water-in-oil-in-water (W/O/W) emulsion stabilized by silica particles, which was then freeze-dried to remove the water and oil phases, before being subsequently reconstituted in water. Different oil phases and aqueous phase compositions were tested for their effect on the survival of the bacteria. The survival of L. casei after encapsulation using decane was 29.8 ± 2.1% in antibubbles containing 10% (w/v) maltodextrin plus 8% (w/v) sucrose, which is comparable to the survival when bacteria were freeze-dried without being encapsulated. Encapsulation within antibubbles led to a 10 to 30 times higher survival of L. casei at pH 2 in comparison with unencapsulated bacteria. This study shows that probiotics can be encapsulated within a shell of gas through the use of antibubbles and that this protects probiotics against a low pH.

Water–propylene glycol sessile droplet shapes and migration: Marangoni mixing and separation of scales

2022 ◽  
Vol 933 ◽  
Author(s):  
J. Charlier ◽  
A.Y. Rednikov ◽  
S. Dehaeck ◽  
P. Colinet ◽  
D. Terwagne
Keyword(s):  
Contact Angle ◽  
Propylene Glycol ◽  
Ambient Air ◽  
Contact Angles ◽  
Apparent Contact Angle ◽  
Sessile Droplet ◽  
Convective Mixing ◽  
Separation Of Scales ◽  
And Migration

New light is shed on morphological features of water–propylene glycol sessile droplets evaporating into ambient air at not too high relative humidity. Such droplets adopt a Marangoni-contracted shape even on perfectly wetting substrates, an effect well known since Cira et al. (Nature, 519, 2015). We here highlight a strong separation of scales normally occurring for such droplets. Namely, there is a narrow high-curvature zone localized at the foot of the droplet, where the apparent contact angle is formed, while the core of the droplet merely adheres to the classical (capillary–gravity) static shape. Experimentally, we rely upon interferometry to discern such fine key details. We detect a maximum of the droplet slope profile in the foot region, which amounts to the apparent contact angle. Theoretically, a local description of the foot region is devised. We indicate a crucial role of convective mixing by the solutal Marangoni flow, here accounted for by the Taylor dispersion, which proves to underlie the separation of scales and ensure self-consistency of the local model. Migration of such droplets in a humidity gradient is also approached within the same experimental and theoretical framework. It is considered that the resulting back–front asymmetry of the apparent contact angles drives the motion similarly to a wettability gradient, although the drag (‘Cox–Voinov’) factor is here found to be different. The predictions, comparing well with the measurements (our own and from the literature), are based on rigorous models, isothermal and as reduced as possible, without any fitting parameters or microphysics effects.

Contact Angles as a Measure of Surface Wetting Properties in Filth Flotation Analysis

1964 ◽  
Vol 47 (3) ◽  
pp. 520-529
Author(s):  
Maryvee G Yakowitz ◽  
William V Eisenberg
Keyword(s):  
Contact Angle ◽  
Aqueous Phase ◽  
Aqueous Media ◽  
Contact Angles ◽  
Surface Wetting ◽  
Inverted Position ◽  
Oil Droplet ◽  
Wetting Properties ◽  
Specimen Material ◽  
Aqueous Solvent

Abstract A study was made of the surface wetting properties exhibited by insect fragments, animal hairs, and food particles in contact with oil and aqueous solvent systems used in oil flotation analytical procedures. The differential wetting phenomena involved in flotation separation procedures of both untreated and preliminarily treated materials can be studied by contact angle measurements, which provide valuable information about the degree of wettability and flotability of both filth and plant particles. The solid specimen material is immersed in an inverted position in the aqueous plase, and the applied oil droplet competes with the aqueous phase for "wetting" the solid. The contact angle is measured at the point where the oil droplet, the aqueous phase, and the solid surface meet. The instrument used for measuring contact angles and the accessory apparatus devised for the addition of oil droplets to inverted specimen mounts while immersed in aqueous media are illustrated.

The Study on Ionic Liquids Oil-in-Water Emulsion Enhancing Carbon Dioxide Absorption

2012 ◽  
Vol 455-456 ◽  
pp. 991-997
Author(s):  
Hong Jing Liu ◽  
Ying Zhang ◽  
Hui Yao ◽  
Wei Zhao ◽  
Hong Jing Liu
Keyword(s):  
Carbon Dioxide ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Mass Transfer Rate ◽  
Phase Volume ◽  
Water Emulsion ◽  
Dispersion Phase ◽  
Phase Volume Fraction ◽  
Oil In Water ◽  
Oil In Water Emulsion

The purpose of this paper is to investigate the effects of ionic liquids (ILs) oil-in-water emulsion on CO2 absorption. 1-octyl-3-methylimidazolium hexafluorophosphate as ILs was dispersed into water forming oil-in-water emulsion to absorb carbon dioxide. Effects of dispersed phase volume fraction, droplet size, and the regeneration of dispersion were studied. Experimental results indicate that ILs oil-in-water emulsion can enhance the CO2 absorption rate under lower dispersion phase volume fraction, and the CO2 mass transfer rate increases with dispersion phase volume fraction. The smaller droplet size can help droplet go into the boundary layer to load CO2 so as to increase the CO2 mass transfer rate. ILs emulsion can be regenerated, but their enhancement effect becomes weaken with the increase of regeneration times.

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