Janus silica film with hydrophobic and hydrophilic surfaces grown at an oil–water interface (original) (raw)
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Journal of Chemical Sciences, 2008
Selective permeation of oil and water across a porous medium, as in oil recovery operations, depends on the preferential wetting properties of the porous medium. We show a profound influence of surfactants in wetting of porous media and thus demonstrate a new route for the control of water-in-oil wetting of porous substrates by changing the concentration of surfactants in an aqueous sub-phase below the substrate. This strategy is employed to engineer partial reversible wetting transitions on a porous silica film. The film itself is grown and stabilized on a flat, macroscopic interface between an oil phase and an aqueous sub-phase. On increasing the surfactant (CTAB) concentration in the sub-phase, contact angle of a water drop (placed on the oil side of the film) changes from 140° to 16° in 25 min by diffusion of the surfactant across the porous film. On further replacement of the sub-phase with pure water, diffusion of the surfactant from the water drop back to the sub-phase was slower, increasing the contact angle in the process from 16° to 90° in 2 h. Wettability control by a cationic surfactant (CTAB) was found to be much faster (6 deg/min) than that offered by an anionic surfactant, SDS (0⋅05 deg/min). Switching of the surface wettability due to the surfactant diffusion may have implications in oil-water separation, chemical bed reactors and microfluidic devices.
Chemical Physics Letters, 2020
The synthesis and study of silica thin films' adhesive properties as a function of dimethyldimethoxysilane: tetraethoxysilane (DMDMS: TEOS (DT)) molar ratio and calcination temperature and its relationship with the silica polymer shape have been conducted. DT molar ratio was very influential on the silica thin film's hydrophobic nature coated on the glass surface and indicated that the water droplets stuck to the silica-coated glass surface, not rolling down. The sticky property mainly originated from the non-uniformity of functional group composition and material surface roughness. The highest hydrophobic properties were obtained from the balanced composition of the DT molar ratio.
Influence of hydrophobic characteristic of organo-modified precursor on wettability of silica film
Bulletin of Materials Science, 2014
The objective of this study is to design new hybrid silica materials as templates with hydrophobic properties, prepared at room temperature by a base catalyzed sol-gel process. As silica sources, organoalkoxysilanes functionalized with short hydrophobic chains were used: tetraethylorthosilicate (TEOS), methyltriethoxysilane (MTES), vinyltriethoxysilane (VTES), octyltriethoxysilane (OTES) and isobutyltriethoxysilane (iTES). It was shown that hydrophobicity of the functionalized silica nanoparticles increased as a function of length of the aliphatic chains (MTES < iTES < OTES) or when, instead of a hydrophobic alkyl chains (substituting group of silica precursors), a monounsaturated group was used (VTES). It was observed that the samples responded in a specific way to each type (hydrophilic or hydrophobic) of the dropped liquid. Even though the experiments were limited to short hydrocarbon chains, they showed that there is a threshold to reach high hydrophobicity of the hybrid surface.
J. Materials Chem. 18, 1021-1028 (2008)
Janus silica film with hydrophobic and hydrophilic surfaces grown at an oil–water interface
We report a new methyltrimethoxysilane (MTMS) based route to growing a Janus silica film at the oil-water interface, which upon drying shows anisotropic wetting by water on its two surfaces. The contact angle of water on the surface grown in contact with the oil-side is found to be 150,butitismuchsmaller,150 , but it is much smaller, 150,butitismuchsmaller,65 , on the side which grew in contact with the aqueous phase. This large difference in the contact angle is found to be primarily because of two reasons: (i) orientation of hydrophobic methyl groups towards the oil-side of the film as confirmed by micro-Raman spectroscopy, and (ii) microstructural differences in the oil and water-side surfaces of the film. The inherently hydrophobic silica cluster network on the oil-side surface also exhibits larger pores that provide an air cushion for the water droplet and engenders a large contact angle. Effects of oil-water interfacial tension on the film growth and on its wetting and microstructural properties are also investigated by addition of cationic and anionic surfactants in the aqueous subphase. Static and dynamic wetting properties of the oil-side surface indicate that these do not change significantly due to variations in either the microstructure or chemical nature of the surface alone, but is a combined effect of both. Interestingly, the Janus films showing asymmetric surface properties can also be grown directly and thus integrated with a variety of porous surfaces like cotton, paper, hydrogel and ceramic substrates by having these surfaces straddle an oil-water interface. † Electronic supplementary information (ESI) available: A movie showing rolling of water drops on the slightly inclined hydrophobic surface of the Janus silica film is supplied as supporting information. See
KONA Powder and Particle Journal, 2000
Microscopic and macroscopic wettabilities of various silica surfaces modified with trimethylsilyl groups were studied, focusing on the effect of their surface geometrical structures. Micro and macro geometrical structures were investigated by water vapor adsorption. Microscopic wettability was determined by water vapor adsorption, while macroscopic wettability was determined by measuring the contact angle. Microscopic wettability affects the continuous two-dimensional water layer, while macroscopic wettability is influenced by capillary condensation and surface roughness. Surface wettability is essentially governed by microscopic wettability, which is a primary property of various silica surfaces. Capillary condensation and surface roughness enhance wettability as a secondary effect which results from the primary property of microscopic wettability.
Sliding behavior of water drops on sol–gel derived hydrophobic silica films
Applied Surface Science, 2010
Control on the wettability of solid state materials is a classical and key issue in surface engineering. Optically transparent methyltriethoxysilane (MTES)-based silica films with water sliding angle as low as 9° were successfully prepared by two-step sol–gel co-precursor method. The emphasis is given to the effect of trimethylethoxysilane (TMES) as a co-precursor on water sliding behavior of silica films. The coating sol was prepared with molar ratio of methyltriethoxysilane (MTES), methanol (MeOH), acidic water (0.01 M, oxalic acid) and basic water (12 M, NH4OH) kept constant at 1:12.73:3.58:3.58 respectively, and the molar ratio of TMES/MTES (M) was varied from 0 to 0.22. The static water contact angle as high as 120° and the water sliding angle as low as 9° was obtained by keeping the molar ratio (M) of TMES/MTES at 0.22. When the modified films were cured at temperature higher than 280 °C, the films became superhydrophilic. Further, the humidity study was carried out at a relat...
Stability of Aqueous Films on Hydrophobic Methylated Silica
Experiments in which a small gas bubble was slowly advanced towards a polished silica plate under dilute aqueous solutions have shown that " thick " equilibrium films are formed not only on clean, hydrophilic, silica, but also on methylated, hydrophobic, silica. The latter films are metastable, collapsing when disturbed and forming a contact angle which may be as large as 90". Surprisingly, the thicknesses of the metastable films are apparently independent of the contact angle.
Wetting Behavior of Silicone Oils on Solid Substrates Immersed in Aqueous Electrolyte Solutions
Langmuir, 2002
Equilibrium contact angles are reported for silicone oils (poly(dimethylsiloxane)s) on polymer-coated and uncoated solid-silicon substrates immersed in aqueous electrolyte solutions. Solid-substrate wettability to water ranges from highly hydrophilic to highly hydrophobic based on water/air contact angles. Although silicone oils in air spread completely on all of the studied substrates, these same surfaces when immersed in aqueous media exhibit finite contact angles against silicone oils that depend strongly on the substrate surface energy. A detailed investigation of the pH influence on the wetting behavior of silicone oil on the solid substrates is pursued where a clear correlation emerges between the changes of substrate-surface zeta potential () and the oil-wetting behavior on substrates immersed in aqueous solution. Also, the influence of inorganic KCl and CaCl2 electrolytes on the wetting behavior of silicone oils on solid substrates is studied. KCl does not produce a noticeable effect on the wetting behavior of silicone oils. CaCl2, in general, increases surface hydrophilicity, with the exception of the chitin-coated silicon-wafer substrate. For this polymer surface, the oil/water contact angle decreases with increasing CaCl 2 concentration, indicating stronger oil wetting. Specific interactions between chitin surface functional groups and calcium ions are confirmed by-potential measurements. Finally, we find that the classic Bartell-Osterhof equation, based on the thermodynamics of ideal wetting, well describes the wetting behavior of silicone oil in water on apolar and moderately polar solid substrates of different functionality, provided that accurate measurements are available for the corresponding air-in-water contact angles and for the equilibrium surface and interfacial tensions. The same Bartell-Osterhof equation yields invalid predictions for contact angles of oils in water on substrates wettable by both liquid phases and for contact angles of water on the substrates studied when they are immersed in silicone oils.
Chemical Engineering & Technology, 1998
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