Switchable Surface Wettability Research Articles

Photo-control of poly(N-[4-[(4-Nitrophenyl)azo]phenyl]acrylamide) brushes on graphene oxide coated silicon surface

Poly(N-[4-[(4-Nitrophenyl)azo]phenyl]acrylamide [poly(NPAPAA)] brushes were obtained via interface-mediated reversible addition–fragmentation chain transfer polymerization to design new photoresponsive surface on the graphene oxide coated silicon substrate. Switchable surface wettability was controlled successfully by these densely packed polymer brushes using light as the exterior stimulation. The relatively nonpolar trans azobenzene polymer brushes were converted to a polar cis form (with a larger dipole moment) utilizing light of the suitable wavelength. This conversion is reversible and can be switched back by employing visible light. Cis–trans photo-induced isomerization provided a reversible contact angle change (~ 9o) with UV and visible light for the poly(NPAPAA) brushes under successive irradiation cycles. This study may be promised to control cell culture surface without leaving any residual in terms of alternative medicine.

Novel robust cellulose-based foam with pH and light dual-response for oil recovery

We fabricated pH and light dual-responsive adsorption materials which could induce the transition of surface wettability between hydrophobicity and hydrophilicity by using ATRP. The structure and morphology of adsorption materials were confirmed by ATR-FTIR, XPS, TGA and SEM. It showed that the modified cellulose (CE)-based foam was hydrophobic, which can adsorb a range of oils and organic solvents in water under pH = 7.0 or visible light irradiation (λ > 500 nm). Meanwhile, the wettability of robust CE-based foam can convert hydrophobicity into hydrophilicity and underwater oleophobicity under pH = 3.0 or UV irradiation (λ = 365 nm), giving rise to release oils and organic solvents. Most important of all, the adsorption and desorption processes of the modified CE-based foam could be switched by external stimuli. Furthermore, the modified CE-based foam was not damaged and still retained original performance after reversible cycle repeated for many times with variation of surface wettability. In short, it indicates that CE-based foam materials with switchable surface wettability are new responsive absorbent materials and have owned potential application in the treatment of oil recovery.

Electro-responsive carbon membranes with reversible superhydrophobicity/superhydrophilicity switch for efficient oil/water separation

Abstract Membrane filtration has shown great potential for the separation of oil-water mixtures. The separation of oil-water mixtures is essentially an interfacial issue, and thus controllable surface wettability of membrane is extremely significant for efficient and cost-effective oil/water separation. Herein, poly-3-methylthiophene (P(3-MTH))/carbon membranes (CMs-P) with switchable surface wettability between superhydrophobicity and superhydrophilicity were designed. The CMs-P, prepared from coating P(3-MTH) on the highly porous and electrically conductive carbon nanofiber membranes, could exhibit the wettability switch by doping or dedoping the P(3-MTH) with ClO4− under electro-stimuli. The switch can be quickly achieved in less than 30 s and shows desired recyclability. Driven by gravity only, the prepared CMs-P are capable of completely separating free oil-water mixture. Furthermore, the separation efficiency reaches to 99.5% for surfactant-stabled emulsions with various oil-water ratios. This work presents new insights into the study for smart gating membranes and the design of novel functional oil/water separation devices.

A methodology for fabrication of thermomechanically activated switchable surface wettability

ABSTRACTIn this study a platform is laid out for the creation of a multitiered surface exhibiting switchable wettability. This is done through a combination of both an acrylate‐based polymer understructure photopolymerized into a pillared array, and selectively placed surface treatments on these pillars. The acrylate‐based polymer is created through a systematic study and is shown to exhibit drastic alterations in material stiffness over a 19 °C temperature transition under aqueous conditions, allowing for stiff, erect pillars in the low temperature state, and pliable pillars that can easily be bent in the high temperature state. The glass transition temperature and onset temperature for the polymer system is found to be 49 and 30 °C, respectively. Three different surface treatments, including trichloro(1H,1H,2H,2H‐perfluorooctyl)silane, polydimethylsiloxane, and polydopamine, are investigated using static contact angle studies, and are selectively deposited onto the pillared surface such that a hydrophobic surface is exposed with the pillars erect, and a hydrophilic surface is exposed with the pillars in the bent state. The surface is shown to transition between first a hydrophobic, then hydrophilic state and return to a hydrophobic state when the investigations are coupled together forming a hierarchical surface structure. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44122.

Switchable Surface Wettability by Using Boronic Ester Chemistry.

Here, we report for the first time the use of a boronic ester as an efficient tool for reversible surface post-functionalization. The boronic ester bond allows surfaces to be reversibly switched from hydrophilic to hydrophobic. Based on the well-known boronic acid/glycol affinity, this strategy offers the opportunity to play with surface hydrophobic properties by adding various boronic acids onto substrates bearing glycol groups. The post-functionalization can then be reversed to regenerate the starting glycol surface. This pathway allows for the preparation of various switchable surfaces for a large range of applications in biosensors, liquid transportation, and separation membranes.

Smart Fiber Membrane for pH-Induced Oil/Water Separation.

Wastewater contaminated with oil or organic compounds poses threats to the environment and humans. Efficient separation of oil and water are highly desired yet still challenging. This paper reports the fabrication of a smart fiber membrane by depositing pH-responsive copolymer fibers on a stainless steel mesh through electrospinning. The cost-effective precursor material poly(methyl methacrylate)-block-poly(4-vinylpyridine) (PMMA-b-P4VP) was synthesized using copper(0)-mediated reversible-deactivation radical polymerization. The pH-responsive P4VP and the underwater oleophilic/hydrophilic PMMA confer the as-prepared membrane with switchable surface wettability toward water and oil. The three-dimensional network structure of the fibers considerably strengthens the oil/water wetting property of the membrane, which is highly desirable in the separation of oil and water mixtures. The as-prepared fiber membrane accomplishes gravity-driven pH-controllable oil/water separations. Oil selectively passes through the membrane, whereas water remains at the initial state; after the membrane is wetted with acidic water (pH 3), a reverse separation is realized. Both separations are highly efficient, and the membrane also exhibits switchable wettability after numerous cycles of the separation process. This cost-effective and easily mass-produced smart fiber membrane with excellent oil-fouling repellency has significant potential in practical applications, such as water purification and oil recovery.

The fabrication of pH-responsive polymeric layer with switchable surface wettability on cotton fabric for oil/water separation

Cotton textile with special surface wettability has a promising future for oil/water separation due to its high adsorption capacity and low cost. A facile method was employed to prepare a durable polymeric layer with pH-triggered switchable surface wettability on cotton fabric. An amino-containing dye intermediate (2-Chloro-4,6-diamino-1,3,5-triazine, CDATA) was used to produce more reactive grafting sites for surface initiated atom transfer radical polymerization (SI-ATRP) of poly(methacrylic acid) (PMAA). The obtained cotton-PMAA fabric showed high pH-responsibility, which was indicated by the shift of O–C=O peaks in Infrared (IR) spectrum and the transition of water/oil contact angle (WCA/OCA). Moreover, with the rising pH, the surface transited from superhydrophobic to superhydrophilic and underwater superoleophobic, leading to efficient oil/water separation. This study provides an innovative way to fabricate smart cotton fabric with high efficiency and high selectivity for oil/water separation.

Thermo-responsive brush copolymers with structure-tunable LCST and switchable surface wettability

Thermo-responsive brush copolymers poly(methyl methacrylate (MMA)-co-2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM)-graft-(N-isopropyl-acrylamide) (NIPAAm)) were synthesized using Cu-mediated “living” radical polymerization (LRP) approach. Varied grafting densities of the brushes were obtained through adjusting backbone structure as random, gradient and block respectively. The effect of grafting densities on their thermo-responsive phase transition behaviors in aqueous solution and on surface were investigated in detail. The lower critical solution temperature (LCST) of brush copolymers in solution was adjusted as 35, 37 and 38 °C through random, gradient and block backbone structure respectively. Their structure tunable thermo-responsive phase transition in solution were further confirmed by the different micelle aggregation behaviors above LCST which monitored by transmission electron microscopy (TEM) images and dynamic light scattering (DLS). In addition, surfaces modified by the resulted brush copolymers have a temperature tunable wettability based on thermo-responsive phase transition in solid, the similar WCA variation range of three brush copolymers implies that the composition of backbone does not much affect the switchable wettability of surfaces.

Correction to “Switchable Wettability in SnO2 Nanowires and SnO2@SnO2 Heterostructures”

■ ABSTRACT Tin oxide nanowires and heterostructures thereof were synthesized by sequential aplication of thermal and plasmaassisted chemical vapor deposition (CVD) methods. The wetting properties of surfaces based on individual nanowires, hyperbranched SnO2@SnO2 structures, and SnO2@SnO2@ SiOx core−shell heterostructures could be modulated from superhydrophilic to superhydrophobic by changing both chemical composition and the geometrical architecture of nanoheterostructures. Whereas the randomly grown SnO2 nanowires with a contact angle of 3° exhibited superhydrophilicity, the contact angle of SnO2@SnO2 heterostructures synthesized by a two-step CVD process increased to 133°. The corresponding contact angle of SnO2@SnO2@SiOx heterostructures was enhanced to 155.8° by a hydrophobic SiOx coating. Switchable surface wettability in SnO2@SnO2@ SiOx heterostructures was observed by alternation of UV irradiation, storage in dark, and O2 annealing, indicating that geometric microstructure was the major determinant in the switchable wettability. The significant change in the surface wettability upon changing the geometrical features is of potential interest in functional coatings such as antifinger print and self-cleaning surfaces.

Switchable Wettability in SnO2 Nanowires and SnO2@SnO2 Heterostructures

We present here the synthesis of SnO2 nanowires SnO2@SnO2 and SnO2@SnO2@SiOx heterostructures via the chemical vapor deposition (CVD) method. Surface wettability could be modulated from superhydrophilic to superhydrophobic by changing both chemical composition and the geometrical architecture of nanoheterostructures. The random SnO2 nanowires with a contact angle of 3° presented a superhydrophilic property. The contact angle of SnO2@SnO2 heterostructures synthesized by a two-step CVD process increased to 133°. The corresponding contact angle of SnO2@SnO2@SiOx heterostructures was 155.8°. Switchable surface wettability of the SnO2@SnO2@SiOx heterostructure was observed by alternation of UV irradiation, dark storage, and O2 annealing, indicating that geometric microstructure was the major determinant in the switchable wettability from superhydrophilic to superhydrophobic. The switchable surface wettability of SnO2 nanostructures may develop the significant potential for industrial coating and self-cleaning ...

Thermally Tunable Surface Wettability of Electrospun Fiber Mats: Polystyrene/Poly(N‐isopropylacrylamide) Blended versus Crosslinked Poly[(N‐isopropylacrylamide)‐co‐(methacrylic acid)

This work reports on thermally tunable surface wettability of electrospun fiber mats of: polystyrene (PS)/poly(N-isopropylacrylamide) (PNIPA) blended (bl-PS/PNIPA) and crosslinked poly[(N-isopropylacrylamide)-co-[methacrylic acid)] (PNIPAMAA) (xl-NIPAMAA). Both the bl-PS/PNIPA and xl-PNIPAMAA fiber mats demonstrate reversibly switchable surface wettability, with the bl-PS/PNIPA fiber mats approaching superhydrophobic ≥150° and superhydrophilic contact angle (CA) values at extreme temperatures. Weight loss studies carried out at 10 °C indicate that the crosslinked PNIPAMAA fiber mats had better structural integrity than the bl-PS/PNIPA fiber mats. PNIPA surface chemistry and the Cassie-Baxter model were used to explain the mechanism behind the observed extreme wettability.

Visible-light-driven reversible and switchable hydrophobic to hydrophilic nitrogen-doped titania surfaces: correlation with photocatalysis

Visible-light-responsive nitrogen-doped titanium dioxide nanorods have been synthesized by a hydrothermal method at low temperature. X-Ray diffraction, scanning electron microscopy, UV-vis spectroscopy, and contact angle measurements were used to obtain the crystal structures, morphologies, visible-light absorbance, and hydrophobicity, respectively, of the prepared nanorods. The surface wettability of the samples could be reversibly tuned from hydrophobic to hydrophilic upon visible-light illumination. This switchable surface wettability is crucial since the photocatalytic activity of this nanoscaled catalyst for the decomposition of organic molecules exhibits a strong dependence on the surface wettability.

Ammonia Responsive Surface Wettability Switched on Indium Hydroxide Films with Micro- and Nanostructures

Switchable surface wettability that can be tuned reversibly between superhydrophobicity and superhydrophilicity has been successfully realized on indium hydroxide films with micro- and nanostructures. The films are superhydrophobic in the air with a water contact angle of 150.4 ± 0.9° while they turn superhydrophilic with a water contact angle of 0° after storage in an ammonia atmosphere, which means an ammonia responsive surface wettablity switch. The novel surface wettability is ascribed to the multiple surface structures and surface free energy conversion of the films. This kind of smart surface wettability is promising in developing new types of ammonia detectors simply by virtue of the surface wettability conversion.

The effect of collection and cooling conditions on water transport characteristics of equine spermatozoa

Recently, two-way oil/water separation materials bearing both “water-removing” and “oil-removing” functions are of great interest for treating environmental water pollution. Despite having switchable surface wettability, these materials are generally designed to possess superhydrophilicity in air, which, standing on the viewpoint of thermodynamics, is unstable and easy to lose the superwetting property. Concerning the full exploitation of sustainable biomass resources, herein, we use soy protein and ramie fiber to fabricate a cross-linked biocomposite whose amphiphilicity can be tuned by introducing a low surface-energy agent, octadecylamine. The resultant composite can be used as a coating for stainless steel meshes, preparing stably hydrophobic surface in air as well as achieving dual superlyophobicity under liquid that is required for efficiently separating light and heavy oils from water. Furthermore, a high separation efficiency is acquired for both light oil/water and heavy oil/water mixtures during cyclic usage. Notably, the fully bio-based coating displays high resistance against mechanical abrasion and harsh chemical corrosions (acid, alkaline, and salt) without losing high separation efficiency, indicating the potential application of such material in oily wastewater treatment.