Browsing by Subject "Superhydrophobic"

Now showing 1 - 11 of 11

Open Access
Development of superhydrophobic electrospun fibrous membrane of polymers of intrinsic microporosity (PIM-2)
(Elsevier, 2018) Satılmış, Bekir; Uyar, Tamer
Polymers of intrinsic microporosity (PIMs) are increasingly recognized as a potential membrane material for adsorption and separation applications due to their permanent porosity and solution processability. PIM-2 can be produced using commercially available 5,5′,6,6′-Tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane and decafluorobiphenyl monomers in the powder form. It possesses considerable amount of fluorine in the polymer backbone and this feature could provide significant hydrophobicity to polymer. This research aims to investigate the fabrication of self-standing PIM-2 fibrous membranes by electrospinning method to introduce a useful material for adsorption applications. Electrospinning was performed using tetrachloroethane as a solvent and beadfree, uniform fibers were produced as confirmed by SEM imaging. Average fiber diameter was calculated as 5.5 ± 1.5 μm for a self-standing fibrous membrane of PIM-2. Structural characterization was conducted using FT-IR, NMR and XPS spectroscopies showing the purity of pristine powder and fibrous membrane of PIM-2. Thermal stability of PIM-2 fibrous membrane was investigated using TGA and it shows no discernible weight loss below 450 °C. The porosity of fibrous membrane was investigated by N2 adsorption/desorption measurements that indicates significant microporosity with ∼600 m2 g−1 BET surface area. In addition, the hydrophobicity of PIM-2 was tested by water contact angle measurements, showing 155 ± 6° WCA, indicating superhydrophobicity owing to rough surface and high fluorine content. Consequently, the combination of straightforward synthesis, solution processability, high thermal stability, high surface area, and superhydrophobicity makes PIM-2 a promising candidate for adsorption applications. Therefore, it was successfully employed in organic and oil adsorption. Fibrous membranes of PIM-2 has shown up to 2200 ± 100% and 1900 ± 100% weight gain after in contact with silicon oil and DMSO respectively. In addition, dense membrane of PIM-2 was prepared by solvent casting method and the uptake ability was compared with fibrous membrane showing that fibrous form is more convenient for liquid adsorption applications.
Open Access
Nano-structured organically modified silica thin films for functional surfaces
(2011) Bayındır, Mehmet; Yıldırım, Adem; Budunoglu, Hülya; Yaman, Mecit; Deniz, Hakan; Güler, Mustafa O.
We report a template-free sol-gel method for preparation of nanoporous ormosil thin films at ambient conditions. The thin films are coated to the surfaces by using colloidal suspensions of ormosil gels. Gels are synthesized by using a trifunctional organosilane monomer, methyltrimethoxysilane (MTMS), with a two-step acid base reaction. We prepared several ormosil thin films on glass, metal, plastic and paper surfaces with different functionalities like superhydrophobic, antireflective, antifogging and ice retarding properties, from gels prepared in different conditions. Also films on flexible substrates exhibits durable surface properties after several bending cycles. In addition, we also demonstrate that these thin films can be used for fluorescent sensing of explosives by doping them with fluorescent dyes.
Open Access
One-pot preparation of fluorinated mesoporous silica nanoparticles for liquid marble formation and superhydrophobic surfaces
(American Chemical Society, 2011) Yildirim, A.; Budunoglu, H.; Daglar, B.; Deniz, H.; Bayındır, Mehmet
One-pot synthesis of fluorinated mesoporous silica nanoparticles (FMSNs) is reported. Uniform mesoporous nanoparticles are prepared by condensation of tetraethyl orthosilicate (TEOS) and fluoroalkyl containing organotriethoxy silane monomers, respectively. The method enables selective deposition of fluorine atoms on the surface of the particles. FMSNs are used to prepare stable liquid marbles with water. An organo-modified silica sol is used with FMSNs to prepare mechanically stable superhydrophobic surfaces (water contact angle of 161 degrees). The mechanical stability of the surface is investigated with water dripping and adhesive tape tests. The prepared FMSNs are promising building blocks for robust, large-area, and multifunctional self-cleaning surfaces.
Open Access
Organically modified silica nanostructures based functional coatings for practical applications
(2015) Tuvshindorj, Urandelger
In the past decades, the fabrication of superhydrophobic surfaces have received considerable attention due to the variety of potential applications ranging from biology to industry. Although significant progress has been made in their fabrication and design, there is still need to solve some problems in real-life use of these coatings, such as low stability against external pressure, lack of long term robustness, challenges in presice control over the degree of wettability and the need for facile fabrication methods. In this context, this thesis seeks simple solutions for mentioned problems based on organically modified silica superhyrophobic coatings. First, we investigate the stability of the Cassie state of wetting in transparent superhydrophobic coatings by comparing a single-layer micro-porous coating with a double-layer micro/nanoporous coating. The stability of the Cassie state in coatings were investigated with droplet compression and evaporation experiments, where external pressures as high as a few thousand Pa are generated at the interface. A droplet on a microporous coating gradually transformed to the Wenzel state with increasing pressure. The resistance of the micro/nano-porous surfaces against Wenzel transition during the experiments were higher than microporous single-layer coating and even higher than leaves of Lotus; prevalent natural superhydrophobic surface. Then, we reported a facile method for the preparation hydrophilic patterns on the superhydrophobic ormosil surfaces. On the defined areas of the superhydrophobic ormosil coatings, wetted micropatterns were produced using Ultraviolet/Ozone (UV/O) treatment which modifies the surface chemistry from hydrophobic to hydrophilic without changing the surface morphology. The degree of wettability of the patterns can be precisely controlled depending on the UV/O exposure duration and extremely wetted spots with water contact angle (WCA) of nearly 0º can be obtained. The ormosil coatings and modified surfaces preserve their wettability for months at room conditions. Furthermore, we demonstrated selective and controlled adsorption of protein and adhesion of bacteria on the superhydrophilic patterns which could be potentially used for biological applications.
Open Access
Robust cassie state of wetting in transparent superhydrophobic coatings
(American Chemical Society, 2014) Tuvshindorj, U.; Yildirim, A.; Ozturk, F. E.; Bayındır, Mehmet
This paper investigates the stability of the Cassie state of wetting in transparent superhydrophobic coatings by comparing a single-layer microporous coating with a double-layer micro/nanoporous coating. Increasing pressure resistance of superhydrophobic coatings is of interest for practical use because high external pressures may be exerted on surfaces during operation. The Cassie state stability against the external pressure of coatings was investigated by squeezing droplets sitting on surfaces with a hydrophobic plate. Droplets on the single-layer coating transformed to the Wenzel state and pinned to the surface after squeezing, whereas droplets on the double-layer micro/nanoporous coating preserved the Cassie state and rolled off the surface easily. In addition, the contact angle and contact-line diameter of water droplets during evaporation from surfaces were in situ investigated to further understand the stability of coatings against Wenzel transition. A droplet on a microporous coating gradually transformed to the Wenzel state and lost its spherical shape as the droplet volume decreased (i.e., the internal pressure of the droplet increased). The contact line of the droplet during evaporation remained almost unchanged. In contrast, a water droplet on a double-layer surface preserved its spherical shape even at the last stages of the evaporation process, where pressure differences as high as a few thousand pascals were generated. For this case, the droplet contact line retracted during evaporation and the droplet recovered the initial water contact angle. The demonstrated method for the preparation of robust transparent superhydrophobic coatings is promising for outdoor applications such as self-cleaning cover glasses for solar cells and nonwetting windows.
Open Access
Robust superhydrophobic fabrics by infusing structured polydimethylsiloxane films
(John Wiley & Sons, Inc., 2021-06-22) Celik, N.; Torun, I.; Ruzi, M.; Mustafa Serdar, Önses
Superhydrophobic coatings have large application potential in self-cleaning textiles. Low durability, high cost of fabrication, and environmental concerns over the usage of chemicals such as fluorocarbons limit the utilization of superhydrophobic coatings. This study reports a convenient and inexpensive approach to fabricate robust and fluorine-free superhydrophobic fabrics based on the transfer of structured polymer films and hydrophobic nanoparticles. In this approach, polydimethylsiloxane (PDMS) is infused between sheets of fabric and paper, followed by curing and removal of the paper. This process results in a fabric infused with PDMS whose structure is a negative replica of the paper surface. Then, hydrophobic nanoparticles are sprayed onto the structured PDMS side of the fabric. The infusion of PDMS and subsequent deposition of the hydrophobic nanoparticles enables strong bonding, as shown by the excellent solvent stability of the superhydrophobic fabric under ultrasonication. The proposed approach is universal in that it can be applied to almost any textiles, which upon coating, exhibited superhydrophobicity with a water contact angle of 172° and a sliding angle of 3°. Furthermore, the superhydrophobic fabric showed robust durability against water spray impact and mechanical bending where it can keep superhydrophobicity for at least 200 cycles of each test.
Open Access
Superhydrophobic and omnidirectional antireflective surfaces from nanostructured ormosil colloids
(American Chemical Society, 2013-02-13) Yildirim, A.; Khudiyev, T.; Daglar, B.; Budunoglu, H.; Okyay, Ali Kemal; Bayındır, Mehmet
A large-area superhydrophobic and omnidirectional antireflective nanostructured organically modified silica coating has been designed and prepared. The coating mimics the self-cleaning property of superhydrophobic lotus leaves and omnidirectional broad band antireflectivity of moth compound eyes, simultaneously. Water contact and sliding angles of the coating are around 160 and 10, respectively. Coating improves the transmittance of the glass substrate around 4%, when coated on a single side of a glass, in visible and near-infrared region at normal incidence angles. At oblique incidence angles (up to 60) improvement in transmission reaches to around 8%. In addition, coatings are mechanically stable against impact of water droplets from considerable heights. We believe that our inexpensive and durable multifunctional coatings are suitable for stepping out of the laboratory to practical outdoor applications.
Open Access
Superhydrophobic coatings for food packaging applications: A review
(Elsevier, 2022-06) Ruzi, M.; Celik, N.; Onses, M. Serdar
Food waste is a serious problem in our modern era, causing economic loss and exacerbating issues like hunger, environmental pollution, and water shortage. Residual food is one main culprit that can be easily eliminated by proper packaging. Advanced packaging techniques with self-cleaning and anti-fouling capabilities are critically important to tackle this issue. In this regard, superhydrophobic coatings are emerging as an innovative approach to address many critical issues in the food industry. Superhydrophobic coatings can prevent fouling and contamination of food packages. An additional capability is the minimization of food waste and improving consumer experience due to the easy sliding of food from the inner side of the package. In this article, we provide an overview of recent studies on the application of superhydrophobic coatings and surfaces for food packaging applications, with a focus on studies aimed at reducing residual food waste via superhydrophobic coatings prepared from edible, nontoxic, and ecofriendly materials.
Open Access
Superhydrophobic hexamethylene diisocyanate modified hydrolyzed polymers of ıntrinsic microporosity electrospun ultrafine fibrous membrane for the adsorption of organic compounds and oil/water separation
(American Chemical Society, 2018) Satılmış, Bekir; Uyar, Tamer
Polymers of intrinsic microporosity (PIMs) have gained significant research interest because of their successful applications in adsorption and separation. PIM-1 is the first and most studied member of this class because it shows specific interactions with some certain organic species. Chemical modification of PIM-1, which can be achieved by simply hydrolyzing the nitrile groups in the backbone, provides an advantage of tailoring its adsorption and separation performances. In this study, electrospinning of ultrafine fibers from hydrolyzed polymer of intrinsic microporosity (HPIM) and blends of hexamethylene diisocyanate (HMDI)/HPIM was achieved in several different ratios of HMDI/HPIM ranging from 1:9 to 1:1 (w/w). Bead-free and uniform fibers were obtained in the form of self-standing ultrafine fibrous membranes, which were then thermally treated at 150 °C to introduce chemical cross-linking between HMDI units and carbonyl groups of HPIM, resulting in HMDI-modified HPIM fibrous membranes (HMDI/HPIM-FMs). The solubility behavior has been altered by an introduced modification that makes membranes insoluble in all common organic solvents. Chemical cross-linking has been confirmed by using a Fourier transform infrared technique showing urethane linkage between HMDI and HPIM, and it was further supported by X-ray photoelectron microscopy and elemental analysis techniques that show a significant increase in the relative ratio of nitrogen in HMDI/HPIM-FMs compared to HPIM-FM. The average fiber diameters of fibrous membranes were found between 1.38 ± 0.29 and 0.96 ± 0.22 μm depending on the blend compositions and applied electrospinning parameters. Moreover, the water contact-angle value for HPIM-FM increased with the introduced HMDI modification from 140 ± 4° to 159 ± 7°, changing the nature of the membrane from hydrophobic to superhydrophobic. Consequently, HMDI/HPIM-FMs were successfully employed in oil/water separation due to the superhydrophobicity. In addition, the adsorption properties of HPIMFM and HMDI/HPIM-FMs were explored for common organic solvents. While both HPIM-FM and HMDI/HPIM-FMs show promising results, the structural stability of HMDI/HPIM-FMs in liquids was found to be more stable and reusable with respect to HPIM-FM. Hence, HMDI/HPIM-FMs are more favorable for organic adsorption and separation purposes from an aqueous system.
Open Access
Superhydrophobic, hybrid, electrospun cellulose acetate nanofibrous mats for oil/water separation by tailored surface modification
(American Chemical Society, 2016) Arslan, O.; Aytac Z.; Uyar, Tamer
Electrospun cellulose acetate nanofibers (CA-NF) have been modified with perfluoro alkoxysilanes (FS/CA-NF) for tailoring their chemical and physical features aiming oil-water separation purposes. Strikingly, hybrid FS/CA-NF showed that perfluoro groups are rigidly positioned on the outer surface of the nanofibers providing superhydrophobic characteristic with a water contact angle of ∼155°. Detailed analysis showed that hydrolysis/condensation reactions led to the modification of the acetylated β(1 → 4) linked d-glucose chains of CA transforming it into a superhydrophobic nanofibrous mat. Analytical data have revealed that CA-NF surfaces can be selectively controlled for fabricating the durable, robust and water resistant hybrid electrospun nanofibrous mat. The -OH groups available on the CA structure allowed the basic sol-gel reactions started by the reactive FS hybrid precursor system which can be monitored by spectroscopic analysis. Since alkoxysilane groups on the perfluoro silane compound are capable of reacting for condensation together with the CA, superhydrophobic nanofibrous mat is obtained via electrospinning. This structural modification led to the facile fabrication of the novel oil/water nanofibrous separator which functions effectively demonstrated by hexane/oil and water separation experiments. Perfluoro groups consequently modified the hydrophilic CA nanofibers into superhydrophobic character and therefore FS/CA-NF could be quite practical for future applications like water/oil separators, as well as self-cleaning or water resistant nanofibrous structures.
Open Access
Synthesis of silica-based nanomaterials and their applications in fluorescent, biological and chemical sensing
(2018-06) Beyazkılıç, Pınar
This thesis describes development of nanoparticle-based liquid sensors and coatings for droplet-based bioassays. Liquid sensors were produced from mesostructured (2-50 nm) hybrid silica nanoparticles. Detection of trace trinitrotoluene (TNT) and dopamine in aqueous phase was shown based on uorescence of nanoparticles. Silica nanoparticles were synthesized using a facile one-pot solgel method. Pyrene molecules were hybridized with hydrophobic parts of cetyltrimethylammonium micelles followed by silica growth around micelles. Nanoparticles showed good dispersibility and colloidal stability in water. Pyrene exhibited bright and highly stable emission. Pyrene emission exhibited a rapid, sensitive and visual uorescence quenching against TNT and dopamine. For droplet-based assays, robust superhydrophilic patterned superhydrophobic coatings were developed. Biomolecular adsorption and droplet mixing were shown on coatings which were prepared using sol-gel method followed by ultraviolet/ ozone (UV/O) treatment. Droplet-based biomolecular detection platforms were developed using superhydrophilic patterned superhydrophobic surfaces. Bene tting from con nement and evaporation-induced shrinkage of droplets on wetted patterns, sensitive glucose and DNA detection was demonstrated. Glucose was detected based on enhancement of polydopamine (PDA) emission by hydrogen peroxide (H2O2) produced in glucose oxidation reaction. Detection in evaporating droplets resulted with bright uorescence and high sensitivity for analyte molecules. This was due to droplet evaporation which concentrated molecules and increased reaction rates. Surfaces and nanoparticles developed in this thesis hold great potential for biological and chemical analysis with low sample volumes owing to their simple production, sensitive detection responses and versatility.