Browsing by Subject "Wettability"

Now showing 1 - 9 of 9

Open Access
Biomimicry of multifunctional nanostructures in the neck feathers of mallard (Anas platyrhynchos L.) drakes
(Nature Publishing Group, 2014-04-22) Khudiyev, T.; Dogan, T.; Bayındır, Mehmet
Biological systems serve as fundamental sources of inspiration for the development of artificially colored devices, and their investigation provides a great number of photonic design opportunities. While several successful biomimetic designs have been detailed in the literature, conventional fabrication techniques nonetheless remain inferior to their natural counterparts in complexity, ease of production and material economy. Here, we investigate the iridescent neck feathers of Anas platyrhynchos drakes, show that they feature an unusual arrangement of two-dimensional (2D) photonic crystals and further exhibit a superhydrophobic surface, and mimic this multifunctional structure using a nanostructure composite fabricated by a recently developed top-down iterative size reduction method, which avoids the above-mentioned fabrication challenges, provides macroscale control and enhances hydrophobicity through the surface structure. Our 2D solid core photonic crystal fibres strongly resemble drake neck plumage in structure and fully polymeric material composition, and can be produced in wide array of colors by minor alterations during the size reduction process.
Open Access
Effects of thermoplastic coating on interfacial interactions in advanced engineering composites for aerospace applications
(2023-05-03) Yavuz, Zelal; Khaligh, Aisan; Öz, Y.; Tuncel, Dönüş
Delamination due to an inferior adhesion between reinforcement material and matrix in carbon fiber-reinforced thermoplastic (CFRTP) composites is a crucial problem to be solved. To this end, this study aims to overcome poor wettability between reinforcing phase, i.e., carbon fiber (CF), and thermoplastic matrix, i.e., polyetherether ketone (PEEK). Herein, CF’s surface was tailored by application of different polymeric sizing agents which have different chemical structures. Morphology and topology analyses were performed by Scanning Electron Microscope and 3D laser scanning, respectively. Later, a variety of wettability results were obtained by the sessile drop method used in Contact Angle (CA) measurements for CFs throughout application of each sizing agent applied by dip coating. Sizing materials were designed such that the chemical structure of CF’s surface could exhibit compatibility with the matrix itself. Consequently, complete wettability (CA: 0°) was achieved for CFs sized by HPEEK (CF/hydroxylated PEEK (HPEEK)) and the surface free energy (SFE) of CF was enhanced from 5.43 to 72.8 mJ/m2 while the SFE of the PEEK matrix is 40.1 mJ/m2. Moreover, sizing by HPEEK improved the average surface roughness of CF by 32% which enables optimized adhesion. Afterward, repetitive tensile tests were carried out to observe effects of improved interfacial interlocking on the mechanical properties of the final CFRTP composite. Stress–strain curves revealed that the tensile strength of CFRTP improved from 473 to 508 MPa through the sizing of CF by HPEEK whereas pristine PEEK has a much smaller tensile strength (98 MPa) than the aforementioned CF-reinforced composites.
Open Access
In vitro biocompatibility of plasma-aided surface-modified 316L stainless steel for intracoronary stents
(Institute of Physics Publishing, 2010) Bayram, C.; Mizrak, A.K.; Aktürk, S.; Kurşaklioǧlu H.; Iyisoy, A.; Ifran, A.; Denkbaş, E.B.
316L-type stainless steel is a raw material mostly used for manufacturing metallic coronary stents. The purpose of this study was to examine the chemical, wettability, cytotoxic and haemocompatibility properties of 316L stainless steel stents which were modified by plasma polymerization. Six different polymeric compounds, polyethylene glycol, 2-hydroxyethyl methacrylate, ethylenediamine, acrylic acid, hexamethyldisilane and hexamethyldisiloxane, were used in a radio frequency glow discharge plasma polymerization system. As a model antiproliferative drug, mitomycin-C was chosen for covalent coupling onto the stent surface. Modified SS 316L stents were characterized by water contact angle measurements (goniometer) and x-ray photoelectron spectroscopy. C1s binding energies showed a good correlation with the literature. Haemocompatibility tests of coated SS 316L stents showed significant latency (t-test, p < 0.05) with respect to SS 316L and control groups in each test. © 2010 IOP Publishing Ltd.
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
Property enhancement in polypropylene ternary blend nanocomposites via a novel poly(ethylene oxide)-grafted polystyrene-block-poly(ethylene/butylene)-block-polystyrene toughener-compatibilizer system
(John Wiley and Sons, 2018) Tekay, E.; Başkır, S.; Nugay, N.; Nugay, T.; Ortaç, Bülend; Şen, S.
Synthesis and characterization of a novel toughener-compatibilizer for polypropylene (PP)-montmorillonite (MMT) nanocomposites were conducted to provide enhanced mechanical and thermal properties. Poly(ethylene oxide) (PEO) blocks were synthetically grafted onto maleic anhydride-grafted polystyrene-block-poly(ethylene/butylene)-block-polystyrene (SEBS-g-MA). Special attention was paid to emphasize the effect of PEO-grafted SEBS (SEBS-g-PEO) against SEBS-g-MA on morphology, static/dynamic mechanical properties and surface hydrophilicity of the resultant blends and nanocomposites. It was found that the silicate layers of neat MMT are well separated by PEO chains chemically bonded to nonpolar SEBS polymer without needing any organophilic modification of the clay as confirmed by X-ray diffraction and transmission electron microscopy analyses. From scanning electron microscopy analyses, elastomeric domains interacting with MMT layers via PEO sites were found to be distributed in the PP matrix with higher number and smaller sizes than the corresponding blend. As a benefit of PEO grafting, SEBS-g-PEO-containing nanocomposite exhibited not only higher toughness/impact strength but also increased creep recovery, as compared to corresponding SEBS-g-MA-containing nanocomposite and neat PP. The damping parameter of the same nanocomposite was also found to be high in a broad range of temperatures as another advantage of the SEBS-g-PEO toughener-compatibilizer. The water contact angles of the blends and nanocomposites were found to be lower than that of neat hydrophobic PP which is desirable for finishing processes such as dyeing and coating.
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
Time-related wettability characteristic of acrylic resin surfaces treated by glow discharge
(Elsevier, 1999-12) Özden, N.; Akaltan, F.; Süzer, Şefik; Akovali, G.
STATEMENT OF PROBLEM: Adhesion and cohesion have important roles in denture retention, and attempts have been made to improve the wettability of the acrylic resin material by surface treatments. PURPOSE: This study examined the initial and subsequent wettability of an acrylic resin denture base material treated under air or argon plasma atmosphere before and after exposure to air or distilled water. MATERIAL AND METHODS: Acrylic resin specimens were treated with plasma under air or argon atmosphere and were either exposed to air or distilled water for up to 60 days. Wettability characteristics of the acrylic resin specimens were determined by contact-angle measurements after 2 hours and after 60 days. Surface composition of the specimens also was analyzed with x-ray photoelectron spectroscopic (XPS) measurements. RESULTS: Statistically significant difference was found between control and each of the plasma treatment groups (P <.05). Although the storage condition and storage period caused statistically significant difference on contact angle values (P <.05), atmosphere type did not have any effect on the results (P >.05). XPS spectra of the plasma-treated specimens differed from control specimens only in the O1s region with a narrower and more intense peak that could be assigned to -COH groups. During 60 days of exposure, the O/C atomic ratios decreased within the first 2 weeks but settled to 0.40 and 0. 32 up to 60 days compared with 0.26 for untreated control specimens. CONCLUSION: Glow discharge plasma altered the surfaces of the acrylic resin and increased thc wettability as shown both by XPS and contact-angle measurements, and plasma treatment seemed to offer a durable (at least up to 60 days) wettability.
Open Access
Tribological transfer of polytetrafluoroethylene onto silicon oxide and polymer surfaces
(2015) Uçar, Ahmet
The main objective of this study is to understand the nature of tribological transfer of polytetrafluoroethylene (PTFE) onto counter thermally-oxidized silicon, polystyrene (PS), polyvinylchloride (PVC) and poly(methyl methacrylate) (PMMA) surfaces, as well as investigating the possible formation of chemical bonds arising at polymer-semiconductor and polymer-polymer interfaces, while or after tribological material transfer. Tuning the wettability characteristics of PTFE transferred surfaces is also aimed. Within these purposes, first part of the research focused on the preparation of silicon oxide and polymer substrates and the utilization of tribological transfer method in order to form desired PTFE patterns on these surfaces. The realization of this transfer was provided by the design of a simple rig to bring about a friction between the surfaces via sliding a piece of PTFE on silicon oxide and polymer specimens. In order to monitor the tribological interaction in a gradual manner as a function of increasing contact force, a very mild inclination (∼0.5◦) along the sliding motion was also employed in some specimens mounted on the inclined aluminum supports. In addition, procedures used to explore the stability of specimens against time and washing / cleaning practices using various organic solvents and boiling water are given within this part. In the second part of the work, characterization of PTFE-contacted silicon oxide and polymer surfaces was carried out using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy and Atomic Force Microscopy (AFM). XPS results were obtained, which revealed that PTFE was faithfully transferred onto the silicon oxide and polymer surfaces upon even at the slightest contact; SEM and AFM images reinforced that stable morphological changes could be imparted onto the counter silicon oxide surfaces. In experiments where the inclined aluminum supports were used to create gradual tribological transfer of PTFE onto counter silicon oxide surfaces, use of relation between the increase in contact force with respect to transferred amount of PTFE helped us to estimate the minimum apparent contact pressure needed to realize the PTFE transfer, which was found to be about 5 kPa. Stability of the patterns imparted towards time and various chemical washing processes lead us to postulate that the interaction was most likely occurred with formation of chemical bonds. Contact angle measurements, which were carried out to monitor the wettability of the silicon oxide surface, showed that upon PTFE transfer the hydrophobicity of the SiO2 surface could be significantly enhanced, depending on the pattern sketched onto the surface. All of these findings show that tribological transfer of PTFE onto various counter surfaces is possible by a simple procedure, which has both academical and commercial importance.
Open Access
Understanding the plasmonic properties of dewetting formed Ag nanoparticles for large area solar cell applications
(Optical Society of American (OSA), 2013) Günendi, M.C.; Tanyeli I.; Akgüç G.B.; Bek, A.; Turan, R.; Gülseren O.
The effects of substrates with technological interest for solar cell industry are examined on the plasmonic properties of Ag nanoparticles fabricated by dewetting technique. Both surface matching (boundary element) and propagator (finite difference time domain) methods are used in numerical simulations to describe plasmonic properties and to interpret experimental data. The uncertainty on the locations of nanoparticles by the substrate in experiment is explained by the simulations of various Ag nanoparticle configurations. The change in plasmon resonance due to the location of nanoparticles with respect to the substrate, interactions among them, their shapes, and sizes as well as dielectric properties of substrate are discussed theoretically and implications of these for the experiment are deliberated. ©2013 Optical Society of America.