Explore the vast range of titles available.

Polytetrafluoroethylene (PTFE), commercially known as Teflon, is a fluoropolymer with a structure containing (CF2–CF2)n. It has high resistance to acids, alkalis and corrosive chemicals. PTFE is hydrophobic in nature with a water contact angle of 140°. Being hydrophobic in nature is a knotty problem, particularly in electrical applications, as it may lead to short circuits and result in reducing the lifetime of electrical equipment. Herein we describe the surface modification of PTFE from hydrophobic to hydrophilic without altering its bulk property. The surface hydrophilicity is achieved by two different techniques, viz., polymer coating (aquivion and nafion) and plasma treatment. Several characterization techniques including FTIR, Raman, XPS, WCA and SEM were used to analyze the surface of PTFE. It was found that 5% of the polymer solution and N2 plasma treatment for 2 min can produce huge differences in the surface property, as evidenced by the reduction in water contact angle from 140° (neat Teflon) to 80° (surface-modified Teflon). The surface morphology of neat PTFE is completely changed and collapsed as evidenced by the SEM images. The FTIR, Raman and XPS analyses confirm the presence of additional hydrophilic functional groups after the polymer coating and plasma treatment. Hence, this method represents a unique approach to modifying the surface property of Teflon, while maintaining its bulk property.

Laser texturing enables site-selective tailoring of wetting characteristics of metallic surfaces, converting the surfaces into hydrophilic or hydrophobic ones. In this study, selective wettability transition of 6061 aluminum alloy (Al 6061) surface is demonstrated by using a nanosecond fiber laser. The conversion of initial wettability of pristine Al 6061 into a near-superhydrophobic surface is achieved through laser irradiation of an Al 6061 plate and the following low-temperature thermal annealing. The wettability change is studied by measuring the water contact angle, and a significant increase in the angle (approximately, from 63.9° of pristine Al 6061 to 146.8°) is observed. Furthermore, the laser-textured hydrophobic surface is transformed into a hydrophilic surface by irradiating the surface again with the laser beam, resulting in superwetting ability. These wettability transitions are site-selectively obtained by exploiting the capability of direct laser writing, showcasing a promising potential in various applications.

This study aims to investigate and compare the behavior of droplets of different volumes on hydrophilic and superhydrophobic surfaces (SHSs) under the effect of air shear flow. The results reveal that the effect of droplet volume on wetting length in the case of a hydrophilic surface is different from that in the case of SHS. On hydrophilic surfaces, droplets with larger volumes exhibit greater wetting length and adhesion, whereas on SHSs, these parameters are similar regardless of droplet volume. Additionally, airflow velocity is one of the critical factors for shear-driven droplet behavior on SHS. At an airspeed of 5 m/s, droplets slide on the SHS; however, they roll on the surface at an airspeed of 15 m/s.

Droplet spreading and transport phenomenon is ubiquitous and has been studied by engineered surfaces with a variety of topographic features. To obtain a directional bias in dynamic wetting, hydrophobic surfaces with a geometrical asymmetry are generally used, attributing the directionality to one-sided pinning. Although the pinning may be useful for directional wetting, it usually limits the droplet mobility, especially for small volumes and over wettable surfaces. Here, we demonstrate a pinning-less approach to rapidly transport millimeter sized droplets on a partially wetting surface. Placing droplets on an asymmetrically structured surfaces with micron-scale roughness and applying symmetric horizontal vibration, they travel rapidly in one direction without pinning. The key, here, is to generate capillary-driven rapid contact-line motion within the time-scale of period of vibration. At the right regime where a friction factor local at the contact line dominates the rapid capillary motion, the asymmetric surface geometry can induce smooth and continuous contact-line movement back and forth at different speed, realizing directional motion of droplets even with small volumes over the wettable surface. We found that the translational speed is selective and strongly dependent on the droplet volume, oscillation frequency, and surface pattern properties, and thus droplets with a specific volume can be efficiently sorted out.

When changing surface wettability and nanostructure size, condensation behavior displays distinct features. In this work, we investigated evaporation on a flat hydrophilic surface and condensation on both hydrophilic and hydrophobic nanostructured surfaces at the nanoscale using molecular dynamics simulations. The simulation results on hydrophilic surfaces indicated that larger groove widths and heights produced more liquid argon atoms, a quicker temperature response, and slower potential energy decline. These three characteristics closely relate to condensation areas or rates, which are determined by groove width and height. For condensation heat transfer, when the groove width was small, the change of groove height had little effect, while change of groove height caused a significant variation in the heat flux with a large groove width. When the cold wall was hydrophobic, the groove height became a significant impact factor, which caused no vapor atoms to condense in the groove with a larger height. The potential energy decreased with the increase of the groove height, which demonstrates a completely opposing trend when compared with hydrophilic surfaces.

An effective antimicrobial packaging or food contact surface should be able to kill or inhibit micro-organisms that cause food-borne illnesses. Setting up such systems, by nisin adsorption on hydrophilic and hydrophobic surfaces, is still a matter of debate. For this purpose, nisin was adsorbed on two types of low-density polyethylene: the hydrophobic native film and the hydrophilic acrylic acid-treated surface. The antibacterial activity was compared for those two films and it was highly dependent on the nature of the surface and the nisin-adsorbed amount. The hydrophilic surfaces presented higher antibacterial activity and higher amount of nisin than the hydrophobic surfaces. The effectiveness of the activated surfaces was assessed against Listeria innocua and the food pathogens Listeria monocytogenes, Bacillus cereus, and Staphylococcus aureus. S. aureus was more sensitive than the three other test bacteria toward both nisin-functionalized films. Simulation tests to mimic refrigerated temperature showed that the films were effective at 20 and 4 °C with no significant difference between the two temperatures after 30 min of exposure to culture media.

Fouling is a ubiquitous and longstanding challenge that causes both economic and environmental problems, especially for underwater detection equipment, as fouling directly limits the normal services and functions of such equipment. Therefore, it is necessary to develop coatings with high transparency and good antifouling performance. Herein, a novel zwitterion compound was synthesized, and an antifouling coating with excellent comprehensive properties was prepared by integrating 3-[[3-(triethoxysilyl)-propyl] amino] propane-1-sulfonic acid (TPAPS) into polyvinyl butyral (PVB) polymer, which possesses excellent mechanical properties and transparency. The physical and chemical, mechanical, and antifouling properties, and the light transmittance of the coating were characterized by the SEM, FT-IR, XPS, UV-VIS. The results show that the coating had good mechanical properties and adhesion to the substrate, and the strong hydration ability of TPAPS endowed the coating with excellent resistance to oil stains and biofouling. More importantly, the structure of the coating was homogenous and its surface roughness was very little, which imparted the coating with high transmittance. This research provides a facile approach for synthesizing high-transparency materials with excellent antifouling and mechanical properties.

In this study, we observed the Geyser phenomenon that occurs in a small-diameter two-phase closed thermosyphon (confinement number of 0.245). This phenomenon interferes with the natural circulation of the internal working fluid and increases the thermal resistance of the system. This study attempts to improve the thermal performance of the system using cellulose nanofiber as the working fluid and hydrophilic surface modification at the inner surface of the evaporator section. As a result, the total thermal resistance showed average reduction rates of 47.51%, 36.69%, and 22.56% at filling ratios of 0.25, 0.5, and 0.75, respectively.

In this study, polyelectrolyte multilayers were fabricated on a polystyrene (PS) plate using a Layer-by-Layer (LbL) self-assembly technique. The resulting functional platform showed improved performance compared with conventional enzyme-linked immunosorbent assay (ELISA) systems. Poly(diallyldimethylammonium chloride) (PDDA) and poly(acrylic acid) (PAA) were used as cationic and anionic polyelectrolytes. On the negatively-charged (PDDA/PAA)3 polyelectrolyte multilayers the hydrophilic PAA surface could efficiently decrease the magnitude of the noise signal, by inhibiting nonspecific adsorption even without blocking reagent adsorption. Moreover, the (PDDA/PAA)3 substrate covalently immobilized the primary antibody, greatly increasing the amount of primary antibody adsorption and enhancing the specific detection signal compared with a conventional PS plate. The calibration curve of the (PDDA/PAA)3 substrate showed a wide linear range, for concentrations from 0.033 to 33 nM, a large specific signal change, and a detection limit of 33 pM, even though the conventional blocking reagent adsorption step was omitted. The (PDDA/PAA)3 substrate provided a high-performance ELISA system with a simple fabrication process and high sensitivity; the system presented here shows potential for a variety of immunosensor applications.

A simple method is presented for the continuous generation of carbon nanotube forests stably anchored on stainless-steel surfaces using a reactive-roll-to-roll (RR2R) configuration. No addition of catalyst nanoparticles is required for the CNT-forest generation; the stainless-steel substrate itself is tuned to generate the catalytic growth sites. The process enables very large surfaces covered with CNT forests to have individual CNT roots anchored to the metallic ground through primary bonds. Fog water harvesting is demonstrated and tested as one potential application using long CNT-covered wires. The RR2R is performed in the gas phase; no solution processing of CNT suspensions is used, contrary to usual R2R CNT-based technologies. Full or partial CNT-forest coverage provides tuning of the ratio and shape of hydrophobic and hydrophilic zones on the surface. This enables the optimization of fog water harvesters for droplet capture through the hydrophobic CNT forest and water removal from the hydrophilic SS surface. Water recovery tests using small harp-type harvesters with CNT-forest generate water capture of up to 2.2 g/cm2·h under ultrasound-generated fog flow. The strong CNT root anchoring on the stainless-steel surfaces provides opportunities for (i) robustness and easy transport of the composite structure and (ii) chemical functionalization and/or nanoparticle decoration of the structures, and it opens the road for a series of applications on large-scale surfaces, including fog harvesting.