The controlled texturing of surfaces at the micro‐ and nanoscales is a powerful method for tailoring how materials interact with liquids, electromagnetic waves, or biological tissues. The increasing ...scientific and technological interest in advanced fibers and fabrics has triggered a strong motivation for leveraging the use of textures on fiber surfaces. Thus far however, fiber‐processing techniques have exhibited an inherent limitation due to the smoothing out of surface textures by polymer reflow, restricting achievable feature sizes. In this article, a theoretical framework is established from which a strategy is developed to reduce the surface tension of the textured polymer, thus drastically slowing down thermal reflow. With this approach the fabrication of potentially kilometers‐long polymer fibers with controlled hierarchical surface textures of unprecedented complexity and with feature sizes down to a few hundreds of nanometers is demonstrated, two orders of magnitude below current configurations. Using such fibers as molds, 3D microchannels are also fabricated with textured inner surfaces within soft polymers such as poly(dimethylsiloxane), at dimensions and a degree of simplicity impossible to reach with current techniques. This strategy for the texturing of high curvature surfaces opens novel opportunities in bioengineering, regenerative scaffolds, microfluidics, and smart textiles.
A novel approach for the simple fabrication of fibers and microchannels with controlled sub‐micrometer surface textures is demonstrated. It is based on surface tension engineering during thermal drawing. This enables to tailor a variety of surface properties, from optical to the influence on the growth of biological cells, for advanced fibers and textiles.
Stability of functionalized surfaces is an often-neglected topic in phase-change heat transfer research. Here, we examine the chemical and morphological changes of textured surfaces on the molecular ...and atomic level after the critical heat flux incipience during saturated pool-boiling of water. SEM imaging, EDS, AES and XPS analyses are used to examine the surface changes. Copper samples were laser textured via ablation using a nanosecond fiber laser under air or argon atmosphere. Multiscale microcavities, which serve as preferential nucleation sites, were produced on the samples, which exhibited significantly enhanced heat transfer performance in pool-boiling tests. Repeated formation of a vapor film and accompanying temperatures of up to 320 °C during the tests resulted in changes of the surface chemistry and nanomorphology. It was determined that Cu (II) oxide and hydroxide transform into Cu (I) oxide and Cu metal as a result of repeated low-temperature annealing of the surface when a vapor film is formed during the transition towards film boiling. This additionally causes a wettability transition of the functionalized surfaces from hydrophilic towards hydrophobic. Both effects importantly influence the solid-liquid-vapor interface during phase-change heat transfer. Overall, surfaces functionalized via laser texturing exhibited significantly enhanced stability and boiling heat transfer performance.
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•Copper surfaces are modified using nanosecond laser-texturing•Pool boiling heat transfer on textured surfaces is significantly enhanced•A shift in boiling curves after the first CHF incipience is observed and investigated•Surface chemical composition is analyzed and correlated with boiling behavior•Conversion of CuO and Cu(OH)2 into Cu2O and Cu as a result of CHF onset is detected
•Cavity- and spear-type TiO2 nanostructures are prepared by hydrothermal treatment.•Nucleation-promoting cavity morphology is superior to spear-like microstructure.•Hydrophobic surface with ...microcavities (CTH) provides HTC enhancement of over 200%.•High nucleation site density on CHT surface narrows surface temperature distribution.•ONB at 2.5 K and Db of 0.55 mm are observed on hydrophobic microcavity surface.
Surface engineering aimed at tuning the wettability and morphology of the boiling surface is a facile approach to moderate and enhance the nucleate boiling process. Key issues include control over the active nucleation site density, bubble departure frequency and liquid replenishment of active nucleation sites while simultaneously reducing the bubble nucleation temperature. In this study, we fabricated spear-type (ST) and cavity-type (CT) TiO2 nanostructures on 25 μm titanium foils via hydrothermal etching in an alkaline solution. High-speed IR and video cameras were used to detect local phenomena in terms of temperature and heat flux fluctuations and observe the bubble dynamics during saturated pool boiling of water. Intrinsically hydrophilic ST and CT surfaces provided a moderate overall enhancement of the heat transfer coefficient compared to an untreated surface due to increased nucleation site density and bubble frequency. The CT surface also decreased the bubble nucleation temperature due to effective vapor-entrapping and nucleation-promoting cavities. In a further step, both surfaces were hydrophobized through chemical vapor deposition of a fluorinated silane to tailor the wettability of the surface into a superhydrophobic state. This further reduced the average surface superheat by at least 40%, while the nucleation frequencies exceeded 200 Hz on the hydrophobized CT surface. In comparison with the untreated reference surface, the heat transfer coefficient on hydrophobized ST and CT surfaces was enhanced by 89% and 237% at 100 kW m−2, respectively. Moreover, the full width at half maximum (FWHM) value of the surface temperature distribution was reduced by 73% and 95% at the same heat flux, respectively. The study confirms that hydrophobic surface treatment can significantly enhance the nucleate boiling process when combined with an appropriate surface structure. Despite the affinity between the vapor and the hydrophobic layer, the cavity-type and spear-type TiO2 structures are able to maintain active nucleation sites well-separated, which prevents the undesirable vapor spreading that possibly leads to an early onset of critical heat flux.
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Candida auris is an emerging pathogenic fungus implicated in healthcare-associated outbreaks and causes bloodstream infections associated with high mortality rates. Biofilm formation represents one ...of the major pathogenetic traits associated with this microorganism. Unlike most other Candida species, C. auris has the ability to survive for weeks on different surfaces. Therefore, there is an urgent need to develop new effective control strategies to combat the threat of C. auris. Advances in nanotechnologies have emerged that carry significant potential impact against Candida biofilms. We obtained pure round silver nanoparticles (AgNPs) (1 to 3 nm in diameter) using a microwave-assisted synthetic approach. When tested against C. auris, our results indicated a potent inhibitory activity both on biofilm formation (half maximal inhibitory concentration (IC50) of 0.06 ppm) and against preformed biofilms (IC50 of 0.48 ppm). Scanning electron microscopy images of AgNP-treated biofilms showed cell wall damage mostly by disruption and distortion of the outer surface of the fungal cell wall. In subsequent experiments AgNPs were used to functionalize medical and environmental surfaces. Silicone elastomers functionalized with AgNPs demonstrated biofilm inhibition (>50%) at relatively low concentrations (2.3 to 0.28 ppm). Bandage dressings loaded with AgNPs inhibited growth of C. auris biofilms by more than 80% (2.3 to 0.017 ppm). Also, to demonstrate long-lasting protection, dressings loaded with AgNPs (0.036 ppm) were washed thoroughly with phosphate-buffered saline, maintaining protection against the C. auris growth from cycles 1 to 3 (>80% inhibition) and from cycles 4 to 6 (>50% inhibition). Our results demonstrate the dose-dependent activity of AgNPs against biofilms formed by C. auris on both medical (silicone elastomer) and environmental (bandage fibers) surfaces. The AgNPs-functionalized fibers retain the fungicidal effect even after repeated thorough washes. Overall these results point to the utility of silver nanoparticles to prevent and control infections caused by this emerging pathogenic fungus.
•Using femtosecond laser surface processing to functionalize Aluminum-6061 surfaces.•Fabricated 116 Al samples with various surface morphologies.•Measured directional and total hemispherical ...emissivity of all samples.•Developed an emissivity prediction model using artificial intelligence techniques.•High-accuracy emissivity prediction capabilities based on surface characteristics.
Tuning surface emissivity has been of great interest in thermal radiation applications, such as thermophotovoltaics and passive radiative cooling. As a low-cost and scalable technique for manufacturing surfaces with desired emissivities, femtosecond laser surface processing (FLSP) has recently drawn enormous attention. Despite the versatility offered by FLSP, there is a knowledge gap in accurately predicting the outcome emissivity prior to fabrication. In this work, we demonstrate the immense advantage of employing artificial intelligence (AI) techniques to predict the emissivity of complex surfaces. For this aim, we used FLSP to fabricate 116 different aluminum samples. A comprehensive dataset was established by collecting surface characteristics, laser operating parameters, and the measured emissivities for all samples. We demonstrate the successful application of AI in two distinct scenarios: (1) effective emissivity classification solely based on 3D surface morphology images, and (2) emissivity prediction based on surface characteristics and FLSP parameters. These findings open new pathways towards extended implementation of AI to predict various surface properties in functionalized samples or extract the required fabrication parameters via reverse engineering.
Modulating the immune system using engineered materials is an emerging strategy to combat bacterial infections. Bacteria adopt immune evasion strategies to ensure their survival, ultimately leading ...to persistence and recurrence of infections. With a rise in antimicrobial resistance and a decrease in antibiotic efficacy, host-directed therapies using immunomodulatory biomaterials are a promising approach to infection management. Here, we review biomaterials developed to modulate the immune system, with an emphasis on innate immunity. We specifically highlight the recent implementation of functionalized surfaces for immunomodulation, including metal ion releasing coatings, stimuli-responsive polymeric coatings, and interleukin releasing surfaces. We also describe immunomodulatory nanoparticles, including lipid-based nanoparticles, biomimetic nanoparticles, and inorganic nanocarriers. Lastly, we explore immunomodulatory hydrogels used primarily for the treatment of wound infections. These approaches offer new strategies for treating bacterial infections and enhancing existing antimicrobial approaches, all while avoiding complications associated with antimicrobial resistance.
The chemical constitution of functionalized supports is an important parameter that determines their performance in a broad range of applications, e.g. for immobilization of biomolecules. Supports ...with amino functionalized surfaces are also often used for DNA microarray experiments. However, spectral data which have been reported for surfaces with amino functionalities suffer from some inconsistencies. In this article a detailed XPS (X-ray photoelectron spectroscopy) and NEXAFS (Near edge X-ray absorption fine structure) database for amino functionalized surfaces is presented. Amino-terminated surfaces prepared from aliphatic and aromatic aminosilanes or aminothiols and a field sample are considered. Effects of aging in air and damage by radiation are addressed as well.
We present a mechanistic study on the formation and dynamic changes of a ligand‐based heterogeneous Pd catalyst for chemoselective hydrogenation of α,β‐unsaturated aldehyde acrolein. Deposition of ...allyl cyanide as a precursor of a ligand layer renders Pd highly active and close to 100 % selective toward propenol formation by promoting acrolein adsorption in a desired configuration via the C=O end. Employing a combination of real‐space microscopic and in‐operando spectroscopic surface‐sensitive techniques, we show that an ordered active ligand layer is formed under operational conditions, consisting of stable N‐butylimine species. In a competing process, unstable amine species evolve on the surface, which desorb in the course of the reaction. Obtained atomistic‐level insights into the formation and dynamic evolution of the active ligand layer under operational conditions provide important input required for controlling chemoselectivity by purposeful surface functionalization.
We present a mechanistic study on the formation and dynamic changes of a ligand‐based heterogeneous Pd catalyst for chemoselective hydrogenation of α,β‐unsaturated aldehyde acrolein. Deposition of allyl cyanide as a precursor of a ligand layer renders Pd highly active and close to 100 % selective toward propenol formation by promoting acrolein adsorption in a desired configuration via the C=O end.
Epoxy‐rich carbon‐based composites are well recognized materials in industries owing to their good mechanical properties and thermal stability. Here, dielectric properties of composites based on ...bisphenol‐A‐epoxy resin loaded with 5, 6, 10, and 15 wt% of graphite flakes (GF) have been studied. The frequency and temperature dependence of the dielectric permittivity, dielectric loss, and ac conductivity have been examined in temperature (−103 to 97°C) and frequency (20 Hz–200 kHz) range. Influence of the filler surface chemistry have been studied for composites loaded with 5 wt% GF obtained: (i) under wet milling, without or with adding Triton‐100x as a surfactant, or (ii) under dry milling in the presence of KOH. The composite made of epoxy loaded with 5 wt% exfoliated expanded graphite flakes (EEG), was also prepared. The surface treatment with KOH notably increased dielectric constant of the composite, keeping low dielectric loss, while treatment with Triton‐100x significantly increased tanδ. The composite loaded with exfoliated expanded graphite shows higher ac conductivity than those obtained with flaky graphite, GF. Possibility to change dielectric properties of the composites without changing the loading content can be used as an approach in tailoring one with desired dielectric properties.
The frequency and temperature dependence of the dielectric properties have been examined. The composites with different weight fractions of graphite flakes (GF) were prepared. Pure epoxy (without fillers), as well as composites: GF‐Tr100x, GF‐KOH and exfoliated expanded graphite flakes (EEG) were examined.
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•The bonding strength of the PA6/GF-Al joint was promoted to 37.8 MPa by the silane.•Even at 90 °C, the bonding strength of PA6/GF-Al joint was about 60 % of that at 20 °C.•After ...annealing, the bonding strength of the PA6/GF-Al joint was improved by 23.2%
It is of great practical importance to efficiently prepare lightweight and high-strength polymer-metal composite joints for energy conservation and pollution reduction. In this study, the ultra-high strength polyamide 6 (PA6)-aluminum alloy (Al) composite joints were rapidly prepared by injection molding, where the Al surface was treated by the sandblasting and the reactive epoxide silane (γ-(2,3-epoxypropoxy) propytrimethoxysilane, denoted as γ-epoxysilane). This study showed that the bonding strength of the composite joints could be increased by 182 % to 37.8 MPa when the Al surface was treated with 10 wt% γ-epoxysilane. Such excellent performance was retainable at elevated temperatures, still reaching 22.5 MPa at 90 °C, which is about 60 % of that at room temperature. Annealing treatment can further elevate the bonding strength to 46.6 MPa, which is among the highest for PA6-Al composite joints. Reactive silane-induced functionalization of the Al surface and failure mechanism of the composite joint was confirmed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). This study demonstrates a facile method to prepare ultra-high strength PA6-Al composite joints, which can hopefully spur new ideas for the development of lightweight engineering components in the future.
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