Fabrication of a Superhydrophobic Surface from a Smectic Liquid‐Crystal Defect Array

A novel fabrication method is developed for the preparation of superhydrophobic surfaces. The procedure uses focal conic structures of semi‐fluorinated smectic liquid crystals (LCs) whose periodic toric focal conic domains (TFCDs) are prepared on a surface modified substrate. Reactive ion etching (RIE) on the periodic TFCD surface leads to a superhydrophobic surface with a water contact angle of ～160° and a sliding angle of ～2° for a 10 µL water droplet. The results show that this phenomenon is due to the development of a dual‐scale surface roughness arising from the nanoscale protuberance caused by applying the RIE process to the top of the microscale TFCD arrays. The unique surface behavior is further verified by demonstrating that RIE on a flat lamellar liquid crystal film, in which the director is aligned parallel with surface, results in a relatively low hydrophobicity as compared to when periodic TFCDs are subjected to REI. The observations made in this publication suggest that a new approach exists for selecting potential candidates of superhydrophic surface formation based on spontaneous self‐assembly in smectic liquid‐crystalline materials.     

Fine‐Tuning of Superhydrophobicity Based on Monolayers of Well‐defined Raspberry Nanoparticles with Variable Dual‐roughness Size and Ratio

Superhydrophobic surfaces have been extensively investigated for self‐cleaning, low‐adhesion, anti‐corrosion or reduced‐drag applications. Roughness and its characteristics, i.e., morphology, overall roughness and individual feature size, is an essential factor for superhydrophobicity. Several experimental methods and theoretical models strived to predict how the surface wettability is affected by the surface roughness. However, due to the difficulty of making practical surfaces with well‐defined roughness profiles, only limited and arbitrary experimental studies focused on practical superhydrophobic films. Here, the roughness factors which determine the wetting properties of films are reported, based on monolayers of well‐defined raspberry silica‐silica nanoparticles, exhibiting a wide‐range and systematic variation of individual features sizes and ratios (large over small features). The advancing water contact angle does not depend on the feature size or ratio, while the contact angle hysteresis (CAH) is strongly dependent on both. The minimum size and size ratio to reach superhydrophobicity were determined. These new insights into the wetting of rough surfaces can be used to direct the design of practical superhydrophobic materials for advanced applications such as solar panels, microelectronics or microfluidic devices.     

Dual‐Mechanism Antimicrobial Polymer–ZnO Nanoparticle and Crystal Violet‐Encapsulated Silicone

The prevalence of healthcare‐associated infection caused by multidrug‐resistant bacteria is of critical concern worldwide. It is reported on the development of a bactericidal surface prepared by use of a simple, upscalable, two‐step dipping strategy to incorporate crystal violet and di(octyl)­phosphinic‐ acid‐capped zinc oxide nanoparticles into medical grade silicone, as a strategy to reduce the risk of infection. The material is characterized by UV–vis absorbance spectroscopy, X‐ray photoelectron spectroscopy (XPS), inductively coupled plasma‐optical emission spectroscopy (ICP‐OES) and transmission electron microscopy (TEM) and confirmed the incorporation of the ZnO nanoparticles in the polymer. The novel system proves to be a highly versatile bactericidal material when tested against both Staphylococcus aureus and Escherichia coli, key causative micro‐organisms for hospital‐acquired infection (HAI). Potent antimicrobial activity is noted under dark conditions, with a significant enhancement exhibits when the surfaces are illuminated with a standard hospital light source. This polymer has the potential to decrease the risk of HAI, by killing bacteria in contact with the surface.     

Self‐Healing Actuating Adhesive Based on Polyelectrolyte Multilayers

Creating actuators capable of mechanical motion in response to external stimuli is a key for design and preparation of smart materials. The lifetime of such materials is limited by their eventual wear. Here, self‐healable and adhesive actuating materials are demonstrated by taking advantage of the solvent responsive of weak polyelectrolyte multilayers consisting of branched poly(ethylenimine)/poly(acrylic acid) (BPEI/PAA). BPEI/PAA multilayers are dehydrated and contract upon contact with organic solvent and become sticky when wetted with water. By constructing an asymmetric heterostructure consisting of a responsive BPEI/PAA multilayer block and a nonresponsive component through either layer‐by‐layer assembly or the paste‐to‐curl process, smart films that actuate upon exposure to alcohol are realized. The curl degree, defined as degrees from horizontal that the actuated material reaches, can be as high as ≈228.9°. With evaporation of the ethanol, the curled film returns to its initial state, and water triggers fast self‐healing extends the actuator's lifetime. Meanwhile, the adhesive nature of the wet material allows it to be attached to various substrates for possible combination with hydrophobic functional surfaces and/or applications in biological environments. This self‐healable adhesive for controlled fast actuation represents a considerable advance in polyelectrolyte multilayers for design and fabrication of robust smart advanced materials.     

Surface Energy‐Controlled SERS Substrates for Molecular Concentration at Plasmonic Nanogaps

Positioning probe molecules at electromagnetic hot spots with nanometer precision is required to achieve highly sensitive and reproducible surface‐enhanced Raman spectroscopy (SERS) analysis. In this article, molecular positioning at plasmonic nanogaps is reported using a high aspect ratio (HAR) plasmonic nanopillar array with a controlled surface energy. A large‐area HAR plasmonic nanopillar array is generated using a nanolithography‐free simple process involving Ar plasma treatment applied to a smooth polymer surface and the subsequent evaporation of metal onto the polymer nanopillars. The surface energy can be precisely controlled through the selective removal of an adsorbed self‐assembled monolayer of low surface‐energy molecules prepared on the plasmonic nanopillars. This process can be used to tune the surface energy and provide a superhydrophobic surface with a water contact angle of 165.8° on the one hand or a hydrophilic surface with a water contact angle of 40.0° on the other. The highly tunable surface wettability is employed to systematically investigate the effects of the surface energy on the capillary‐force‐induced clustering among the HAR plasmonic nanopillars as well as on molecular concentration at the collapsed nanogaps present at the tops of the clustered nanopillars.     

Copper‐Based Nanostructured Coatings on Natural Cellulose: Nanocomposites Exhibiting Rapid and Efficient Inhibition of a Multi‐Drug Resistant Wound Pathogen,A. baumannii,and Mammalian Cell Biocompatibility In Vitro

This paper describes a layer‐by‐layer (LBL) electrostatic self‐assembly process for fabricating highly efficient antimicrobial nanocoatings on a natural cellulose substrate. The composite materials comprise a chemically modified cotton substrate and a layer of sub‐5 nm copper‐based nanoparticles. The LBL process involves a chemical preconditioning step to impart high negative surface charge on the cotton substrate for chelation controlled binding of cupric ions (Cu²⁺), followed by chemical reduction to yield nanostructured coatings on cotton fibers. These model wound dressings exhibit rapid and efficient killing of a multidrug resistant bacterial wound pathogen, A. baumannii, where an 8‐log reduction in bacterial growth can be achieved in as little as 10 min of contact. Comparative silver‐based nanocoated wound dressings–a more conventional antimicrobial composite material–exhibit much lower antimicrobial efficiencies; a 5‐log reduction in A. baumannii growth is possible after 24 h exposure times to silver nanoparticle‐coated cotton substrates. The copper nanoparticle–cotton composites described herein also resist leaching of copper species in the presence of buffer, and exhibit an order of magnitude higher killing efficiency using 20 times less total metal when compared to tests using soluble Cu²⁺. Together these data suggest that copper‐based nanoparticle‐coated cotton materials have facile antimicrobial properties in the presence of A. baumannii through a process that may be associated with contact killing, and not simply due to enhanced release of metal ion. The biocompatibility of these copper‐cotton composites toward embryonic fibroblast stem cells in vitro suggests their potential as a new paradigm in metal‐based wound care and combating pathogenic bacterial infections.     

Lubricant‐Infused Nanoparticulate Coatings Assembled by Layer‐by‐Layer Deposition

Omniphobic coatings are designed to repel a wide range of liquids without leaving stains on the surface. A practical coating should exhibit stable repellency, show no interference with color or transparency of the underlying substrate and, ideally, be deposited in a simple process on arbitrarily shaped surfaces. We use layer‐by‐layer (LbL) deposition of negatively charged silica nanoparticles and positively charged polyelectrolytes to create nanoscale surface structures that are further surface‐functionalized with fluorinated silanes and infiltrated with fluorinated oil, forming a smooth, highly repellent coating on surfaces of different materials and shapes. We show that four or more LbL cycles introduce sufficient surface roughness to effectively immobilize the lubricant into the nanoporous coating and provide a stable liquid interface that repels water, low‐surface‐tension liquids and complex fluids. The absence of hierarchical structures and the small size of the silica nanoparticles enables complete transparency of the coating, with light transmittance exceeding that of normal glass. The coating is mechanically robust, maintains its repellency after exposure to continuous flow for several days and prevents adsorption of streptavidin as a model protein. The LbL process is conceptually simple, of low cost, environmentally benign, scalable, automatable and therefore may present an efficient synthetic route to non‐fouling materials.     

One‐Pot Synthesis of Antimony‐Embedded Silicon Oxycarbide Materials for High‐Performance Sodium‐Ion Batteries

Sodium‐ion batteries have recently attracted intensive attention due to their natural abundance and low cost. Antimony is a desirable candidate for an anode material for sodium‐ion batteries due to its high theoretical capacity (660 mA h g^?1). However, the utilization of alloy‐based anodes is still limited by their inherent huge volume changes and sluggish kinetics. The Sb‐embedded silicon oxycarbide (SiOC) composites are simply synthesized via a one‐pot pyrolysis process at 900 °C without any additives or surfactants, taking advantage of the superior self‐dispersion properties of antimony acetate powders in silicone oil. The structural and morphological characterizations confirm that Sb nanoparticles are homogeneously embedded into the amorphous SiOC matrix. The composite materials exhibit an initial desodiation capacity of around 510 mA h g^?1 and maintained an excellent capacity retention above 97% after 250 cycles. The rate capability test reveals that the composites deliver capacity greater than 453 mA h g^?1, even at the high current density of 20 C rate, owing to the free‐carbon domain of SiOC material. The electrochemical and postmortem analyses confirm that the SiOC matrix with a uniform distribution of Sb nanoparticles provides the mechanical strength without degradation in conductive characteristics, suppressing the agglomeration of Sb particles during the electrochemical reaction.     

Interaction of Zoospores of the Green Alga Ulva with Bioinspired Micro‐ and Nanostructured Surfaces Prepared by Polyelectrolyte Layer‐by‐Layer Self‐Assembly

The interaction of spores of Ulva with bioinspired structured surfaces in the nanometer–micrometer size range is investigated using a series of coatings with systematically varying morphology and chemistry, which allows separation of the contributions of morphology and surface chemistry to settlement (attachment) and adhesion strength. Structured surfaces are prepared by layer‐by‐layer spray‐coating deposition of polyelectrolytes. By changing the pH during application of oppositely charged poly(acrylic acid) and polyethylenimine polyelectrolytes, the surface structures are systematically varied, which allows the influence of morphology on the biological response to be determined. In order to discriminate morphological from chemical effects, surfaces are chemically modified with poly(ethylene glycol) and tridecafluoroctyltriethoxysilane. This chemical modification changes the water contact angles while the influence of the morphology is retained. The lowest level of settlement is observed for structures of the order 2 µm. All surfaces are characterized with respect to their wettability, chemical composition, and morphological properties by contact angle measurement, X‐ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy.     

In Situ Self‐Assembled Polyoxotitanate Cages on Flexible Cellulosic Substrates: Multifunctional Coating for Hydrophobic,Antibacterial, and UV‐Blocking Applications

Surface coating is a powerful approach to fabricate multifunctional materials that are essential for numerous applications. However, to achieve such multifunctional coating with a facile single‐step procedure, especially on flexible substrates, is still a big challenge, as current fabrication protocols usually require sophisticated equipment and complicated procedures. Here, a novel coating technology involving in situ self‐assembly of the polyoxotitanate (POT) cage [Ti₁₈Mn₄O₃₀(OEt)₂₀Phen₃] is reported to fabricate multifunctional cotton fabrics in a single step. The in situ generated spherical microparticles of 0.8 µm average diameter are firmly mounted on the underlying cotton substrate, imparting the coated surface with robust hydrophobicity (water contact angle of 148.1 ± 5.4°), antibacterial activity (against Escherichia coli, Staphylococcus epidermidis, and Staphylococcus aureus), and excellent UV‐blocking performance (89% blocked at 350 nm). This coating technology is efficient, straightforward, requires no specialized equipment, and most importantly, is readily extendable to other flexible substrates. Combined with the rapidly developing area of POT cages and similar molecular materials, the reported technology based on in situ self‐assembly holds great promise for further advancing the fabrication of multifunctional flexible devices via a single‐step coating operation.     

Bacterium‐Templated Polymer for Self‐Selective Ablation of Multidrug‐Resistant Bacteria

The recognition and inactivation of specific pathogenic bacteria remain an enormous scientific challenge and an important therapeutic goal. Therefore, materials that can selectively target and kill specific pathogenic bacteria, without harming beneficial strains are highly desirable. Here, a material platform is reported that exploits bacteria as a template to synthesize polymers with aggregation‐induced emission (AIE) characteristic by copper‐catalyzed atom transfer radical polymerization for self‐selective killing of the bacteria that templates them with no antimicrobial resistance. The bacteria‐templated polymers show very weak fluorescence in aqueous media, however, the fluorescence is turned on upon recognition of the bacteria used as the template to synthesize the polymer even at a low concentration of 600 ng mL^?1. Moreover, the incorporated AIE fluorogens (AIEgens) can act as an efficient photosensitizer for reactive oxygen species (ROS) generation after bacteria surface binding, which endows the templated polymers with the capability for selective bacterial killing. The bacterium‐templated synthesis is generally applicable to a wide range of bacteria, including clinically isolated multidrug‐resistant bacterial strains. It is envisioned that the bacterium‐templated method provides a new strategy for bacteria‐specific diagnostic and therapeutic applications.     

Anti‐reflection and hydrophobic characteristics of M‐PDMS based moth‐eye nano‐patterns on protection glass of photovoltaic systems

To maximize the incident light, moth‐eye nano‐patterns were formed on a glass plate that was used as the protection glass for photovoltaic systems. These moth‐eye nano‐patterns were formed using a nano‐imprint lithography process and increased the transmittance of the glass plate by minimizing the reflection of light at the surface. After the formation of the moth‐eye nano‐patterns, the surface was coated with a trichloro‐silane based self‐assembled monolayer in order to create a hydrophobic surface because the hydrophobic surface induced a self‐cleaning effect. The transmittance of the glass plate increased from 91 to 94% at wavelength of 500 nm after the moth‐eye structure was introduced. Thus, the short circuit current (J_SC) of the I–V characteristics and the charged capacity of the photovoltaic system increased up to 6% after replacing the conventional protection glass with the moth‐eye nano‐patterned glass. The durability of the moth‐eye nano‐patterns was evaluated with respect to an acidic environment, high temperatures and UV irradiation. From these evaluation results, the values of the transmittance and contact angle did not decrease after the nano‐patterns were soaked in sulfuric acid solutions with a pH of 2.0 for 48 h, exposed to a temperature of 120°C for 48 h, and irradiated 10 times with UV light for 4 h. Copyright © 2010 John Wiley & Sons, Ltd.     

Nonstick,Modulus‐Tunable and Gas‐Permeable Replicas for Mold‐Based,High‐Resolution Nanolithography

A fundamental approach to fabricating a nonstick replica mold with high performance for the manufacturing of high‐resolution nanostructures using mold‐based lithography is presented. Low‐viscosity liquid blends consisting of methacrylate multi‐functionalized silsesquioxane (SSQMA), difunctional acrylics, and a small amount of silicone diacrylate (Si‐DA) with low surface tension were used as nonstick replica‐mold materials. The cured SSQMA/acrylic/Si‐DA networks showed a high resistance to organic solvents (<1.2 wt.%), high UV transparency (>90% at 365 nm), hydrophobicity (water contact angle >90°), high modulus and wide‐range modulus tunability (0.6–4.42 GPa) and small shrinkage (<3% in height). The mold materials with a nonstick property conferred by Si‐DA possessed the ability to form sub‐25‐nm features with a high line‐to‐space ratio (1:1) and a high aspect ratio (4:1). In addition, a sufficiently cured replica mold with a low concentration of residual, uncross‐linked (meth)acrylates was able to successfully replicate sub‐25‐nm features with a high line‐to‐space ratio (1:1) and a high aspect ratio (4:1), even if the release agent was not modified. Furthermore, replica molds can potentially be used to fabricate patterns free of bubble defects because of sufficient gas permeability.     

Self‐Healing Materials via Reversible Crosslinking of Poly(ethylene oxide)‐Block‐Poly(furfuryl glycidyl ether) (PEO‐b‐PFGE) Block Copolymer Films

The application of well‐defined poly(furfuryl glycidyl ether) (PFGE) homopolymers and poly(ethylene oxide)‐b‐poly(furfuryl glycidyl ether) (PEO‐b‐PFGE) block copolymers synthesized by living anionic polymerization as self‐healing materials is demonstrated. This is achieved by thermo‐reversible network formation via (retro) Diels‐Alder chemistry between the furan groups in the side‐chain of the PFGE segments and a bifunctional maleimide crosslinker within drop‐cast polymer films. The process is studied in detail by differential scanning calorimetry (DSC), depth‐sensing indentation, and profilometry. It is shown that such materials are capable of healing complex scratch patterns, also multiple times. Furthermore, microphase separation within PEO‐b‐PFGE block copolymer films is indicated by small angle X‐ray scattering (lamellar morphology with a domain spacing of approximately 19 nm), differential scanning calorimetry, and contact angle measurements.     

Adhesion and Surface Interactions of a Self‐Healing Polymer with Multiple Hydrogen‐Bonding Groups

The surface properties and self‐adhesion mechanism of self‐healing poly(butyl acrylate) (PBA) copolymers containing comonomers with 2‐ureido‐4[1H]‐pyrimidinone quadruple hydrogen bonding groups (UPy) are investigated using a surface forces apparatus (SFA) coupled with a top‐view optical microscope. The surface energies of PBA–UPy4.0 and PBA–UPy7.2 (with mole percentages of UPy 4.0% and 7.2%, respectively) are estimated to be 45–56 mJ m^?2 under dry condition by contact angle measurements using a three probe liquid method and also by contact and adhesion mechanics tests, as compared to the reported literature value of 31–34 mJ m^?2 for PBA, an increase that is attributed to the strong UPy–UPy H‐bonding interactions. The adhesion strengths of PBA–UPy polymers depend on the UPy content, contact time, temperature and humidity level. Fractured PBA–UPy films can fully recover their self‐adhesion strength to 40, 81, and 100% in 10 s, 3 h, and 50 h, respectively, under almost zero external load. The fracture patterns (i.e., viscous fingers and highly “self‐organized” parallel stripe patterns) have implications for fabricating patterned surfaces in materials science and nanotechnology. These results provide new insights into the fundamental understanding of adhesive mechanisms of multiple hydrogen‐bonding polymers and development of novel self‐healing and stimuli‐responsive materials.     

Contact Angle Analysis During the Electro‐oxidation of Self‐Assembled Monolayers Formed by n‐Octadecyltrichlorosilane

The electrochemical oxidation process of self‐assembled monolayers formed by n‐octadecyltrichlorosilane (OTS) molecules on silicon wafers has been studied in a droplet of water by means of in situ water contact angle measurements. The application of different bias voltages between the substrate and a counter electrode placed into the droplet resulted in changes of the chemical nature of the monolayer, which yielded a significant alteration of the surfaces properties. Due to the changes of the wetting properties of the monolayer during the electro‐oxidation process a change in the contact angles of the water droplet is concomitantly observed. This allows the in situ monitoring of the electro‐oxidation process for large modified areas of several millimeters in diameter. The chosen approach represents an easy way to screen the major parameters that influence the oxidation process. Afterwards, the oxidized regions are characterized by Fourier‐transform infrared (FT‐IR) spectroscopy, X‐ray photoelectron spectroscopy (XPS) measurements, and atomic force microscopy (AFM) investigations to obtain more information about the electro‐oxidation process. The observations are correlated to experimental results obtained for oxidations performed on a smaller dimension range in the water meniscus of a conductive, biased AFM tip. A good correlation of the results in the different dimension ranges could be found.     

Control of the Homeotropic Order of Discotic Hexa‐peri‐hexabenzocoronenes

The thermal properties and self‐organization of hexa‐peri‐hexabenzocoronene (HBC) derivatives with dove‐tailed alkyl chains of various lengths have been investigated using polarized optical microscopy and wide‐angle X‐ray scattering. It is shown that the size‐related increase of steric interactions among the peripheral side chains substituted to the aromatic core leads to a dramatically lowered isotropization temperature, allowing thermal processing at practical temperatures. Additionally, the introduction of ether linkages within the side chains enhances the affinity of the discotic molecules towards polar surfaces, resulting in homeotropic self‐assembly when the compounds are processed from the isotropic state between two surfaces and, for the first time, as a thin film on a single surface. It is established that the degree of homeotropic order is influenced by the phase behavior, the supramolecular order in the bulk, and the surface affinity of the corresponding derivatives. These results are important for the design of photovoltaic cells based on HBC derivatives.     

Liquid‐Infused Smooth Coating with Transparency,Super‐Durability,and Extraordinary Hydrophobicity

Liquid‐infused coatings are because of their fluidity of considerable technological importance for hydrophobic materials with multifunctional properties, such as self‐healing, transmittance, and durability. However, conventional coatings absorb viscous liquid into their sponge‐like structured surface, causing uncontrollable liquid layer formation or liquid transport. In addition, a hydrophobic‐liquid‐retained surface can cause instability and lead to limitation of the hydrophobicity, optical properties, and flexibility due to liquid layer evaporation. Here, we report a strategy for controllable liquid‐layer formation on smooth surfaces (R _rms < 1 nm) by π ‐electron interactions. Using this technology, superoleophilic wetting of decyltrimethoxysilane results in the design of a surface with π ‐interaction liquid adsorption, smoothness, and hydrophobicity (SPLASH), that shows extraordinary hydrophobicity (CAH = 0.75°), and stable repellence for various water‐based solutions including micrometer‐sized mist. The smoothness of the solid under a liquid layer enabled the SPLASH to exhibit stable hydrophobicity, transparency (>90%), structure damage durability and flexibility, regardless of the liquid layer thickness by bending or evaporation. Furthermore, the patterned π ‐electrons' localization on the smooth coating enables controlled liquid‐layer formation and liquid transport. This strategy may provide new insights into designing functional liquid surfaces and our designed surface with multifunctional properties could be developed for various applications.     

Peptide‐Based Nanostructured Materials with Intrinsic Proapoptotic Activities in CXCR4+ Solid Tumors

Protein materials are gaining interest in nanomedicine because of the unique combination of regulatable function and structure. A main application of protein nanoparticles is as vehicles for cell‐targeted drug delivery in the form of nanoconjugates, in which a conventional or innovative drug is associated to a carrier protein. Here, a new nanomedical approach based on self‐assembling protein nanoparticles is developed in which a chemically homogeneous protein material acts, simultaneously, as vehicle and drug. For that, three proapoptotic peptidic factors are engineered to self‐assemble as protein‐only, fully stable nanoparticles that escape renal clearance, for the multivalent display of a CXCR4 ligand and the intracellular delivery into CXCR4⁺ colorectal cancer models. These materials, produced and purified in a single step from bacterial cells, show an excellent biodistribution upon systemic administration and local antitumoral effects. The design and generation of intrinsically therapeutic protein‐based materials offer unexpected opportunities in targeted drug delivery based on fully biocompatible, tailor‐made constructs.     

Metal‐Based Nanomaterials in Biomedical Applications: Antimicrobial Activity and Cytotoxicity Aspects

Microbial colonization on material surfaces is ubiquitous. Biofilms derived from surface‐colonized microbes pose serious problems to the society from both an economical perspective and a health concern. Incorporation of antimicrobial nanocompounds within or on the surface of materials, or by coatings, to prevent microbial adhesion or kill the microorganisms after their attachment to biofilms, represents an important strategy in an increasingly challenging field. Over the last decade, many studies have been devoted to preparing meta‐based nanomaterials that possess antibacterial, antiviral, and antifungal activities to combat pathogen‐related diseases. Herein, an overview on the state‐of‐the‐art antimicrobial nanosized metal‐based compounds is provided, including metal and metal oxide nanoparticles as well as transition metal nanosheets. The antimicrobial mechanism of these nanostructures and their biomedical applications such as catheters, implants, medical delivery systems, tissue engineering, and dentistry are discussed. Their properties as well as potential caveats such as cytotoxicity, diminishing efficacy, and induction of antimicrobial resistance of materials incorporating these nanostructures are reviewed to provide a backdrop for future research.