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Inspired by the Stenocara beetle's hydrophobic-hydrophilic surface, we fabricated hexagonally patterned hydrophobic-hydrophilic surfaces consisting of silicon and gold regions using colloidal lithography and selective surface functionalization. We investigated surface wettability for different patterns (hexagonally ordered nanotriangles and nanoholes) and the influence of surface functionalization (octadecanethiol and 16-mercaptohexadecanoic acid/octadecyltrichlorosilane (MHA/OTS)). The as-prepared patterned substrates exhibit hydrophilicity, which transforms to hydrophobicity after surface functionalization. The MHA/OTS functionalization results in maximum enhancement in the contact angle (114 ± 0.4°) with the least contact angle hysteresis (19 ± 2°). Fog harvesting studies show that the patterned substrate has a higher water collection rate, a factor of 1.32, than the nonpatterned substrates. A further enhancement in water collection (almost twice) is observed with selective functionalization. The patterned (nanohole) and functionalized (MHA/OTS) substrate facilitates rapid falling of droplets at a frequency of 20 mHz and an average droplet mass of 15 ± 2 mg/cm2. Furthermore, it yielded a maximum water collection rate of 1051 ± 132 mg cm-2 h-1. This work provides valuable insights into the influence of surface wettability and morphology for fog harvesting applications.

To enable area-selective atomic layer deposition (AS-ALD), self-assembled monolayers (SAMs) have been used as the surface inhibitor to block a variety of ALD processes. The integrity of the SAM throughout the ALD process is critical to AS-ALD. Despite the demonstrated effectiveness of inhibition by SAMs, nucleation during ALD eventually occurs on SAM-protected surfaces, but its impact on SAM structures is still not fully understood. In this study, we chose the octadecyltrichlorosilane (ODTS) SAM as a model system to investigate the evolution of crystallinity and structure of SAMs before and after ALD. The breakdown behavior of SAMs when exposed to ZnO and Al2O3 ALD was systematically studied by combining synchrotron X-ray techniques and electron microscopy. We show that the crystallinity and structure of ODTS SAMs grown on Si substrates remain intact until a significant amount of material deposition takes place. In addition, the undesired ALD materials that grow on ODTS SAMs present contrasting morphologies: dispersed nanoparticles for ZnO while relatively continuous film for Al2O3. Lastly, substrate dependency was explored by comparing a Si substrate to single-crystal sapphire. Similar results in the evolution of SAM crystallinity and formation of ALD nuclei on top of SAM are observed in the ODTS-sapphire system. This study provides an in-depth view of the influence of ALD processes on the SAM structure and the nucleation behavior of ALD on SAM-protected surfaces.

Quantitative atomic force microscope (AFM) measurements are performed by using both unmodified and octadecyltrichlorosilane self-assembled monolayers (OTS-SAMs)-functionalized AFM silicon (Si) tips in contact with the uncoated SiO2 substrate, OTS-SAMs coated SiO2 substrate and SiO2 substrate with graphene (Gr) sheet on its surface, providing six pairs of frictional interfaces. Drastic differences in the adhesion and friction responses of these six pairs of friction interfaces are observed. Lower adhesion force and friction force occur with OTS-SAMs coated on either tips or substrates, and the friction force is ultralow when Gr presented on the substrate with OTS-coated tips sliding against it. The observed ultralow friction is attributed to the hydrophobicity and incommensurate contact between Gr and OTS-SAMs. This work has important impact on designing approaches of friction pairs to achieve ultralow friction.

Tooth surfaces of silicon-based MEMS microgears are described as smooth surfaces covered by adhesive asperities (nanoblocks). To reduce adhesive effects, the tooth surfaces are functionalized by OTS-SAM (Octadecyltrichlorosilane self-assembly monomolecular) carbon-based functionalized coatings. The wear of the coating is modelled using the modified Goryacheva-Torskaya model of damage accumulation. The amount of energy dissipated by different physical and chemical mechanisms along with energy dissipated by mechanical deformation of the counterparts is used to evaluate the frictional force. The main scenarios of wear process within the coating are described and discussed. The damage evolution is described for several levels of external load.

We study the assembly of magnetite nanoparticles in water-based ferrofluids in wetting layers close to silicon substrates with different functionalization without and with an out-of-plane magnetic field. For particles of nominal sizes 5, 15, and 25 nm, we extract density profiles from neutron reflectivity measurements. We show that self-assembly is only promoted by a magnetic field if a seed layer is formed at the silicon substrate. Such a layer can be formed by chemisorption of activated N-hydroxysuccinimide ester-coated nanoparticles at a (3-aminopropyl)triethoxysilane functionalized surface. Less dense packing is reported for physisorption of the same particles at a piranha-treated (strongly hydrophilic) silicon wafer, and no wetting layer is found for a self-assembled monolayer of octadecyltrichlorosilane (strongly hydrophobic) at the interface. We show that once the seed layer is formed and under an out-of-plane magnetic field further wetting layers assemble. These layers become denser with time, larger magnetic fields, higher particle concentrations, and larger moment of the nanoparticles.

Superhydrophobic treatment of wood surfaces can effectively prevent the contact between the external moisture and wood, which improves the service life of the wood. In this study, different rough surfaces of wood were constructed, derived from the self-polymerization of dopamine (DA) in weak base solution to form a polydopamine (PDA) coating and the deprotonation of the PDA coating in a strong base solution. Furthermore, octadecyltrichlorosilane (OTS) was used as a low-surface-free-energy agent to modify rough surface in order to prepare superhydrophobic woods: Wood@PDA&ndash, NaOH&ndash, OTS and the Wood@PDA&ndash, NaOH/SiO2&ndash, OTS. The contact angles (CAs) and sliding angles (SAs) of the resulting superhydrophobic woods were tested. The results showed that the CA and SA of the Wood@PDA&ndash, OTS were 151&deg, and 4.8&deg, respectively, the CA and SA of the Wood@PDA&ndash, OTS were 155.1&deg, and 5.0&deg, respectively. Surface electron microscopy (SEM) images presented that NaOH successfully etched the PDA coating, and the roughness was further improved by adding nano-SiO2. Atomic force microscope images (AFM) revealed that the nano-SiO2 particles could effectively provide nanolevel roughness, which was beneficial to the wood&rsquo, s superhydrophobic properties. In addition, the obtained superhydrophobic wood possessed strong surface stability and anti-loss property, as well as resistance to acid-base solution and organic solvent.

We present a novel laser-induced surface treatment process to rapidly control the spatial wettabilities of various functional solutions with submicron to micron resolutions. Ultrathin hydrophobic self-assembled monolayers (SAMs) that little absorb typical laser lights due to short penetration depth were selectively deactivated by instantaneous interaction with laser-induced metallic plasmas. The spatial region of the deactivated SAM, which corresponds to process resolution, is adjustable by controlling the spatial propagation of the plasma. This method leads to the parallel formation of hydrophilic functional solutions on glass substrates with a minimum resolution on the submicron scale. To show its feasibility in device engineering fields, this method was applied to the cost-effective fabrication of electronics and biosensors. Rapid self-patterning of electronic and biological functional solutions (silver nanoparticle solution and streptavidin protein solution) was successfully realized by selective deactivation of two different SAMs (tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) for electronics and the hetero-hybrid SAM (octadecyltrichlorosilane (OTS)/2-[methoxy(polyethyleneoxy)propyl] trichlorosilane (PEG)) for biosensors). As a result, this method can be exploited for the rapid and low-cost fabrication of various thin film devices such as electronics, biosensors, energy, displays, and photonics.

The interaction forces between silica surfaces modified to different degrees of hydrophobicity were measured using colloidal probe atomic force microscopy (AFM). A highly hydrophobic silica particle was prepared with octadecyltrichlorosilane (OTS), and the interaction forces were measured against silica substrates modified to produce surfaces of varying hydrophobicity. The interaction forces between the highly hydrophobic particle and a completely hydrophilic silicon wafer surface fitted well to the DLVO theory, indicating that no additional (non-DLVO) forces act between the surfaces. When the silicon wafer surface was treated to produce a contact angle of water on surface of 40°, an additional attractive force that is longer ranged than the van der Waals force was observed between the surfaces. The range and magnitude of the attractive force increase with the contact angle of water on the substrate. Beyond the effect on the contact angle, the hydrocarbon chain length and the terminal groups of hydrophobic layer on the substrate only have a minor effect on the magnitude of the force, even when the substrate is terminated with polar carboxyl groups, provided the hydrophobicity of the other surface is high.

Molecular films of octadecyltrichlorosilane (OTS) silanized on silicon substrates were obtained by a succession of fabrication steps consisting in plasma hydroxylation of silicon surface, formation of a water layer adsorbed on hydroxylated surface by substrate exposure to water vapor and OTS vapor deposition. All fabrication steps were realized in the same vacuum chamber to avoid surface contamination and to control the amount of water adsorbed on the hydroxylated surface. It is proved that the amount of water on the substrate surface plays a key role in fabrication of smooth OTS molecular films, large amounts of water on substrates resulting in formation of 3D OTS aggregates. The atomic force microscopy (AFM) investigations of the film surface revealed formation of liquid-expanded and liquid-condensed domains in OTS molecular films. Annealing of the OTS films promotes film dehydration, increases the film hydrophobicity and reduces nanoscopic adhesion and friction forces between silicon AFM tips and film surface.

The performances of organic thin film transistor devices are crucially connected with electronic and structural properties at organic semiconductor/dielectric interfaces. In our studies, Silicon substrates with native SiO 2 layer were made hydrophilic according to Radio Corporation of America (RCA) cleaning procedure (RCA treated SiO 2 , RCA/SiO 2 ) and hydrophobic by following octadecyltrichlorosilane (OTS) modification method (OTS treated SiO 2 , OTS/SiO 2 ). The surface morphology, molecular orientation and nature of interaction have been studied at rubrene/RCA treated SiO 2 and rubrene/OTS treated SiO 2 interfaces with increasing thickness of rubrene film from sub-monolayer to multilayer. The angle dependent near edge x-ray absorption fine structure (NEXAFS) spectroscopy and atomic force microscopy (AFM) were used to probe the evolution of molecular configuration and surface morphology of rubrene thin films respectively. The nature of interaction was investigated by X-ray photoemission spectroscopy (XPS) techniques. XPS and NEXAFS studies indicate that the rubrene molecules were physically adsorbed onto both substrates. Angle dependent NEXAFS data suggest that OTS molecules were in standing up configuration on SiO 2 surface while rubrene molecules were randomly oriented on both RCA and OTS treated SiO 2 substrates. On RCA/SiO 2 substrate the percentage of rubrene molecules with twisted backbone was higher compared to that on OTS/SiO 2 for 20 nm thick films. The rubrene films were found to grow with different features onto two studied substrates due to their difference in surface energy. At lower coverage, the grain size was larger and nucleation density was smaller onto hydrophilic RCA/SiO 2 surface, compared to hydrophobic OTS/SiO 2 . Hydrophobation of the dielectric substrate surface tends to hinder the diffusion of rubrene molecules resulting in smaller grains for hydrophobic substrate compared to hydrophilic one.

The nanofriction between a silicon nitride probe and both a silicon wafer and an octadecyltrichlorosilane (OTS)-coated surface is studied in saline solution by using lateral force microscopy (LFM). The effects of surface charge on the nanofriction in an electrolyte as well as its velocity dependence are studied, while the surface charge at the solid-liquid interface is adjusted by changing the pH value of the electrolyte. The results show that the nanofrictional behavior between the probe and the samples in an electrolyte depends strongly on the surface charge at the solid-liquid interface. When the probe and the sample in the electrolyte are charged with the same sign, a repulsive electrostatic interaction between the probe and the sample is produced, leading to a reduction in nanofriction. In contrast, when the two surfaces are charged with the opposite sign, nanofriction is enhanced by the attractive electrostatic interaction between the probe and the sample. The velocity dependence of nanofriction in an electrolyte is believed to be tied to charge regulation referring to a decreasing trend in surface charge densities for the two approaching charged surfaces in an electrolyte. When the probe slides on the sample at a low velocity, charge regulation occurs and weakens the electrostatic interaction between the probe and the sample. As a result, nanofriction is reduced for surfaces charged with the opposite sign, and it is enhanced for surfaces charged with the same sign. When the sliding velocity between the probe and the sample is high, there is insufficient time for charge regulation to occur. Thus, the friction pair shows a larger nanofriction when the surfaces are charged with the opposite sign and a smaller nanofriction when the surfaces are charged with the same sign when compared to the case of a lower sliding velocity.

Dendritic polyglycerols (PGs) were synthesized and postmodified by grafting of poly(ethylene glycol) (PEG) and polypropylene glycol (PPG) diglycidyl ether groups, and their antifouling and fouling-release properties were tested. Coating characterization by spectroscopic ellipsometry, contact angle goniometry, attenuated total internal reflection-Fourier transform infrared spectroscopy (ATR-FTIR), and atomic force microscopy showed brushlike morphologies with a high degree of microscale roughness and the ability to absorb large amounts of water within seconds. PGs with three different thicknesses were tested in laboratory assays against settlement of larvae of the barnacle Balanus improvisus and against the settlement and removal of zoospores of the alga Ulva linza. Very low coating thicknesses, e.g., 11 nm, reduced the settlement of barnacles, under static conditions, to 2% compared with 55% for an octadecyltrichlorosilane reference surface. In contrast, zoospores of U. linza settled readily but the vast majority were removed by exposure to a shear force of 52 Pa. Both PEG and PPG modification increased the antifouling properties of the PG films, providing a direct comparison of the ultralow fouling properties of all three polymers. Both, the modified and the nonmodified PGs are promising components for incorporation into amphiphilic fouling-resistant coatings.

We present a step by step guide to optimize the fabrication process and develop Pentacene transistors with greatly diminished non-idealities. The issues addressed in this work are (a) non-Ohmic metal-semiconductor interface (b) trap states at the insulator-semiconductor and metal-semiconductor interfaces and (c) gate leakage. These factors ((a)-(c)) limit the charge carrier transport and this is reflected as distortions in the electrical characteristics compared to that expected for an ideal case. We demonstrate a simple model to correct the gate leakage in the experimental data. An integrated shadow mask is employed to reduce the gate leakage in the transistors. Palladium as an injection layer with chromium as an adhesion layer is found to show the least contact limitation effect (i.e. elimination of S-type output characteristics). Thiols and organosilane are used to treat the insulator surface to reduce the current-voltage hysteresis and adjust the switch-on voltage. OctaDecylTrichloroSilane treatment is found to yield near zero switch-on voltage with negligible current-voltage hysteresis.

Anodic titanium dioxide (ATO) has been investigated for decades of years. It can be widely used in microextraction fiber for sample pretreatment because of its rich variety of morphologies such as nanotube, nanowires, nanoparticles and so on. In this work, TiO2 nanotube clusters in situ growth were prepared on titanium substrate by anodization method. The effects of anodization distance, anodizing time and temperature of electrolyte were investigated. The results showed that uniform nanotube clusters coating can be obtained under the conditions of 1.5 cm anodizing distance, 50 min anodizing time and 60 °C anodizing temperature. On this basis, a novel, simple and fast octadecyl functionalization was followed by one step chemical self-assembly method based on the chemical reaction between octadecyltrichlorosilane and surface titanium hydroxyl groups (Ti-OH). The electrochemical scanning microscope (SEM), energy dispersive spectrometer (EDS) and XPS were employed for sample characterization, which showed that octadecyl groups were successfully assembled on the surface of TiO2 nanotube clusters. Moreover, the surface corrosion resistance of the fibers was also tested by electrochemical methods.

The fabrication techniques of hydrophobic and superhydrophobic surfaces have received attention from many researchers. In this study, the change of water contact angle of the glass surface modified with chlorosilane or trichlorosilane compound was investigated. The microscope glass with water contact angle of 88° and 107° were obtained by treating with trimethylchlorosilane (TMCS) and octadecyltrichlorosilane (OTS), respectively. The chemical resistance of hydrophobic layer was evaluated by immersing the treated samples into an acidic or a basic solution. The result showed that OTS bonded to the glass surface more strongly than TMCS. The superhydrophobic state with the highest contact angle of 154° (sliding angle 17°) could be achieved with the glass microfiber filter by using OTS. The similar phenomenon could not be observed with TMCS because the TMCS-treated glass filter remained completely wetted with all investigated concentrations. The hydrophobic layer on the glass slides was strongly affected by abrasive force while the contact angle value of more than 154° was detected in the treated glass filter after 50 cycles of abrasion test on a sandpaper. The scanning electron microscope (SEM) images had revealed the aggregation of the OTS molecules on the glass filter surface. The chemically-treated filter performed both superhydrophobic and superoleophilic properties. The OTS coating showed strong resistance to the organic solvent. Separation of mixture n-hexane and water was successfully demonstrated using the modified filter.

Micro-scale wear characteristics of ultra-fine gold wires with a diameter of ~28 μm was investigated under a low contact force over a long sliding distance up to ~200 km. The tip of the wire was slid against a silicon wafer under a low normal force of 5 μN. Wear of the gold wire was quantified from the images of the tip obtained by a 3D laser microscope and a scanning electron microscope before and after the wear test. The dimensionless Archard relationship wear coefficient was in the order of 10 −7 which was extremely low considering that sliding was carried out in dry condition. Such a low wear characteristics was attributed to low contact pressure that could be achieved by formation of a conformal contact due to flattening of the wire tip as sliding wear progressed. Wear behavior of the gold wire could be characterized by formation of thin flakes of wear debris that were generated as a result of adhesive shear stress imparted at the sliding interface. As an effort to reduce the wear coefficient even further, octadecyltrichlorosilane self-assembled monolayer was deposited on the silicon to serve as a nano-lubricant. It was effective in improving the wear resistance by about two-fold.

The adhesion strength between a thin film and substrate is often the critical parameter that controls the initiation as well as the mode of film failure. In this work, a laser-based spallation method is used to determine the adhesion strength of “as deposited” lead zirconate titanate (PZT) sol-gel thin films on the two functionally different substrates. For the first case, PZT sol-gel film is deposited onto bare Si/SiO2 substrates via spin casting. The extremely high adhesion strength between the film and the substrate necessitated an additional platinum mass superlayer to be deposited on top of the PZT film in order to induce interfacial failure. For the superlayer film system, a hybrid experimental/numerical method is employed for determining the substrate/film interfacial strength, quantified to be in the range of 460–480 MPa. A second substrate variation with lower adhesion strength is also prepared by applying a self-assembled octadecyltrichlorosilane (ODS) monolayer to the Si/SiO2 substrate prior to the film deposition. For the monolayer-coated substrate case, the adhesion strength is observed to be significantly lower (54.7 MPa) when compared to the earlier case.

In order to improve the service life of Si devices applied in micro-electro-mechanical systems (MEMS), anti-wear octadecyltrichlorosilane/silica nanoparticles (OTS/SiO2) composite films were prepared on silicon by sol-gel and self-assembly techniques. The structure, morphology, chemical composition, wettability, anti-adhesion and tribological properties of the films were characterized. The prepared OTS/SiO2 composite films were hydrophobic with water contact angle of 119.0 ± 0.5° and textured by OTS modified SiO2 nanoparticles with long chain structures. Compared with Si substrate and OTS self-assembled monolayer (SAM), OTS/SiO2 composite films could not only reduce adhesive force to 17.7 ± 0.5 nN but also reduce friction coefficient to 0.18 ± 0.02 under a load of 1 N. The anti-wear lifetime was prolonged to 40,897 s, while OTS SAM was gradually worn out in 104 s under the same friction conditions. The synergistic effect of the transferring of OTS SAM as lubrication films and the repairing of abrasive areas by SiO2 nanoparticles accounted for the preeminent wear resistance. OTS/SiO2 composite films are expected to be effectively used in MEMS as high-performance lubrication films.

A self-assembled bilayer film of 1,2-bis(triethoxysilyl) ethane–octadecyltrichlorosilane (BTSE–OTS) was prepared on single-crystal silicon substrates by utilizing BTSE as an intermediate layer. The surface morphology of the film was characterized by small round protuberances, with a surface roughness of about 1.82 nm. Moreover, the BTSE–OTS bilayer film displayed comparable hydrophobicity and nano-scale friction behaviors to the OTS monolayer owing to their identical surface composition and similar surface morphology. The investigation of the micro-tribological properties revealed that the BTSE–OTS bilayer film possessed much higher anti-wear durability and load-carrying capacity than the OTS monolayer while maintaining the low friction coefficient (~ 0.05). The BTSE–OTS bilayer film may find expanded applications in the lubrication of micro-/nano-electromechanical systems as compared to the conventional OTS monolayer.

In this study, we reported the first example of multi-functional 1-triacontanol-polymerized-octadecylsiloxane (1-triacontanol-PODS) coatings. The multi-functional 1-triacontanol-PODS coatings are formed on various substrates including cotton wool, filter paper, sponge, and glass via immersing the substrates in hot solutions (∼50 °C) of 1-triacontanol, octadecyltrichlorosilane (OTS) and ethanol. After coating, it is found that the 1-triacontanol-PODS-coated materials possess with superhydrophobicity, superoleophilicity and anti-corrosion ability. Furthermore, highly efficient oil/water separation and excellent self-cleaning ability were also observed on the 1-triacontanol-PODS-coated materials. For instance, the flux of 1-triacontanol-PODS coating modified cotton wool for ClCH 2 CH 2 Cl/H 2 O separation was ranged from 5677 to 32,157 L m −2 h −1 after 50 cycles, and the mass-based absorption capacities for the oils are in the range 15–31; Both micro (>20 μm) and nano dust particles (∼50 nm) were fully removed from 1-triacontanol-PODS coating-modified glass substrate.

The protective effect of a hydrophobic surface against acid erosion was validated in the present work using octadecyltrichlorosilane (OTS) on hydroxyapatite films (HA) and on dental samples. The acid erosion was firstly evaluated on films made of HA and fluorapatite (HAF), and subsequently on films of HA coated by OTS. Our results have shown that the two first films were completely eroded during this evaluation and that no significant erosion was observed for the last film. Indeed, teeth coated with OTS showed no erosion at all after seven days of exposure to citric acid. The evaluation was based on QCM-D measurements, SEM images and water contact angle characterization. The results validate that a hydrophobic surface may be an effective tooth protector against acid erosion.

Multifunctional wood materials with magnetic, superhydrophobic and anti-ultraviolet properties were obtained successfully by precipitated CoFe 2 O 4 nanoparticles on the wood surface and then treated with a layer of octadecyltrichlorosilane (OTS). The as-fabricated wood composites exhibited excellent magnetic property and the water contact angle of the OTS-modified magnetic wood surface reached as high as 150°, revealed the superhydrophobic property. Moreover, accelerated aging tests suggested that the treated wood composites also have an excellent anti-ultraviolet property.

Self-assembled monolayers (SAM) of dodecyltrichlorosilane (DTS) and octadecyltrichlorosilane (OTS) on silica are studied by molecular dynamics simulations at 298 K and 1 bar. The coverage (number of alkylsilane molecules per surface area) is systematically varied. The results yield insight into the properties of the alkylsilane SAMs, which complement experimental studies from the literature. Relationships are reported between thickness, tilt angle, and coverage of alkylsilane SAMs, which also hold for alkylsilanes other than DTS and OTS. They are interpreted based on the information on molecular ordering in the SAMs taken form the simulation data. System size and simulation time are much larger than in most former simulation works on the topic. This reduces the influence of the initial configuration as well as the periodic boundary conditions and hence minimizes the risk of artificial ordering. At the same time, more reliable statistics for the calculated properties can be provided. The evaluation of experimental data in the field is often based on strongly simplified models. The present simulation results suggest that some of these lead to errors, concerning the interpretation of experimental results, which could be avoided by introducing more realistic models.

Textured silicon (Si) substrate were prepared using various texturing methods both chemical and physical and their water contact angle, surface topography and Raman spectra were studied and investigated. The effect of plasma and chemical treatment on micro/nanostructure and roughness of the surface with and without deposition of Octadecyltrichlorosilane (ODTS, Cl3Si (CH3)(17)), self-assembled monolayer (SAM) is investigated for achieving higher water contact angle (theta(c)). The importance of synergism of texturing with deposition of ODTS SAM in preparing superhydrophobic silicon surfaces has been discussed. It is shown that superhydrophobic silicon surfaces can be achieved on silicon surfaces by coating with ODTS, irrespective of whether it is textured or not, polished or unpolished, provided a chemical treatment is given to the surface prior to the ODTS coating.

Superhydrophobic and superoleophilic sponges were fabricated by immersion in an ethanol solution of octadecyltrichlorosilane. The resulting coating strongly adheres to the sponges after curing at 45 °C for 24 h. Absorption capacities of 42-68 times the polymerized octadecylsiloxane sponge weight were obtained for toluene, light petroleum, and methylsilicone oil. These adsorption capacities were maintained after 50 cycles.

Quinoxaline cavitands (QxCav) are transferred by Langmuir-Schaefer method on selfassembled monolayers (SAMs) of octadecyltrichlorosilane (OTS) and N,N-dimethyl-N-octadecyl-3- aminopropyltrimethoxysilyl chloride (DMOAP) on fused silica substrates. The molecular architectures of both the hydrophobic SAMs templates and the hybrid cavitand-organosilanes bilayers at the solid-air interface are investigated and correlated by sum-frequency vibrational spectroscopy. The results show that QxCav are always in the closed vase configuration and orient with their principal axis normal to the substrates. The role of the alkyl chains density in the SAM templates on the QxCav transfer ratio is pointed out.

Hierarchical structures of ZnO nanowires (NWs) with different lengths on well-defined micropillars are fabricated by UV soft imprinting and hydrothermal growth. X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS) are employed to characterize the crystal structure, morphology and chemical composition of the hierarchical structures of ZnO nanowires on micropillars. By varying the growth time, ZnO NWs of different lengths and morphology were obtained, showing distinct wettability which can be further modified by surface coating with octadecyltrichlorosilane (OTS). Our results show that under optimal growth conditions, the water contact angle (CA) and contact angle hysteresis (CAH) of the fabricated hierarchical structures after OTS surface treatment can reach 159 ± 1° and 6°, respectively.

Metastable neutral helium atoms are highly chemical sensitive to surface dangling bonds. As the basis of a new lithographic technique, a method for fabrication of self-assembled monolayers (SAMs) and mixed SAMs by the irradiation-promoted exchange reaction has been recently developed. Metastable helium atoms irradiation is shown to modify organosilane SAM films and Si–H and Si–OH covering surfaces, which render the surface amendable to further SAM modification. The exposure regions can undergo a second chemisorption reaction to produce an assembly of octadecyltrichlorosilane SAMs. Metastable helium atom beam patterned films can be used as templates for selective buildup of fluorophores, amino group, and biological cells to obtain further surface functionalization. Copyright © 2014 John Wiley & Sons, Ltd.

We synthesized porous aluminum oxide nanostructures directly on a quartz crystal microresonator and investigated the properties of superhydrophobic surfaces, including the surface wettability, water permeation, and underwater superhydrophobic stability. After increasing the pore diameter to 80 nm (AAO80), a gold film was deposited onto the AAO80 membrane, and the pore entrance size was reduced to 30 nm (AAO30). The surfaces of the AAO80 and AAO30 were made to be hydrophobic through chemical modification by incubation with octadecanethiol (ODT) or octadecyltrichlorosilane (OTS), which produced three different types of superhydrophobic surfaces on quartz microresonators: OTS-modified AAO80 (OTS-AAO80), ODT-modified AAO30 (ODT-AAO30), and ODT-OTS-modified AAO30 (TS-AAO30). The loading of a water droplet onto a microresonator or the immersion of a resonator into water induced changes in the resonance frequency that corresponded to the water permeation into the nanopores. TS-AAO30 exhibited the best performance, with a low degree of water permeation, and a high stability. These features were attributed to the presence of sealed air pockets and the narrow pore entrance diameter.

To achieve a better understanding of the mechanical effects of adsorbed films at surface contacts, methods were developed to map and examine the pressure distribution of nanoasperity contacts, modeled by molecular dynamics simulation. The methods employ smoothing functions to project the atomic forces obtained in contact simulation onto the contact plane for fitting to standard continuum contact models and subsequent analysis. Importantly, these methods allow for contact evolution between nanoscopic asperity-asperity contacts to be examined because these are the central load-bearing junctions at interfaces. To demonstrate the application and features of this approach, it was employed to examine the evolution of contact between silica nanoasperities, with an increasing density of octadecyltrichlorosilane (OTS) films employed as a model adsorbate film. Linearly increasing contact radius and linearly decreasing maximal pressure were observed as a function of the film packing density. Because contact between the underlying, high-energy silica surfaces is undesirable, the evolution of silica contact was also examined using these same methods. As more molecules were introduced into the contact, a sharp transition was observed from the narrow, high-pressure interaction between the underlying substrates, to a broad, substantially lower pressure interaction, indicating a sharp transition from the dry to lubricated condition. To study the dependence of these behaviors on contact morphology, silica nanoasperities in contact with a flat silica surface were also examined. Similar behavior, including the broadening of the contact area and the minimization of direct surface contact, were observed. The method developed herein is applicable to a variety of systems and can be employed to optimize surface protection and pressure redistribution by boundary lubricants. This method can also be extended to AFM adhesion measurements where a detailed understanding of the true contact area is critical for the quantitative determinations of molecular forces and local surface mechanics.

Self-assembled octadecyltrichlorosilane ((OTS), CH3(CH2)17SiCl3) layers on hydroxyl-terminated silicon oxide (SiO2) were prepared. The monolayers were characterized with atomic force microscopy (AFM) and contact angle measurements; their conformation was studied before, during, and after contact with a polymer (either PDMS or PTFE) surface using the vibrational sum frequency spectroscopy (VSFS) technique. During contact, the effect of pressure was studied for both polymer surfaces, but in the case of PTFE, the effect of shear rate on the contact was simultaneously studied. The VSFS response of the monolayers with pressure was almost entirely due to changes in the real area of contact with the polymer and therefore the Fresnel factors, whereas sliding caused disorder in the previously all-trans monolayer, as evidenced by a significant increase in the population of gauche defects.

We report a series of studies aimed at investigating the stability of phosphonate self-assembled monolayers (SAMs) made from octadecylphosphonic acid (ODPA) or a perfluorinated phosphonic acid (PFPA) on hafnium and aluminum oxide surfaces deposited by atomic layer deposition (ALD). The monolayers were deposited by a series of techniques including self-assembly from solution, tethering by aggregation and growth, and the Langmuir–Blodgett (LB) method. SAMs prepared by LB method were primarily used in our stability investigations because they were found to be the most uniform and reproducible. All films deposited on ALD oxide-coated substrates were characterized by means of water contact angle measurements, spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). XPS data conclusively showed covalent phosphonate formation on both substrates. SAMs formed on both Al 2 O 3 and HfO 2 were stable upon exposure to water. PFPA SAMs on HfO 2 were found to be the most stable SAMs studied here in either water or phosphate buffer (PBS) at room temperature. We also show that similar silane-based SAMs made from octadecyltrichlorosilane (OTS) on silicon oxide (SiO 2 ) are less stable in PBS than phosphonate SAMs on atomic layer deposited HfO 2 substrates. These data suggest that phosphonate SAMs should be considered for use in (bio)molecular sensing and actuator devices that utilize ALD and require longer-term stability under aqueous conditions.

The boundary slip condition is an important property, and its existence can reduce fluid drag in micro/nanofluidic systems. The boundary slip on various surfaces immersed in water and various electrolytes has been widely studied. For the surfaces immersed in oil, the boundary slip on superoleophilic and oleophilic surfaces has been studied, but there is no data on oleophobic and superoleophobic surfaces. In this paper, experiments are carried out to study electrostatic force and boundary slip on superoleophilic, oleophobic, and superoleophobic surfaces immersed in deionized (DI) water, hexadecane, and ethylene glycol. In addition, the surface charge density of the samples immersed in DI water is quantified. Results show that the electrostatic force and the absolute value of the surface charge density of an octadecyltrichlorosilane surface are larger than that of a polystyrene surface, and the electrostatic force and the absolute value of surface charge density of a superoleophilic surface are larger than that of oleophobic and superoleophobic surfaces. For the same liquid, the larger contact angle leads to a larger slip length at the solid-liquid interface. For the same surface, the larger liquid viscosity leads to a larger slip length. The relevant mechanisms are discussed in this paper.

We report that a chemical patterning technique based on local plasma modification of self-assembled monolayers has been utilized to fabricate surfaces for domain liquid crystal alignment. Highly hydrophobic octadecyltrichlorosilane monolayers deposited on glass substrates coated with Indium-Tin-Oxide were brought into contact with elastomeric stamps comprising trenches on a micro scale, and then exposed to an oxygen plasma. In the regions exposed to the plasma the monolayer was etched away leaving a patterned surface that exhibited surface energy differences between surface domains. The surfaces that bear the micropatterns have been shown to be capable of producing patterned alignment of nematic liquid crystal.

The kinetics and thermodynamics of octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) on vapor deposited alumina were quantified. Ozone cleaning serves to create well-defined hydrophilic surfaces for OTS attachment, and the use of heptane as a solvent enables the formation of high quality SAMs under ambient conditions. The kinetics was characterized as a function of OTS concentration using contact angle goniometry, ellipsometry and Fourier transform infrared (FTIR) spectroscopy. The kinetics of SAM formation and the saturation contact angle (∼100) on alumina are comparable to what has been observed for OTS on silicon. The free energy of adsorption with ΔGads values ranged from −7.5 to −5.4 kcal/mol, and the SAMs were stable up to 230 C. The critical surface tension of the OTS monolayer was found to be 21.4 dyne/cm.

Metal patterning has been useful for fabricating many optical and electronic devices. Among all the patterning methods, selective electroless plating in combination with micro-contact printing (μCP) is a simple process compatible with roll-to-roll processing. However, this process suffers from the difficulty to avoid lateral growth during the electroless plating of metal. That will place a limitation on the fabrication of nanoscale patterns, such as the metal wire grid polarizer. In this study, we launch a new approach to restrict the lateral growth of metal by depositing metal selectively in the grooves of a three-dimensional template. The template was first treated with a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) only on the protrusion surface using μCP, and then treated in SnCl2 solution to activate the surface of the trenches for the selective electroless plating (ELP) of silver inside the trenches. A wire-grid polarizer was thus fabricated by selectively depositing 70 nm-thick silver in the trenches of a nanograting template with a trench width of 100 nm and a pitch of 180 nm. The maximum extinction ratio of the polarizer thus obtained was about 130 in the wavelength range of 635–650 nm.

Electrical measurements on copper phthalocyanine (CuPc)-based organic field effect transistors using SiO2 dielectric revealed hysteresis and threshold voltage instability to be due to the combined effect of both hole- and electron-trapping mechanisms, with the electron-trap density being higher than hole-trap density. Hysteresis was found to increase further after modifying the SiO2 surface with octadecyltrichlorosilane (OTS) while it reduced drastically after polystyrene (PS) modification. Individual contribution of holes and electrons to hysteresis and the cause of increased/reduced trapping of the same for interface modified devices were identified. The increase in hysteresis with OTS-modified devices was attributed to increase in hole-trap density arising from a larger grain-boundary density of CuPc films. Minimum grain-boundary density and efficient removal of trap centers at dielectric/semiconductor interface using PS modification resulted in minimum hysteresis. Comparison of hole- and electron-trap densities estimated for measurements under different ambient conditions, like high humidity conditions and oxygen flow, showed that hole-trap density increased with increase in humidity. Under oxygen flow, hysteresis, and hole-trap density were found to reduce considerably, which could be attributed to creation of excess holes that readily fill hole traps, thereby resulting in increased mobile carrier concentrations.

Various thermo-responsive polymeric surfaces were evaluated in terms of cell adhesion/detachment and surface analysis. Three kinds of thermo-responsive poly(N-isopropylacrylamide) (PIPAAm) surfaces were prepared by an electron beam irradiation (PIPAAm-EB), a reversible addition fragmentation polymerization (PIPAAm-RAFT), and a redox polymerization (PIPAAm-Redox). Although cell adhesion and detachment on surfaces of PIPAAm-EB and PIPAAm-RAFT were able to be modulated by altering their surface characters with changing the amounts of polymers, the adhesion and detachment were hardly controlled on PIPAAm-Redox surfaces, even though the amounts of polymers on the surface were able to be modulated. Atomic force microscopy (AFM) probed the interactions between AFM tip and the polymeric surface for further investigating a different conformation of polymeric surface. The modification of AFM tip surface coated with octadecyltrichlorosilane was found to change the interaction between the thermo-responsive surface and the tip. Adhesion force analysis clearly showed changes in the hydrophilic/hydrophobic characters of three kinds of thermo-responsive surfaces immediately after a change in temperature. From the kinetics study of AFM, PIPAAm-EB and PIPAAm-RAFT surfaces became hydrophilic less than 30 min after temperature decrease, but PIPAAm-Redox surfaces required 120 min to become hydrophilic after temperature reduction. These results indicated that a faster conformational change triggered cell detachment and a slow conformation change hardly affected cell detachment. Therefore, polymeric conformation on solid substrate was an important factor for modulating cell adhesion and detachment.

Reduction of fluid drag is important in the micro-/nanofluidic systems. Surface charge and boundary slip can affect the fluid drag, and surface charge is also believed to affect boundary slip. The quantification of surface charge and boundary slip at a solid-liquid interface has been widely studied, but there is a lack of understanding of the effect of surface charge on boundary slip. In this paper, the surface charge density of borosilicate glass and octadecyltrichlorosilane (OTS) surfaces immersed in saline solutions with two ionic concentrations and deionized (DI) water with different pH values and electric field values is quantified by fitting experimental atomic force microscopy (AFM) electrostatic force data using a theoretical model relating the surface charge density and electrostatic force. Results show that pH and electric field can affect the surface charge density of glass and OTS surfaces immersed in saline solutions and DI water. The mechanisms of the effect of pH and electric field on the surface charge density are discussed. The slip length of the OTS surface immersed in saline solutions with two ionic concentrations and DI water with different pH values and electric field values is measured, and their effects on the slip length are analyzed from the point of surface charge. Results show that a larger absolute value of surface charge density leads to a smaller slip length for the OTS surface.

The self-polymerization of 4-chloromethylphenyltrichlorosilane (CMPS) was studied within spatially confined nanoholes on Si(111) using atomic force microscopy (AFM). Surface platforms of nanoholes were fabricated within a film of octadecyltrichlorosilane using immersion particle lithography. A heating step was developed to temporarily solder the silica mesospheres to the surface, to enable sustained immersion of mesoparticle masks in solvent solutions for the particle lithography protocol. Substrates with a film of mesospheres were heated briefly to anneal the particles to the surface, followed by a rinsing step with sonication to remove the silica beads to generate nanopores within an octadecyltrichlorosilane (OTS) film. Nanopatterned surface templates were immersed in CMPS solutions and removed at different time points to monitor the successive growth of nanostructures over time. Analysis of AFM images after progressive exposure of the nanoholes to solutions of CMPS provided quantitative information and details of the surface self-assembly reaction. Pillar nanostructures of CMPS with different heights and diameters were produced exclusively within the exposed areas of the substrates. Throughout the reaction, the surrounding matrix of OTS-passivated substrate did not evidence growth of CMPS; the surface assembly of CMPS was strictly confined within the nanopores. The diameter of the CMPS nanostructures grew to match the initial sizes of the confined areas of Si(111) but did not spread out beyond the edges of the OTS nanocontainers. However, the vertical growth of columns was affected by the initial size of the sites of uncovered substrate, evidencing a direct correspondence; larger sites produced taller structures, and correspondingly the growth of shorter structures was observed within smaller nanoholes. The heights of CMPS nanostructures indicate that multilayers were formed, with taller columns generated after longer immersion times. These experiments offer intriguing possibilities for using particle lithography as a general approach for nanoscale studies of molecular self-assembly.

Gallium nitride, with a thin passivating layer of Ga2O3, has been functionalized with octadecyltrichlorosilane (OTS) and aminopropyltriethoxysilane (APTES) self-assembled monolayers (SAMs). Water contact angles, atomic force microscopy, and X-ray photoelectron spectroscopy were used for characterization of the bare and functionalized surfaces. The SAMs are stable in acetonitrile, but both the hydrophobic OTS SAM and the hydrophilic APTES SAM completely desorb after 1-24 h of immersion in water and common buffers. The concentration of gallium in solution after a clean GaN chip is immersed in water is consistent with dissolution of roughly one monolayer of interfacial gallium oxide. Dissolution of this oxide layer could account for the loss of SAMs from GaN surfaces.

We have employed in situ X-ray reflectivity (IXRR) to study the adsorption of a variety of proteins (lysozyme, cytochrome c, myoglobin, hemoglobin, serum albumin, and immunoglobulin G) on model hydrophilic (silicon oxide) and hydrophobic surfaces (octadecyltrichlorosilane self-assembled monolayers), evaluating this recently developed technique for its applicability in the area of biomolecular studies. We report herein the highest resolution depiction of adsorbed protein films, greatly improving on the precision of previous neutron reflectivity (NR) results and previous IXRR studies. We were able to perform complete scans in 5 min or less with the maximum momentum transfer of at least 0.52 Å(-1), allowing for some time-resolved information about the evolution of the protein film structure. The three smallest proteins (lysozyme, cytochrome c, and myoglobin) were seen to deposit as fully hydrated, nondenatured molecules onto hydrophilic surfaces, with indications of particular preferential orientations. Time evolution was observed for both lysozyme and myoglobin films. The larger proteins were not observed to deposit on the hydrophilic substrates, perhaps because of contrast limitations. On hydrophobic surfaces, all proteins were seen to denature extensively in a qualitatively similar way but with a rough trend that the larger proteins resulted in lower coverage. We have generated high-resolution electron density profiles of these denatured films, including capturing the growth of a lysozyme film. Because the solution interface of these denatured films is diffuse, IXRR cannot unambiguously determine the film extent and coverage, a drawback compared to NR. X-ray radiation damage was systematically evaluated, including the controlled exposure of protein films to high-intensity X-rays and exposure of the hydrophobic surface to X-rays before adsorption. Our analysis showed that standard measuring procedures used for XRR studies may lead to altered protein films; therefore, we used modified procedures to limit the influence of X-ray damage.

Bacterial attachment on solid surfaces has various implications in environmental, industrial and medical applications. In this study, the effects of rhamnolipid biosurfactants on initial attachment of bacteria on hydrophilic glass and hydrophobic octadecyltrichlorosilane (OTS) modified glass were evaluated under continuous-flow conditions. The bacteria investigated were three Gram-negative species Pseudomonas aeruginosa , Pseudomonas putida , and Escherichia coli , and two Gram-positive species Staphylcoccus epidermidis and Bacillus subtilis . Rhamnolipids, at 10 and 200 mg/l, significantly reduced the attachment of all but S. epidermidis on both glass and OTS-modified glass. For S. epidermidis rhamnolipids reduced the attachment on OTS-modified glass but not on glass. Studies were further done to identify the mechanism(s) by which rhamnolipids reduced the cell attachment. The following potential properties of rhamnolipids were investigated: inhibition of microbial growth, change of cell surface hydrophobicity, easier detachment of cells already attached to substratum, and modification of substratum surface properties. Results showed that rhamnolipids were ineffective for the latter two effects. Rhamnolipids, up to 200 mg/l, inhibited the growth of B. subtilis , S. epidermidis and P. aeruginosa PAO1 but not the growth of E. coli , P. putida and P. aeruginosa E0340. Also, rhamnolipids tended to increase the hydrophobicity of P. aeruginosa PAO1 and E. coli , decrease the hydrophobicity of P. putida and S. epidermidis , and have no clear effect on the hydrophobicity of B. subtillis . These trends however did not correlate with the observed trend of cell attachment reduction. The responsible mechanism(s) remained unknown.

Silicon substrates were modified with octadecyltrichlorosilane and 3-Aminopropyl-triethoxysilane molecules by chemical adsorption process. The surface properties, morphology and composition were characterised by means of contact angle measurement, atomic force microscopic (AFM) analysis and X-ray photoelectron spectroscopy. To achieve quantitative results, it is important to implement the proper force calibration in AFMs. Both the lateral and the normal spring constants of the AFM cantilever were calibrated. The nanotribological properties including adhesion, friction and antiwear of silane derived surface modification are comparatively studied with the calibrated AFM cantilever. The results demonstrated that the silane derived surface modification reduces adhesion and friction. Hydrophobic methyl terminated modification possesses better friction reduction and antiwear capacity than hydrophilic amine terminated surface.

Taking plasma-enhanced chemical vapor deposited porous SiOCH (p-SiOCH) and octadecyltrichlorosilane (OTS) as model cases, this study elucidates the chemical reaction pathways for alkyl-based self-assembled monolayers (SAMs) on porous carbon-doped organosilica films under N(2)-H(2) vacuum plasma illumination. In contrast to previous findings that carboxylic groups are found in alkyl-based SAMs only by exposure to oxygen-based plasma, this study discovers that, upon exposure to reductive nitrogen-based vacuum plasma, surface carboxylic functional groups can be instantly formed on OTS-coated p-SiOCH films. Particular attention is given to developing a multisurface modification process, starting with the modification of p-SiOCH films by N(2)-H(2) plasma and continuing with SAM deposition and plasma patterning; this ultimately leads to site-selective seeding for the spatially controlled fabrication of Cu-wire metallization by electroless deposition. Plasma diagnosis and X-ray near-edge absorption and Fourier transform infrared spectroscopies show that, by adequately controlling the plasma parameters, the bulk of the p-SiOCH films are free from plasma damage (in terms of degradation in bonding structures and electrical properties); the formation of the seed-trapping carboxylic functional groups on the surface, the key factor for the validity of this new seeding process, is due to a water-mediated chemical oxygenation route.

A uniform closely packed hexagonal array of porous anodic alumina (PAA) film with an average pore diameter of ~100 nm and a pore height of ~330 nm was obtained by anodizing in oxalic acid solution. Low surface energy molecules of perfluoropolyether (PFPE) and octadecyltrichlorosilane (OTS) were used to enhance the hydrophobicity of the PAA and aluminum (Al) surface. The tribological performances were investigated in detail. The results showed that the static friction coefficient of PAA was much lower than that of smooth Al, which could be due to the higher hardness of the PAA than that of Al. PAA modified with PFPE was characterized by lower friction coefficient and longer wear life as compared with bare Al, PAA, and PAA modified with OTS. This is caused by the combined effects of flexibility, mobility, and inherent lubricity of PFPE molecules and the nanoporous structure of PAA as a reservoir for lubricants and wear particles.

The modification of dielectric surface with a self-assembled monolayer (SAM) such as octadecyltrichlorosilane (OTS) is a widely used method to tune the electrical property of diverse electronic devices based on organic semiconductors, graphene, transition metal dichalcogenides (TMDs), and so forth. The surface roughness of self-assembled OTS monolayer is a key factor in determining its effect on device performance, but the preparation of an ultrasmooth OTS monolayer is a technologically challenging task. In this work, an ultrasmooth OTS monolayer is prepared via a facile peeling method, which may serve as a postremedy strategy to remove the protuberant aggregates. Such a method has not been reported before. With organic semiconductors as a testing model, ultrasmooth OTS may significantly improve the charge mobility of organic field-effect transistors (OFETs). P-type dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) OFET with an ultrasmooth OTS monolayer yields good reproducibility and unprecendented maximum mobility of 8.16 cm(2) V(-1) s(-1), which is remarkably superior to that of the OFET with a pristine OTS monolayer. This work develops a simple method to resolve the common and significant problem of the quality of OTS modification, which would be highly promising for electronic applications as well as other fields such as surface and interface engineering.

We investigate the surface-directed phase separation of spin-coated polystyrene/poly(methyl methacrylate) (PS/PMMA) blends on prepatterned octadecyltrichlorosilane (OTS)-glass substrates under various experimental conditions. As a result of tandem processes of spinodal decomposition and selective wetting of polymer components during spin-coating, low-energy OTS stripes and high-energy glass surfaces laterally arrange the phase-separated polymers according to the chemical pattern on the substrate. Optimal pattern replication was achieved when the length scale of phase separation, controlled via the polymer concentration of the spin-coating solution, matched the smallest feature dimension in a striped chemical pattern possessing two alternating distances between stripes. It was also shown that polymer blend patterns were most closely registered with the underlying substrate when the PS/PMMA composition ratio (30/70, w/w) matched the areal fraction of OTS on the glass surface (∼30%). The influence of solvents demonstrated that a solvent with a relatively low volatility, such toluene, was required for patterning so that domain feature sizes were able to coarsen to the size of the patterned features before film vitrification. As well, we showed that the technique and optimized conditions developed in this study could be applied to pattern photoluminescent CdS quantum dots into microscale arrays of parallel lines via spin-coating onto transparent OTS-glass substrates.

Vanadium pentoxide (V2O5) nanowires have been synthesized on Au-coated Si substrates by a physical vapor deposition process. The synthesized nanowires are randomly oriented with a diameter around 40–200 nm and length of several micrometers. The crystalline structure of the nanowires analyzed by using X-ray diffraction and Raman spectroscopy corresponds to single crystalline orthorhombic V2O5 phase with [0 0 1] growth orientation. The transmission electron microscopy and energy-dispersive X-ray analysis suggests a possible vapor–solid (VS) growth mechanism for the V2O5 nanowires. A self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) was deposited on the V2O5 nanowires to obtain superhydrophobic V2O5 nanowire surfaces with water contact angle (CA) of 157.5°. The superhydrophobic behavior is attributed to the high surface roughness provided by the nanowire surface and low surface energy due to SAM layer deposition. The impact dynamics of water droplets impinging on the superhydrophobic surface is also investigated.

Bacterial biofilm can have significant effects on the behaviors and/or performance of natural and man-made systems. Understanding the factors governing initial bacterial attachment is critical to biofilm management. In this study, the initial attachment of three bacteria, Pseudomonas aeruginosa, Escherichia coli and Pseudomonas putida, on two substrates, glass and octadecyltrichlorosilane (OTS) modified glass, was examined in flow chambers. The flow chambers were designed and operated to mimic slow moving water bodies and minimize the gravitational settlement of cells. The hydrophobicity of bacterial surface was evaluated by partitioning of cells to the water-hexadecane interface and the liquid contact angles on cell layers collected on filter papers. On the more hydrophilic glass surface, the attachment trend was found to be E. coli>P. putida>P. aeruginosa, while the opposite trend was observed on the hydrophobic, OTS modified surface. The attachment trend on glass could be explained by the magnitude of the negative interaction energy at secondary minima, as predicted by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The much higher attachments of P. aeruginosa and P. putida on the OTS-modified substrate, on the other hand, suggested that these cells could overcome the energy barrier between the primary and secondary minima of interaction energy to become attached to the primary minimum. The extent of primary-minimum attachment appeared to correlate with the scale of the energy barrier, with higher attachments in the bacteria-substrate combinations of lower energy barriers. The study generated important insights into the effects of cell and substrate surface properties on initial bacterial attachment.