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Phospholipid monolayers at oil-water interfaces are often obtained via vesicle adsorption. However, the interaction mechanisms of vesicles with these oil-water interfaces remain unclear. Herein, we studied the adsorption of giant unilamellar vesicles (GUVs) of approximately 2-5 μm diameter onto silicone oil-water interfaces and glass surfaces modified with hexamethyldisilazane (HMDS) and octadecyltrimethoxysilane (ODTMS) using fluorescence microscopy. The GUVs exhibited various modes of interaction, adsorbing on the silanized glass surfaces without sizable deformation, whereas GUVs bound to the silicone oil-water interface exhibited large deformation. After adsorption, GUV rupture occurred within 350, 110, and 3 ms on HMDS-modified glass, ODTMS-modified glass, and silicone oil-water interface, respectively. On glass surfaces, GUV rupture was often initiated and proceeded with pore formation near the surface. The monolayer patches formed by GUV rupture on HMDS-modified glass remained for at least 1 h over an area approximately twice of that estimated from the original GUV. On the ODTMS-modified glass and silicone oil surfaces, the monolayer patch structures disappeared in milliseconds owing to lipid diffusion across the interface. When adsorbed on the oil-water interface, the GUVs spontaneously underwent dynamic shape changes, internal vesicle formation, and desorption without rupture. Thus, it can be concluded that these different pathways arose from different lipid-surface affinities.

The effect of the triangular pinning region on the sliding of water droplets on the smooth hydrophobic surface was investigated. Smooth hydrophobic silane coatings with various regular triangle hydrophilic regions were prepared using photolithography and octadecyltrimethoxysilane (ODS). The hydrophilic area in the surfaces was aligned hexagonally with a constant area fraction. Thereby water contact angles of the coatings were almost equivalent. The water droplet sliding velocity increased continuously with increasing pattern size. Anisotropic sliding velocity was observed on the surface, suggesting different pinning effects. The sliding motion of water droplets on the gradient surface with changing hydrophilic region size deflects against the downward direction. The deflection length depends on the direction of triangle hydrophilic regions and the initial sliding position. These results demonstrate that control of the sliding velocity while sustaining the static contact angle is feasible by designing the shape and alignment of chemical heterogeneity.

Ion rectification is one of the important characteristics of biological ion channels. Inspired by the function of biological ion channels, creation of artificial nanochannels that show analogous ion rectification characteristics has attracted a great interest recently. Herein, we demonstrate a new type of artificial solid-state nanochannel with ion rectification characteristics. The creation of artificial nanochannels includes the formation of asymmetric TiO2 nanotubes by electrochemical anodization of Ti metal, followed by chemical modification with octadecyltrimethoxysilane (OTS) molecules. The carboxylic groups are introduced onto the tip side of TiO2 nanotubes via photocatalytic decomposition of OTS molecules by TiO2 photocatalysis under ultraviolet light. When the radius of tip side of TiO2 nanotubular channels is comparable to the thickness of electric double layer, the negatively charged surface in neutral electrolyte in combination with the asymmetric pore geometry contributes to the ion rectification characteristics. Compared with previous artificial nanochannels, our new type of artificial nanochannel is more facile to fabricate and behaves as a diode that rectifies the ion transport, which also shows some other potential applications, such as sensor and separation materials.

The composition and structure of a binary mixed self-assembled monolayer (SAM) of 3-aminopropyltriethoxysilane (APS, NH(2)(CH(2))(3)Si(OCH(2)CH(3))(3)) and octadecyltrimethoxysilane (ODS, CH(3)(CH(2))(17)Si(OCH(3))(3)) on a silicon oxide surface have been characterized by water contact-angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and sum frequency generation (SFG) vibrational spectroscopy. XPS demonstrated that APS in the mixed SAM is significantly enriched in comparison to that in solution, indicating the preferential adsorption of APS during the SAM formation. AFM observations showed that the mixed SAM becomes rougher. SFG revealed that the coadsorption of APS induced a conformation disordering in the ODS molecules present in the mixed SAM. The surface enrichment of APS has been explained in terms of differences in the surface adsorption rates of the two components as well as in the self-congregation states of APS molecules in the bulk solution. Furthermore, the structure of the water molecules on the mixed SAM surface in contact with the aqueous solutions at different pH's has also been studied. The results indicate that the mixed-SAM modified surface is positively charged at pH5 and negatively charged at pH7.

ZnO nanowire (NW) array was conformally coated with an ultrathin SiO(2) shell by a bioinspired layer-by-layer deposition in order to obtain ultraviolet (UV)-durable superhydrophobic property. Uniform SiO(2) shell was prepared on ZnO NW by alternative reactive deposition of polyethylenimine and silicic acid. Despite the highly curved morphology of ZnO NW array, the thickness of SiO(2) shell increased linearly with the number of deposition cycles, with a thickness increment being of approximately 4.17 nm per deposition cycle. The SiO(2) shell only had a slight influence on the superhydrophobic property of ZnO NW array after modification with a monolayer of octadecyltrimethoxysilane (OTS). However, it greatly improved the UV durability of the superhydrophobic property of ZnO NW array due to the confinement effect of insulating SiO(2) layer on the photogenerated electron-hole pairs in ZnO NW.

We combine convective/capillary deposition and oxidation lithography by atomic force microscopy to direct the close-packed assembly of colloids on SiOx patterns fabricated on silicon substrates previously functionalized with a hydrophobic monolayer of octadecyltrimethoxysilane. The efficiency of this original generic method, which is well adapted to integrate colloids into silicon devices, is demonstrated for 100 nm colloidal latex nanoparticles and Escherichia coli bacteria in aqueous suspensions. A three-step mechanism involving convective flow and capillary forces appears to be responsible for these close-packed assemblies of colloids onto SiOx patterns.

Core-shell nanocapsules intended to be used as drug scavengers were prepared using a surfactant mixture containing octadecyltrimethoxysilane (OTMS) as a reactive amphiphile, to form spherical templates. A siloxane shell was grown on the surface of the templates by reacting tetramethoxysilane (TMOS) with the silanol groups obtained after the hydrolysis and condensation of OTMS. Dynamic light scattering (DLS) showed that particles with diameters in the range of 100-200 nm were obtained, with core and shell sizes controlled by varying component compositions. Atomic force microscopy (AFM) was used to study the effect of the silica coating of the templates on their robustness after deposition on a substrate. Subsequently, we present studies on the encapsulation of two hydrophobic fluorescent dyes, which are sensors of polarity and rigidity. Steady-state fluorescence spectroscopy was used to examine the fluorescence response of the dyes before and after shell growth. Changes in the emission of the encapsulated dyes were related to changes in the polarity and rigidity of the microenvironment where the dyes were located and correlated to the AFM results. Finally, dye-free core-shell particles were used to sequester the dyes from aqueous suspensions. Fluorescence of the sequestered species was compared to the dye-loaded particles to determine the final fate of the fluorophores in the nanoparticles.

Self-assembled monolayers (SAMs), a molecular-level assembly that forms spontaneously, provide a vehicle for investigating specific interactions at interfaces. This is particularly true for mixed SAMs that are composed of organosilanes with different chain lengths and/or chemical functionalities because they offer an adjustable surface for constructing 3D structures containing a variety of moieties. We recently observed that coadsorbed monolayers with different organosilanes on a Si wafer were separated into several tens or hundreds of nanometer domains that were rich in individual components. Several organosilanes, such as octadecyltrichlorosilane (OTS), octadecyltrimethoxysilane (OTMS), (3-mercaptopropyl)trimethoxysilane (MPTMS), and (3-aminopropryl)trimethoxysilane (APTMS), were used for regional separation. In this study, we propose a stepwise deposition method, namely, the deposition of a second siliane on a SAM substrate that creates intentional defects in the first silane. The surface morphologies were adjusted by the deposition sequence and immersion time of the silanes. As a result, a mixed SAM prepared by the proposed method showed effectively functionalized films compared to that prepared by the one-step method.

The effect of an acidic surfactant, perfluorotetradecanoic acid (PFTDA), on the gelation of octadecyltrimethoxysilane (ODTMS) monolayers at the air/water interface was investigated using a Langmuir film balance, attenuated total reflection (ATR) infrared spectroscopy, and atomic force microscopy (AFM). The gelation of ODTMS was greatly accelerated by adding only 2 mol % PFTDA into the monolayer; in this case, the hydrolysis of ODTMS was completed within a few minutes, whereas otherwise it took 18 h. ATR-IR spectroscopy clearly demonstrated that the gelation of a 49:1 ODTMS/PFTDA monolayer proceeded on a pure water subphase mainly via hydrolysis followed by condensation. In the presence of PFTDA, the local acidity at specific sites is presumed to be very high, catalyzing the hydrolysis of ODTMS. The extremely fast rate is attributed not only to the lateral diffusion of PFTDA in the mixed monolayer but also to proton propagation where the proton(s) involved in the initial hydrolysis are transposed rapidly to the nearby methoxy groups for subsequent hydrolysis. The catalytic activity of PFTDA can be neutralized, however, simply by the addition of multivalent metallic ions such as Cd2+ to form saltlike complexes with PFTDA; the rate of 2-D sol-gel processes can thus be easily regulated by a minute amount of PFTDA and/or Cd2+ added into the reaction system.