Tuning the hydrophobic properties of silica particles by surface silanization using mixed self-assembled monolayers

Here we describe a novel method of preparing hydrophobic silica particles (100-150 nm; water contact angle of dropcasted film ranging from 60 degrees to 168 degrees) by surface functionalization using different alkyltrichlorosilanes. During their preparation, the molecular surface roughness is also concurrently engineered facilitating a change in both the surface chemical composition and the geometrical microstructure to generate hierarchical structures. The water contact angle has been measured on drop-cast film surface. The enhancement in the water contact angle on 3D (curved) SAMs in comparison to that on 2D (planar) surface is discussed using the Cassie-Baxter equation. These silica particles can be utilized for many potential applications including selective adsorbents and catalysts, chromatographic supports and separators in microfluidic devices.     

Tuning the hydrophobicity of mica surfaces by hyperthermal Ar ion irradiation

The hydrophobicity of surfaces has a strong influence on their interactions with biomolecules such as proteins. Therefore, for in vitro studies of bio-surface interactions model surfaces with tailored hydrophobicity are of utmost importance. Here, we present a method for tuning the hydrophobicity of atomically flat mica surfaces by hyperthermal Ar ion irradiation. Due to the sub-100 eV energies, only negligible roughening of the surface is observed at low ion fluences and also the chemical composition of the mica crystal remains almost undisturbed. However, the ion irradiation induces the preferential removal of the outermost layer of K(+) ions from the surface, leading to the exposure of the underlying aluminosilicate sheets which feature a large number of centers for C adsorption. The irradiated surface thus exhibits an enhanced chemical reactivity toward hydrocarbons, resulting in the adsorption of a thin hydrocarbon film from the environment. Aging these surfaces under ambient conditions leads to a continuous increase of their contact angle until a fully hydrophobic surface with a contact angle >80° is obtained after a period of about 3 months. This method thus enables the fabrication of ultrasmooth biological model surfaces with precisely tailored hydrophobicity.     

Effects of rugged nanoprotrusions on the surface hydrophobicity and water adhesion of anisotropic micropatterns

A facile laser-etching method was used for the one-step creation of various controllable dimensions of anisotropic micropatterns consisting of an alternating arrangement of microgrooves and microstripes with rugged nanoprotrusions, which after modified with fluoroalkylsilane reagent, showed perfect isotropic superhydrophobicity without apparent CA hystereses, water adhesion, and drag resistance, other than the conventional view of anisotropic surface microstructures with anisotropic surface dewetting. The detailed experiments and analyses have indicated that the introduction of the rugged nanoprotrusions on the surface of microstripes provided ideal 3D roughness, which could not only enhance the apparent contact angles close to 180 degrees by the "point" contact fashion to maximally reduce the liquid-solid contact area but, most importantly, make droplets easily roll off the surface without apparent CA hysteresis by regulating the triple-phase contact line (TCL) to become extremely discrete. These findings would be helpful in understanding the role of complex micro- and nanostructures on natural superhydrophobic biosurfaces and guiding the design of perfect artificial superhydrophobic materials for technological innovations such as the raindrop easy-cleaning, aquatic super-floating, and drag-reducing coatings.     

Staudinger–Vilarassa reaction versus Huisgen reaction for the control of surface hydrophobicity and water adhesion

Surface modifications are keys for a great number of applications. In order to perfectly control the surface properties, it is important to control the modification pathways. Two general pathways can be described in order to introduce modification on surfaces: the post‐strategies and the ante‐strategies. In this work, we focus on the comparison between the Huisgen and the Staudinger–Vilarrasa reaction for both post‐surface and ante‐surface modifications. Here, we focused on the possibility to use both two reactions to obtain superhydrophobic and oleophobic properties. This work includes monomer synthesis, surface modifications with alkyl, aryl or perfluoroalkyl chain. Copyright © 2016 John Wiley & Sons, Ltd.     

Tuning hydrophobicity of a fluorinated terpolymer in differently assembled thin films

In the current report, casting from good solvent (acetone) and casting from mixed solvent and nonsolvent were employed for preparing thin films of terpolymer of T etrafluoroethylene (TFE), H exafluoropropylene (HFP), and V inylidene fluoride (VDF) (THV), on silicon wafers. These films revealed various morphologies and wetting behaviors depending on the solution concentration, temperature, and thin film preparation method. The THV thin films prepared by casting from good solvent showed smooth morphology with holes. The thin film prepared from a 3 wt % THV/acetone solution by casting from good solvent at 15 °C demonstrated spheres in addition to the smooth morphology, while the thin film prepared from a 5 wt % THV/acetone solution at 15 °C by casting from good solvent had a mesh‐like structure with some linked spheres. Casting the thin films from mixed solvent and nonsolvent resulted in various morphologies such as different sphere sizes embedded in a dense film layer, and hexagonal close packed structures. The thin films prepared by casting from good solvent showed a slightly hydrophobic character, with a measured water contact angle of approximately 99°, while the nonsolvent cast films had a water contact angle as high as 145°. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 643–657     

Tuning the surface hydrophobicity of polymer/nanoparticle composite films in the Wenzel regime by composition

Surface hydrophobicity of composite films containing polymer and nanoparticles has been studied as a function of composition. We show that the hydrophobicity can be tuned by adjusting the amount of particles in the two-component system. A sharp transition from a polymer-rich surface to a nanoparticles-rich surface was observed with increasing mass fraction of particles in spin-coated thin films. Water drops on the films did not slide down even at tilt angles of 90 degrees . Contact angle hysteresis increased with the mass fraction of particles indicating that the surface roughness increased as the surfaces remained in the Wenzel regime. Contact angle hysteresis data were quantitatively consistent with predictions of a recent theory.     

Optimization of silica silanization by 3-aminopropyltriethoxysilane

Thin films of 3-aminopropyltriethoxysilane (APTES) are commonly used to promote adhesion between silica substrates and organic or metallic materials with applications ranging from advanced composites to biomolecular lab-on-a-chip. Unfortunately, there is confusion as to which reaction conditions will result in consistently aminated surfaces. A wide range of conflicting experimental methods are used with researchers often assuming the creation of smooth self-assembled monolayers. A range of film morphologies based on the film deposition conditions are presented here to establish an optimized method of APTES film formation. The effect of reaction temperature, solution concentration, and reaction time on the structure and morphology was studied for the system of APTES on silica. Three basic morphologies were observed: smooth thin film, smooth thick film, and roughened thick film.     

New silanization coating for DNA fragment analysis by capillary electrophoresis

We propose a new coating technique for fused silica capillaries using silanization with trimethylchlorosilane and diethylamine as a mediating agent in DNA separation using capillary electrophoresis. The proposed coating technique is simple and stable at a high pH. Capillaries coated by the new preparation method give excellent reproducibility for DNA fragment analysis with a good relative standard deviation of less than 0.7% for 150 runs and good stability at pH 8.2. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1405–1420, 2002     

Characterization of the hydrophobicity of mesoporous silicas and clays with silica pillars by water adsorption and DRIFT

The hydrophobic-hydrophilic properties of a solid are related to the material chemistry and, often, these properties are relevant to the applications of a particular material. Contrarily to what happens with other properties, such as specific surface areas or pore volumes, the methodologies to ascertain on the hydrophilicity of a porous material are not well defined. In this work, we discuss and relate the information on the hydrophobicity degree obtained from water adsorption isotherms and from diffuse reflectance infrared Fourier transform (DRIFT), in a set of porous materials. The studied materials were mainly mesoporous solids, namely of MCM-41 and SBA-15 types, two xerogels and also different porous clays heterostructures. Both techniques were informative on the hydrophobic-hydrophilic properties of the studied samples, but the correlation between the information obtained by each technique was not straightforward. Water adsorption isotherms are much more sensitive to the differences of the studied materials than the DRIFT spectra. For silica-based mesoporous materials with similar surface chemistry, the water adsorption process and hence, the hydrophobic-hydrophilic properties, is mainly dependent on the pore diameters. However, water adsorption is much more sensitive to changes in the nature of the adsorbent surface than to changes in the pore diameter.     

Selective fabrication of porous iron oxides hollow spheres and nanofibers by electrospinning for photocatalytic water purification

Porous hematite (α-Fe₂O₃) hollow spheres and nanofibers could be obtained via electrospinning and subsequent thermal decomposition in air. The precursor could be fabricated by electrospinning using Fe(NO₃)₃ as the iron source and Polyvinylpyrrolidone (PVP) as a complexing reagent. Upon calcination, pure porous α-Fe₂O₃ hollow spheres and nanofibers could be obtained at 650 °C for 3 h. The novel hollow spheres have an abundantly porous structure as well as large surface areas. Benefitting from the special porous structure, narrow bandgap, and higher surface area, porous α-Fe₂O₃ hollow materials are used as visible-light-responsive photocatalysts. So we have investigated the visible light photodegradation behavior of porous hematite (α-Fe₂O₃) hollow spheres and nanofibers towards organic dyes, as Rhodamine B (RhB). The synergetic effects of higher surface area, pore structures promoted the photocatalytic efficiency for RhB degradation under visible light and contributed to achieving the enhanced and stable photocatalytic activity.     

Polymer nanofibers assembled by electrospinning

Electrospinning is a process by which polymer nanofibers (with diameter lower than 100 nm and lengths up to kilometres) can be produced using an electrostatically driven jet of polymer solution (or polymer melt). Simple alignment of electrospun nanofibers constructs unique functional nanostructures such as nanotubes and nanowires. Significant progress has been made in this area throughout the past few years and this technology has been exploited to a wide range of applications. Most of the recent work on electrospinning has focused either on trying to understand deeper the fundamental aspects of the process in order to gain control of nanofiber morphology, structure, surface functionality, and strategies for assembling them or on determining appropriate conditions for electrospinning of various polymers and biopolymers.     

Role of lactobacillus cell surface hydrophobicity as probed by AFM in adhesion to surfaces at low and high ionic strength

The S-layer present at the outermost cell surface of some lactobacillus species is known to convey hydrophobicity to the lactobacillus cell surface. Yet, it is commonly found that adhesion of lactobacilli to solid substrata does not proceed according to expectations based on cell surface hydrophobicity. In this paper, the role of cell surface hydrophobicity of two lactobacillus strains with and without a surface layer protein (SLP) layer has been investigated with regard to their adhesion to hydrophobically or hydrophilically functionalized glass surfaces under well-defined flow conditions and in low and high ionic strength suspensions. Similarly, the interaction of the lactobacilli with similarly functionalized atomic force microscope (AFM) tips was measured. In a low ionic strength suspension, both lactobacillus strains show higher initial deposition rates to hydrophobic glass than to hydrophilic glass, whereas in a high ionic strength suspension no clear influence of cell surface hydrophobicity on adhesion is observed. Independent of ionic strength, however, AFM detects stronger interaction forces when both bacteria and tip are hydrophobic or hydrophilic than when bacteria and tip have opposite hydrophobicities. This suggest that the interaction develops in a different way when a bacterium is forced into contact with the tip surface, like in AFM, as compared with contacts developing between a cell surface and a macroscopic substratum under flow. In addition, the distance dependence of the total Gibbs energy of interaction could only be qualitatively correlated with bacterial deposition and desorption in the parallel plate flow chamber.     

Stabilization of hydroxyl-group-terminated SERS-marker molecules on microAg particles by silanization

Surfactant modified montmorillonitic clays synthesized by ion exchange using the hydrothermal reaction method have been compared using XRD and thermal analysis. X-ray diffraction (XRD) shows the changes in the surface properties of organoclays through expansion with surfactant loading. A polynomial relationship exists between the basal spacing and the CEC loading described by the equation y=0.3232x(2) + 0.2052x+1.2834 with R(2)=0.9955. Different arrangements of the surfactant molecules in the organoclays are inferred from the changes in basal spacings. para-Nitrophenol also causes the expansion of the montmorillonite clay and affects the arrangements of the surfactant molecules within the clay layers. Changes in the surfactant molecular arrangements were analyzed by thermogravimetry. Additional thermal decomposition steps were observed when para-nitrophenol is adsorbed on the organoclay.     

Kinetically stable complexes in water: the role of hydration and hydrophobicity

We describe here the synthesis and characterization of a molecular receptor that forms kinetically and thermodynamically stable host-guest complexes in water. This cavitand-based host is composed of a preorganized aromatic pocket whose rim is decorated with four negatively charged carboxylate groups. (1)H NMR and isothermal titration calorimetry have been used to characterize the behavior of the resulting complexes in response to changes in pH, buffer identity, and salt concentration and in the presence of sodium dodecyl sulfate micelles.     

Tuning of thermo-responsive self-assembly monolayers on gold for cell-type-specific control of adhesion

Self-assembled monolayers (SAMs) on gold containing a thermo-responsive poly( N-isopropylacrylamide)-poly(ethylene glycol)-thiol copolymer were formed. These layers show considerable potential for inducing enzyme-free and gentle detachment of cultivated cells. In an effort to optimize detachment of cells, including strongly adhering ones, two approaches are presented. First, two thermo-responsive copolymers with different poly(ethylene glycol) (PEG) contents of 15 wt % ("P15") and 19 wt % ("P19") were grafted to Au surfaces. Second, mixed monolayers were formed containing P19 and various concentrations of thiol bearing PEG. X-ray photoelectron spectroscopy (XPS) on pure and mixed P19 containing layers confirmed the expected layer compositions. Contact angle measurements showed good functionality of all surfaces prepared. Upon a temperature decrease below the lower critical solution temperature (LCST), the duration until cultivated fibroblasts detached from pure P19 surfaces was half of the one determined on P15. Strongly adherent human osteosarcoma cells could not be detached from pure P19 layers. Through co-adsorption of P19 and thiol-bearing PEG of a molar composition of 1:6, layers were formed that allowed good spreading of osteosarcoma cells above LCST and their efficient detachment below LCST.     

静电纺丝法制备MgO纳米纤维

以聚乙烯醇(PVA)作为络合剂与醋酸镁反应制得前驱体，采用静电纺丝法制得聚乙烯醇(PVA)／醋酸镁复合纤维，经焙烧后得到分布均匀、具有较高比表面积和多孔结构的。MgO纳米纤维．对所制得的纳米纤维的结晶度、纯度和表面形貌，分别采用X射线粉末衍射、差热一热重分析(TG-DTA)、红外光谱(IR)、扫描电镜(SEM)等分析测试手段进行了表征．结果表明，煅烧温度对纳米纤维的结晶度和形貌有很大影响．     

Fibroin nanofibers production by electrospinning method

Silk fibroin, which has many characteristic properties such as low inflammation reaction, biodegradation, suppleness, good antithrombogenic details, biocompatibility and high tensile strength is a very good candidate for biomedical applications. Electrospinning procures high surface area, porous, nanofiber dimension fiber generation, which is a plain method. An experimental study was carried out to produce nanofiber structure from silk fibroin by electrospinning and the electrospinning parameters for the spinning of uniform, continuous and silk fibroin fibers were optimized. As a result, the effect of variables of concentration, distance and applied voltage on the strength, thickness, surface structure, fiber diameter of nanomaterial was investigated. Then, in vitro cell viability of the silk fibroin mat was analyzed. It was seen that the strength, mat thickness, and fiber diameter increased with solution concentration rise. It was found that the values of the fiber diameter and tensile strength decreased with increasing distance. It was determined that the effect of distance varies depending on the concentration in the mat thicknesses. The tensile strength was affected inversely proportional the applied voltage rises and distance. It was found that the fiber diameter values decreased together with increasing applied voltage. At cell viability of silk fibroin mat was occurred high cell viability after 24 h, but it was obtained low cell viability at the 48th h.     

The hydrophobicity of non-aqueous liquids and their dispersion in water under degassed conditions

Several recent studies have shown that many oils, such as hydrocarbons, fluorocarbons, silicone and natural oils, are more readily dispersed as fine (micron-sized) droplets in water when the mixtures are almost completely degassed. These observations have not yet been fully explained and so this paper examines the nature of hydrophobicity of a wide range of oils and considers both the cavitation process and the surface charging expected during the separation of hydrophobic materials in water. Cavitation inside porous hydrophobic solids immersed in water is also considered. We also introduce a quick, easy and alternative method to freeze–thaw degassing, by which enhanced dispersions can be formed, which gives further support to the central role of degassing.     

Flat polymer ribbons and other shapes by electrospinning

In addition to round nanofibers, electrospinning a polymer solution can produce thin fibers with a variety of cross‐sectional shapes. Branched fibers, flat ribbons, ribbons with other shapes, and fibers that were split longitudinally from larger fibers were observed. The transverse dimensions of these asymmetric fibers were typically 1 or 2 μm, measured in the widest direction. A correlation of the branches and bends, observed in high‐frame‐rate videography of the electrified jets of polymer solutions from which the ribbons and branched fibers were produced, suggest that these phenomena occur at scales ranging from around 1 mm to 1 μm. The observation of fibers with these cross‐sectional shapes from a number of different kinds of polymers and solvents indicates that fluid mechanical effects, electrical charge carried with the jet, and evaporation of the solvent all contributed to the formation of the fibers. The influence of a skin on the jets of polymer solutions accounts for a number of the observations. The observed shapes can be used as guides for the extension of mathematical or computer‐generated models for the electrospinning process. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2598–2606, 2001     

Crimped polymer nanofibres by air-driven electrospinning

Electrospinning is a well-known process for producing sub-micron scale polymer filaments through an electrostatic field. This paper presents a very simple “confined” air-driven electrospinning system, in which polyamide nanofibres are produced in the form of continuous crimped filaments. The reported system consists of a vertical cylinder with a weak tangential air-flow feeding from the top, placed between the capillary source electrode and the grounded target collector. The air-flow drives the polymer jet inside the electrostatic field, curls up the filament and reduces the deposition area on the collector surface. Numerical evaluations of both the electrostatic field and the air-flow path within the chamber are reported. The proposed configuration has been successfully tested electrospinning a solution of polyamide-6 in formic acid, varying the applied voltage and the distance between the electrodes. SEM observations of the electrospun fibres revealed that a large amount of crimped nanofibres was produced free from bead defects.