Characterisation and stability of hydrophobic surfaces in water (original) (raw)
Thin Solid Films, 2003
The formation and quality of highly hydrophobic coatings deposited from water dispersible organosilanes onto pre-oxidized single crystal silicon were studied using atomic force microscopy, ellipsometry, dynamic contact angle measurements and electrochemical impedance spectroscopy (EIS). Highly hydrophobic films of a commercially available water dispersible silane and two different cationic alkoxysilanes were prepared by dip coating. It was found using atomic force microscopy that, in general, the structure of these highly hydrophobic films is a continuous film with some particulates attributed to bulk polymerization of the precursor molecule in water. Film defects were quantified using EIS by the value of charge transfer resistance at the hydrofluoric acidysilicon interface. Potential applications of this type of coatings include reductionyelimination of stiction in micro-electromechanical systems, contact printing in materials microfabrication, inhibition of corrosion and oxidation, prevention of water wetting, lubrication and protein adsorption. ᮊ
Functionalization of hydrogenated (111) silicon surface with hydrophobic polymer chains
Physical Review B, 2011
The first stage functionalization of hydrogenated (111) Si surface with methyl-terminated monolayers to form hydrophobic coatings has been studied by accurate ab initio density functional total energy calculations. The first stage adsorption events involving one or two deposited n-alkane and n-alkyl-silane molecules have been characterized from the geometrical and the energetic points of view; the ground-state adsorption configurations together with the geometrical and the energetic parameters relevant to self-assembling processes have been obtained, such as the polymers tilt angles, the rotation energy barriers, the binding energies, and the electrostatic interactions. The above-mentioned quantities have been related to the stability properties of self-assembled monolayers and have been recognized to affect critically the stability and the uniformity of the hydrophobic film elucidating the reasons why some commonly used polymers behave differently.
Hydrophobicity, Hydrophilicity and Silane Surface Modification
Hydrophobicity, Hydrophilicity and Silane Surface Modification, 2011
Surface modification with organosilanes is reviewed in the context of modes of interaction with water. Physical and chemical properties of silicon reagents are tabulated along with deposition techniques.
i ABSTRACT Water affinity and condensation on Si-based surfaces is investigated to address the problem of fogging on silicone intraocular lenses (IOL) during cataract surgery, using Si(100), silica (SiO 2 ) and polydimethylsiloxane (PDMS) silicone (SiOC 2 H 6 ) n . Condensation is described by two step nucleation and growth where roughness controls heterogeneous nucleation of droplets followed by Ostwald ripening. Wetting on hydrophilic surfaces consists of continuous aqueous films while hydrophobic surfaces exhibit fogging with discrete droplets. Si-based surfaces with wavelength above 200 nm exhibit fogging during condensation. Below 200 nm, surfaces are found to wet during condensation. Water affinity of Si-based surfaces is quantified via the surface free energy (SFE) using Sessile drop contact angle analysis, the Young-Dupré equation, and Van Oss theory. Topography is analyzed using tapping mode atomic force microscopy (TMAFM). Polymer adsorption and ion beam modification of materials (IBMM) can modify surface topography, composition, and SFE, and alter water affinity of the Si-based surfaces we studied. Wet adsorption of hydroxypropyl methylcellulose (HPMC) C 32 H 60 O 19 with areal densities ranging from 10 18 atom/cm 2 to 10 19 atom/cm 2 characterized via Rutherford backscattering spectrometry (RBS), allows for the substrate to adopt the topography of the HPMC film and its hydrophilic properties. The HPMC surface composition maintains a bulk stoichiometric ratio as confirmed by 4.265 MeV 12 C( , ) 12 C and 3.045 MeV 16 O( , ) 16 O, and 2.8 MeV He ++ elastic recoil detection (ERD) of hydrogen. Both PIXE and RBS ii methods give comparable areal density results of polymer films on Si(100), silica, and PDMS silicone substrates. The SFE and topography of PDMS silicone polymers used for IOLs can also be modified by IBMM. IBMM of HPMC cellulose occurs during IBA as well. Damage curves and ERD are shown to characterize surface desorption accurately during IBMM so that ion beam damage can be accounted for during analysis of polymer areal density and composition. IBMM of Si(100)-SiO 2 ordered interfaces also induces changes of SFE, as ions disorder surface atoms. The SFE converges for all surfaces, hydrophobic and hydrophilic, as ions alter electrochemical properties of the surface via atomic and electronic displacements.
ACS Nano, 2013
We have synthesized model hydrophobic silicone thin films on gold surfaces by a two-step covalent grafting procedure. An amino-functionalized gold surface reacts with monoepoxy-terminated polydimethylsiloxane (PDMS) via a click reaction, resulting in a covalently attached nanoscale thin film of PDMS, and the click chemistry synthesis route provides great selectivity, reproducibility, and stability in the resulting model hydrophobic silicone thin films. The asymmetric interaction forces between the PDMS thin films and mica surfaces were measured with the surface forces apparatus in aqueous sodium chloride solutions. At an acidic pH of 3, attractive interactions are measured, resulting in instabilities during both approach (jump-in)
Langmuir, 2001
Here we describe a new and simple method for preparing alkyl monolayers on silicon, which consists of mechanically scribing oxide-coated silicon while it is wet with 1-alkenes or 1-alkynes (neat or in inert solvents) under ambient conditions. X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, wetting data, and stability tests suggest covalent bonding of unsaturated species to exposed silicon surfaces. Enclosures (hydrophobic corrals) made by scribing silicon that is wet with unsaturated hydrophobic species hold droplets of water and liquids with substantially lower surface tensions. Wetting tests suggest that 1-alkynes make better hydrophobic corrals than 1-alkenes, and theoretical results suggest it should be more difficult for alkyl chains of chemisorbed 1-alkenes to pack than those of 1-alkynes. Underivatized interior regions of hydrophobic corrals are functionalized with polyelectrolyte multilayers. Theoretical energies for water and methanol droplets (gravitational and surface) in hydrophobic corrals are calculated, and a model of failure of liquid droplets in hydrophobic corrals is presented. * (1) Yoshinobu, J.; Tsuda, H.; Onchi, M.; Nishijima, M.
Micro-and nanostructured silicon-based superomniphobic surfaces
Journal of Colloid and Interface Science, 2014
We report on the fabrication of silicon nanostructured superhydrophobic and superoleophobic surfaces also called ''superomniphobic'' surfaces. For this purpose, silicon interfaces with different surface morphologies, single or double scale structuration, were investigated. These structured surfaces were chemically treated with perfluorodecyltrichlorosilane (PFTS), a low surface energy molecule. The morphology of the resulting surfaces was characterized using scanning electron microscopy (SEM). Their wetting properties: static contact angle (CA) and contact angle hysteresis (CAH) were investigated using liquids of various surface tensions. Despite that we found that all the different morphologies display a superhydrophobic character (CA > 150°for water) and superoleophobic behavior (CA % 140°for hexadecane), values of hysteresis are strongly dependent on the liquid surface tension and surface morphology. The best surface described in this study was composed of a dual scale texturation i.e. silicon micropillars covered by silicon nanowires. Indeed, this surface displayed high static contact angles and low hysteresis for all tested liquids.
Enhanced Hydrolytic Stability of Siliceous Surfaces Modified with Pendant Dipodal Silanes
Chemistry - A European Journal, 2014
Dipodal silanes possess two silicon atoms that can covalently bond to a surface. They offer a distinct advantage over conventional silanes commonly used for surface modification in terms of maintaining the integrity of surface coatings, adhesive primers, and composites in aqueous environments. New nonfunctional and functional dipodal silanes with structures containing "pendant" rather than "bridged" organofunctionality are introduced. The stability of surfaces in aqueous environments prepared from dipodal silanes with hydrophobic alkyl functionality is compared to the stability of similar surfaces prepared from the conventional si-lanes. In strongly acidic and brine environments, surfaces modified with dipodal silanes demonstrate markedly improved resistance to hydrolysis compared to surfaces prepared from conventional silanes. Pendant dipodal silanes exhibit greater stability than bridged dipodal silanes. The apparent equilibrium constant for the formation of silanol species by the hydrolysis of a disiloxane bond was determined as K c = [SiOH] 2 /[Si-O-Si][H 2 O] = 6 AE 1 10 À5 and is helpful in understanding the enhanced hydrolytic stability of surfaces modified with dipodal silanes.
Nano Research, 2009
A novel way of producing superhydrophobic surfaces by applying a self-assembled monolayer (SAM) to silicon micro/nano-textured surfaces is presented in this paper. The micro/nano-textured surfaces on silicon substrates were generated by the aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) technique. Octadecyltrichlorosilane (OTS) SAMs were then applied to the textured surfaces by dip coating. The topography and wetting properties of the resulting surfaces were characterized using scanning electron microscopy (SEM) and a video-based contact angle measurement system. The results show that by introducing OTS SAMs on the silicon micro/nano-textured surfaces, superhydrophobic surfaces with water contact angles (WCAs) of 155° were obtained, as compared to the WCAs of OTS-modifi ed smooth silicon surfaces of about 112°. Surface topography was found to directly infl uence the WCA as predicted by the Cassie-Baxter model.
Journal of Colloid and Interface Science, 2013
Surface force measurements conducted with thiolated gold surfaces showed previously that hydrophobic interaction entails a decrease in excess film entropy, suggesting that hydrophobic force originates from changes in the structure of the medium (water) confined between hydrophobic surfaces [1]. As a follow-up work, surface force measurements have been conducted in the present work using an atomic force microscope (AFM) with silica surfaces coated with octadecyltrichlorosilane (OTS) at temperatures in the range of 10-40°C. A thermodynamic analysis of the results show that both the excess film entropy (DS f) and excess film enthalpy (DH f) decrease with decreasing thickness of the water films between the hydrophobic surfaces. It has been found also that |DH f | > |TDS f |, which represents a necessary condition for the excess free energy change (DG f) to be negative and hence the hydrophobic interaction be attractive. Thus, the results obtained with both the thiolated and silylated surfaces show that hydrophobic forces originate from the structural changes in the medium. It is believed that the water molecules in the thin liquid films (TLFs) of water form clusters as a means to reduce the free energy when they cannot form H-bonds to neighboring hydrophobic surfaces.
Surface Science, 2010
Herein reported is the synthesis of functionalised oligoethylene glycol molecules, with an azido group at one end and an ionisable group at the other end, and their attachment onto alkyne-terminated silicon(100) surfaces using 'click' chemistry. The modified surfaces were characterised using X-ray photoelectron spectroscopy (XPS) and water contact angle goniometry. The antifouling behaviour of these surfaces was assessed and it was shown that while surfaces presenting both charged and ethylene glycol moieties are antifouling, the antifouling effectiveness is influenced by the surface charge as modulated via the pH of the solution.
Comparison between wettability gradients made on gold and on Si/SiO2 substrates
Colloids and Surfaces B: Biointerfaces, 1999
We have previously shown that wettability gradients on Si/SiO 2 can be used to analyze in detail the interactions of surfactants and proteins with the vast number of different surface properties that a gradient represents. We have also shown that the interactions of surfactants can be used to characterize the surface. In this report we discuss a new kind of wettability gradient that is composed from alkanethiols on gold. Surfactant and protein adsorption phenomena are investigated and compared with analogous experiments made on gradients prepared from chlorosilanes on Si/SiO 2 substrates. Surfactant adsorption studies were used to investigate the surface properties. Through their electrostatic interactions negatively charged groups on the surface could be detected and through their hydrophobic interactions defects in the surface layer resulting in hydrophobic groups could be detected. The alkanethiol gradient had at the extreme OH-side an advancing contact angle to water between 30 and 40°. Still this surface had a lower adsorbed amount of fibrinogen compared to a (completely wetting) silica surface covered with negatively charged and uncharged silanol groups, indicating that the fibrinogen molecules also interacts electrostatically through their positively charged amino acid residues. This shows that the amount of fibrinogen adsorbed is not solely dependent on the surface hydrophilicity.
Activation of Surface Hydroxyl Groups by Modification of H-Terminated Si(111) Surfaces
Journal of the American Chemical Society, 2012
Chemical functionalization of semiconductor surfaces, particularly silicon oxide, has enabled many technologically important applications (e.g., sensing, photovoltaics, and catalysis). For such processes, hydroxyl groups terminating the oxide surface constitute the primary reaction sites. However, their reactivity is often poor, hindering technologically important processes, such as surface phosphonation requiring a lengthy postprocessing annealing step at 140°C with poor control of the bonding geometry. Using a novel oxidefree surface featuring a well-defined nanopatterned OH coverage, we demonstrate that hydroxyl groups on oxide-free silicon are more reactive than on silicon oxide. On this model surface, we show that a perfectly ordered layer of monodentate phosphonic acid molecules is chemically grafted at room temperature, and explain why it remains completely stable in aqueous environments, in contrast to phosphonates grafted on silicon oxides. This fundamental understanding of chemical activity and surface stability suggests new directions to functionalize silicon for sensors, photovoltaic devices, and nanoelectronics.
Enhanced Hydrolytic Stability of Surfaces Modified with Pendant Dipodal Silanes
Chemistry - A European Journal, 2014
Dipodal silanes possess two silicon atoms that can covalently bond to a surface. They offer a distinct advantage over conventional silanes commonly used for surface modification in terms of maintaining the integrity of surface coatings, adhesive primers, and composites in aqueous environments. New nonfunctional and functional dipodal silanes with structures containing “pendant” rather than “bridged” organofunctionality are introduced. The stability of surfaces in aqueous environments prepared from dipodal silanes with hydrophobic alkyl functionality is compared to the stability of similar surfaces prepared from the conventional silanes. In strongly acidic and brine environments, surfaces modified with dipodal silanes demonstrate markedly improved resistance to hydrolysis compared to surfaces prepared from conventional silanes. Pendant dipodal silanes exhibit greater stability than bridged dipodal silanes. The equilibrium constant for siloxane hydrolysis is reported.
Nanomaterials, 2017
Ultra-hydrophobic bilayer coatings on a glass surface were fabricated by sol-gel process using hexadecyltrimethoxysilane (C 16 TMS) and tetramethoxysilane (TMOS) (1:4 molar ratio) as precursors. After coating, silica nanoparticles (SiO 2 NPs) functionalized with different mono-alkoxy derivatives (methoxytrimethylsilane, TMeMS; ethoxydimethylvinylsilane, DMeVES; ethoxydimethylphenylsilane, DMePhES; and methoxydimethyloctylsilane, DMeC 8 MS) were added, assuring the microscale roughness on the glass surface. Influences of the functionalized SiO 2 NPs and surface morphology on the hydrophobicity of the hybrid films were discussed. The successful functionalization of SiO 2 NPs with hydrophobic alkyl groups were confirmed by Fourier transform infrared spectroscopy (FTIR). The thermal stability of hydrophobic SiO 2 NPs showed that the degradation of the alkyl groups takes place in the 200-400 • C range. Bilayer coating with C 16 TMS/TMOS and SiO 2 NPs modified with alkoxysilane substituted with C 8 alkyl chain (SiO 2 NP-C 8) has micro/nano structure. Hydrophobicity of functionalized SiO 2 NPs-C 8 and its higher degree of nanometer-scale roughness gave rise to ultra-hydrophobicity performance for bilayer coating C 16 TMS/TMOS + SiO 2 NPs-C 8 (145 •), compared to other similar hybrid structures. Our synthesis method for the functionalization of SiO 2 NPs is useful for the modification of surface polarity and roughness.
Hydrophobic properties of surfaces coated with fluoroalkylsiloxane and alkylsiloxane monolayers
Surface Science, 2004
A comparative analysis of hydrophobicity of fluoroalkylsiloxane and alkylsiloxane monolayers is presented. In order to compare wetting behavior on smooth and rough substrates, a simple model considering various self-assembly degrees of organic molecules and various area fractions of air inclusion is used. Sliding behavior for water on rough silanized needle-like surfaces is also evaluated. On smooth surfaces, regardless of assembly degree of coatings, contact angles of fluoroalkylsiloxane monolayers are always $10°larger. The difference, however, decreases when rough substrates with air inclusion are used. It is shown that assembly order of silane molecules and reduced water-solid contact area are the key factors leading to both high contact angles and low sliding angles. Such coatings are expected to be potential snowand ice-repellent materials.
The effects of nanostructure and composition on the hydrophobic properties of solid surfaces
Journal of Adhesion Science and Technology, 2006
The effects of nanoroughness and chemical composition on the contact and sliding angles on hydrophobic surfaces were studied theoretically and experimentally. A theoretical model based on forces developed at the contact area between a liquid drop and hydrophobic smooth or nanoroughened surface was developed and compared with the existing models, which are based on forces developed at the periphery between the drop and the solid surface. The contact area based model gives rise to an interfacial adhesion strength parameter that better describes the drop-sliding phenomenon. Consequently, relationships were derived describing the dependence between the interfacial adhesion strength of the liquid drop to the surface of a given composition, the mass of the drop, the measured contact angles and the sliding angle. For a given surface chemistry, the sliding angle on a nanometric roughened surface can be predicted based on measurements of contact angles and the sliding angle on the respective smooth surface. Various hydrophobic coatings having different surface nanoroughnesses were prepared and, subsequently, contact angles and sliding angles on them as a function of drop volume were measured. The validity of the proposed model was investigated and compared with the existing models and the proposed model demonstrated good agreement with experimental results.
A short route of covalent biofunctionaliztion of silicon surfaces
Sensors and Actuators B-chemical, 2011
Covalently attached organic monolayers on etched Si(1 1 1) surfaces were prepared by heating solutions of 1-alkenes and 1-alkynes in a refluxing mesitylene. Surface modification was monitored by measurement of the static water contact angle, X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRRAS), and atomic force microscopy (AFM). Flat and clean N-hydroxysuccinimide (NHS)ester-terminated/1-decyl mixed monolayers were covalently attached in one step onto a silicon surface. This procedure allows a mild and rapid functionalization of the surface by substitution of the NHSester moieties with amines at room temperature. The NHS-ester groups were shown to be fully intact onto the surface. The surface reactivity of the NHS-ester moieties toward amines was qualitatively and quantitatively evaluated via the reaction with methoxytetraethyleneglycolamine (TEGamine) and finally functionalized with single strand and complete DNA molecules.
Chemistry of Materials, 2002
Silicon is arguably the most important material in modern technology and there has been much recent interest in chemically modifying its surface. 1,2 Linford and co-workers 3 recently published a new method of simultaneously preparing alkyl monolayers on silicon and patterning silicon by scribing it with a diamond-tipped rod while it is wet with 1-alkenes or 1-alkynes. They proposed that scribing creates highly active Si species that condense with unsaturated molecules. Here, we report that monolayers on Si can also be produced and Si surfaces concomitantly patterned by scribing Si that is wet with 1-chloro-, 1-bromo-, and 1-iodoalkanes. 4 As before, 3 this process takes place under ambient conditions, without the need to degas reagents. A dry Si surface with its thin (10-20 Å) native oxide layer is simply wet with an alkyl halide and the surface is scribed. We propose that surface species on scribed silicon, which may include SidSi (double) bonds and Si dangling bonds (Si • ), as are present on Si(100)-(2 × 1) and Si(111)-(7 × 7), respectively, 2 react with alkyl halides to produce Si-X (X is Cl, Br, or I) and Si-alkyl species. This process is shown below for Si • : homolytic scission of a C-X bond is followed by condensation of Si • with an alkyl radical.