Improvement of water and oil repellency on wood substrates by using fluorinated silica nanocoating

We have investigated a one-step fabrication of fluoro-containing silica coating on wooden substrates, showing multi-functions including super repellency toward water and sunflower oil, low sliding angles, good durability, and low adsorption capacity of moisture. The repellent slurry, consisting of well-mixing silica nanospheres and perfluoroalkyl methacrylic copolymer, is simply prepared and subsequently sprayed over wooden substrates with good adhesion. It has shown that the decoration of silica nanospheres on microscaled wooden texture acts as a crucial role in improving the repellency toward water and sunflower oil droplets. The maximal contact angles can reach as high as 168.3° and 153.6° for water and sunflower oil drops, respectively. These analyses of wetted fraction and work of adhesion also demonstrate the improved repellency due to the addition of silica. This improvement of the repellencies is ascribed to the fact that the drops partially sit on F-coated silica spheres, leaving a layer of air underneath the droplet (i.e., Cassie state). On the basis of the results, the multi-functional coating on wooden substrates delivers a promising commercial feasibility on a variety of woodworks.     

Transparent water repellent silica films by sol-gel process

Non-wettable surfaces with high contact angles and facile sliding angle of water droplets have received tremendous attention in recent years. The present paper describes the room temperature (∼27 °C) synthesis of dip coated water repellent silica coatings on glass substrates using iso-butyltrimethoxysilane (iso-BTMS) as a co-precursor. Emphasis is given to the influence of the hydrophobic reagent (iso-BTMS) on the water repellent properties of the silica films. Silica sol was prepared by keeping the molar ratio of tetraethoxysilane (TEOS) precursor, methanol (MeOH) solvent, water (H₂O) constant at 1:16.53:8.26 respectively, with 0.01 M NH₄F throughout the experiment and the molar ratio of iso-BTMS/TEOS (M) was varied from 0 to 0.965. The effect of M on the surface structure and hydrophobicity has been researched. The static water contact angle values of the silica films increased from 65° to 140° and water sliding angle values decreased from 42° to 16° with an increase in the M value from 0 to 0.965. The water repellent silica films are thermally stable up to a temperature of 280 °C and above this temperature the film shows hydrophilic behavior. The water repellent silica films were characterized by the Fourier Transform Infrared (FT-IR) Spectroscopy, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), % of optical transmission, thermal and chemical aging tests, humidity tests, static and dynamic water contact angle measurements.     

TMOS based water repellent silica thin films by co-precursor method using TMES as a hydrophobic agent

The present paper describes the room temperature synthesis of dip coated water repellent silica coatings on glass substrates using trimethylethoxysilane (TMES) as a co-precursor. Silica sol was prepared by keeping the molar ratio of tetramethoxysilane (TMOS) precursor, methanol (MeOH) solvent, water (H₂O) constant at 1:29.27:2.09 respectively, with 0.5 M NH₄OH throughout the experiments and the TMES/TMOS molar ratio (M) was varied from 0 to 3.8. It was found that with an increase in M value, the roughness and hydrophobicity of the films increased, however the optical transmission decreased from 93% to 57% in the visible range. The hydrophobic silica films retained their hydrophobicity up to a temperature of 250 °C and above this temperature the films became hydrophilic. The hydrophobic silica thin films were characterized by taking into consideration the surface roughness studies, Fourier transform infrared (FT-IR) spectroscopy, percentage of optical transmission, scanning electron microscopy (SEM) and contact angle measurements.     

Sliding behavior of water drops on sol-gel derived hydrophobic silica films

Control on the wettability of solid state materials is a classical and key issue in surface engineering. Optically transparent methyltriethoxysilane (MTES)-based silica films with water sliding angle as low as 9° were successfully prepared by two-step sol-gel co-precursor method. The emphasis is given to the effect of trimethylethoxysilane (TMES) as a co-precursor on water sliding behavior of silica films. The coating sol was prepared with molar ratio of methyltriethoxysilane (MTES), methanol (MeOH), acidic water (0.01 M, oxalic acid) and basic water (12 M, NH₄OH) kept constant at 1:12.73:3.58:3.58 respectively, and the molar ratio of TMES/MTES (M) was varied from 0 to 0.22. The static water contact angle as high as 120° and the water sliding angle as low as 9° was obtained by keeping the molar ratio (M) of TMES/MTES at 0.22. When the modified films were cured at temperature higher than 280 °C, the films became superhydrophilic. Further, the humidity study was carried out at a relative humidity of 90% at 30 °C over 60 days. We characterized the water repellent silica films by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), % of optical transmission, humidity tests and static and dynamic water contact angle (CA) measurements.     

Synthesis of mesoporous silica nanosphere using different templates

Synthesis of mesoporous silica nanosphere were carried out using polyvinyl pyrrolidine and different templates with surfactant property, namely cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, n-octylamine, tetrapropylammonium bromide (TPABr) and these amines give good yield except TPABr. Attempts with other amines without surfactant properties, such as n-propylamine, diethylamine, triethylamine, triethanolamine templates did not give any precipitate in the present reaction scheme. The above synthesis followed by sonication did not change the trend. However addition of dodeycl sodium sulfate surfactant before sonication gave precipitate in all amines, which shows particle growth is induced by surfactant.     

Plasma treatment of polyester fabric to impart the water repellency property

Polyester fabric is treated with DCDMS solution by two methods: dipping the fabric directly in DCDMS solution for different intervals and dipping the fabric in DCDMS solution after its exposure into RF plasma chamber for different durations at optimized exposure power conditions. The physical properties of polyester fabric treated with DCDMS in the presence or absence of air plasma have been compared with control fabric. Different characterization techniques like scanning electron microscope, attenuated total reflectance-IR and Dataflash 100 colour measurement spectrophotometer are used to assess the surface morphology, composition and change in colour parameters. Water repellency property of both untreated and modified polyester fabric is studied using AATCC test method 39 (1971). The effectiveness of the water repellency property of modified polyester fabric is checked by repeated washing up to ten cycles. This article was presented at the Second International Conference on the Frontiers of Plasma Physics and Technology, 21–25 February 2005, Goa, India.     

Study of radon transport through concrete modified with silica fume

The concentration of radon in soil usually varies between a few kBq/m³ and tens or hundreds of kBq/m³ depending upon the geographical region. This causes the transport of radon from the soil to indoor environments by diffusion and advection through the pore space of concrete. To reduce indoor radon levels, the use of concrete with low porosity and a low radon diffusion coefficient is recommended. A method of reducing the radon diffusion coefficient through concrete and hence the indoor radon concentration by using silica fume to replace an optimum level of cement was studied. The diffusion coefficient of the concrete was reduced from (1.63 ± 0.3) × 10⁻⁷ to (0.65 ± 0.01) × 10⁻⁸ m²/s using 30% substitution of cement with silica fume. The compressive strength of the concrete increased as the silica-fume content increased, while radon exhalation rate and porosity of the concrete decreased. This study suggests a cost-effective method of reducing indoor radon levels.     

Study of chromium ion sorption on modified silica ordered materials

The sensitivity of chemical sensors depends on the number of receptors on the surface; hence, an important role is played by the accessible support surface. Films based on silica mesoporous mesophase materials feature the highest specific surface area for silica materials, and their walls can be modified by various functional groups. In this paper, we propose to use mesoporous mesophase films as supports of sensitive elements for Cr³⁺ ions.     

Porosity depth profiling of spin-coated silica thin films produced by different precursors sols

The structural evolution of nanoporous silica thin films was studied by Doppler broadening spectroscopy (DBS), 2-3 gamma ratio of positronium (3γ-PAS) and Fourier transform infrared spectroscopy (FT-IR). Four series of silica films with thickness in the 300-600 nm range were deposited by spin coating on Si substrate changing the content of sacrificial porogen in the sol precursors. The effect on the porosity of different amount of porogen and of the thermal treatments in the 400-900 °C temperature range have been highlighted. The evolution of the porosity is discussed considering the removal of porogen and of the silanol Si-OH groups by thermal treatments as pointed out by FT-IR. Pores with size from less than 1 nm up to sizes larger than 2.0 nm have been detected. In samples with maximum porogen load oPs escaping was observed indicating onset of connected porosity. At temperatures higher than 700 °C a decrease of the porosity due to a progressive pore collapsing was evidenced. A strong correlation was found between the shift of the Si-O-Si transversal optical (TO₃) mode in the FT-IR spectra and the pore size in the porous silica films as revealed by DBS and 3γ-PAS.     

Positron annihilation studies of mesoporous silica films using a slow positron beam

Positron annihilation lifetime spectra were measured for mesoporous silica films, which were synthesized using triblock copolymer (EO₁₀₆PO₇₀EO₁₀₆) as a structure-directing agent. Different positron lifetime spectra for the deposited and calcined films indicated the formation of meso-structure after calcination, which was confirmed by Fourier transform infrared (FTIR) spectra and field emission-scanning electron microscopy (FE-SEM) observation. Open porosity or pore interconnectivity of a silica film might be evaluated by a two-dimensional positron annihilation lifetime spectrum of an uncapped film. Pore sizes and their distributions in the silica films were found to be affected by thermal treatments.     

Enhancement in hydrophobicity of silica films using metal acetylacetonate and heat treatment

Water is one of the most affecting chemicals that can cause damage to the solid surface. To protect the surface due to the action of water, the surface should be made hydrophobic. In the present study, the improvement in hydrophobicity of silica films using metal acetylacetonate (M-acac) by employing heat treatment to methyltrimethoxy silane (MTMS) based silica coatings is reported as a novel attempt. Instead of following the established trends of the surface derivatization or co-precursor method, iron acetylacetonate Fe(acac)₃, copper acetylacetonate Cu(acac)₂ and heat treatment were used to incorporate hydrophobicity with silica coatings. As M-acac is readily soluble in organic solvents, Fe(acac)₃ and Cu(acac)₂ were dissolved in methanol (MeOH) and their concentration was varied from 0 to 0.025 M. The coating solution was prepared by optimizing molar ratio of MTMS:MeOH:basic H₂O to 1:7.15:6.34, respectively. Gelation time (t_g) for Cu(acac)₂ containing silica sol and that containing Fe(acac)₃ were noted to be 30 and 55 min, respectively. The substrates were taken out after gelation and heat treated at 150 °C for 2 h. The heat treated films showed a dramatic increase in the static water contact angle from 82° to as high as 142°.     

Preparation of colloidal films with different degrees of disorder from monodisperse spherical silica particles

The process of coagulation of suspensions of monodisperse spherical silica particles driven by appropriate coagulants (NH₄Cl, HCl, C₁₆H₃₃N(CH₃)₃Br) has been studied. Films of photonic crystals and photonic glasses have been grown by the sedimentation method. The possibility of controlling the degree of structural disorder in colloidal films by properly varying the resistance of the water suspension of particles to aggregation has been demonstrated.     

Hexagonal mesoporous silica modified with 2-mercaptothiazoline for removing mercury from water solution

A method for the attachment of 2-mercaptothiazoline (MTZ) to modified silica gel has been developed. In the first step, a new silylant agent was synthesized, named SiMTZ, by the reaction between MTZ molecule and chloropropyltrimethoxysilane (SiCl). SiMTZ and tetraethylortosilicate were co-condensed in the presence of n-dodecylamine, a neutral surfactant template, to produce a modified ordered hexagonal mesoporous silica named HMTZ. The modified material contained 0.89 ± 0.03 mmol of 2-mercaptothiazoline per gram of silica. FT-IR, FT-Raman, ²⁹Si- and ¹³C-NMR spectra were in agreement with the proposed structure of the modified mesoporous silica in the solid state. HMTZ material has been used for divalent mercury adsorption from aqueous solution at 298 ± 1 K. The series of adsorption isotherms were adjusted to a modified Langmuir equation. The maximum number of moles of mercury adsorbed gave 2.34 ± 0.09 mmol/g of material. The same interaction was followed by calorimetric titration on an isoperibol calorimeter. The HMTZ presented a high capacity for the removal of the contaminant mercury from water. The ΔH and ΔG values for the interaction were determined to be −56.34 ± 1.07 and −2.14 ± 0.11 kJ mol⁻¹. This interaction process was accompanied by a decrease of entropy value (−182 J mol⁻¹ K⁻¹). Thus, the interaction between mercury and HMTZ resulted in a spontaneous thermodynamic system with a high favorable exothermic enthalpic effect.     

Strong water repellency effect on SiO<Subscript>2</Subscript> films processed at a nanometric scale

The present study deals with the creation of nano-rough surfaces with stable and controlled high hydrophobicity. These surfaces were obtained by combining the ion track etching technique with a simple functionalization by grafting perfluoroctyltrichlorosilane (PFOTS) molecules. Surface morphology was investigated by AFM observations which evidenced a self-affine fractal structure with a fractal dimension D_f ~ 2.6. The study of the wetting properties of these surfaces allowed to elucidate the conditions for observing a high hydrophobicity phenomenon and to predict the contact angle values for surfaces designed at a nanometric scale.     

Photoluminescence study of Ce-doped silica films

Ce-doped silica films with different Ce concentrations were prepared by ion-beam sputtering and ion implantation. The films containing 1.2 at% Ce were annealed at temperatures from 500 °C to 1200 °C in air ambient, and were annealed in different ambient at 1100 °C. Ce-related photoluminescence was observed in films sensitive to the Ce concentrations, annealing temperatures and the annealing ambient. The peak intensity of the photoluminescence band is approximately linear with Ce concentrations. Also, the photoluminescence intensity is dependent on the annealing temperatures and reaches its highest value after annealing at 700 °C. In addition, the experimental results show that compared with the annealing in an air ambient, the photoluminescence intensity can be enhanced with nitrogen gas. There would be no obvious change for the photoluminescence position or shape.     

Study of the multilayer metallic films topography modified by laser interference irradiation

The thin bimetallic film systems Fe–Al, Fe–Ni, Ti–Al, and Ti–Ni were irradiated using a laser interference pattern with laser fluence values from 50 to 250 mJ/cm². The thermal simulation was carried out to analyze the topographical effects. It was found that according to the laser fluence value, three different types of topographies can be obtained. For lower laser fluence values, the molten material in the lower layer induces deformation over the upper one obtaining a periodic pattern with a structure depth in the order of the layer thickness. If the laser fluence is high enough so that the upper layer reaches the melting point, this last is broken obtaining a high structured pattern consisting on a large depression and next two consecutive peaks. This threshold value can be estimated using the thermal simulation calculating the laser fluence at which the upper layer starts to melt. For higher laser fluence values, this pattern transforms into a periodical peak–valley structure with high structure depth. In both last two cases, the material at the interference peaks is removed. A model is suggested for explaining this behavior.     

Superhydrophobicity of silica nanoparticles modified with polystyrene

Polystyrene/silica nanoparticles were prepared by radical polymerization of silica nanoparticles possessing vinyl groups and styrene with benzoyl peroxide. The resulting vinyl silica nanoparticles, polystyrene/silica nanoparticles were characterized by means of Fourier transformation infrared spectroscopy, scanning electron microscopy and UV-vis absorption spectroscopy. The results indicated that polystyrene had been successfully grafted onto vinyl silica nanoparticles via covalent bond. The morphological structure of polystyrene/silica nanoparticles film, investigated by scanning electron microscopy, showed a characteristic rough structure. Surface wetting properties of the polystyrene/silica nanoparticles film were evaluated by measuring water contact angle and the sliding angle using a contact angle goniometer, which were measured to be 159° and 2°, respectively. The excellent superhydrophobic property enlarges potential applications of the superhydrophobic surfaces.     

Ultralow-refractive-index optical thin films through nanoscale etching of ordered mesoporous silica films

A great deal of intensive research has been conducted to obtain high-quality transparent ultralow-refractive-index and ultralow-dielectric-constant thin films for microptics and microelectronics applications. Here, we report a simple procedure to prepare highly porous silica thin films with high optical quality and water resistance through nano-etching of mesoporous silica films followed by fluoroalkylsilane surface modification. The films possess an ultralow refractive index of 1.03 (800 nm) and an ultralow dielectric constant of 1.30 (100 kHz), to our knowledge the lowest values ever reported in thin film materials. The films are superhydrophobic (water contact angle=156 deg), thus exhibit high moisture stability.     

Reactions of evaporated lithium films with silica surfaces

Reactions of thin films of clean lithium with freshly cleaved silica surfaces have been characterized by X-ray photoelectron spectroscopy (XPS). Reaction rates (near room temperature) are low enough that spectroscopic analysis is possible during the entire course of the reaction. The major product of the reaction is composed of oxidized lithium, a metasilicate (SiO^2-₃) species, and a unique form of reduced Si, possibly a lithium-rich alloy phase. For confined regions, where the lithium concentration can be made extremely high (as in these thin film depositions) the reaction with the active metal gives a product distribution not predicted by previous thermodynamic arguments.