Sol-gel Silica Films Research Articles

Controlled hydrophilic/hydrophobic property of silica films by manipulating the hydrolysis and condensation of tetraethoxysilane

Controlling surface wettability is an important road to afford the materials with anticipated functional properties, such as anti-fogging, anti-icing and self-cleaning. Manipulating the surface topography and chemical composition is a promising strategy to achieve the expected functional properties. Herein, we concurrently realized the control of surface topography and chemical composition of the film materials via exploiting a simply one step method through the hydrolysis and condensation of tetraethoxysilane (TEOS) to form silica sol-gel films. By adjusting the amount of water, TEOS and basic catalyst, the hydrophilic or hydrophobic chemical groups on the silica particles surface were well controlled. As a result, the sol-gel silica films exhibiting a controllable and wide range contact angles from 7.7±1.5° to 121.6±1.8° were obtained by this simple one-step method. The inorganic nonmetallic, metallic and polymer materials surface could maintain different wettability by the modification of controlled wettability silica films. Furthermore the wettability of silica film could be easily changed from hydrophobicity to superhydrophilicity through a heat-treatment due to the decrease of hydrophobic chemical groups conforming to the time-temperature equivalence principle. Raising temperature and extending holding time were equivalent to chemical bond breaking which result in the wettability change of silica films.

Ultralow-threshold neodymium-doped microsphere lasers on a silicon chip

We demonstrate ultralow-threshold neodymium-doped silica microsphere lasers on a silicon chip with lasing wavelengths of ~900nm and ~1060nm. Neodymium-doped microsphere cavities are fabricated with a series of doping concentrations using silica sol–gel films. Experimentally, we observe single-mode lasing emissions from the high-Q microsphere cavities with a threshold of as low as 1.2µW.

Photo-assisted electrodeposition of sol–gel films on p-type semiconductors

A new approach for the deposition of sol–gel films on semiconducting substrate using photo-electrochemical technique is presented. The deposition is based on accelerating sol–gel condensation reaction by the catalyzing effect of electrochemically generated OH− ions when applying both negative potentials and light irradiation onto p-type semiconductors. Results show that both the negative shift in potential and the increase in light intensity facilitate the deposition kinetics of silica sol–gel films. Surface patterning is further achieved with the assistance of a laser.

Demonstration of ultralow-threshold 2 micrometer microlasers on chip

We demonstrate ultralow-threshold thulium-doped, as well as thulium-holmium-codoped, microtoroid lasers on silicon chips, operating at the wavelength of around 2 μm. High quality factor whispering gallery mode (WGM) microtoroid cavities with proper thulium and holmium concentrations are fabricated from the silica sol-gel films. The highly confined WGMs make the microcavity lasers operate with ultralow thresholds, approximately 2.8 μW and 2.7 μW for the thulium-doped and the thulium-holmium-codoped microlasers, respectively.

Electrochemical deposition of silica sol–gel films on stainless steel: preliminary analysis of key variables

The sol–gel electrodeposition of coatings on conductive substrates has been presented the first time in 1999, and since then, a significant number of papers have been published, mainly devoted to explore the possibilities of application. However, a clear and complete picture of the fundamental aspects and of the role of the many parameters involved is still lacking. In this work, which is intended to be a preliminary approach to a systematic study, the effect of potential and time on the coating thickness was studied, trying to analyze the different factors that make experimentation difficult, looking for possible solutions and putting the basis for a more complete and analytic investigation. Simple tetraethyl orthosilicate-based acidic solutions were used to coat planar stainless steel samples. Different starting solutions were tested, varying the amount of precursor, water and hydrochloric acid. The role of working temperature, oxygen concentration and the presence of potassium nitrate until saturation was tested. Morphology, thickness, cyclic voltammetry and chronoamperometry were used to characterize the coatings and to monitor the current in function of potential and time. The thickness was found to increase with both the concentration of the solution and the HCl/TEOS ratio. Temperature was found to be an important factor, but also the amount of oxygen and electrolyte (KNO3) in solution seems to influence the thickness of coatings.

Flexible humidity sensor based on Au nanoparticles/graphene oxide/thiolated silica sol–gel film

Novel flexible impedance-type humidity sensors that were based on gold nanoparticles (AuNPs) and graphene oxide (GO) were fabricated by a combination of self-assembly and the sol–gel technique. A hydrolyzed 3-mercaptopropyltrimethoxysilane (MPTMOS) sol–gel solution that contained GO was firstly dropped on to the surface of a pair of comb-like Au electrodes on a polyethylene terephthalate (PET) substrate, and then AuNPs were assembled onto the thiol groups of the sol–gel network. The formed AuNPs were characterized by UV–vis spectroscopy. The microstructure of the AuNPs/GO/MPTMOS sol–gel film was analyzed by atomic force microscope (AFM) and scanning electron microscopy (SEM). The effects of the AuNPs and the amount of GO added on the flexibility, electrical and humidity sensing properties of the AuNPs/GO/MPTMOS sol–gel films on a PET substrate were investigated. The sensor that was made from the AuNPs/GO/MPTMOS sol–gel film with 9.0wt% added GO exhibited the greatest flexibility, sensitivity, linearity and long-term stability. The effects of applied frequency, ambient temperature, response and recovery times on the impedance of the flexible humidity sensor were also investigated. The sensing mechanism of the AuNPs/GO/MPTMOS sol–gel film was explained with reference to impedance plots.

Silica sol–gel anchoring on aluminum pigments surface for corrosion resistance based on aluminum oxidized by hydrogen peroxide

The waterborne aluminum pigments were prepared by sol–gel encapsulation method using tetraethoxysilane and γ-aminopropyl triethoxysilane as precursors with H2O2 as anchoring agent. Fourier transformation infrared and X-ray diffraction results indicated that the boehmite formed by H2O2 oxidizing aluminum can successfully reacted with silanol to make the silica sol–gel film anchored on the aluminum surface in the encapsulation process. The reaction conditions were optimized and the products were characterized by scanning electron microscopy, optical microscopy and stability test. It was found that when controlling the pH value of encapsulation media at about 9.5 and H2O2 concentration of 5.1 × 10−5 mol/m2 of aluminum flake surfaces, the boehmite on aluminum flake surfaces carried a strong positive charge and the silica sol–gel film carried a negative charge, which conduct the most anchorage efficiency. A crack free, smooth and dense coating was formed and exhibited best corrosion resistance on the aluminum flake surfaces.

Silica sol–gel anchoring on aluminum pigments surface for corrosion protection based on aluminum oxidized by copper ammonia complex ion

To reduce the volatile organic compounds emission led to the development of waterborne coatings. Correspondingly, waterborne aluminum pigment is desirable to develop. Here, the waterborne aluminum pigments were prepared by sol–gel encapsulation method using tetraethoxysilane and γ-aminopropyl triethoxysilane as precursors with [Cu(NH3)4]2+ as anchoring agent. Fourier transformation infrared and X-ray diffraction results showed that the boehmite formed by [Cu(NH3)4]2+ oxidizing aluminum can successfully react with silanol to make the silica sol–gel film anchored on the aluminum surface in the encapsulation process. The reaction conditions were optimized and the products were characterized by scanning electron microscopy, optical microscopy and stability test. It was found that control the pH of encapsulated media between 8.77 and 10.10, the boehmite on aluminum flake surfaces carried a strong positive charge and the silica sol–gel film carried a negative charge, which conduct the most anchorage efficiency, and the waterborne aluminum pigment exhibit best stability.

TEM, XPS and thermo-mechanical properties of novel sustainable hybrid coatings

This work contributes to the development of a new generation of protective coatings composed of organic–inorganic materials. A silica based hybrid film was used in this work as high performance materials. The silica sol–gel film reveals enhanced thermo-mechanical properties in comparison with the pure polymer film. Herein, we demonstrate the possibility of employing cheap SiO2 as prospective nano-fillers for hybrid coatings with active thermo-mechanical properties. Organic–inorganic hybrid coatings based on polyimide and silica were synthesized through a simple physical mixing technique. 3,3′,4,4′-Biphenyltetracarboxylic dianhydride (BPDA), benzene-1,3-diamine (BDA), 3,3′-oxydianiline (ODA) and SiO2, were used as precursors for the hybrid coatings. These hybrid coatings were deposited via spin coating onto a galvanized iron, aluminum and copper in order to study the adhesive strength. The effects induced by the silica content on the mechanical properties of the coated samples were investigated. The mechanical properties of hybrid composite were found to be enhanced compared to polyimide coating. The main objective was to observe potential improvements in the mechanical and thermal properties of PI–silica hybrid films. Morphology, and structural changes in the composite films were studied as well as adhesion and impact strength and these characteristics were compared with those of unreinforced polyimide films.

Synthesis and structural evaluation of freeze-cast porous alumina

In this work we fabricated alumina samples by the freeze-casting technique using tert-butanol as the solvent. The prepared materials were examined by scanning electron microscopy and X-ray microtomography. Next, they were coated with sol–gel silica films by dip-coating. Permeability tests were carried out in order to assess the permeation behavior of the materials processed in this study. We observed that the sintering time and alumina loading showed a remarkable effect on both the structural properties and flexural strength of the freeze-cast samples. Nitrogen adsorption tests revealed that the silica prepared in this study exhibited a microporous structure. It was observed that the presence of silica coatings on the alumina surface decreased the CO2 permeance by about one order of magnitude. Because of the similar kinetic diameters of nitrogen and carbon dioxide, the CO2/N2 system showed a separation efficiency that was lower than that observed for the He/CO2 and He/N2 systems. We noticed that increasing the feed pressure improved the separation capacity of the obtained materials.

The Influencing Factors for the Thickness of Silica Sol-Gel Film by the Dip Coating Process

The porous sol-gel silica thin films were prepared on silicon substrate by the dip coating process. The surface roughness and microstructure of the film was measured by optical microscopy and AFM .Coating thickness and refractive index were measured by ellipsometry method. Influence of withdrawal speed and concentration of colloid was investigated for the thickness of silica. The relation of the thickness and withdrawal speed was fitted by the linear and power functions, and the results were analyzed and compared. It was found that the films with the same thickness prepared by different concentrations of colloid have different refractive indexes. The experimental results indicated that the thickness and refractive index of the film can be controlled by changing the withdrawal speed and colloid concentration.

Magic sol–gel silica films encapsulating hydrophobic and hydrophilic quantum dots for white-light-emission

A sol–gel silica film was fabricated by a spraying approach on various substrates with a 3-dimensional surface for white LEDs.

Changes of thickness and refractive index of silica sol-gel film by dip coating process

采用提拉法在硅基底上制备了多孔溶胶凝胶SiO2膜，用椭偏法测量薄膜的厚度与折射率，考察了提拉速度和胶体浓度对膜层厚度与折射率的影响。对厚度与提拉速度的关系进行线性与幂函数拟合，并比较分析两种拟合的关系及其对工艺流程的作用。比较了不同浓度胶体所得到的同一厚度薄膜的折射率变化规律。结果表明: 对于同一胶体浓度下薄膜厚度与提拉速度的正相关关系，线性拟合相比幂函数拟合可以更好地解释实验结果的规律性。同时，折射率在一定范围内也会随着提拉速度的增加而减小。镀同一厚度膜时，浓度大的胶体膜层折射率大。通过对提拉速度和胶体浓度的控制可以得到理想的薄膜厚度与折射率。

提拉法SiO2化学膜厚度与折射率的变化规律研究

提拉法SiO₂化学膜厚度与折射率的变化规律研究

Lu2O3:Eu3+ glass ceramic films: Synthesis, structural and spectroscopic studies

For the first time, transparent and crack free europium-doped lutetia silica sol–gel films were synthesized using the dip-coating technique on silica quartz substrates. In this study, we examined the effects of incorporating polyvinylpyrrolidone (PVP) and silica (SiO2) into different precursor solutions for different Lu–Si molar ratios: 4:1, 6:1, 8:1 and 10:1. Different systems, such as Lu2O3:Eu3+@SiO2 (using the above Lu:Si molar ratios), were synthesized by sol–gel and by dip-coating technique, employing acetylacetonate lutetium and tetraethylorthosilicate as Lu and Si precursors, in order to produce Lu2O3:Eu3+ (5mol%)@SiO2 glass–ceramic films. The film microstructure was studied by microRaman spectroscopy (MRS) and X-ray diffraction (XRD) for different Lu:Si molar ratios on films annealed at 700°C. X-ray diffraction results showed that the lutetium oxide cubic phase crystallizes in the silica matrix at 700°C, and the crystallite size of Lu2O3:Eu3+@SiO2 films varies from 5nm to 17nm according to the respective Lu:Si molar ratios. Opto-geometrical parameters determined by m-lines spectroscopy using a 632.5nm He–Ne laser showed that the Eu3+ doped films heat-treated at 700°C presented a thickness and density of 1.7μm (8.8gcm−3), 970nm (9.2gcm−3), 1μm (9.3gcm−3) and 1.3μm (9.25gcm−3) for the Lu:Si=4:1, 6:1, 8:1 and 10:1 molar ratio systems, respectively. The Lu:Si=8:1 system 611nm emission presented an improvement. These results were provided by photoluminescent spectroscopy.

Correlation between sol–gel reactivity and wettability of silica films deposited on stainless steel

Sol–gel silica films were deposited on 316L and 409 stainless steel substrates in order to investigate their wettability properties. These films were deposited by dip-coating varying some parameters of the sol–gel process, including the acid used in the synthesis, its concentration, and the heat treatment temperature. Water and oil contact angles were measured on the surfaces and discussed regarding the physico-chemical and morphological properties of the prepared films. The findings shown in this work allow correlating the wettability behavior of silica coatings with the sol–gel reactivity of sols prepared using various amounts of nitric acid. It was observed that the more reactive the silica sol, the more hydrophilic and oleophilic the prepared coating. The presence in the films of alkoxy residues due to an incomplete condensation reaction could decrease both the polar and dispersive components of the coating surface energy, respectively responsible for water and oil wetting.

Sol–gel silica controlled release thin films for the inhibition of methicillin-resistant Staphylococcus aureus

The incidence of methicillin-resistant Staphylococcus aureus (MRSA) infection has significantly increased. Generally, the success of this bacterium as a pathogen is attributed to its ability to adhere to surfaces and remain there, under the protection of an extracellular matrix known as biofilm. To combat MRSA with regular doses of vancomycin, efforts are continuously underway to increase its effectiveness. A promising technique is to use combinational therapeutics. In vitro experiments showed that farnesol can be used as an adjuvant with conventional antibiotics. Farnesol is a natural sesquiterpenoid and quorum-sensing molecule. The biggest obstacle to using this concept is that farnesol is highly water insoluble. This compromises its bioavailability if it were to be used along with vancomycin at the site of infection when the treatment needs to be administered in vivo. Herein we designed an efficient therapeutic strategy for the simultaneous delivery of both antibiotic and adjuvant in order to treat MRSA infections. We demonstrate that sufficient quantities of both vancomycin and farnesol can be incorporated into sol–gel silica applied as thin films on an implant surface. The incorporation of the hydrophobic farnesol does not affect the stability of the thin films and neither does it affect the controlled release of vancomycin. The data demonstrate the potent adjuvant effect of farnesol on vancomycin in inhibiting MRSA infection. In vitro experiments show the complete inhibition (106 fold reduction in growth compared to control) of methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) when the ratio of vancomycin to farnesol in the sol–gel silica films is optimized. The local delivery of antibiotics minimizes the need for systemic antibiotics. The incorporation of vancomycin and farnesol into thin sol–gel films represents a new treatment paradigm for the topical delivery of antibiotics with adjuvant. The potential clinical benefits are significant and include avoiding the need for revision surgery, preventing surgical site infection and controlling healthcare costs.

Demonstration of an erbium-doped microsphere laser on a silicon chip

We demonstrate a low-threshold microsphere laser on a silicon chip, fabricated from erbium-doped silica sol–gel film. Single-longitudinal mode lasing emission is observed from a 37 μm diameter microsphere cavity with an erbium ion concentration of 2 × 1019 cm−3. The measured lasing threshold of the silica microsphere laser is as low as 4.8 μW.

Photodegradation of rhodamine 6G dimers in silica sol–gel films

Abstract The process of dimerization of rhodamine 6G at high concentrations in solution and when incorporated in a solid state matrix is well known but the dimer response to photodegration is still not well understood. Silica sol–gel films have been doped with rhodamine 6G with a concentration up to 10−1 M to form large amounts of dimers within the matrix. Fluorescence and UV absorption spectra have shown that both not-fluorescent H-dimers and fluorescent J-dimers together with the monomer form of rhodamine 6G are present in the matrix. Upon exposure up to 11 h to UV light a selective photodegradation of the different species has been finally observed. Analysis of the absorption spectra has shown that the H-type dimers are more resistant to photodegradation with respect to the J-type dimers.

Estimation of contact angle for hydrophobic silica nanoparticles in their hexagonally ordered layer

Wetting properties of bilayered nanostructured coatings were studied in this work. Coatings were prepared by stratifying a compact silica sol–gel (SG) film and a Langmuir–Blodgett (LB) layer of differently sized (84, 131 and 227 nm) Stöber silica particles onto glass substrates. Joint high temperature annealing of the layers increased the mechanical stability of the particulate film facilitating its further investigations.Regular structure of LB layers allowed us to carry out wetting model investigations. Close-packed arrangement of particles was reinforced by optical measurements. Transmittance spectra of LB films were taken and evaluated by a theoretical model. Resulting effective refractive index and film thickness values indicated a good agreement between the real and the supposed (hexagonally close packed, monodisperse spherical particles) layer structure. It was confirmed by field emission scanning electron microscopy (FESEM) images, too.Advancing and receding water contact angles (CA) on differently (with mono- and bifunctional chlorosilanes) hydrophobized SG and combined films were measured applying the sessile drop method. SG films showed approximately the same CA-s after different silylation processes without considerable contact angle hysteresis (CAH). In case of combined films ca. 30° higher advancing CA-s were measured at stronger silylation and only the milder silylation resulted in significant CAH. It was explained by the surface heterogeneity of constituent particles. Layers of differently sized particles showed the same wetting properties in all cases in agreement to the Cassie–Baxter equation which was used for the estimation of CA values for the individual silica particles (88–90° and 105–106° depending on the silylation conditions).