Silica-based Films Research Articles

Color-tunable fluorescent silica-based hybrid film of stacked structure based on a single amphiphilic AIEgen

The large-area and color-tunable fluorescent (FL) films have great potential applications in light-emitting devices and color displays. Yet, the challenge of realizing truly color-tunable emissions using a single fluorophore remains. Herein, we present a large-area, transparent and ultra-stable free-standing FL silica-based film (FSFSF) with color-tunable emissions prepared by using an amphiphilic aggregation-induced emission (AIE) luminogen (AIEgen) as both a structure-directing agent and a light-emitting source. The color-tunable FSFSFs have been facilely prepared at the gas–liquid (GL-FSFSF) and solid–liquid interfaces (SL-FSFSF) by simply stacking the AIEgen/SiO2 composite layers with different self-assembled structures using an approach combining self-assembly with sol-gel process. These films exhibited variable excitation-dependent emission colors, emitting bright blue and green fluorescences as well as dark red fluorescence from one single visual field under excitation with UV, blue, and green lights, respectively. The research found that the resulting GL-FSFSF had a sandwich-like structure with an alternate arrangement of cylindrical and spherical AIEgen micelles in the silica matrix, and exhibited unusual excitation-dependent multi-wavelength and morphology-dependent dual-center emission characteristics. It has been reported that the luminescence of many AIE compounds is morphology-dependent. Therefore, we speculate that the two emission centers of the film are related to the two self-assembled morphologies of amphiphilic AIEgen. Its bright blue and green fluorescence is attributed to the same emission intensity of the two luminescent centers. This study has demonstrated that morphology- and excitation-dependent color-tunable emissions based on one AIE fluorophore can be achieved by incorporating AIEgen aggregates with different self-assembled morphologies in the matrix. Such a simple strategy can be extended to construct other multicolor-tunable FL hybrid materials.

Composite Silica-Based Films as Platforms for Electrochemical Sensors.

Sol-gel-derived silica thin films generated onto electrode surfaces in the form of organic-inorganic hybrid coatings or other composite layers have found tremendous interest for being used as platforms for the development of electrochemical sensors and biosensors. After a brief description of the strategies applied to prepare such materials, and their interest as electrode modifier, this review will summarize the major advances made so far with composite silica-based films in electroanalysis. It will primarily focus on electrochemical sensors involving both non-ordered composite films and vertically oriented mesoporous membranes, the biosensors exploiting the concept of sol-gel bioencapsulation on electrode, the spectroelectrochemical sensors, and some others.

Internal wettability investigation of mesoporous silica materials by ellipsometric porosimetry

Silica-based mesoporous films have been widely applied in the fabrication of advanced functional materials, such as anti-reflective coatings, bio-, and chemical sensing devices, due to their unique properties, e.g., high surface area, controlled porosity, and the ease and tailorability of their synthesis. Precise knowledge of their pore architecture is crucial, highlighting the need for accurate characterization tools. In this sense, ellipsometric porosimetry represents a powerful and versatile characterization platform, providing access to reliable information about total porosity, pore size, pore size dispersity, mechanical properties (Young's modulus) and surface area of a great variety of mesoporous thin films.While the underlying framework of modeling capillary condensation via the Kelvin equation is well established, one descriptor, the internal wettability of mesoporous architectures remains a challenging variable for reliable material characterization. Wetting on the nanoscale cannot be observed via the traditional drop-shape method, while approximating internal wetting by the macroscopic property can be inaccurate as the two wetting behaviors do not necessarily correlate. Herein, we present a method based on vacuum ellipsometric porosimetry for the determination of the internal contact angle of functionalized mesoporous silica thin films. Tuning of the surface energy for a known mesoporous architecture by methyl-functionalization enabled us to relate differences in the pore filling for various adsorptives (water, methanol, toluene, cyclohexane) to their internal contact angles. Our study serves as a guide for generalized internal contact angle determination suitable for a wide range of organic adsorptives and mesoporous sorbent materials.

Antimicrobial surface processing of polymethyl methacrylate denture base resin using a novel silica-based coating technology.

This study investigated the surface characteristics of denture base resin coatings prepared using a novel silica-based film containing hinokitiol and assessed the effect of this coating on Candida albicans adhesion and growth. Silica-based coating solutions (control solution; CS) and CS containing hinokitiol (CS-H) were prepared. C. albicans biofilm formed on denture base specimens coated with each solution and these uncoated specimens (control) were analyzed using colony-forming unit (CFU) assay, fluorescence microscopy, and scanning electron microscopy (SEM). Specimen surfaces were analyzed by measuring the surface roughness and wettability and with Fourier-transform infrared (FT-IR) and proton nuclear magnetic resonance (1H NMR). Stability of coated specimens was assessed via immersion in water for 1week for each group (control-1w, CS-1w, and CS-H-1w) followed by CFU assay, measurement of surface roughness and wettability, and FT-IR. CS-H and CS-H-1w contained significantly lower CFUs than those present in the control and control-1w, which was also confirmed via SEM. Fluorescence microscopy from the CS-H group identified several dead cells. The values of surface roughness from coating groups were significantly less than those from the control and control-1w. The surface wettability from all coating groups exhibited high hydrophobicity. FT-IR analyses demonstrated that specimens were successfully coated, and 1H NMR analyses showed that hinokitiol was incorporated inside CS-H. A silica-based denture coating that incorporates hinokitiol inhibits C. albicans growth on denture. We provide a novel antifungal denture coating which can be helpful for the treatment of denture stomatitis.

Synergistically improved flame retardancy of the cotton fabric finished by silica-coupling agent-zinc borate hybrid sol

The sol-gel process has been applied to cotton fabrics to cover the fibers with a silica-based film, which can improve their thermal oxidation and combustion behaviors. Silica sol, silane coupling agent 3-glycidoxypropyltrimethoxysilane (KH560) and flame retardant zinc borate (ZB) are used together to prepare SiO2-KH560-ZB hybrid sol, which is then finished on the surface of cotton fabric through impregnation and baking. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), limiting oxygen index analysis (LOI) and microscale combustion calorimetry (MCC) are used to characterize functional groups, thermal stability and flammability properties of finished fabrics. Surface morphology of sol modified cotton fabrics are analyzed by scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDX). Results show the sols are successfully converted into gel coatings onto cotton fabrics, and continuous smoldering phenomenon of resulted fabrics disappears. ΔLOI/Δm of SiO2-KH560-ZB coated cotton fabric reaches the highest of 0.37%/g, char residue rate is as high as 28.43% and the peak heat release rate (PHRR) is reduced by 26.9% (83.7 W/g). KH560 has a significant coupling effect on combining components in the sol system and increases compatibility between sols and cotton fabrics. ZB (cooling, separation, dilution and suppression), silica sol (physical barrier) and KH560 show excellent synergistic effects in enhancing overall flame retardancy.

Improved abrasion resistance of silica-based CVD thin films on polycarbonate substrates for automotive applications

A silica-based thin film was synthesized on polycarbonate substrates topped with acrylic primer. The synthesis was performed by chemical vapor deposition under a remote-type atmospheric pressure plasma. The source gas used was TrMS/O2, and the carrier gas used was either He or Ar. The abrasion resistance and adhesion strength were improved by changing the carrier gas from He to Ar. After a standard Taber abrasion test, the minimum change in haze value was approximately 1.3% for a sample synthesized under Ar (below the 2.0% requirement for vehicle window glass). The adhesion strength between the thin film and the substrate probably improved because of the etching effect of the primer by the Ar plasma during the deposition. The results confirmed that atmospheric remote technology can synthesize silica-based films and demonstrated that the technology is applicable to manufacturing vehicle window glass replacements.

Carbon screen-printed electrodes modified with composite films based on silica for H2O2 determination

In this study, a nanostructured screen-printed carbon electrode (nanoSPCE) was modified with silica-based composite films containing metal oxides (MnO2 or CuO) without and with graphene oxide (GO). According to scanning electron microscopy results, uniform thin films with encapsulated metal oxides and GO were formed on the surface of nanoSPCEs. The electrochemical parameters of the modified electrodes were measured by cyclic voltammetry for the non-enzymatic determination of H2O2. Because of the combined action of GO and metal oxides, the modified electrodes have improved electrocatalytic performance for the determination of H2O2 in phosphate buffer solutions. NanoSPCE/MnO2/GO/SiO2 and nanoSPCE/CuO/GO/SiO2 exhibited stable current-voltage responses and good sensing for H2O2 with a wide linear detection range of 0.005–0.5 mM and 0.05–0.3 mM, respectively.

Enhancing Wettability of Radio Frequency Magnetron-Sputtered Glass Films by Exploiting Structural Defects.

Silica-based films were prepared by radio-frequency magnetron sputtering to investigate the influence of the chemical compositions of the target glass on the structure and wettability of the sputtered films. The sputtered films were more hydrophilic than the untreated glasses. Oxygen defects formed in the silica units of the sputtered films and resulted in the formation of hydroxyl groups, regardless of the chemical composition of the glass. The three-phase contact lines were distorted by chemical heterogeneities on the surfaces of the sputtered films.

Patterned Cellulose Nanocrystal Aerogel Films with Tunable Dimensions and Morphologies as Ultra-Porous Scaffolds for Cell Culture

Aerogel films are interesting as coatings due to their unique properties including high surface area, sorption capacity and insulating properties. To date, silica-based aerogel films have been most...

Anisotropic and Reversible Deformation of Mesopores and Mesostructures in Silica-Based Films under Mechanical Stimuli toward Adaptive Optical Components

Deformation of the mesostructures in surfactant/silica hybrid films and mesoporous silica films prepared on bulky elastomeric substrates is investigated by compressing the substrates along an in-plane direction of the films. The mesostructure in the surfactant/silica hybrid film consists of organized micelles and a silica matrix. The micelles are removed in the mesoporous silica films to leave mesopores. A grazing-incidence small-angle X-ray scattering investigation reveals that the mesostructures with C2mm symmetry anisotropically change under a compressive strain of 6% in both films; shrinkage of the lattice parameters is along the direction of compression and extension in the normal direction. Deformation is reversible below a strain as high as 6%. Anisotropic deformation of the mesostructures results in an anisotropic change of the refractive indices normal and parallel to the direction of the compression. Compression of the surfactant/silica hybrid film induces a decrease of the refractive index para...

Engineering of Silica Thin-Film Nanoporosity via Alkali-Ion-Assisted Reconstruction

We report a method to prepare patterned mesoporous silica-based films with fine control of the pore sizes and the porous fraction by combining the sol–gel approach with an alkali ion post-treatment...

Rice–Bernasconi Gorkov–Eliashberg Effect of Giant Dielectric Permittivity in Silica-Based Films Containing Interrupted Silver Nanowires

Silver nanowires of diameter ~ 5 nm were grown within thick films (0.6 µm thickness) of sol–gel-derived silica-based glasses of composition xAg2O(1 − x)SiO2; x having values of 30 and 40, respectively, by an electrodeposition method. By applying suitable voltage pulses to the composites, interrupted silver nanowires were produced with lengths having values in the range 4000–5000 nm. The samples exhibited dielectric constant with values of the order of 105 and a low dielectric loss (~ 0.01). The dielectric constant values calculated by using Rice–Bernasconi model which originated from Gorkov–Eliashberg theory of metallic nanoparticles were in satisfactory agreement with the experimental results. The present work not only provides strong evidence for the basis of Rice–Bernasconi model but also opens up a simple method to synthesize high dielectric constant materials which will be useful in fabricating devices for very large-scale integration applications, among others.

Conference Proceedingon Nanomaterials and Nanochemistry Hard Carbon and Silica based Films Synthesized under Atmospheric Pressure

Atmospheric pressure-plasma enhanced chemical vapor deposition (AP-PECVD) method using a dielectric barrier discharge (DBD)is a cost-effective process because of no need of vacuum process. In this study, we synthesized silicabased films (SiO:CH) and hydrogenated amorphous carbon films (A-C:H) by AP-PECVD method. We synthesized SiO:CH films from tetramethoxysilane (TMOS) and O2 diluted with N2 and investigated the effect of the substrate temperature and the TMOS flow rate on hardness of the films. The hardness increased from 4.0 to 6.9 GPa as the substrate temperature increased from 80 to 300°C. To synthesize a-C:H films, filamentary DBD (FDBD) was used to improve the hardness compared to the films synthesized by glow DBD (GDBD), which is generally used for APCVD.The hardness of the films increased from 3.7 to 11.9 GPa by using FDBD.

Assembly of methylated hollow silica nanospheres toward humidity-resistant antireflective porous films with ultralow refractive indices

Humidity-resistant antireflective (AR) porous films with ultralow refractive indices were prepared via an one-step sol–gel process by assembly of methylated hollow silica nanospheres (HSNs). The hydrophobicity and refractive indices of silica-based AR porous films could be varied between 66.0° and 115.0°, and between 1.08 and 1.14, respectively, by tuning the MTES/TEOS molar ratios. A possible assembly mechanism was proposed according to the microstructure of methylated HSNs and porous films. The various properties of silica-based AR porous films were investigated and the AR porous film could demonstrate a good AR capability of 97.6% and excellent humidity resistance.

Gas barrier property of silica-based films on PET synthesized by atmospheric pressure plasma enhanced CVD

Abstract In this study, silica-based films were synthesized on polyethylene terephthalate (PET) using the mixture gas of trimethylsilane (TrMS), N2, and O2 by the atmospheric pressure plasma enhanced CVD (AP-PECVD) method. We investigated the effect of the oxygen flow rate on the gas barrier property of silica-based films with various O2 flow rates ranging from 0 mL/min to 1000 mL/min. As the O2 flow rate increased to 500 mL/min, the oxygen transmission rate (OTR) of the films decreased to 8.2 cm3/m2/24 h/atm, which is approximately one third of that of the uncoated PET. On the other hand, the OTR increased when the O2 flow rate exceeded 500 mL/min. From the fourier-transform infrared (FT-IR) spectra, the intensity of Si-O-Si peaks increased and the shape of Si-O-Si peaks changed to be sharp with increasing the O2 flow rate, indicating that the structure of the films became dense. Oxygen molecules could not permeate through the highly dense films, so that the gas barrier property was improved. Using the atomic force microscope (AFM), many pinholes with a diameter of approximately 30 nm were observed on the film surface at the O2 flow rate over 500 mL/min. From the observation of the uncoated PET exposed to N2/O2 plasma, the surface texture hardly changed and kept its smooth surface at less O2 flow rate up to 500 mL/min, while the rugged texture were obviously observed at the O2 flow rate over 500 mL/min because of the etching effect in plasma. The holes were formed because the films were synthesized at the PET surface in the rugged shape. Therefore, the formation of the pinholes on the film surface could allow oxygen molecules to diffuse into the films.

Selective Cu filling of nanopores using supercritical carbon dioxide

Supercritical fluid chemical deposition is known for its superior capability of filling metals into nanofeatures. The mechanism behind this filling capability has not been well understood and can be very different from those of other deposition techniques such as chemical vapor deposition. We have proposed a filling mechanism where the precursor condenses preferentially in narrow concave features and then converts into a metal deposit. In accordance with these two sequential phenomena, the narrower the feature is, the better the filling will be achieved. In this article, selective Cu deposition into nanopores of a silica-based porous thin film is described. When the conventional supercritical fluid deposition method was employed, a significant amount of Cu penetrated into the nanopores along with the continuous film formation on the substrate surface. By illuminating UV light before the start of Cu nucleation, Cu deposited selectively only inside the nanopores. During the selective deposition, optical changes in the porous film were investigated by in situ ellipsometry. These results indicate that the precursor condenses preferentially only in the nanopores and converts into a metal deposit.

Controlling mesopore size and processability of transparent enzyme-loaded silica films for biosensing applications.

Silica-based nanoporous thin films including large mesopores are relevant as enzyme supports for applications in biosensing. The diffusion and immobilization of large biomolecules such as enzymes in such porous films require the presence of large mesopores. Creating such morphologies based on a bottom-up synthesis using colloidal templates is a challenge in view of the combination of desired material properties and the robustness of the casting process for the fabrication of thin films. Here a strategy to reproducibly synthesize transparent porous silica thin films with submicrometer thickness and homogeneously distributed porosity is presented. For this purpose, polystyrene-poly-2-vinylpyridine (PS-P2VP) amphiphilic block copolymers are used as porogenic templates. Low-chain alcohols are employed as both selective solvents for the P2VP blocks and reaction media for silica synthesis. Rheology measurements reveal a strong influence of the block copolymer length on the behavior of PS-P2VP micelles in suspension. The pore distribution and accessibility into the film are controlled by adjusting the silica to block copolymer weight ratio. The solvent choice is shown to control not only the micelle size and the generated pore morphology but also the structural homogeneity of the films. Finally, the suitability of the synthesized films as supports for enzymes is tested using a model enzyme, horseradish peroxidase EC 1.11.1.7. Our approach is innovative, robust, and reproducible and provides a convenient alternative to synthesize large mesopores up to small macropores (20-100 nm) in nanostructured thin films with applications in biosensing and functional coatings.

Alcohol-Assisted Water Condensation and Stabilization into Hydrophobic Mesoporosity

In this work, we report the condensation and stabilization of water vapors into water-repellent, methyl-functionalized, mesoporous, silica-based films at room temperature and atmospheric pressure using a soft alcohol-assisted method. The capillary pore fillings due to water adsorption were ensured by a fine control of partial vapor pressures of alcohol and water. A synergic coadsorption of alcohol and water was observed due to a reversible surface energy switching from hydrophobic to hydrophilic induced by the preferential interaction of the alkyl side of the surfactant alcohol molecules with the hydrophobic walls. The influences of the film mesoprosity as well as the type of the alcoholic coadsorbate (methanol, ethanol, and 1-propanol) were investigated, revealing various Kelvin’s law-like adsorption behaviors, depending on the alcohol carbon chain length. Interestingly, the stabilization of condensed domains of quasi-pure water phases was obtained in confined hydrophobic spaces by a presumed selective alcohol desorption. It was demonstrated that a small quantity of remaining Si–OH groups at the pore surface was sufficient to stabilize water nanodomains in hydrophobic pores. These results were based on in situ ellipsometric investigations, that further allowed measuring the wetting angle of water droplets trapped within the porous network, from which we could evaluate the quantity of polar −OH groups remaining in the methyl-functionalized, mesoporous, silica-based films. This first insight in alcohol/water coadsorption may open the door toward new generation of alcohol sensors.

Adhesion to Y-TZP ceramic: Study of silica nanofilm coating on the surface of Y-TZP

This study evaluated the influence of silica-based film coatings on the surface of yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP), in particular on the durability of the bond strength between the ceramic and resin cement. Eighty Y-TZP (In-Ceram YZ, Vita) blocks (4 × 4 × 3 mm) were obtained and divided into four groups according to the surface treatments (n = 20): tribochemical silica coating (TBS; Cojet, 3M/ESPE), 5 nm SiO2 nanofilm and silanization (F-5), 500 nm SiO2 nanofilm and silanization (F-500), and 500 nm SiO2 nanofilm + hydrofluoric-acid-etching + silanization (F-500HF). Specimens of composite resin (3.25 mm in diameter and 3 mm in height) were cemented to Y-TZP blocks using resin cement (Relyx ARC). Half of the specimens from each group were tested 24 h after adhesion (B: baseline condition), and the other half were subjected to aging (A: storage for 90 days and 10,000 thermal cycles). The specimens were subjected to shear testing (SBS) (1 mm/min). After testing, the surfaces were analyzed with a stereomicroscope and scanning electron microscope. Micromorphologic and elemental chemical analyses of the treated Y-TZP surface were made by X-ray energy dispersive spectroscopy. Bond strength data were statistically analyzed by Kruskal-Wallis/Mann-Whitney tests (α = 0.05). The surface treatment showed significant differences for B (p = 0.0001) and A (p = 0.0000) conditions. In both storage conditions, TBS and F-5 groups promoted the significantly highest bond strength. Most of the specimens presented adhesive failure. The X-ray energy dispersive spectroscopy analysis depicted the highest peak of silica in the TBS, F-5, and F-500 groups. The adhesion to zirconia can be improved if the surface receives a 5 nm layer of SiO2 nanofilm or is subjected to sandblasting with silica particles, followed by silanization.

Sol–Gel Based Hydrophobic Antireflective Coatings on Organic Substrates: A Detailed Investigation of Ammonia Vapor Treatment (AVT)

We report a method to prepare hydrophobic, antireflective mesoporous silica-based films on polymer substrates from sol–gel approaches combined with an ammonia vapor treatment (AVT) to avoid any thermal curing. Strategies involving the combination of direct co-condensation of pure and methylated-hybrid silica precursors with further post-functionalization with methyl groups were used. Coatings with the best reflectance (transmittances up to 99.6% in the visible range), full water repellence, and good resistance to abrasion (failures occurred at the substrate interfaces) were obtained by optimizing both sol–gel and AVT conditions. Using in situ, time-resolved, spectroscopic ellipsometry, we demonstrate that the structure of the film can be significantly and rapidly modified from molecular to mesoscales, under the action of H2O and NH3 vapors. The identified mechanism follows a local dissolution/condensation associated to Ostwald ripening that can easily be controlled by adjusting the applied conditions. The...