Superhydrophilic coatings with enhanced transmittance fabricated from solid and mesoporous silica nanoparticles

Superhydrophilic coatings with high transmittance were fabricated from solid and mesoporous silica nanoparticles (NPs) via layer-by-layer assembly followed by calcination. These porous silica coatings were highly transparent and superhydrophilic. The maximum transmittance reached as high as 96.1%, while that of the glass substrate was 91%. The time for a droplet to spread flat (water contact angle lower than 5°) is <1?s. Scanning and transmission electron microscopies were used to observe the morphology and structure of both NPs and coating surfaces. Transmission spectra and their changes after calcination were characterized by UV–vis spectrophotometry. The surface wettability was studied using a contact angle/interface system.     

Template-free synthesis of uniform hollow silica nanoparticles for controllable antireflection coatings

Antireflection coatings consisting of nanoparticles have promising applications in a wide range of UV optical fields, such as high-power laser systems and space telescopes. However, an open question for these coatings is how to minimize light scattering caused by the nanoparticles. Here, we utilize hollow silica nanoparticles to realize antireflection coatings, which largely diminish light scattering and, hence, exhibit excellent transmission even at UV wavelengths. The hollow silica nanoparticles were synthesized using a template-free approach and then dip coated onto fused silica substrates to form antireflection coatings. The coatings were found to exhibit nearly 100% transmission at any wavelength ranging from the UV to IR bands by variation of the coating thickness. Moreover, the coatings showed relatively high environmental stability because their hollow structures were insensitive to contaminants. This study provides a novel route to fabricate UV antireflection coatings with improved optical properties and good environmental stability, which will help promote the understanding, design and fabrication of optical coatings.     

H2-induced copper and silver nanoparticle precipitation inside sol-gel silica optical fiber preforms

ABSTRACT: Ionic copper- or silver-doped dense silica rods have been prepared by sintering sol-gel porous silica xerogels doped with ionic precursors. The precipitation of Cu or Ag nanoparticles was achieved by heat treatment under hydrogen followed by annealing under air atmosphere. The surface plasmon resonance bands of copper and silver nanoparticles have been clearly observed in the absorption spectra. The spectral positions of these bands were found to depend slightly on the particle size, which could be tuned by varying the annealing conditions. Hence, transmission electron microscopy showed the formation of spherical copper nanoparticles with diameters in the range of 3.3 to 5.6 nm. On the other hand, in the case of silver, both spherical nanoparticles with diameters in the range of 3 to 6 nm and nano-rods were obtained.     

Atomic force microscopy study on structure and properties of irradiation grafted silica particles in polypropylene‐based nanocomposites

Nanosilica particles treated by irradiation grafting polymerization can effectively improve the strength and toughness of a thermoplastic polymer at a rather low filler content. A detailed investigation on the modified nanoparticles in the absence and presence of a polypropylene matrix is carried out by using atomic force microscopy. The results indicate that the loosen agglomerates of the untreated SiO₂ became more compact due to the linkage between the nanoparticles offered by the grafting polymer. In addition, the molecules of the polypropylene matrix are able to diffuse into the modified nanoparticle agglomerates during the melt processing. Entanglement between the molecules of the grafting polymer and the matrix is thus available, which in turn facilitates a strong particle–matrix interfacial interaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2218–2227, 2001     

Preparation and characterization of water reducible alkyd resin/colloidal silica nanocomposite coatings

In this study, water reducible alkyd resins containing different amounts of colloidal silica were synthesized for the first time. In order to achieve this, alkyd resin, which has an oil content of 35%, was prepared with tall oil fatty acid, isophthalic acid, trimellitic anhydride, and trimethylolpropane. The alkyd resin was neutralized with triethylamine, and was dissolved in an isobutyl alcohol-isopropyl alcohol-butyl glycol mixture to produce 75% (wt.) solution, which was called stock alkyd resin. The stock alkyd resin was diluted with water to 50% (wt.) concentration with water and colloidal silica mixture in order to prepare an alkyd solution containing 0%, 5%, 10%, 15% and 20% colloidal silica. Then the effect of the silica nanoparticle addition on the surface coating properties, thermal behaviors and surface morphologies of water reducible alkyd resins was investigated. As a result, the addition of colloidal silica has improved surface coating properties and thermal behaviors of nanocomposite water reducible alkyd resin.     

Highly bright and photostable cyanine dye-doped silica nanoparticles for optical imaging: Photophysical characterization and cell tests

Spherical silica nanoparticles containing fluorescent trimethine indocyanine dyes (λ_abs = 547 nm, λ_em = 570 nm) were prepared using a water-in-oil microemulsion method. The nanoparticles were of 50 nm diameter and were almost monodispersed in aqueous solution at pH 5.5. Entrapment of dye molecules in the silica matrix stabilised photoemission over several hours of continuous irradiation. The photoemission intensity of the indocyanine was increased 13-fold over that recorded in solution. As each nanoparticle contained 110 dye molecules, the photoemission brightness of each particle was enhanced by three orders of magnitude. The fluorescent nanoparticles have been tested as imaging tools in in vitro tests. As an example of non-macrophagic cells, a highly differentiated neuronal cell line (GT1-7) was used and the results showed that the prepared nanoparticles can be incorporated into these cells with no apparent toxicity for up to three days.     

Preparation of silica/epoxy hybrid polymers as sealing layers on ceramic coatings and their stability study upon thermal treatment

Amine end silica sol (NH₂-silica) was prepared to react with epoxy to make hybrid polymers. With the addition of NH₂-silica, the viscosity exhibited a declining trend until their amount reached around 20%. The hybrids possessed higher decomposing temperatures and higher residues relative to neat epoxy in air; their decomposing behaviors depended on the silica additions, attributing to the joint effects of incorporation of Si-O segments and unstable state of silica sol upon heating. When these hybrids were brushed on ceramic coatings, they infiltrated into a depth of around 60 μm. As sealing layers, they probably experienced partially decomposing, slumping, and then filling the internal defects of the ceramic coatings, some hybrid residue even moved to the boundary areas adjacent to the steel substrates after repeated heating. These hybrids may be applied as sealants on ceramic coatings to prolong the lifespan of steel construction structure at high temperature. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47481.     

Formation and structure of polyacrylamide–silica nanocomposites by sol–gel process

The formation of nanocomposites by the sol–gel reaction of tetraethoxysilane (TEOS) in polyacrylamide (PAAm) is studied. The nanocomposites are prepared in aqueous solution. Fourier transform IR spectroscopy shows that substantial hydrogen bonding occurs in the nanocomposites. The fracture surfaces of the nanocomposites are observed by atomic force microscopy (AFM) as a function of the TEOS content. The AFM images reveal that the PAAm–silica nanocomposite exhibits particle–matrix morphology. It is also found that aggregate formation is more dominant than the particle growth with the TEOS contents. The solution of composite precursor is also applied to spin coating. Furthermore, during the calcination there is an observable change in the silica networks, and then a microinterconnected structure is generated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1817–1823, 2002     

Influence of the fused silica surface dehydroxylation on the adhesion of epoxyacrylate protective coatings used for optical fibers

Measurements have been made of the adhesion of liquid and UV-cured epoxyacrylates to a fused silica surface. The fused silica surface was dehydroxylated in the 200-900°C temperature range. Also, the contact angles of water, diiodomethane and formamide on the fused silica surface were measured. Using the contact angle results, the 'harmonic mean' method and the acid-base interactions approach, the dispersion (Lifshitz-van der Waals) and electron donor and electron acceptor components of the fused silica surface as well as epoxyacrylate polymer surface free energy were calculated. It was found that, probably because of the physically adsorbed water, the hydroxylated surface of the fused silica is basic and that the adhesion of the epoxyacrylate polymer to this surface depends on its basicity.     

Immobilization of glucose oxidase and platinum on mesoporous silica nanoparticles for the fabrication of glucose biosensor

In this study, amino group modified mesoporous silica nanoparticles (MSN) were prepared and used to immobilize both platinum nanoparticles (PtNP) and glucose oxidase (GOx). The prepared MSN–PtNP demonstrated high stability and reactivity for catalyzing H₂O₂ electro-reduction, mainly due to the large amount of PtNP immobilized, the high surface area of these catalysts and the unique nanostructures formed through the synthetic route. Working at −0.2 V, the linear range in response to H₂O₂ by the prepared MSN–PtNP can be 5 × 10⁻⁷ to 6 × 10⁻² mol L⁻¹. After immobilizing GOx onto MSN–PtNP, the resulting MSN–PtNP–GOx was capable of interference-free determination of glucose with the linear range as wide as 1 × 10⁻⁶ to 2.6 × 10⁻² mol L⁻¹. Furthermore, the fabricated glucose biosensor can offer significant advantages compared with its conventional counterparts, typically like the high sensitivity, good reproducibility and stability, and rapid response ability as well. The fabricated glucose biosensor demonstrated its potential in clinical applications, so as to enable the determination of glucose in real serum samples.     

Measurement of adhesion for thermally sprayed materials

Thermally sprayed coatings have a distinctive microstructure which can be described as 'a three-dimensional layered structure of discs which are interlaced to form a material of composite nature'. The coatings are normally greater than 25 μm in thickness and can thus be described as bulk coatings. The minimum microstructural detail would be a single splat (often described as a lamella), which is about 5 μm in thickness and up to 80 μm in diameter. This paper focuses on methods used to define and measure the adhesion of coatings or deposits formed by thermal spray technology. The properties distinguished include those of strength and toughness. Measurements such as the tensile adhesion (according to ASTM C633) and double cantilever beam (DCB) tests will be addressed to illustrate the relevance (if any) of such methods to present industrial practice. Acoustic emission studies have also assessed a function termed as the 'crack density function', i.e. a product of the number of cracks and crack size. Other measuring methods applied to this technology include micro-hardness and scratch testing. The former technique has demonstrated that the material properties of coatings are anisotropic, and the latter method is being considered within the biomedical industry to assess the adhesion of hydroxyapatite to orthopedic prostheses. These techniques, among others, may be used for both fundamental understanding of coating performance (i.e. life prediction and cracking mechanisms) and as tests for quality control.     

Effect of silica on the ZnS nanoparticles for stable and sustainable antibacterial application

Silica-capped Zinc Sulfide (ZnS) nanoparticles were synthesized for the use as stable and long-term antibacterial agents because silica is a very important component in food packaging applications for moisture absorption in tune with its property of biocompatibility and water solubility. The variation in morphological and optical properties of core-shell nanostructures was studied by changing the concentration of silica in a core-shell combination. The structural and morphological properties of silica-capped ZnS have been observed by powder X-ray diffraction (PXRD) and transmission electron microscopic (TEM) studies, respectively. Uncapped ZnS nanoparticles with particle size of 2-4 nm in a highly agglomerated state have been observed from TEM, which shows that they can be used only for short-term antibacterial action despite its excellent zone of inhibition (antibiotic sensitivity). However, ZnS/SiO₂ core-shell nanostructures are highly monodisperse in nature and the particle size increases up to 5-8 nm with increase in silica concentration. Fourier-transform infrared spectroscopy (FTIR) analysis confirms the formation of silica capping on the ZnS surface. The inhibition of defect-related emission by silica capping in energy-resolved photoluminescence studies also shows the formation of very stable ZnS nanoparticles. To study the antibacterial properties of the pure and silica-capped ZnS nanostructure the agar-well diffusion method was employed against both gram-positive and gram-negative bacteria. The obtained results indicate that pure ZnS shows excellent antibacterial action but it can last only for few days.     

Chitosan nanoparticles for loading of toothpaste actives and adhesion on tooth analogs

Delivery and sustained release of toothpaste actives is an important but unexplored area. In this work, chitosan nanoparticles were prepared by a water‐in‐oil emulsion/glutaraldehyde crosslinking method. The typical number average diameter of chitosan and toothpaste active (cetylpyridiniumchloride and NaF) nanoparticles was within the range of 100–500 nm. The particles increased their size at higher pH value. The morphology, adherence, and stability of these nanoparticles were investigated by scanning electron microscopy, transmission electron microscopy, and X‐ray photoelectron spectroscopy. The size of the chitosan/NaF nanoparticles was doubled after they were stored at 4°C for 20 days, and then kept constant till 251 days, the examined time so far. These particles showed good stability in toothpaste lixivium after incubated at 60°C for 30 days too. By contrast, the chitosan/cetylpyridiniumchloride nanoparticles were easy to form floccules in the toothpaste lixivium. The loaded toothpaste actives showed a sustained released behavior for at least 10 h. All the particles could adhere onto the tooth analogs such as hydroxyapatite discs and glass slides in a simulated brushing and rinsing process. In vitro cell culture did not find any cytotoxicity of the as‐prepared chitosan nanoparticles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Surface modification and biological evaluation of kojic acid/silica nanoparticles as platforms for biomedical systems

Kojic acid (KA), an important compound with medical, cosmetic, and industrial applications, was loaded in 3-aminopropyltriethoxysilane-functionalized silica nanoparticle (MSNAPTES-KA5). This nanoparticle with acid was prepared to evaluate its application as a drug delivery system due to its interesting characteristic as large surface area, high pore volume, and good biocompatibility. The samples were characterized using different techniques that demonstrate success in the functionalization and loading process, as can be seen from the results obtained by FTIR, XPS, TGA, and CHN, that confirmed the presence of APTES and KA in the nanoparticles. KA drug loading was estimated using UV-Vis, TGA, and CHN, which revealed 12% loading of KA in the nanoparticles that showed slow rate of release. Antimicrobial assay was performed to evaluate the antimicrobial activity of the samples against different microorganisms. The results showed greater MSNAPTES-KA5 antibacterial activity than free-kojic acid for Candida albicans and Staphylococcus aureus. In relation to the acetylcholinesterase (AChE) inhibition assay; a higher inhibition of MSNAPTES-KA5, than the inhibition with free-kojic acid was observed. In addition, MSNAPTES-KA5 sample was also effective in inhibiting tyrosinase, proving the efficiency of the MSNAPTES base. These studies afford evidence of the possible beneficial biological activities of MSNAPTES-KA5 nanoparticle in pharmaceutical applications.     

A mechanistic study of the fire performance of the silica and zinc borate nanoparticles-incorporated intumescent coatings based on epoxy resin

An epoxy-based intumescent coating containing the silica and zinc borate nanoparticles was fabricated. The fire performance of the coating with the optimum formulation was investigated in terms of the changes in the physical and chemical structure of the formed char layer during the exposure to a temperature of 1000°C. The state of the chemical structure was analyzed by performing the Fourier-transform infrared spectroscopy, x-ray diffraction, and x-ray photoelectron spectroscopy analysis from the char layer at the three-time intervals of 10, 30, and 60 min of the heating process. The innovative Condorcet method was also employed to examine the changes in the physical structure of the formed char layer. Some instabilities were detected in the physical structure of the char layer in the middle period of heating. Moreover, a gradual formation of silicon carbide crystalline structure was observed on top of the surface, followed by its oxidation to silica over time. In contrast, in the bulk structure, silicon crystalline structures (Coesite) intensified with time. Boron nitride was also increasingly created on the top surface and in the bulk of the coating over the heating time. These findings proved the effective role of the silica and zinc-borate nanoparticles in the fire performance of epoxy-based intumescent coatings.     

Mechanics of the indentation test and its use to assess the adhesion of polymeric coatings

The indentation test provides a simple means by which the adhesion of coatings can be qualitatively assessed. On the way to establishing a quantitative measurement of the adhesion strength of coatings and films, it is important that the mechanics of this test are clearly understood. To investigate the influence of factors such as the coating thickness, the indenter radius, and friction during the test, numerical simulations of the indentation of a typical polymeric coating, polymethylmethacrylate (PMMA), bonded to a rigid substrate were conducted by using the finite element method. The stress generated during the indentation test were obtained by employing an accurate constitutive model of the elastic-viscoplastic behaviour of the polymeric coating under consideration. The results of this analysis illustrate the effects of the factors mentioned above on the deformation of the coating during indentation, its confinement, and interfacial shear, and the normal, shear, and hoop stress distributions occurring during indentation. These results provide insight into the possible failure mechanisms operative during the indentation of thin coatings and the important effects of the coating thickness during such tests.     

塑料涂料用马来酸酐接枝氯化聚丙烯的合成与性能

以甲苯为溶剂、过氧化苯甲酰(BPO)为引发剂、马来酸酐(MAH)为接枝单体,对氯化聚丙烯(CPP)进行接枝改性.考察了引发剂和接枝单体用量、反应温度、反应时间以及原料的含氯量对接枝率的影响,并对改性产物进行了傅立叶红外光谱表征.结果表明,氯化聚丙烯成功地接枝上马来酸酐,反应条件和原料的含氯量会影响接枝率,优化的工艺条件为:m(BPO)/m(CPP)=0.04,m(MAH)/m(CPP)=1.1,反应温度为100 ℃,反应时间为3 h.涂料性能测试结果说明,改性产物在部分酮酯类溶剂中的溶解性能优良,对多种塑料材料有良好的附着性能,而附着力的大小受到接枝率的直接影响.     

Sol-gel synthesis and characterizations of organically modified silica coatings on knitted cellulose for fixation applications

In order to improve the fixation properties, a novel organically modified silica coating (OMSC) was deposited on knitted cellulose fabric printed with pigment based ink. The organically modified silica sol (OMSS) was prepared by adding tetraethoxysilane (TEOS), γ-glycidoxypropyltrimethoxysilane (GPTMS), ethanol, H₂O and HCl. The color fastnesses of knitted fabrics treated with the OMSS were improved significantly. The coating treatment with OMSS (concentration 4-8 wt%) was beneficial to the washing fastness, and the fade rate of washing was reduced more than 50%. The dry and wet rubbing fastnesses were enhanced one or more grades. The scanning electron microscope (SEM) photographs of knitted cellulose fabrics indicated that continuous OMSCs were formed on the fiber surface, which contributed to the washing and rubbing fastnesses. The bending properties of fabric demonstrated that the fixing treatment had slight effect on the handle. These results suggest fixation with OMSS is an effective pathway to improve the color fastness of knitted cellulose fabrics.     

Measurement of the practical adhesion of paint coatings to metallic sheets by the pull-off and three-point flexure tests

In this paper, we compare the practical adhesion measurements of alkyd, vinyl, epoxy, and polyurethane paints on cold-rolled steel using the pull-off and three-point flexure tests. It has been shown that (a) in the pull-off test, the ultimate load and ultimate strain values depend on the stud area. During trimming, cracks are created within the system which are responsible for a large decrease in the parameters measured. On the other hand, it is impossible to differentiate between the failure initiation and the failure propagation zones; (b) in the three-point flexure test, the area (W) subtended by the load/displacement curves corresponding to samples with and without stiffener does not depend on the bonded width or on the substrate compliance. After carrying out such a mechanical test, it is also possible to discriminate between failure initiation and failure propagation using appropriate tools for observation, such as scanning electron microscopy, and for analysis, such as electron microprobe analysis and Fourier transform infrared spectroscopy. W is shown to be representative of the failure initiation energy. To give a clear indication of the formation of the paint/substrate interphasial zone, we have studied the practical adhesion of different types of acrylic paint (thermoplastic acrylic binder filled with TiO₂, BaSO₄, or CaCO₃, with or without crosslinked polyurethane) applied onto aluminium substrates (treated in a sulphochromic acid bath). Five different types of failure initiation were observed, each type corresponding to quite different energies (W). Failure initiation takes place within the interphasial layer for thin coatings (thickness 70 μm). For thicker paint layers, cohesive failures were observed. A model showing the composition of the paint/metal interphase is proposed.     

太阳能背板粘结层用涂料的制备及其性能研究

采用氟碳树脂、固化剂、颜料、溶剂和助剂制备了太阳能背板粘结层用氟碳涂料,研究了氟碳树脂、固化剂的种类以及固化剂中异氰酸根与氟碳树脂中羟基的比例对粘结层性能的影响,结果发现：选用中等羟值的三氟氯乙烯与乙烯基醚的氟碳树脂, HDI三聚体为固化剂,固化剂中异氰酸根与氟碳树脂中羟基的物质的量比为 1∶1,可得综合性能较优的涂层。涂层 PCT 48 h后的附着力仍为 0级,紫外辐射 120 kWh/m²后的黄变为 0.68,与 EVA的粘结力初始为 96 N/cm,双 95湿热老化 10 d后的粘结力为 60 N/cm。