Aminopropyl-modified silica as cross-linkers of polysiloxane containing γ-chloropropyl groups for preparing heat-curable silicone rubber

A series of aminopropyl-modified silica (APS) with different amine contents was prepared and, subsequently, used as cross-linkers of polysiloxane containing γ-chloropropyl groups (CPPS) to prepare heat-curable silicone rubber (MCSR). The dispersion of APS in polysiloxane matrix was studied by scanning electron microscopy. The curing characteristics, mechanical and thermal properties of the MCSR were analyzed by a rheometer, mechanical testing and thermal gravimetric analysis (TGA), respectively. The effects of the silica (TS530) content and the molar ratio of APS/CPPS on the curing characteristics were studied. The influence of the amounts of TS530 and APS, and the kind of APS, on the comprehensive mechanical properties of MCSR is discussed. The optimized conditions to prepare MCSR were obtained as follows: the amount of TS530, 55 parts per hundreds of polysiloxane in weight; the molar ratio of [NH]/[γ-chloropropyl], 1.5: 1; and the amount of amino groups on the surface of APS, 0.65 mmol/g. Additionally, TGA results show that MCSR has high thermal stability.     

Using Taguchi experimental design to reveal the impact of parameters affecting the abrasion resistance of sol–gel based UV curable nanocomposite films on polycarbonate

This work aims at studying the abrasion resistance of differently formulated organic–inorganic hybrid coatings prepared by sol–gel method. The organic phase contained UV curable urethane acrylate oligomers and monomers having different functionalities. The inorganic phase was composed of tetraethyl orthosilicate (TEOS) and 3-methacryloxy propyltrimethoxy silane (MEMO). Through a Taguchi experimental design, the impact of influencing parameters such as molar ratio of precursors, hydrolysis ratio (R), post-curing temperature, post-curing time and weight percentage of inorganic to organic part were investigated. Very high transparency of hybrid coatings indicated that nano sized inorganic phase had formed. MEMO could facilitate the connection of two phases, preventing macro phase separation. However, high levels of MEMO lead to ‘defect structure’ in silica network as well as to decreased transparency and mechanical properties. The optimum condition in which highly transparent films with great abrasion resistance occurred was observed at equimolar ratio of water to alkoxide and TEOS: MEMO ratio being unity. Statistical analysis revealed that thermal post-curing was not significantly important.     

The coating performance of adipic acid modified and methacrylated bisphenol- A based epoxy oligomers

In the present work adipic acid modified and methacrylated bisphenol A based epoxy resins were prepared. The structures of oligomers were characterized by FT-IR. UV curable clear coatings were applied on aluminum substrates. The physical and mechanical properties of UV-cured coatings such as gel content, solvent resistance, hardness, gloss, flexibility and tensile tests were examined. In addition, the thermal behavior of coatings was also evaluated. It is observed that the tensile properties and thermal stabilities of modified epoxy methacrylate coatings mainly depend on the adipic acid content. The best results were obtained with 5 wt% adipic acid modification. Copyright © 2007 John Wiley & Sons, Ltd.     

Strontium-doped hardystonite plasma sprayed coatings with robust antimicrobial activity

A strontium-doped hardystonite (Sr-HT) bioceramic, in bulk form, demonstrates excellent bioactivity for bone regeneration with high fracture toughness and compressive strength. This work examines the antibacterial and mechanical properties of Sr-HT coatings on an alpha-beta titanium alloy with a high specific strength and excellent corrosion resistance (Ti-6Al-4V) produced by atmospheric plasma spray (APS) as the deposition coating technique. A hydroxyapatite (HAp) APS coating, a commercial bioceramic coating, is chosen as the control. The in-situ observation showed that Sr-HT powders experience temperatures during plasma processing that exceeded their melting point to form a coating well adhered to the substrate. It was demonstrated that the Sr-HT coating possessed superior antibacterial properties against Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative Pseudomonas aeruginosa. In addition, the Sr-HT coating exhibits a uniform distribution of hardness and elastic moduli, higher nanohardness and elastic moduli compared to the equivalent properties of the HAp coating. Moreover, the Sr-HT coating outperforms the HAp coating regarding scratch and wear resistance. The bonding and shear strength of the Sr-HT coating are higher than the values required for orthopedic implant coatings. The Sr-HT coating also allows efficient zinc, silicon and strontium ions release when immersed in cell culture media. In summary, the antibacterial capabilities and the mechanical properties of the Sr-HT APS coating exceed those of the commercial HAp APS coating. Therefore, Sr-HT APS coatings are candidates for bioceramic coating applications in orthopedic implants.     

Preparation of photocurable silica–titania hybrid coatings by an anhydrous sol–gel process

Photocurable silica-titania hybrid coatings were prepared through an anhydrous sol–gel process. Moreover, test samples were prepared by the addition of definite ratios of fluoro acrylate oligomers into the formulations to manage the optical properties of transmitted light. Formulations were applied to corona-treated polycarbonate substrates. Upon adding the inorganic component to the coating material, thermal, mechanical, and other properties, such as hardness, gloss, contact angle, and flame resistance were improved. The photocured hybrid films showed an increase in the refractive index with increasing the titanium tetraisopropoxide content. As expected, a decrease was observed in the refractive index of the coatings with the incorporation of fluoro acrylate resin. The surface morphology of the hybrid films was characterized by ESEM analysis. In addition the chemical composition of the surface of the coatings was identified by ESEM–EDS technique. ESEM studies indicated that inorganic particles were dispersed homogenously throughout the organic matrix.     

Scratch Resistant and Transparent UV-Protective Coating on Polycarbonate

UV-protective coating material has been developed to improve the scratch resistance and transparency of polycarbonate substrates. Acetyl acetone (AcAc) chelated silanes and 3-glycidoxypropyl-trimethoxysilane (GPTMS) modified nano-titania sols were used for the UV-protective hard coating materials by the sol-gel technique. The hybrid network is formed as a result of the controlled hydrolysis and condensation of the MTMS (Methyl Tri Methoxy Silane) and DMDMS (Di Methyl Di Methoxy Silane). Surface modified TiO₂ nano particles were dispersed in sterically stabilized in the hybrid network by the chelating agent. The coatings dried at 130°C after spray coating were shown to have excellent scratch resistance and adhesion and in addition, it roles as efficient UV-protector under UV irradiation. The long time UV test resulted in no crack formation, without loss of adhesion within the test period of 20 weeks.     

Sol–gel composite coatings from methyltriethoxysilane and polymethylhydrosiloxane

New composite coatings were prepared by mixing pre-hydrolyzed methyltriethoxysilane (MTES) sol by an acidic catalyst dibutyltin dilaurate (DBTDL) and polymethylhydrosiloxane (PMHS) in gasoline at room temperature. The gel process was thoroughly investigated regarding the use of different basic catalyst [3-aminopropyltriethoxysilane (APTES) or triethylamine (TEA)], as well as the ratios of pre-hydrolyzed MTES sol and PMHS with various content of active H. It was revealed that the composite coating from 2:1 ratio (w/w) of pre-hydrolyzed MTES sol with equimolar amounts of water and PMHS_1.55 under the catalysis of APTES demonstrated high pencil hardness, and excellent resistance against contamination and corrosion. This composite coating (MTPM21-A) was further characterized by FTIR, ²⁹Si NMR, DSC and TGA.     

Reliable Condensation Curing Silicone Elastomers with Tailorable Properties

The long-term stability of condensation curing silicone elastomers can be affected by many factors such as curing environment, cross-linker type and concentration, and catalyst concentration. Mechanically unstable silicone elastomers may lead to undesirable application failure or reduced lifetime. This study investigates the stability of different condensation curing silicone elastomer compositions. Elastomers are prepared via the reaction of telechelic silanol-terminated polydimethylsiloxane (HO-PDMS-OH) with trimethoxysilane-terminated polysiloxane ((MeO)₃Si-PDMS-Si(OMe)₃) and ethoxy-terminated octakis(dimethylsiloxy)-T8-silsesquioxane ((QM^OEt)₈), respectively. Two post-curing reactions are found to significantly affect both the stability of mechanical properties over time and final properties of the resulting elastomers: Namely, the condensation of dangling and/or unreacted polymer chains, and the reaction between cross-linker molecules. Findings from the stability study are then used to prepare reliable silicone elastomer coatings. Coating properties are tailored by varying the cross-linker molecular weight, type, and concentration. Finally, it is shown that, by proper choice of all three parameters, a coating with excellent scratch resistance and electrical breakdown strength can be produced even without an addition of fillers.     

Inclusion of W in electroless Ni–B coating developed from a stabilizer free bath and investigation of its tribological behaviour

In the present study, tribological and corrosion behaviour of electroless Ni–B–W (ENB-W) coatings prepared from stabilizer-free baths and deposited on AISI 1040 steel substrates were examined. Three distinct coating bath temperatures (85 °C, 90 °C, and 95 °C) were varied for coating deposition. The coatings showed nodular morphology. Thermogravimetric study of ENB-W coatings revealed improved thermal stability attained at 95 °C bath temperature. The microhardness of ENB-W coating was 645, 690, and 720 HV₁₀₀ at bath temperatures of 85 °C, 90 °C, and 95 °C respectively. The inclusion of W to Ni–B coating enhanced the hardness by ∼150 HV₁₀₀. On a pin-on-disc tribometer, wear test was conducted. The precipitation of Ni (111) and its borides occurred post sliding wear at high temperatures (300 °C). Ni (111) crystallite size decreased because of high temperature sliding wear at 300 °C with an increase in coating bath temperature. With a reduction in crystallite size at high temperatures, both wear rate and COF decreases. The scratch hardness and first critical load of failure of the coatings was determined using a scratch tester. Using potentiodynamic polarization, corrosion resistance of ENB-W coatings in 3.5% NaCl was investigated. ENB-W coatings could provide shielding to AISI 1040 steel from corrosion. Though the corrosion resistance is poor with respect to lead stabilized coatings.     

Imide-containing oligomers as alkyd resin modifiers

Organo-soluble imide-containing oligomers (oligomaleimidohydroxyphenylene and oligoimide derived from benzalazine and m-phenylenebismaleimide) were examined as modifiers for melamine-alkyd and alkyd resins. Addition of these modifiers enhances the hardness, impact strength, and corrosion resistance of the coatings and their adhesion to metal surfaces, i.e., improves the service properties of the coatings.     

Synthesis and characterization of polydimethylsiloxane-cyanopropyltriethoxysilane-derived hybrid coating for stir bar sorptive extraction

New inorganic–organic hybrid materials were synthesized by hydrolysis and condensation of cyanopropyltriethoxysilane (CNPrTEOS) and polydimethylsiloxane (PDMS) in the presence of hydrochloric acid, HCl catalyst and methyl trimethylmethoxysilane as precursor via sol–gel method and coated on glass encased stir bar for use in stir bar sorptive extraction (SBSE). The cyano part provides polar moiety, which may improve the extraction of polar analytes. The physico-chemical properties and extraction ability of PDMS-CNPrTEOS-derived hybrid coatings can be fine tuned via manipulation of solvents (tetrahydrofuran (THF)-based and dichloromethane (DCM)-based) and PDMS-CNPrTEOS molar concentrations during the sol synthesis. Clear, homogeneous PDMS-CNPrTEOS-derived hybrid sols were obtained using THF and DCM at optimized molar ratios. The optimized molar ratios of THF:CNPrTEOS and THF:PDMS were 5:1 and 25:1, respectively. The optimized molar ratios of DCM:CNPrTEOS and DCM:PDMS were 10:1 and 70:1, respectively. FTIR spectrum showed that the intensity of the CN peak increased with increasing content of CNPrTEOS in the PDMS;CNPrTEOS-derived hybrid. The Field Emission Scanning Electron micrographs of prepared coatings revealed smooth, homogenous surfaces and crack-free coatings with film thickness of 200 nm to 2.5 μm attributing to different solvent types. All coatings prepared were thermally stable at temperature higher than 200 °C. The DCM-based PDMS-CNPrTEOS-derived coating shows more advantages in terms of physical characteristics and extraction ability compared to THF-based PDMS-CNPrTEOS-derived coatings due to higher cyano part content and its thicker coating. The PDMS-CNPrTEOS-derived hybrid coatings can be used as extraction sorbent for analysis of non steroidal anti-inflammatory drugs namely ketoprofen and diclofenac sodium in SBSE.     

UV-curable coatings of highly crosslinked trimethylmelamine based acrylates and methacrylates

The synthesis and characterization of N¹,N²,N³-trimethylmelamine based (meth)acrylates and their application as components of UV-curable lacquers is described. A pre-condensed oligomeric mixture with a degree of condensation up to five is obtained via a one-pot conversion. Dividing the synthesis into two steps gives access to the mostly monomeric tris(meth)acrylates in overall yields higher than 76%. In general, the prepared compounds can easily be applied on glass, metal, and polystyrene glass affording highly transparent, hard, and scratch resistant coatings after UV-curing. The UV-cured monomeric trimethylmelamine trisacrylate was fully characterized by means of hardness, gloss, scratch-, abrasion-, and chemical resistance. Remarkably, the trimethylmelamine trisacrylate does not release cancerogen formaldehyde even at 150 °C.     

Sol–gel-derived nanocomposite coatings filled with inorganic fullerene-like WS<Subscript>2</Subscript>

Silica coatings filled with nanoscaled inorganic fullerene-like tungsten disulphide (IF-WS₂) have been prepared through a sol–gel process on stainless steel substrates, and the structure and mechanical properties have been investigated. The precursor was prepared from a mixture of colloidal silica, 3-glycidoxypropyltrimethoxysilane (GLYMO), water and ethanol, adjusted to pH 4 with HNO₃. In this solution WS₂ is dispersed and in some cases immediately before coating ethylenediamine (ED) is added. The stainless steel substrates are dip-coated, dried in air and heat-treated in the temperature range of either 150–360 °C in air or up to 900 °C in vacuum. The solidification process is followed by differential thermal analysis (DTA). The resulting brown coloured coatings have a thickness of 1.5–4 μm. Scanning electron microscopy investigations (SEM) show that the WS₂ nanoparticles are embedded as small aggregates in a hybrid silica matrix. X-ray diffraction (XRD) measurements prove that most of the tungsten disulphide embedded in the matrix can be protected against oxidation even after curing the samples at temperatures up to 900 °C. Hardness and modulus of the hybrid silica films were measured through an instrumented indentation test. Increasing the temperature of the heat treatment yields an increase of hardness from 0.3 to 1 GPa and of modulus from 3 to 17 GPa. The amount of up to 10 wt.% WS₂ in the coatings has no remarkable influence on hardness and modulus of the samples.     

Microstructural Characterization and Mechanical Property of Iridium Coating Produced by Double Glow Plasma

Ir is the most interesting as an effective oxygen diffusion barrier for super high-temperature structural materials. In this study, an Ir coating, approximately 7 μm thick, was deposited onto Mo substrate by double glow plasma at substrate temperature of about 1,120 K in an argon atmosphere. The crystal orientation, morphology and mechanical property of the Ir coating were investigated by XRD, SEM, AFM, TEM, nanoindentation and scratch test. The results indicated that the (220)-oriented Ir coating was composed of the columnar grains. The surface roughness of the Ir coating was higher than that of the substrate. The hardness and the elastic modulus of the Ir coating were about 9.5 and 340 GPa, respectively. The coating had a high hardness due to the sub-micrometer size grains. The coating had good scratch resistance due to the strong adhesion of the coating to the substrate.     

Thermal and neutron shielding properties of 10B containing UV cured hybrid coatings

¹⁰B containing organic–inorganic hybrid coating material based on a UV-curable formulation was prepared via anhydrous sol–gel technique. UV curable coatings were applied on Plexiglas (PMMA) substrates. The molecular structure of the coating material was analyzed by ATR-FTIR spectroscopy technique. The characterization of the UV-curable coating was evaluated by various techniques such as gel content, abrasion resistance, chemical resistance, pencil hardness, pendulum hardness, MEK rubbing test, contact angle, cross-cut test, gloss, transmittance test, neutron absorption, Limiting Oxygen Index and stress–strain tests. Hybrid coatings showed a significant enhancement in radiation shielding properties. The thermal behavior of coatings was also evaluated. It is observed that the thermal stability of coatings mainly depends on their boron and silicate contents. Results of all analysis conducted on hybrid films, and coatings were discussed.     

Synthesis and characterization of hybrid borosiloxane gels as precursors for Si–B–O–C fibers

The sol–gel method has been used for the synthesis of borosilicate gels from mixtures of methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES) and boric acid. The use of boric acid, B(OH)₃ allows the hydrolysis and condensation of hybrid silicon alkoxides without further addition of water or catalyst. The use of difunctional silicon units, –(CH₃)₂SiO– promote the formation, during the sol–gel process, of linear oligomers which facilitate fiber drawing before gelation. Gel characterization performed by FT-IR, XRD, TG-DTA and DCS analysis indicates the formation of a mixed network with incorporation of the boron units via =B-O-Si≡ bridges. The formation of borosiloxane bonds seems favored by the presence of DMDES. SiBOC glasses were obtained after pyrolysis of the borosilicate gels in argon atmosphere at 1000 °C. TG-DTA study indicates that the ceramic yield decreases by increasing the amount of DMDES. Gel fibers were successfully prepared from convenient partially-aged solutions by hand drawing. Pyrolysis of the obtained gel fibers under argon atmosphere at 1000 °C open the possibility to produce SiBOC homogeneous glass fibers with diameter as low as 10 μm.     

Synthesis of poly(styrene-co-3-trimethoxysilyl propyl methacrylate) microspheres coated with polysiloxane layer

A procedure has been developed to coat micron-sized poly(styrene-co-3-trimethoxysilyl propyl methacrylate) microspheres with a smooth layer of polysiloxane by the hydrolysis and condensation of methyl trimethoxylsilane (MTMS). Firstly, polystyrene microspheres containing silanol groups were prepared by conventional dispersion polymerization using 3-(trimethoxysilyl) propyl methacrylate (MPS) as a functional comonomer in an ethanol/water medium. Secondly, the synthesis of the polysiloxane shell was carried out using a sol–gel process of MTMS. The thickness of the shells can be easily varied with different copolymer seeds and MTMS feed ratio. When we used copolymer particles with 2.00 μm diameter as seeds, the thickness of the polysiloxane shells can be varied from 0.10 to 0.18 μm. The core/shell structure of the composite microspheres was characterized by transmission electron microscope (TEM).     

甲基三乙氧基硅烷修饰的Ti3+/SiO2复合薄膜的发光性能

采用溶胶-凝胶(Sol-Gel)法, 以正硅酸乙酯(TEOS)和甲基三乙氧基硅烷(MTES)为先驱物, 盐酸为催化剂, 用二步水解法制备了Ti3+/SiO2薄膜和甲基三乙氧基硅烷修饰的Ti3+/SiO2复合薄膜. 采用红外光谱仪、X射线衍射仪、椭偏仪、荧光光谱仪等对膜层性质进行了分析. 结果表明, 掺杂Ti3+的SiO2薄膜分别在250 nm附近有一弱的激发峰, 294 nm附近有一强的激发峰, 在393 nm附近出现一强的发射峰. IR光谱发现, MTES修饰的Ti3+/SiO2复合薄膜的Si—OH的吸收峰强度比Ti3+/SiO2薄膜的略减小, Si—O—Si的吸收峰明显增强, 表明复合薄膜硅氧网络结构更规则, 有利于Ti3+的均匀分散. Ti3+/SiO2薄膜与复合薄膜的孔隙率分别为13.64%和6.66%, 表明MTES的加入使薄膜更致密. 在空气中陈放30 d后, Ti3+/SiO2薄膜已经检测不到荧光发射峰, 而MTES修饰的Ti3+/SiO2复合薄膜荧光强度只下降了18%. 在氮气中陈放30 d后, 普通薄膜与复合薄膜的荧光强度均仅下降了10%. 表明Ti3+的荧光猝灭的主要原因是由于Ti3+被氧化造成的. 溶胶中加入MTES后, 薄膜表面结构得到改善, 有效地防止了Ti3+的氧化, 荧光强度更稳定.     

Novel toughened automotive clearcoats modified by a polyester‐amide hyperbranched polymer: structural and mechanical aspects

The present work attempts to study the mechanical properties and toughness behavior of a typical acrylic melamine clearcoat modified by a polyester‐amide hyperbranched polymer (HBP). Formulations were such that 0, 5, 10, 25 and 50% (molar percent) of total acrylic hydroxyl groups were stoichiometrically substituted by those of HBP. Bulk and surface of the clearcoats were studied by various mechanical techniques including hardness, tensile, dynamic mechanical thermal analysis (DMTA), nano‐indentation and scratch tests. In addition a scanning electron microscope (SEM) was utilized to observe the morphology of the fractured films. The bulk mechanical properties showed that a low loading (5 molar %) of HBP was sufficient to considerably increase the bulk hardness, cross‐linking density and toughness. DMTA and SEM results proved the occurrence of a single‐phase blend and that the shear deformation was the main toughening mechanism of HBP modified clearcoats. In general, it was revealed that the HBP not only could act as an excellent compatible toughening agent, but also maintained the clarity of the clearcoat and increased its scratch resistance. Copyright © 2013 John Wiley & Sons, Ltd.     

Preparation and evaluation of high-transparent scratch-resistant thin films on plasma treated polycarbonate substrate

New simple aqueous sol–gel procedure has been used for producing hard transparent organic–inorganic coatings on polycarbonate (PC). Sol-gel thins films were prepared by mixing Si and Al aqueous alkoxides and applied on the plasma treated PC. Tetraethyl orthosilicate (TEOS), 3-glycidoxypropyltrimethoxysilane (GPTMS) and aluminum tri sec-butoxide were used as main precursors. Before applying coatings PC were treated by Dielectric Barrier Discharge (DBD) system being conducted at atmosphere pressure. The effects of temperature, sols volume ratios and aging time on the coatings properties were scrutinized. Chemical, structural, morphological, optical and mechanical analyses of the samples were done by ATR-FTIR, EDS, XRD, FE-SEM, TEM, UV/vis spectroscopy, ellipsometry, pencil hardness and eraser scratch methods. TEM results showed well-dispersed nano-particles in the liquid sol. All of the films showed higher average transmittance (89 %) than the raw PC (86 %) that was stemmed from the lower refractive index (1.481) than raw PC (1.58). Films indicated good adhesion onto the plasma treated substrates (5B). The pencil hardness of the PC substrate (4B) improved to 3H (8 pencil grade increment) with just a single layer coating (775 nm thickness) due to the preparation of new hard structures of interlocked Si and Al atoms.