A novel technique for preparing organophilic silica by water-in-oil microemulsions

Summary A novel technique to prepare ultramicro spherical silica particles containing vinyl groups on their surfaces is presented. This process is a combination of the sol-gel technique and the water-in-oil microemulsion technique in which hydrolysis and condensation of TEOS [Si(OEt)₄] and MPS (trimethoxysilylpropylmethacrylate) take place. Spherical silica particles with a size range from 20 to 70 nm were obtained and the surface concentrations of the double bonds per nm² were from 4 to 7.     

Effects of water on the preparation,morphology, and properties of polyimide/silica nanocomposite films prepared by sol–gel process

Polyimide/silica (PI/SiO₂) nanocomposite films with 10 wt % of silica content were prepared by sol–gel process under the conditions with and without additional water. The presence of additional water has great effect on the silica particle size and thus on the properties of the prepared PI/SiO₂ films. The results indicated that with additional water, the silica particles formed before the imidization of poly(amic acid) (PAA) and aggregated with the increasing of temperature and degree of the proceeding imidization process. For the nonaqueous process, the hydrolysis condensation reaction of tetraethoxysilane (TEOS) did not occur until the imidization of PAA took place, and no silica particles were found in the unimidized PAA films. The hydrolysis–condensation reaction of TEOS was initiated simultaneously by the trace water released from the imidization reaction, the self‐catalysis mechanism of the approach provide a means of achieving uniformly dispersed silica particles formed in the PI matrix with particle size in the range of 30–70 nm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1579–1586, 2007     

Synthesis and characterization of hybrid films from hyperbranched polyester using a sol–gel process

Hybrid organic/inorganic materials were prepared by an in situ sol–gel process using tetraethoxysilane (TEOS) in the presence of hyperbranched polyester. The influences of hyperbranched polyester molar mass as well as the amount of TEOS were examined. The condensation degree was characterized by solid state ²⁹Si NMR. The combination of solubility tests, calcination tests, SAXS and dynamic mechanical analysis allowed us to investigate the hybrid material nanostructure. The results show high compatibility between the inorganic silica phase and the organic polymer phase, due to the spherical shape of the hyperbranched polymer and its numerous hydroxyl groups. As a consequence, a continuous inorganic phase was formed even with a low silica precursor content without any macroscopic phase separation. These hybrid materials have a high T_g and high storage modulus even at an elevated temperature combined with improved thermal stability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39830.     

Hybrid nanocomposites containing silica and PEO segments: preparation through dual-curing process and characterization

Hybrid organic-inorganic nanocomposites containing PEO segments linked to an acrylate-methacrylate network were prepared through a dual-curing process, involving photopolymerization and condensation of alkoxysilane groups. A Polyethyleneglycol 600 α,ω diacrylate (PEGDA 600) and a similar oligomer containing a Bisphenol A unit and α,ω methacrylate groups (BEMA 1400) were used. Mixtures of the oligomers together with methacryloyloxypropyltrimethoxysilane (MEMO) and tetraethoxysilane (TEOS) were prepared.The kinetics of the reactions of photopolymerization and condensation was investigated. The conditions suitable for obtaining a complete conversion of both the reactive groups were settled up.The obtained films were perfectly transparent and amorphous. The T_g values of the hybrids were found to increase by increasing the TEOS content and the alkoxysilane groups condensation.TEM analyses indicated the formation of silica phases at a nanometric level; TGA curves revealed a higher thermal stability of the hybrid structures.     

Ionomer-silica hybrids via sol-gel reaction

Ionomer-silica hybrid materials were made from polyethylene-co-acrylic acid neutralized by a zinc salt (PI) and tetraethoxy silane (TEOS) via the sol-gel reaction. The effects of various experimental parameters such as solvents, H₂O/Si ratio and the amount of TEOS in the ionomer solution on the hybrid structure and properties were examined. The spectroscopic results show that solvents do not affect the structure of the hybrids, but influence the thermal properties. The hybrids made using highly polar solvent exhibit better thermal stability and dynamic mechanical properties at high TEOS contents. The amount of water used for hydrolysis and subsequent condensation play a significant role in the network formation. The varying amount of TEOS in solutions gives rise to different silica content of the hybrid. Above 50 wt%, the sample becomes opaque due to silica aggregation. The high ratio of H₂O/Si leads to phase separation during the reaction. Transparent hybrid materials can only be obtained when the ratio of H₂O/Si is below 5.     

Surface free energies and steam stability of methyl-modified silica membranes

Methyl-modified silica membranes have been prepared by acid-catalyzed co-hydrolysis and condensation reactions of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES). The surface wettability, micro-structure and gas permeance of the methyl-modified silica membranes were investigated. The values of dispersion force γ_S^d, dipole force γ_S^P and hydrogen bonding force γ_S^h to the surface tensions for the silica membranes were evaluated by the extended Fowkes equation. The surface free energy and surface wettability of the silica membranes decrease greatly with the increasing of MTES/TEOS ratio mainly because of the contribution of hydrogen bonding force. FTIR analysis shows that the reason is the increase of Si–CH₃ group amount and the decrease of O–H group amount on the surfaces of silica membranes. After aging in steam circumstances, the increase of surface free energies results from the increase of O–H amount present on the silica membrane surfaces. The methyl ligands can make the mean pore size and total pore volume of silica membrane larger. Compared with the unmodified silica membrane, the gas permselectivities of the MTES-modified silica membranes have no obvious decrease in despite of the greatly increase of gas permeation rates. As the silica membranes are aged in steam circumstances, the decrease of gas permeation rates in the silica membrane with MTES/TEOS = 0 is far more than that in the silica membrane with MTES/TEOS = 0.8 while their H₂/CO₂ selectivities have no notable change.     

二氧化硅修饰MMT及其在酚醛树脂中的应用研究

采用溶胶-凝胶法制备二氧化硅修饰蒙脱土(MMT),用硅烷偶联剂(KH-550)对其进行改性,并制备了水溶性酚醛树脂(WPF)/MMT复合材料.采用傅立叶变换红外光谱仪、扫描电子显微镜等对其进行分析.结果表明,二氧化硅粒子与羟基发生了缩聚反应;MMT表面上修饰了粒径在400 nm以下的二氧化硅粒子,而且二氧化硅粒子修饰密度可以通过改变正硅酸乙酯与MMT的质量比来改变.MMT在WPF基体中呈现"树枝"状分布,并且形成插层结构和局部剥离结构;加入修饰MMT后WPF在高温下的耐热性得到了明显的提高.当MMT质量分数为5%时,WPF/MMT复合材料具有较好的力学性能.     

Polymeric curing agent reinforced silicone rubber composites with low viscosity and low volume shrinkage

A new type of polymeric curing agent (PCA) was synthesized to improve processing property, increase mechanical properties, and decrease volume shrinkage of silicone rubber. The PCA was prepared by co‐hydrolysis condensation of dimethyldiethoxysilane (DDS) and polyethoxysiloxane, then modified by hexamethylcyclotrisilazane (D₃^N). Commercial silica and tetraethoxysilane (TEOS) were used as controls simultaneously. The properties of polydimethylsiloxane (PDMS) composites were characterized by shear viscosity measurements, room temperature mass loss, linear volume shrinkage, stress‐strain tests, swelling behaviors and thermogravimetric analysis (TGA). PDMS composites using PCA show lower shear viscosity than those using commercial silica. Compared with the traditional PDMS/TEOS curing systems, PDMS/PCA curing systems behave relatively lower volume shrinkage, better reinforcement and thermal properties. In short, PCA acts as a good compromise in providing the best balance of processing property, volume shrinkage, mechanical properties and thermal stability in silicone rubber composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of hybrid nanocomposite coatings by photopolymerization and sol-gel process

Organic-inorganic nanocomposite hybrid coatings were prepared through a dual-cure process involving cationic photopolymerization of epoxy groups and subsequent condensation of alkoxysilane groups. The kinetics of the photopolymerization and condensation reactions were investigated; suitable conditions for obtaining a complete conversion of both reactive groups were found. The obtained films are transparent to visible light. The T_g values of the hybrids increase by increasing the TEOS content in the photocurable formulation. Also, a significant increase in surface hardness could be obtained for the hybrid systems. AFM analysis gave evidence of a strong interaction between the organic and inorganic phase with the formation of silica domains in the nanoscale range.     

Effect of evolved interactions in poly(butylene succinate)/fumed silica biodegradable in situ prepared nanocomposites on molecular weight,material properties,and biodegradability

Poly(butylene succinate) (PBSu)/fumed silica nanocomposites were prepared in situ by condensation polymerization. TEM micrographs verified that the dispersion of the nanoparticles was homogeneous in the PBSu matrix, while some small agglomerates were also formed at a higher SiO₂ content. ¹³C NMR spectra affirmed that the hydroxyl end groups of PBSu could form covalent bonds with the surface silanol groups of SiO₂. These interactions affected the molecular weight of the prepared nanocomposites. At low concentrations the SiO₂ nanoparticles acted as chain extenders, increasing the molecular weight of PBSu, while at higher loadings they resulted in extended branching and crosslinking reactions, leading to gradually decreased molecular weights. Silica nanoparticles acted as nucleating agents, increasing the crystallization rate of PBSu. However, the degree of crystallinity was slightly reduced. Tensile strength and Young's modulus were significantly increased with increasing SiO₂ content. The presence of the nanoparticles resulted in reduced enzymatic hydrolysis rates compared to pure PBSu, attributed to the smaller available organic surface, due to the incorporation of SiO₂, and to the existence of branched and crosslinked macromolecules. Dynamic mechanical and rheological properties were also extensively studied. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Abrasion resistance of waterborne polyurethane films incorporated with PU/silica hybrids

We describe polyurethane (PU)/silica hybrids (PSHs) prepared through hydrolysis and condensation reactions of tetraethoxysilane (TEOS) with or without methyltriethoxysilane (MTES) in the presence of polyurethane dispersion, which were subsequently incorporated into waterborne polyurethane (WPU) to prepare composites. The effects of the solid mass ratio of PSHs/WPU on the particle size of composite emulsions, the dispersion of silica nanoparticles in composite films, and the hardness and abrasion resistance of the corresponding films were examined. Composite emulsions possess a nanoscale particle size when incorporated with PSHs prepared using TEOS and MTES as precursors, and are superior to those with PSHs prepared using TEOS alone. Transmission electron microscopy revealed that silica nanoparticles had a uniform distribution in the polymer matrix and agglomerates could be almost completely avoided through in situ modification of silica with Si-CH₃ groups in the polyurethane dispersion. Composite films prepared with this method exhibited a superior hardness and abrasion resistance even at a lower silica content compared with that containing unmodified silica. In particular, optical microscopy and scanning probe microscopy observations demonstrated wear behavior differences among these composite films from the macro- and nanoscale viewpoints, respectively. It is proved that abrasive wear occurs, and surface morphology studies are in accordance with the results of abrasion resistance tests.     

Sol–gel incorporation of silica nanofillers for tuning the anti-corrosion protection of acrylate-based coatings

The aim of the present work is to synthesize through sol–gel approach new hybrid polymeric nanocomposites to be used as coating materials. An acrylic-based polymer was prepared by free-radical copolymerization of two monomers widely used for coatings, namely 2-ethylhexylacrylate (EHA) and glycidyl methacrylate (GMA) bearing epoxy moieties, in which silica nanoparticles were incorporated by in situ acid hydrolysis and subsequent condensation of tetraethoxysilane (TEOS). Glycidoxypropyl trimethoxysilane (GPTS) was used as coupling agent to fine-tune the compatibility between organic and inorganic phases. The morphology, mechanical properties and corrosion resistance of thin films applied on aluminum alloys were optimized by varying the content of silica nanoparticles whose properties were strongly affected by the TEOS/GPTS ratios. Performances of the obtained hybrid materials were scrutinized by atomic force microscopy (AFM), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and electrochemical impedance spectroscopy (EIS). Thus it was evidenced that an optimum amount of silica nanoparticles with a precise morphology and composition in term of TEOS/GPTS ratio is needed to maintain good coating barrier properties. Outstanding anti-corrosion protection was reached by using optimized hybrid films.     

Characterization of surface charge and zeta potential of colloidal silica prepared by various methods

Colloidal silica is prepared by hydrolysis of TEOS, direct oxidation of Si powder, condensation of silicic acid, etc. There are differences in surface reactivity of silica particle due to the preparation routes. Therefore, it is useful to evaluate surface properties accurately in order to understand the physiochemical properties of the products. The surface charge density, site density and zeta potential with respect to three types of colloidal silica were estimated and discussed. The surface charge density was different depending on preparation method. It is decreasing in the order of direct oxidation, ion exchange, TEOS hydrolysis. The zeta potential is decreasing in the order of ion exchange, TEOS hydrolysis, direct oxidation. The order in surface charge density is different from that in zeta potential because of the difference in stability depending on the particle size and surface charge density.     

Improvement of thermal stability of ZrO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> aerogels by an inorganic–organic synergetic surface modification

The thermal stability of ZrO₂–SiO₂ aerogels was significantly improved by inorganic–organic synergetic surface modifications: inorganic ions [Fe(III)] surface modification and hexamethyldisilazane gas phase modification. The replacement of Hs from surface hydroxyl groups on the aerogel by Fe(III) ions and silyl groups played a critical role in isolating the hydrous particles of ZrO₂–SiO₂ aerogels. So the particle growth caused by the condensation of hydroxyl groups upon firing was inhibited. Meanwhile, the decomposition of the silyl groups upon heat treatment produced SiO₂ particles, which could serve as pining particle to inhibit the crystallization of ZrO₂. Hence, the porous microstructure of the modified aerogels was still well preserved up to 1000 °C, with a high specific surface area of 203.5 m²/g, and a considerable pore volume of 0.721 cc/g. These characteristics of the modified aerogels suggest that it has great potential on ultrahigh-temperature applications in the fields of thermal insulation, catalysis, and catalyst support, etc.     

Sulfonated poly(ether sulfone)/silica composite membranes for direct methanol fuel cells

A series of sulfonated poly(ether sulfone) (SPES)/silica composite membranes were prepared by sol–gel method using tetraethylorthosilicate (TEOS) hydrolysis. Physico–chemical properties of the composite membranes were characterized by thermogravimetric analysis (TGA), X‐ray diffraction (XRD), scanning electron microscope–energy dispersive X‐ray (SEM–EDX), and water uptake. Compared to a pure SPES membrane, SiO₂ doping in the membranes led to a higher thermal stability and water uptake. SEM–EDX indicated that SiO₂ particles were uniformly embedded throughout the SPES matrix. Proper silica loadings (below 5 wt %) in the composite membranes helped to inhibit methanol permeation. The permeability coefficient of the composite membrane with 5 wt % SiO₂ was 1.06 × 10^?7 cm²/s, which was lower than that of the SPES and just one tenth of that of Nafion® 112. Although proton conductivity of the composite membranes decreased with increasing silica content, the selectivity (the ratio of proton conductivity and methanol permeability) of the composite membrane with 5 wt % silica loading was higher than that of the SPES and Nafion® 112 membrane. This excellent selectivity of SPES/SiO₂ composite membranes could indicate a potential feasibility as a promising electrolyte for direct methanol fuel cell. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fabrication of hollow silica particles using copolymeric spheres prepared in supercritical carbon dioxide

Amine functional polymeric spheres were prepared via the dispersion polymerization of 2-dimethylaminoethyl methacrylate and methylmethacrylate in supercritical carbon dioxide, and they were employed efficiently as templates for the fabrication of hollow silica particles. A small amount of divinyl benzene was used as a crosslinking agent to control the morphology of the copolymeric particles from clumpy solid to spherical shape. The assembly of the polymeric spheres with tetraethylorthosilicate (TEOS) through hydrothermal methods produced core-shell type hybrid particles. The whole process required neither surface treatment for the polymeric particles nor addition of any acidic or basic catalyst for the hydrolysis of silica precursor because dimethylamino groups of the copolymeric spheres were able to absorb water and catalyze the hydrolysis of TEOS for the deposition of the silica gel network. The polymeric cores were completely removed by calcination process and silica hollow particles with well-defined structure were obtained finally. The silica hollow particles were characterized by scanning electron microscopy and transmission electron microscopy, which clearly revealed that the silica spheres had the hollow structure with 151 nm wall thickness.     

Preparation and properties of cardanol‐based polybenzoxazine/SiO2 hybrids by sol‐gel technique

A new cardanol‐based benzoxazine monomer containing a hydroxyl group (CBZ) was synthesized and characterized by FT‐IR and ¹H NMR spectroscopy. The formation mechanism of cardanol‐based polybenzoxazine/SiO₂ hybrids from CBZ and tetraethoxysilane (TEOS) by sol‐gel technique was invested by FT‐IR analysis. FT‐IR and SEM confirmed that there were many SiO₂ particles formed and embedded in the cardanol‐based polybenzoxazine. A phase separation occurred when the ratio (wt) of TEOS to CBZ was not less than 3 : 5. TGA results illuminated the thermal stability and char yield of cardanol‐based polybenzoxazine could be enhanced due to the formation of SiO₂ particles in the polybenzoxazine matrix. Incorporation of SiO₂ could improve the surface de‐wetting and anti‐ultraviolet properties of the films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polylactide/nano and microscale silica composite films. I. Preparation and characterization

Polylactide (PLA)/silica composite films were prepared by two methods: blending nanoscale colloidal silica sol and sol–gel. The nano and microscale silica particles, respectively, were well dispersed in PLA when observed using scanning electron microscopy and transmission electron microscope. The mechanical and thermal stability of composite films were measured before and after hydrolysis by Instron and thermogravimetric analysis. The fillers increase tensile strength, Young's modulus, thermal stability, and hydrolysis resistance with increasing silica content. The nanoscale particles exhibit better effects than the microscale ones. The activation energy, E_a, of thermal decomposition is also simulated by the Kissinger and Ozawa equation. The results also show that the thermal stability is increased by the incorporation of silica particles and is lowered by hydrolysis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of silica and coupling agent loading on thermal, morphological and mechanical properties of hybrid membranes

Hybrid polyetherimide-silica (PEI-SiO₂) membranes were synthesized via the sol–gel method through the hydrolysis of tetraethoxysilane (TEOS) with 3-aminopropyltriethoxysilane (APTEOS) as a coupling agent. The effects of silica content and the APTEOS/TEOS ratio in thermal, morphological and mechanical properties of the hybrid membranes were studied. Although many studies report improvements in the structure or properties of composite materials when a coupling agent is used, these contributions do not investigate the effect of the coupling agent loading on the properties of the new material synthesized. In this study, we prepared hybrid membrane with a fixed amount of APTEOS modifying TEOS content to analyze the silica content effect. Conversely, to determine the coupling agent effect, hybrid membranes were prepared varying the APTEOS content while the amount of TEOS was kept constant. All hybrid membranes have a dense and uniform internal structure and exhibit good thermal resistance with a degradation temperature above 544 °C. Membranes with 10 wt% of silica showed better tensile strength with a high modulus and low rupture elongation indicating an effective load transfer between the phases. Concerning the coupling agent effect, the maximum modulus was observed for membranes with 10 wt% of APTEOS, suggesting a greater interaction between the organic and inorganic phases.     

Synthesis of poly(methylphenylsiloxane)/phenylene‐silica hybrid material with interpenetrating networks and its performance as thermal resistant coating

In this study, poly(methylphenylsiloxane) (PMPS) and phenylene‐silica based hybrid material with interpenetrating networks was prepared by a two‐step sol–gel process. Firstly, in the presence of H₂SO₄, the phenylene‐silica was formed as sol particles with high branching degree by cohydrolysis and condensation of phenylene‐bridged monomer, tetraethoxysilane (TEOS), and hexamethyldisiloxane (MM). Then, the intermediate transformed into gel framework in polymer matrix using alkali catalyst, in order to produce a homogenous hybrid material with interpenetrating networks. The structure of prepared hybrid material was characterized by FTIR and NMR, suggesting that phenylene‐silica framework was imported into polymer matrix and the hybrid products have a much higher network chain density than neat PMPS. The thermogravimetric analysis (TGA) shows that the prepared materials start to degrade at around 490°C. The results of tensile test indicate that the typical PMPS/phenylene‐silica hybrid material has a tensile strength up to 26 MPa and demonstrate a certain degree of flexibility. An increase of phenylene content in phenylene‐silica particles tends to produce hybrid materials with improved thermal stability and tensile strength. The hybrid coating films after calcinating at 350 and 400°C for 2 h exhibit a good mechanical performance on adhesion, impact strength and flexibility. Electrochemical impedance spectroscopy (EIS) measurements show that the investigated films have an extremely high electric resistance (10¹⁰ Ohm·cm²) and a satisfied impermeability to 3.5 wt % sodium chloride solution. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013