Thermomechanical properties,phase structure,and conductivity of organic/inorganic hybrid material filled with a conductive filler

Novel epoxy‐based organic/inorganic hybrid materials filled with carbon black (CB) were synthesized from an epoxy resin and silane alkoxide via a sol–gel process. The phase structure and thermal and mechanical properties of the hybrid materials were studied in detail. It was revealed by transmission electron microscope observations that the filled CB particles formed a secondary aggregation structure and were uniformly dispersed in the aggregate. The storage modulus in the rubbery region increased and the peak area of the tan δ curve in the glass‐transition region decreased with the hybridization of silica. Moreover, the conductive properties of the CB‐filled hybrid systems were investigated. In the same volume fraction of CB, the conductivity of the hybrid systems was much higher than that of the unmodified system. This result was attributed to the excluded volume effect of the silica network. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1980–1984, 2003     

Nanocomposite coatings via simultaneous organic–inorganic photo‐induced polymerization: synthesis,structural investigation and mechanical characterization

Hybrid sol–gel films were prepared via a simultaneous organic‐inorganic UV‐curing process using a diaryliodonium salt as a superacid photogenerator. In this single‐step procedure, an epoxy functionalized reactive resin mixed with a variable amount of either of two epoxy trialkoxysilane precursors was UV‐irradiated, causing both the initiation of epoxy ring‐opening copolymerization and the catalysis of trialkoxysilyl sol–gel reactions. The concomitant photo‐induced sol–gel process was found to have a significant effect on the two related propagation mechanisms in competition for the oxirane ring‐opening—the active chain‐end and the activated monomer mechanisms—as proved by a systematic examination of the hybrid material microstructure through ²⁹Si and ¹³C solid‐state NMR spectroscopy. The effect of the oxo‐silica network generation on the epoxy reaction kinetics was also evaluated using real‐time Fourier transform infrared spectroscopy upon varying the epoxysilane structure and its concentration. Thermal and dynamic mechanical analyses were systematically performed on these hybrids, by studying thoroughly their structure–property interdependence. Other mechanical characterizations through tribological and scratch tests suggested that the present photopolymer–silica hybrid material provides a powerful tool to tailor mechanical property profiles. Copyright © 2010 Society of Chemical Industry     

Preparation and anticorrosive properties of hybrid coatings based on epoxy‐silica hybrid materials

A series of sol‐gel derived organic–inorganic hybrid coatings consisting of organic epoxy resin and inorganic silica were successfully synthesized through sol‐gel approach by using 3‐glycidoxypropyl‐trimethoxysilane as coupling agent. Transparent organic–inorganic hybrid sol‐gel coatings with different contents of silica were always achieved. The hybrid sol‐gel coatings with low silica loading on cold‐rolled steel coupons were found much superior improvement in anticorrosion efficiently. The as‐synthesized hybrid sol‐gel materials were characterized by Fourier‐transformation infrared spectroscopy, ²⁹Si‐nuclear magnetic resonance spectroscopy and transmission electron microscopy. Effects of the material composition of epoxy resins along with hybrid materials on the thermal stability, Viscoelasticity properties and surface morphology were also studied, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of baking treatment and materials composition on the properties of bulky PMMA–silica hybrid sol–gel materials with low volume shrinkage

A series of bulky PMMA–silica hybrid sol–gel materials had been successfully prepared through the conventional HCl‐catalyzed sol–gel approach with 2‐hydroxyethyl methyl methacrylate (HEMA) as coupling agent under pumping pretreatment (i.e., exhaustive vacuum evacuation). In this work, the hydroxyl groups of HEMA monomers were first cohydrolyzed with various contents of tetraethyl orthosilicate (TEOS) to afford chemical bonding for the forming silica networks by removal of solvent and byproduct of sol–gel reactions through pumping pretreatment before gelation reactions. Subsequently, the resultant viscous solution was then copolymerized with methyl methacrylate (MMA) monomers at specific feeding ratios by using benzoyl peroxide (BPO) as free‐radical initiator. Eventually, transparent bulky organic–inorganic hybrid sol–gel materials loaded with different silica content were always achieved. The obtained bulky hybrid sol–gel materials were found to be transparent, crack‐free, and of relatively low volume shrinkages even in high silica content. The as‐prepared bulky hybrid sol–gel materials were then characterized through silicon element mapping studies of energy‐dispersive X‐ray (EDX) and transmission electron microscopy (TEM). Effect of heating process at 150°C for 5 h after polymerization and material composition on the thermal properties, mechanical strength, and optical clarity of a series of bulky PMMA–silica hybrid sol–gel materials was investigated and compared by thermogravimetric analysis (TGA), thermomechanical analysis (TMA), hardness test, dynamic mechanical analysis (DMA), and UV–vis transmission spectroscopy, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1151–1159, 2006     

High‐Tg,heat resistant epoxy–silica hybrids with a low content of silica generated by nonaqueous sol–gel process

The epoxy‐silica hybrids showing high T_g and thermal stability are prepared by the non‐aqueous sol–gel process initiated with borontriflouride monoethylamine. Tetramethoxysilane (TMOS) is used as a precursor of silica and 3‐glycidyloxypropyl trimethoxysilane as a coupling agent to strengthen the interphase interaction with an epoxy matrix. The basic factors governing the nonaqueous sol–gel process are studied in order to reveal the formation–structure–properties relationships and to optimize the hybrid composition as well as conditions of the nonaqueous synthesis. The formation of the hybrid, its structure, thermomechanical properties and thermal stability are followed by chemorheology experiments, NMR, DMA and TGA. The most efficient reinforcement of the epoxy network is achieved by the combination of both alkoxysilanes, showing synergy effects. The hybrids with a low content (～10 wt %) of the in situ generated silica exhibit dramatic increase in T_g and the high modulus, 335 MPa, up to the temperature 300°C. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40899.     

Preparation of epoxy resin/silica hybrid composites for epoxy molding compounds

Phenolic novolac/silica and cresol novolac epoxy/silica hybrids were prepared through in situ sol‐gel reaction of tetraethoxysilane (TEOS). The formed hybrids were utilized as a curing agent and an epoxy resin in epoxy curing compositions, respectively. Via the two‐step preparation route, the resulting epoxy resin/silica hybrid nanocomposites exhibited good thermal stability, high glass transition temperatures, and low coefficients of thermal expansion. High condensation degree of the condensed silica was observed with a high content of siloxane bridges, p > 85%, measured by ²⁹Si NMR. The two‐step route also provides feasibility of preparation of epoxy resin/silica hybrid nanocomposites compatible with the current processes of manufacturing of epoxy molding compounds. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 4047–4053, 2003     

Organic–inorganic hybrid materials derived from epoxy resin and polysiloxanes: Synthesis and characterization

In this study, hybrid materials based on epoxy resin were prepared as transparent self‐supported films by a sol–gel process. 4,4′‐Diaminodiphenylmethane or oligomeric epoxy resin were used as precursors, which were conveniently functionalized with trialkoxysilanes as end‐groups. The effect of the introduction of poly (dimethylsiloxane) was also investigated. The hybrid films showed good thermal stability, a nondefined glass transition temperature, and a dense morphology without phase segregation. The tendency to a flat surface could be observed by atomic force microscopy. The hybrid films also showed good performance as coatings for glass plates, with an improved hydrophobic character in comparison to neat epoxy resin. POLYM. ENG. SCI., 48:141–148, 2008. © 2007 Society of Plastics Engineers     

Thermally and mechanically enhanced epoxy resin‐silica hybrid materials containing primary amine‐modified silica nanoparticles

In this article, a series of hybrid materials consisted of epoxy resin matrix and well‐dispersed amino‐modified silica (denoted by AMS) nanoparticles were successfully prepared. First of all, the AMS nanoparticles were synthesized by performing the conventional acid‐catalyzed sol–gel reactions of tetraethyl orthosilicate (TEOS), which acts as acceded sol–gel precursor in the presence of 3‐aminopropyl trimethoxysilane (APTES), a silane coupling agent molecules. The as‐prepared AMS nanoparticles were then characterized by FTIR, ¹³C‐NMR, and ²⁹Si‐NMR spectroscopy. Subsequently, a series of hybrid materials were prepared by performing in situ thermal ring‐opening polymerization reactions of epoxy resin in the presence of as‐prepared AMS nanoparticles and raw silica (RS) particles (i.e., pristine silica). AMS nanoparticles were found to show better dispersion capability in the polymer matrices than that of RS particles based on the morphological observation of transmission electron microscopy (TEM) study. The better dispersion capability of AMS nanoparticles in hybrid materials was found to lead enhanced thermal, mechanical properties, reduced moisture absorption, and gas permeability based on the measurements of thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and gas permeability analysis (GPA), respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

In situ sol‐gel process of polystyrene/silica hybrid materials: Effect of silane‐coupling agents

The polystyrene–silica hybrid materials have been successfully prepared from styrene and tetraethoxysilane in the presence of silane‐coupling agents by an in situ sol‐gel process. Triethoxysilyl group can be incorporated into polystyrene as side chains by the free‐radical copolymerization of polystyrene with silane‐coupling agents, and simultaneously polystyrene–silica hybrid materials with covalent bonds between two phases were formed via the sol‐gel reaction. The 3‐(trimethoxysilyl)‐propyl‐methacrylate (MPS) systems were found to be more homogeneous than the corresponding allytrimethoxysilane hybrid system of equal molar content. In the MPS‐introduced system, the thermal properties of the materials were greatly affected by the presence of MPS. FTIR results indicate successful formation of the silica networks and covalent bonding formation of coupling agents with styrene. The homogeneity of polystyrene–silica systems was examined by scanning electron microscope and atomic force microscope. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2074–2083, 2002     

Effect of 3‐aminopropyltriethoxysilane on properties of poly(butyl acrylate‐co‐maleic anhydride)/silica hybrid materials

The transparent poly(butyl acrylate‐co‐maleic anhydride)/silica [P(BA‐co‐MAn)/SiO₂] has been successfully prepared from butyl acrylate‐maleic anhydride copolymer P(BA‐co‐MAn) and tetraethoxysilane (TEOS) in the presence of 3‐aminopropyltriethoxysilane (APTES) by an in situ sol–gel process. Triethoxysilyl group can be readily incorporated into P(BA‐co‐MAn) as pendant side chains by the aminolysis of maleic anhydride unit of copolymer with APTES, and then organic polymer/silica hybrid materials with covalent bonds between two phases can be formed via the hydrolytic polycondensation of triethoxysilyl group‐functionalized polymer with TEOS. It was found that the amount of APTES could dramatically affect the gel time of sol–gel system, the sol fraction of resultant hybrid materials, and the thermal properties of hybrid materials obtained. The decomposition temperature of hybrid materials and the final residual weight of thermogravimetry of hybrid both increase with the increasing of APTES. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that the morphology of hybrid materials prepared in the presence of APTES was a co‐continual phase structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 419–424, 1999     

Cryostructuring of polymer systems. XXVI. Heterophase organic–inorganic cryogels prepared via freezing–thawing of aqueous solutions of poly(vinyl alcohol) with added tetramethoxysilane

Composite heterophase organic–inorganic hybrid cryogels of poly(vinyl alcohol) (PVA) containing silica constituents were prepared and studied. Such constituents were formed in the course of hydrolytic polycondensation (sol‐gel process) of tetramethoxysilane (TMOS) introduced in to the aqueous polymer solution prior to its freeze–thaw treatment. It was shown that moderate (over the range of ?15 to ?30°C) freezing, then frozen storage, and subsequent thawing of the water/PVA/TMOS systems resulted in the formation of macroporous composite cryogels filled with dispersed silica particles (discrete phase). The continuous phase of such gel materials represents the supramolecular PVA network, which is supposed to be additionally cured with the silicon‐containing oligomeric cross agents formed from TMOS in the course of hydrolytic polycondensation. The incorporated silica components influenced the morphology of cryogels. The effects of significant increase in gel strength and heat resistance with increasing TMOS concentration in the initial feed and with thawing rate decreasing have also been observed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Environmental aging of cold‐cured epoxy‐silica hybrids prepared by sol−gel process

The article investigates the effects of long term environmental aging on thermal and mechanical properties of epoxy‐silica hybrids. These nanostructured materials, prepared by non‐aqueous sol‐gel process and in situ generation of nanosilica during epoxy curing at room temperature, present the potential to be used as cold‐cured adhesives for civil engineering and Cultural Heritage applications. A specifically developed conditioning procedure for these cold‐cured nanostructured materials was applied before moisture/water absorption tests. The work evidenced the superior durability of the studied epoxy‐silica hybrid, which kept its performances in severe, but realistic, environmental conditions with respect to traditional epoxy adhesives. The reduction in the glass transition temperature and mechanical properties of the studied epoxy‐silica hybrid, observed in the first weeks of environmental aging, was followed by a significant recovery. This was attributed to two concomitant phenomena: the reactivation of the incomplete curing reactions in the epoxy domains and the continuation of the condensation reactions in the siloxane domains activated by the absorbed water. Finally, the Fickian behavior, presented by the studied epoxy‐silica hybrid, was used as an indirect indication of the homogeneity of achieved microstructure, with well dispersed silica nanostructures in the epoxy network. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40093.     

Study on preparation and tribological properties of epoxy resin/SiO2 hybrid thin film

A series of organic–inorganic hybrid thin films are prepared by means of the sol–gel process in curing epoxy and hydrolyzing tetraethoxysilane. The epoxy group of γ‐glycidyloxipropyltrimethoxysilane can be incorporated into the sol–gel network to form the interaction between the inorganic and organic phases. Inorganic and organic components can be mixed on the nanometer scales, thereby leading to the formation of so‐called hybrid materials. Transmission electron microscopy examinations and atomic force microscopy are employed to study the morphology and roughness of the samples, respectively. In addition, the tribological behavior of dip‐coating thin films is evaluated by the use of a dynamic/static friction precision measurement apparatus (unidirectional sliding tester). The influences of the contents of both the filler and the coupling agent on the tribological properties of the nanocomposite thin films are systematically studied. These results indicate that the films sliding against a GCr15 steel ball display excellent antiwear and friction reduction performance. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 38–43, 2005     

Preparation and characterization of epoxy resin modified with alkoxysilane‐ functionalized poly(urethane‐imide) by the sol–gel process

The sol–gel process has been frequently employed for preparation of high performance silica/polymer composites. In this paper, novel sol–gel precursor triethoxysilane‐terminated poly(urethane‐imide) (PUI‐Si), combining the advantages of polyurethane (PU) and polyimide, was synthesized and characterized. Then PUI‐Si was incorporated into the epoxy resin matrix to prepare a series of EP/PUI‐Si organic‐inorganic hybrids through an in situ sol–gel process and crosslinking reactions. The thermal stability of EP/PUI‐Si hybrids was evaluated by thermogravimetric analysis and the results show that the PUI‐Si could significantly improve the thermal properties of epoxy resin. The initial decomposition temperature of composites with 50 wt% PUI‐Si reached 347.1 °C, 157.3 °C higher than that of neat epoxy resin. Furthermore, the tensile strength and breaking elongation can also be clearly improved by adding a suitable amount of PUI‐Si. Similarly, the water contact angle increased to 97.4° with 70 wt% PUI‐Si, showing a hydrophobic surface. The morphology was investigated by transmission electron microscopy and the results reveal that the silica particles are smaller than 20 nm and have a strong interaction with the epoxy resin matrix, resulting in the above‐mentioned high performance properties. Copyright © 2011 Society of Chemical Industry     

New epoxy/silica‐titania hybrid materials prepared by the sol–gel process

A new type of inorganic‐polymer hybrid materials of epoxy/silica‐titania had been prepared by incorporating grafted epoxy, which had been synthesized by epoxy and tetraethoxysilane (TEOS), with highly reactive TEOS and tetrabutyltitanate (TBT) by using the in situ sol–gel process. The grafted epoxy was confirmed by Fourier transform infrared spectroscopy (FT‐IR) and ¹H‐NMR spectroscopic technique. Results of FT‐IR spectroscopy and atomic force microscopy (AFM) demonstrated that epoxy chains have been covalently bonded to the surface of the SiO₂‐TiO₂ particles. The particles size of SiO₂‐TiO₂ are about 20–50 nm, as characterized by AFM. The experimental results showed that the glass‐transition temperatures and the modulus of the modified systems were higher than that of the unmodified system, and the impact strength was enhanced by two to three times compared with that of the neat epoxy. The morphological structure of impact fracture surface and the surface of the hybrid materials were observed by scanning electron microscopy and AFM, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1075–1081, 2006     

Environmental effects on the adhesion properties of nanostructured epoxy‐silica hybrids

A nanostructured epoxy‐silica hybrid based on epoxy systems with interpenetrating silica domains was designed for a possible use as a structural adhesive for civil engineering applications. Silica domains were obtained in situ during the curing of the thermosetting matrix by means of the sol‐gel process, which was able to chemically bind the organic phase with the inorganic one. To assess the ability of the developed epoxy‐silica hybrid system of overcoming some of the well known deficiencies of conventional epoxy adhesives used in civil engineering field, the environmental effects on the adhesion properties of these novel systems were investigated. First, flexural tests were undertaken on cast epoxy‐silica specimens to determine the mechanical properties of the nanostructured adhesive when exposed to different environmental conditions, that is, moderate temperature or immersion in water. For comparison purposes, a control sample of epoxy resin, representative of a commercially available adhesive, was tested after the same exposure regimes. In order to assess their durability in service, concrete/concrete joints, bonded or with the hybrid epoxy‐silica or with the control epoxy adhesive, were exposed to the same environmental conditions and subjected to adhesion tests according to the “slant shear test.” The results obtained on both cast specimens and concrete/concrete adhesive joints proved the significantly better retention of properties of the nanostructured organic–inorganic adhesive compared to the control resin after exposure to moderate temperature or immersion in water. This constitutes a distinct advantage of the hybrid system over the corresponding conventional epoxy resins cured at ambient temperature for civil engineering applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42514.     

Mechanical and thermal properties of polyimide/silica hybrids with imide‐modified silica network structures

A series of hybrid materials incorporating imide‐modified silica (IM‐silica) network structures into a polyimide (PI) matrix were produced with a sol–gel technique from solution mixtures of poly(amic acid) and tetraethoxysilane (TEOS) containing alkoxysilane‐terminated amic acids with various degrees of polymerization. The hybrid films, obtained by solvent evaporation, were heated successively to a maximum temperature of 300°C to carry out the imidization process and silica network formation in the PI matrix. The morphology and mechanical properties of these hybrids with IM‐silica networks were studied and compared with the properties of one in which reinforcement of the matrix was achieved with a pure silica network generated from TEOS. The introduction of longer imide spacer groups into the silica network led to a drastic decrease in the silica particle size. Improved tensile modulus was observed in such compatibilized hybrid systems. Comparative thermogravimetric measurements of these hybrids showed improved thermooxidative resistance. A PI hybrid with 30% IM‐silica had a thermal decomposition temperature nearly 260°C higher than that of the pure PI matrix. The high surface area of the interconnected silica domains and increased interfacial interaction were believed to restrict the segmental motion of the polymer and thus slow the diffusion of oxygen in the matrix, thereby slowing the oxidative decomposition of the polymer. The reinforcement of existing and new PIs by this method offers an opportunity for improving their thermooxidative stability without degrading their mechanical strength. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Novel epoxy–silica nano-composites using epoxy-modified silica hyper-branched structure

Epoxy-based nano-composite films with organically modified silica reinforcement have been synthesized and characterized for their thermal and mechanical properties. Silica network generated from the sol–gel process using tetraethoxysilane (TEOS) was suitably modified to have epoxy groups within an extended silica network structure. For this purpose glycidoxypropyltrimethoxysilane and aminophenyltriethoxysilane were reacted to produce epoxide chains having alkoxy end-groups. The precursor molecules having both epoxy and alkoxide functionalities were then mixed with TEOS to produce epoxymodified silica network within a diglycidal ether of bisphenol-A (DEGEBA) matrix. Cross-linking of the matrix using jeffamine D-400 and the sol–gel process was carried out simultaneously. Epoxy–silica hybrids with different silica contents were characterized by scattering electron and atomic force microscopic techniques. Visco-elastic properties, thermal stability and coefficient of thermal expansion of the resulting hybrids were measured through dynamical thermal mechanical, thermogravimetric and thermal mechanical analyses. Large interfacial interaction between the organic and inorganic phases and the distribution of silica at nano-level using epoxy-modified silica in the matrix results in considerable improvement in mechanical properties whereas the coefficient of thermal expansion is reduced in contrast to the neat epoxy system.     

Study the factors affecting the performance of organic–inorganic hybrid coatings

In this article, a series of hybrid organic–inorganic coatings based on silica‐epoxy composite resins were prepared with the sol‐gel method by using γ‐aminopropyl triethoxysilane as a coupling agent. Especially, the research emphasized on the factors that influenced on the properties of the prepared hybrid coatings. Firstly, epoxy resin was reacted with γ‐aminopropyl triethoxysilane at a specific feeding molar ratio; subsequently, the asprepared sol–gel precursor was cohydrolyzed with tetraethoxysilane (TEOS) at various contents to afford chemical bondings to form silica networks and give a series of organic–inorganic hybrid coatings. They were loaded and cured on steel panels and characterized for FTIR, TGA, DSC, water contact angles (WCA), pencil hardness, surface & three‐dimensional morphological studies, and potentiodynamic polarization tests. The surfaces of the hybrid coatings showed Sea‐Island or Inverting Sea‐Island morphologies at a certain relative content of two components, which made the coatings possess hydrophobic property. Due to the contribution of organic and inorganic components, the prepared hybrid coatings possess a lot of properties such as pencil hardness, thermotolerance, and corrosion resistance. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41010.     

Structure–property relationship in epoxy‐silica hybrid nanocomposites: The role of organic solvent in achieving silica domains

The thermo‐mechanical properties of a series of epoxy‐silica hybrid composites prepared through sol–gel process are evaluated in a manner that the effect of organic solvent on the formation of silica domains is highlighted. By means of infrared spectroscopy, small‐angle X‐ray scattering, scanning electron microscope, dynamic mechanical thermal analysis, and thermo‐gravimetric analyzer, the specimens were morphologically studied varying the type of organic solvent. Among polar and nonpolar solvents incorporated by the organic–inorganic hybrid system, a mixture of xylene and ethanol (3:1) was properly comparable with tetrahydrofuran (THF) solvent regarding appearance and thermo‐mechanical characteristics. Enhanced thermal stability and modulus was observed upon increasing solvent content. Also, a proper dispersion of silica domains throughout the epoxy was seen in the case that the xylene/ethanol mixture or THF served as solvent. It is to be emphasized that the assigned mixture is environmentally better than that of THF. J. VINYL ADDIT. TECHNOL., 21:305–313, 2015. © 2014 Society of Plastics Engineers