Epoxy/Silica Nanohybrids or Nanocomposites: Atomic Force Microscopy and X-ray Photoelectron Spectroscopy Investigation of the Processing–Structure–Property Relationships

The structural and morphological features influencing the glass transition temperature of epoxy/silica nanohybrid and nanocomposite materials containing 25–30 phr of nanoscale silica phases are discussed in this letter to answer the questions related to the processing–structure–property relationships. X-ray photoelectron spectroscopy and atomic force microscopy are used to study the surface chemical structure and morphology of epoxy/silica nanohybrids and nanocomposites. Nanohybrids are synthesized via in situ sol-gel process, while the respective nanocomposites are prepared by mechanical blending of preformed silica nanoparticles into epoxy resin. Differential scanning calorimetry is used to determine glass transition temperature of different materials. The surface analytical characterizations reveal that in situ sol-gel process is more suitable for producing organic–inorganic hybrid materials with superior glass transition temperature owing to the achievement of stronger interfacial compatibility and greater crosslink density. A number of other factors affecting glass transition temperature are explored and discussed with reference to surface chemistry, microstructure, and morphology of epoxy/silica nanohybrids and nanocomposites, respectively.     

Organic–inorganic polymer hybrids prepared by the sol-gel method

This review focuses on some aspects of organic-inorganic hybrid materials prepared by the sol-gel method. This field has been studied worldwide as one of the nanotechnologies, and is now of current interest for both organic and inorganic scientists. The elaboration of organic–inorganic polymer hybrid materials using the sol-gel process can be accomplished by various approaches. The simplest method is increasing the compatibility by using physical interactions, covalent bonding and compatibilizer between organic polymer and silica gel. Other novel approaches, such as an in-situ method, NHSG (Non- Hydrolysis Sol-Gel) process, and use of reactive polymer hybrids resulted in the preparation of novel transparent organic–inorganic polymer hybrid materials. Stimulus responsive polymer hybrids are also mentioned. Furthermore, nano-structured organic–inorganic polymer hybrids are created by using supermolecular and self-assembly of organic molecules or polymers recently. The obtained nano-structured hybrid materials showed unique properties that could not be found in amorphous hybrid materials. The possibilities and applications of organic–inorganic polymer hybrid materials are also described in this review.     

二氧化硅多孔介质气凝胶和干凝胶的分形结构研究

二氧化硅多孔介质气凝胶和干凝胶的结构用小角Ｘ射线散射进行了研究．实验表明，用一步法制备的各种气凝胶全部具有分形结构．而干凝胶和用两步法制备的气凝胶没有分形结构．实验还证明干凝胶由尺度较大的球形颗粒组成     

实验条件对纳米多孔SiO2薄膜结构及特性的影响

关键词：     

Influence of interface interaction on enthalpy relaxation in polysiloxane-modified epoxy resin

The enthalpy relaxation and dynamic relaxation properties of phenol-formaldehyde novolac-cured o-cresol novolac epoxy resin modified with hydroxyl-terminated polysiloxane were studied by differential scanning calorimeter (DSC) and torsional pendulum analysis. The results show that the extent and rate of enthalpy relaxation are closely related to the amount of modifier and the ratio of modifier and coupling agent: the (β′ relaxation that appeared at around 40°C in the dynamic relaxation spectra is found to be correlated with the interfacial stress at the interface between the epoxy resin matrix and polysiloxane domain.     

Preparation and Properties of Nano‐SiO2/Epoxy Composites Cured by Mannich Amine

Nano‐SiO₂/epoxy composites cured by Mannich Amine (type T‐31) were prepared and studied and the results are reported in this paper. The nano‐SiO₂ was pretreated by a silane coupling agent (type KH‐550) and mixed with epoxy resin (type E‐51) using an ultrasonic processor. Amounts of filler loading ranged from 1% to 5% of the weight of the epoxy resin. Some properties of the resulting composites were characterized by X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results of tensile tests and impact tests showed that the composite with 3% nano‐SiO₂ loading presented the best mechanical performances. The tribological performance and thermal stability of the materials were also improved with the addition of nano‐SiO₂.     

Friction and wear properties of hybrid sol-gel nanocomposite coatings against steel: Influence of their intrinsic properties

A dual UV-curing process inducing in a single step cationic photopolymerization and a photoinduced sol-gel process was used to obtain novel hybrid coatings. For this, an epoxy resin based on hydrogenated diglycidyl ether bisphenol A was mixed with an epoxy trimethoxysilane precursor (GPTMS, TRIMO) in the presence of photoacid generator based on diaryliodonium salt. Various UV-cured coatings were prepared with different amounts of the hybrid monomer (20 and 50 wt%), and two thicknesses: 15 and 80 μm. The friction and wear properties of these coatings were characterized on a ball-on-disc tribometer (steel ball; applied normal load: 6 N; sliding speed: 5 cm/s). Both the coating thickness and the addition of the hybrid monomer tend to improve the stiffness of the pure epoxy resin; however, these two parameters also induce an increase of the dynamic friction value.     

Curing behavior and physical properties of an epoxy nanocomposite with amine-functionalized graphene nanoplatelets

Amine-functionalized graphene nanoplatelets (AGNPs) were prepared via an easy simple one-step process, treating graphite powder with 4-aminobenzoic acid in polyphosphoric acid, and then the effects of the AGNPs on the curing and physical properties of an epoxy resin were studied. The formation of the AGNPs was confirmed by scanning electronic microscopy (SEM), Fourier transform infrared spectroscopy, and thermogravimetric analyzer. Curing behavior of the epoxy/AGNPs nanocomposite was investigated by differential scanning calorimeter. The AGNPs made the epoxide curing reaction with amine groups slightly faster. The physical properties of the epoxy/AGNPs nanocomposite were investigated by dynamic mechanical analyzer, thermomechanical analyzer, and impact test. The AGNPs improved T_g by 21.4 °C, and storage modulus and impact strength of the epoxy resin 23 and 73%, respectively, much more effective than the graphite powder at the same filler loading of 1 phr. SEM images for the fracture surfaces of the epoxy/AGNPs nanocomposite showed improved interfacial bonding between the epoxy matrix and the nanofillers due to the amine functional groups of the AGNPs.     

Study of microstructure and properties of HEC-g-AA/SiO2 organic-inorganic hybrid materials

HEC-g-AA/SiO₂ hybrid materials are prepared through a graft copolymerization reaction between acrylic acid (AA) monomer and hydroxyethyl cellulose (HEC), in the presence of a silica sol. The microstructure and properties of the hybrid materials are characterized by Fourier transform infrared spectra (FTIR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively. The results show that a rigid inorganic phase SiO₂ is dispersed in flexible organic continuous phase uniformly. HEC-g-AA/SiO₂ hybrid material has no obvious phase separation in the presence of the crosslinking agent. The thermal performances of HEC-g-AA/SiO₂ are excellent, and the glass transition temperature (T _g) increases with the increased amount of the crosslinking agent.     

Polyimide/hollow silica sphere hybrid films with low dielectric constant

Abstract

Polyimide (PI)/hollow silica (HS) sphere hybrid films with low dielectric constant values (low-k) were synthesized via thermal imidization process using pyromellitic dianhydride (PMDA)/4,4′-oxydianiline (ODA) as the polymer matrix and HS spheres as inorganic particles with the closed air voids. The monodispersed HS spheres were synthesized via a one-step process, which means that the formation of silica shells and dissolution of the core particles (polystyrene particles) occurs in the same medium. The HS particles have uniform size of ca. 1.5 μm in diameter and ca. 100 nm in shell thickness. PI/HS sphere hybrid films synthesized using mixture of polyamic acid (PAA) and HS spheres prepared via one-pot process, which means that the production of PAA and HS spheres mixture occurs with the polymerization of PMDA and ODA in the same bottle. HS spheres of two different kinds (pristine HS spheres (PHS spheres) and amine-modified HS spheres (AHS spheres)) were used for the preparation of the hybrid films. With the varying contents of AHS spheres in the range of 1–10 wt%, the dielectric constants of the PI/AHS sphere hybrid films were reduced from 3.1 of pure PI to 1.81 by incorporating 5 wt% AHS. The dielectric constants of the PI/PHS sphere hybrid films were reduced to 1.86 by incorporating 5 wt% PHS. Organic–inorganic hybrid porous polyimides may be expected as prime candidates for polymeric insulators due to their high thermal stability, good mechanical properties, solvent resistance, and low-k.     

Fabrication and characterization of superhydrophobic thin films based on TEOS/RF hybrid

Preparation of superhydrophobic silica-based thin film by adjusting different concentration of reverse (W/O) emulsion of resorcinol formaldehyde resin (re-RF) which was hybridised with silica sol has been developed. The hybrid films were coated by the mixing solution which included precursor solution (sol-gel process) and re-RF (sol-gel process). Rough surfaces were obtained by removing the organic polymer at high temperature and then the hydrophobic groups bonded onto the films were obtained by the reaction with trimethylchlorosilane (TMCS). Characteristic properties of the as-prepared cross-section and surface of the films were analyzed by scanning electron microscopy (SEM) and atom force microscopy (AFM). The experimental parameters are mainly varied the weight ratio of re-RF to silica sol from 0.2 to 4.0. The result showed that the contact angle of the modified silica film was greater than 160° when the weight ratio of re-RF to silica sol was 2.0.     

Role of curing conditions and silanization of glass fibers on carbon nanotubes (CNTs) reinforced glass fiber epoxy composites

Curing behavior of amino-functionalized carbon nanotubes (ACNT) used as reinforcing agent in epoxy resin has been examined by thermal analysis. Experiments performed as per supplier’s curing conditions showed that modification of the curing schedule influences the thermo-mechanical properties of the nanocomposites. Specifically, the glass transition temperature (T_g) of ACNT-reinforced composites increased likely due to the immobility of polymer molecules, held strongly by amino carbon nanotubes. Further, a set of composites were prepared by implementing the experimentally determined optimal curing schedule to examine its effect on the mechanical properties of different GFRP compositions, while focusing primarily on reinforced ACNT and pristine nanotube (PCNT) matrix with silane-treated glass fibers. From the silane treatment of glass fibers in ACNT matrix composition it has been observed that amino silane is much better amongst all the mechanical (tensile and flexural) properties studied. This is because of strong interface between amino silane-treated glass fibers and modified epoxy resin containing uniformly dispersed amino-CNTs. On the other hand, PCNT GFRP composites with epoxy silanes demonstrated enhanced results for the mechanical properties under investigation which may be attributed to the presence of strong covalent bonding between epoxy silane of glass fiber and epoxy–amine matrix.     

Preparation and Characterization of Nano-Calcium Carbonate/Silane Coupling Agent Master Batch and Its Effect on Epoxy Resin

A nano-calcium carbonate (CaCO₃)/silane coupling agent (NCC/SCA) master batch was prepared by the reaction of SCA (γ-aminopropyl triethoxy silane, trade name KH550) with the hydroxyl groups of nano-CaCO₃. Both Fourier transform infrared spectroscopy and thermal gravimetric analysis indicated that the nanoparticles were grafted by SCA. An epoxy resin was modified by adding the NCC/SCA master batch. A simple dipping test suggested that a better dispersion of the treated NCC in epoxy could be obtained than that of the untreated NCC. Then samples of epoxy nano-composites were prepared by a hot press process. The compressive property of epoxy nano-composites was investigated; the results of these mechanical property tests revealed that the compressive strength, elastic modulus, and the total fracture work of the epoxy matrix filled with the treated NCC were significantly improved relative to that filled with the untreated NCC.     

High-pressure effects on nanometric hybrid xerogels, p-phenylenediamine/silica and p-anisidine/silica

The hybrid xerogels p-phenylenediamine/silica and p-anisidine/silica were prepared with different surface areas and porosities and they were processed at high pressure (7.7 GPa or ∼76000 atm) in a quasi-hydrostatic medium at room temperature. The morphologies of the materials were studied before and after the high-pressure treatment by using N₂ adsorption–desorption isotherms, scanning electron microscopy and infrared thermal analysis. The porous hybrid p-phenylenediamine /silica presented after the high-pressure treatment a surface-area reduction and an entrapment of organics in closed pores. However, the less porous hybrid p-anisidine /silica showed a surprising behavior, a pressure-induced increase in surface area with opening of pores. We propose a mechanism based on the inhibition of the cold sintering process by the organics to explain these results. PACS 81.20.-n; 81.40.Vw; 81.05.-t     

微米水合氧化铝/环氧复合材料脉冲真空闪络影响因素

 研究了微米Al₂O₃·3H₂O/环氧复合材料的脉冲真空闪络影响因素。分别给出了固化剂、分散方法、偶联剂对复合材料闪络特性的影响和纯环氧表面抛光前后的脉冲真空闪络特性。实验结果表明:酸酐固化的试样比胺类固化试样闪络电压要高;高速分散方法与超声波分散方法相比,采用前者制备的复合材料有更好的分散特性;使用偶联剂处理填料比不使用时得到的环氧复合材料闪络电压高;抛光后的纯环氧试样有较高的闪络电压。     

Effect of sizing agent on interfacial properties of aramid knitted structural composites

Tensile tests have been carried out on aramid knitted fabrics/epoxy resin composites in which the aramid knitted fabrics are treated with different sizing agents. Two kinds of surface treatment are performed; one uses an epoxy sizing agent and the other uses a polyethylene sizing agent. Tensile modulus and strength of epoxy-sized composites are higher than those of polyethylene-sized composites. The fracture process is different between epoxy- and polyethylene-sized materials. This difference in fracture process is caused by the different interphase made from either epoxy or polyethylene sizing treatments, resulting in the different tensile performance. Moreover, the tensile properties of the wale specimen are more affected than those of the course specimen by the interphase.     

Study on the Structure and Properties of UHMWPE/Epoxy Resin Composite Fiber

The preparation, crystallization behavior, and fiber structure and properties of ultrahigh molecular weight polyethylene (UHMWPE) epoxy resin composite fiber were studied by means of differential scanning calorimeter (DSC), X‐ray diffraction (XRD), Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and tensile testing. The morphology showed a different behavior from pure polyethylene (PE) fiber. The fiber mechanical properties, creep behavior, and thermal properties of UHMWPE fiber can be improved by adding epoxy resin. It's believed that the epoxy can serve as a physical cross‐linking agent to limit the motion or migration of PE molecules and consequently improve the fiber creep property. However, when the content of epoxy resin is higher than 5 wt%, all of the behavior and properties deteriorate.     

Novel epoxy-silicone thermolytic transparent packaging adhesives chemical modified by ZnO nanowires for HB LEDs

A novel high transparent thermolytic epoxy-silicone for high-brightness light-emitting diode (HB-LED) is introduced, which was synthesized by polymerization using silicone matrix via diglycidyl ether bisphenol-A epoxy resin (DGEBA) as reinforcing agent, and filling ZnO nanowires to modify thermal conductivity and control refractive index of the hybrid material. The interactions of ZnO nanowires with polymers are mediated by the ligands attached to the nanoparticles. Thus, the ligands markedly influence the properties of ZnO nanowires/epoxy-silicone composites. The refractive indices of the prepared hybrid adhesives can be tuned by the ZnO nanowires from 1.4711 to 1.5605. Light transmittance can be increased by 20% from 80 to 95%. The thermal conductivity of the transparent packaging adhesives is 0.89–0.90 W/mK.     

Acoustic and thermal properties of a cellulose nonwoven natural fabric (barkcloth)

The desire to mitigate climate change due to greenhouse gas emissions has led to the exploration of plant fibers as alternative materials for various industrial applications, sound absorption inclusive. In this investigation, sound absorption properties of Antiaris toxicaria barkcloth, and the thermal insulation properties of the barkcloth epoxy laminar composites were characterized. Theoretical sound absorption models were utilized to validate the experimental data and the empirical models were in agreement with experimental data. The lowest thermal conductivity was achieved by the Antiaris toxicaria epoxy composites.     

Hyperbranched Polyimide-Silica Hybrid Materials: Synthesis,Structure, Dynamics,and Gas Transport Properties

A series of organic–inorganic hybrid materials were prepared from a hyperbranched polyimide precursor (hyperbranched polyamic acid), tetramethoxysilane, and/or 3-glycidyloxypropyl-trimethoxysilane via a sol-gel process. The hyperbranched polyimide-silica hybrids, whose polyimide moieties were based on commercially available monomers 4,4′,4^″-triaminotriphenylmethane and 4,4′-oxydiphthalic anhydride taken in molar ratio 1:1, contained from 10 to 30 wt% silica. Their morphology and dynamics were characterized by using scanning electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, laser-interferometric creep rate spectroscopy, and wide-angle X-ray diffraction. Attention was also focused on the relation between morphology/dynamics and gas transport properties of these materials.