Modification Of Carbon Nanotubes And Epoxy Functional Modification

Epoxy resins are widely used in protective coatings,structural adhesives,low-stress electronic-encapsulates,and as matrices of high performance composites.However, epoxy resins are converted into highly crosslinked and rigid matrices after their curing process,which have the limitation of high brittleness and low impact resistance.In order to overcome this limitation,extensive research has been carried out to toughen epoxies by incorporating a variety of additives.Epoxy resins can be substantially toughened by the addition of a rubber phase,but the improvement in toughness is inevitably accompanied by a significant loss in modulus and yield stress.Linear thermoplastics,which are inherently tough,can reduce the brittleness while retain advantageous properties of epoxy resins.The mechanical properties of a thermoplastic-modified epoxy can only be improved if a good adhesion between phases is obtained.Miscible thermosetting polymer blends for special applications, where tansparency is desired,are under intensive study since early 1990s. Poly(ethylene glycol)(PEG),which shows excellent flexibility and biocompatibility, is a very important and commercial crystalline polymer.It is widely used in miscible polymer blends.In this dissertation,thermosetting polymer blends of novolac epoxy resin(EPN) and PEG were studied.The miscibility and crystallization behavior of the blends before curing reaction were investigated by polarized optical microscopy and differential scanning calorimetry(DSC).Overall uncured blend compositions were homogeneous in amorphous state.Single compositiondependent glass-transition temperature(T_g) for each blend could be observed,and the experimental T_g's of blends with EPN content≥40 wt%could be explained well by the Gordon-Taylor equation.Thermal properties of blends cured with 4,4'-diaminodiphenylmethane were also determined by DSC.The capability of PEG to crystallize in cured blends was different from that in uncured ones because of the topological effect of highly crosslinking structure.On the basis of Fourier transform infrared spectroscopy results, it was judged that there were intermolecular hydrogen-bonding interactions between EPN and PEG in both cured and uncured blends.Flexural test were used to investigate the miscibility and properties of the composites.The results showed that DDM-cured blends were fully miscible in amorphous state;the biggest improvement of thermal stability and flexural strength were achieved when 10 wt%PEG was added in EPN.Magnetic nanoparticles have been among the appealing research topics of nanoscience due to their unique properties and potential applications.Although there are several kinds of interesting magnetic nanoparticles,iron oxide particles-magnetite (Fe₃O₄) and its oxidized form maghemite(γ-Fe₂O₃)-have attracted more attention because they are non-toxic and less susceptible to changes due to oxidation. These facts make this kind of nanoparticles one of the most studied materials for biomedical applications.In our paper,magnetic nanoparticles were generated by thermal decomposition of ferric triacetylacetonate[Fe(acac)₃]in the presence of l-methyl-2-pyrrolidone,a functional solvent.The particle size and shape could be varied by altering reaction parameters.For example,with the addition of oleic acid surfactant,smaller particles were produced.In addition,step elevation of reaction temperature was in favor of regular particle morphology.The obtained iron oxide nanoparticleswere characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),Fourier-transform infrared(FTIR) spectroscopy, thermogravimetric analysis(TGA) and vibrating sample magnetometer(VSM).All of the experimental evidences supported that we succeeded in synthesizing monodisperse iron oxide nanoparticles via a facile and effective route.Moreover, when the oleic acid was added,l-methyl-2-pyrrolidone and oleic acid possibly forms an intercalated monolayer on the particle surface.Since the discovery of carbon nanotubes(CNTs) in 1991,they have been the focus of intense research due to their unique structure,which could provide excellent electrical,mechanical and thermal properties.By employing their fascinating tubular hollow cavity,CNTs can be utilized as containers and reactors to prepare nanodevices and nanostructures.In addition,the convex surface of CNTs is proved to be very helpful to transfer mass or ions and support guest compounds as a substrate.Therefore, many useful materials have been coated or attached onto CNTs by covalent linkage, physical adsorption,chemical vapor deposition and other techniques.In our paper, magnetic nanoparticles were facilely attached to multi-walled carbon nanotubes (MWNTs) by hightemperature reaction of ferric triacetylacetonate in l-methyl-2-pyrrolidone in the presence of carboxylated MWNTs.XRD,TEM morphology and TGA were used to demonstrate the successful attachment of iron oxide nanoparticles to MWNTs.It was found that the attached nanoparticles were mainly magnetite.Investigations using Fourier transform infrared spectroscopy proved that the tight attachment was due to the robust linkages:metal-carbonyl coordination.Modified carbon nanotubes were introduced into epoxy resins to fabricate magnetic nanocomposites.Magnetic properties were analyzed by vibrating sample magnetometer.Magnetic single-walled carbon nanotubes(SWNTs) were synthesized in a process consisting of two steps:(a)covalent in-situ polymerization of poly(acrylic acid) (PAA) on the surface of SWNTs,followed by(b)thermal decomposition of[Fe (acac)₃]to produce magnetite nanoparticles on the PAA grafted SWNTs.It was demonstrated that magnetic SWNTs dispersed in water by sonication would respond to an external magnetic field.Upon such functionalization,the reorientation of SWNTs in an epoxy matrix could be produced using a common magnet.This endowed the composites with good magnetic and mechanical properties.