Investigation On Morphology And Mechanism Of Dielectric Characteristics Of Montmorillonite/Epoxy Nanocomposite

Up till now, related researches on the relevance between the morphology ofnanocomposite and dielectric properties have been evolved for entirely whole20years, since the concept of nanodielectric was introduced by Lewis, however, asatisfactory conclusion has not been reached. The primary reason for suchsluggishness is that the structure morphology of the nanocomposites depends notonly on the characteristics, scales and shapes of the polymer matrix and inorganicnanoparticles, but also closely correlates with the compounding process, types ofthe third component and preparation methods, and so forth. As a consequence,probing into the method of controlling and characterizing the morphology ofnanocomposite is of crucial importance for revealing the connection between themesoscopic structure and macroscopic dielectric properties of nanocomposites,and developing novel dielectric materials with excellent properties.On the basis of current research status of polymer-based nanodielectric,purposed to explore the relationship between interface structure and macroscopicproperties of nanodielectric, different montmorillonite/epoxy nanocompositeswere prepared severally via melting intercalation method, in which, bisphenol Aepoxy resin was recommend as matrix, and disparately treated montmorillonitewas dispersed phase. The structure and morphology were characterized by usingX-ray diffraction, Fourier infrared spectrum, scanning electron microscope andtransmission electron microscopy. The results have shown that the lamellarspacing enlarged from1.26nm to2.38nm after organic modification. Theemerging stretching vibration peaks on account of C—N and O—N bondsindicated that a new bonding formed between alkyl ammonium andelectronegative lamellar of montmorillonite by cation exchange reaction. Duing to that, the compatibility of montmorillonite with epoxy resin improved inleading to developing partially exfoliated discrete phase which were evenlydispersed in matrix in nanometric scale. Accroding to that, a physical model ofmanipulating mesoscopic structure of nanocomposite was proposed based onprinciples of thermodynamic and electrostatic force.The influences of compounding process parameters, modification andcontents of montmorillonite on the dielectric properties of nanocomposite wereexperimentally investigated. The experimental results showed that, in hightemperature, the relative permittivity of nanocomposite was mainly impacted bycuring temperature. On160°C, the permittivity of nanocomposites, which werecured in120°C,150°C and180°C, were8.2,6.7and3.7respectively, with thecorresponding, the loss factors were0.45,0.30and0.10. Simultaneously, thepermittivity and loss factor of organic montmorillonite compounded with epoxywere significantly lower than those of pure epoxy resin and untreatedmontmorillonite/epoxy composite with the same contents of inorganics. Theparameters diminished with the increasing of organic montmorillonite content upto5wt%, and showed a recovering tendency over that. In view of the above, amodel of restricting orientation polarization was put forward based on principlesof dynamics and electrostatic force.Some experiments were done to study the influences of organic treatmentand contents of inorganic particles on the conductivity and breakdowncharacteristics of montmorillonite/epoxy nanocomposites. The experiment resultsindicated that there were significant effects of conductivity of epoxy resin underDC field by introducing montmorillonite. The growth ratio of conductivity wasmuch larger than montmorillonite content increment. The activation energy ofnanocomposite little decreased with the increase of organic montmorillonite. Itreduced0.02~0.18eV, or6.4%~58%, in the low temperature region, and reduced0.1~0.4eV, a drop of about5.6~22.6%, in the high temperature zone. Thecompounding with montmorillonite makes the AC breakdown strength of epoxyresin was improved in varying degrees. The breakdown strength of themontmorillonilte/epoxy composite and organic montmorillonite/epoxynanocomposite was27%and31%higher than the pure epoxy resin respectively.The rules of interface affected on the ionic conductance barrier in low electric field were elucidated according to the principle which is described as that theorganic modification turns the dispersion phase from micrometer to nanometer inscale with the compatibility gets to be better. A thesis which can explain thedecline of breakdown strength was put forward started from free electrontransport mechanism. It was predicated that the free path of electrons in interfaceregion would extend due to overlapped interface which could be presentedfollowing the increase of nano-filler content.