Spectroscopic analysis of nanodielectric interfaces

Abstract

Polymeric nanocomposites have received an exceptional amount of attention over the recent years as they have the ability to possess enhanced properties. The use of nanosized phases in composite materials, as opposed to their microsized counterpart, delivers characteristics which allow nanodielectric systems to operate at an increased performance and improved efficiency. The requirements of the polymeric system can easily be tailored to suit specific applications with as little as 2 wt.% filler loading, whilst maintaining the typical weight of the virgin material. With the transition from micrometric to nanomeric phases, the volume of the interfacial region increases dramatically and this is where the mechanisms behind nanocomposite behaviour are believed to occur. As the potential for nanodielectrics is endless, the importance of in-depth studies into the filler-matrix interface is fundamental. Many studies have already partaken in research which uses organosilanes as a coupling agent, however few the quantity of organosilane as a variable parameter, or compared the use of hydrous and anhydrous functionalisation methods. This study investigates the consequences of introducing differently functionalised nanosilicas into epoxy systems; a number of spectroscopic techniques (Raman spectroscopy, Fourier transform infrared spectroscopy and combustion analysis) were employed to quantify the level of surface modification on the surface of silica nanoparticles, before mixing methods were developed in an attempt to reach nanoparticle homogeneity in an epoxy matrix. Scanning electron microscopy was employed to investigate the dispersion state of the filler with respect to the degree of functionalisation, whilst data from AC breakdown studies, differential scanning calorimetry and dielectric spectroscopy were analysed to determine the effects of differently functionalised nanosilica in a dielectric system. The investigation shows how condensation reactions within the interphase has an infuence dielectric behaviour, and highlights how changes in the stoichiometry of the epoxy system alters the polymer architecture to have an effect on the electrical properties of the nanocomposites. Further studies explore the use of confocal Raman spectroscopy as a tool in probing the nanofiller-matrix interface. A simulation based on the scattering of incident photons was compared with empirical data from a range of dielectric films; modifications to the scattering photon approach relates physically obtained values for bulk attenuation directly to those observed in confocal Raman depth profiles. Although it was found that the revised model was able to produce confocal Raman depth profiles that closely match experimental data from the nanocomposite films, the nature of nanoparticle agglomeration during functionalisation and the typical resolution of confocal Raman systems do not allow for the detection of chemical changes on the filler.

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ORCID for A.S. Vaughan: orcid.org/0000-0002-0535-513X

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