Presentation on theme: "The Functionalisation and Analysis of Silica-based Nanofillers C. Yeung and A. S. Vaughan University of Southampton, Southampton, UK Introduction The interest."— Presentation transcript:
The Functionalisation and Analysis of Silica-based Nanofillers C. Yeung and A. S. Vaughan University of Southampton, Southampton, UK Introduction The interest in nanocomposites has grown exponentially since the early 1990s. With an increase in understanding of nanoparticle-matrix interactions, the ability to engineer materials and optimise desired properties became well established. However, detailed studies on the fundamental concept of varying surface functionalisations and how this can aid mixing, seems to have been neglected. A possible reason for this is that any such systematic study requires the surface chemistry to be quantitatively characterized. For fillers such as nanosilica, the surface chemistry can easily be changed using commercial silanes. By using such technologies, it is possible to modify the chemistry and extent of the interphase regions, as well as modifying dispersion. Here we study the effects of the functionalisation of nanosilica in epoxy and analyse the effects of the quantity of functionalistion has on nanodielectrics. University of Southampton, Highfield, Southampton, SO17 1BJ, UK Contact details : Results & Discussion Results and Discussion (continued…) Scanning Electron Microscopy Epoxy samples were first fractured in LN 2. Figure 4. shows S.E.M images of increasing degrees of functionalisation of the nanosilica. With the aid of Energy Dispersive X-ray spectroscopy (E.D.X.) and the back scattered electron detector, it is possible to locate agglomerations of nanosilica. These are more evident in the 800 mg functionalised nanosilica epoxy than the unfilled epoxy. The epoxy containing the nanosilica processed with the highest concentration of silane had fractured differently to the other five samples. This could be an effect of the oversaturation of nanosilica in the initial silane processes. Conclusions Raman and FTIR spectroscopy can not currently provide information concerning the chemical state of functionalised silica. In the case of FTIR spectroscopy, optical scattering appears to compromise the simplistic application of the classical Beer Lambert equation. Breakdown data and Weibull analyses are able to show the effects of different degrees of functionalisation of nanosilica when dispersed in epoxy. There is an optimum functionalisation concentration before the breakdown threshold is reduced. Finally, SEM allows us to physically see the nanofiller dispersed in matrix. A degree of agglomeration of nanosilica is present despite sonicating and mixing. Samples & Experimental Sample Preparation Samples were produced using D.E.R. 332 resin cured with Jeffamine D-230 using a previously established flat-plate, guide peg press technique. Samples were cured at 100 °C for 4 h, producing air and defect free specimens with a thickness of 80 µm. Six samples, one unfilled epoxy, were produced by the addition of 100 mg nanosilica, with varying degrees of functionalisation, introduced pre-curing by sonicating the mixture for 1 h and magnetically stirring for 10 min. Nanosilica functionalisation 400 mg of nanosilica in 30 g of methanol was sonicated for 10 minutes. 0, 400, 800, 1600 or 2000 mg of silane (Dow Corning Z-6040) was introduced and magnetically stirred for 10 min then left to functionalise for 24 h. The excess silane was removed by methanol washing and evaporation in an oven. Figure 3. Weibull plot of filled epoxies containing differently functionalised nanosilica. Figure 2. Weibull plot of unfilled epoxy (black) and unfunctionalised filled epoxy (red). Figure 4. S.E.M images of epoxy with nanosilica of 0 mg, 800 mg and 1600 mg silane functionalisation (from top to bottom). Left images from secondary electron detection, right images from back-scattered electrons. Raman & FTIR Spectroscopy These two spectroscopic techniques were used to measure the effects of surface functionalisation of the nanosilica before dispersing in epoxy. Raman and FTIR spectroscopy were unable to detect the degree of functionalisation. FTIR only confirmed the scattering effects are evident with increasing the amount of nanosilica present in the specimen. After dispersion, Raman spectroscopy was used to analyse changes in optical properties of epoxy with the increase addition of silane. Figure 1. Shows the Raman spectra for unfilled epoxy and epoxy with the 400 mg and 2000 mg functionalisation. There is no change in spectral data from samples containing nanosilica of different functionalisation levels. Figure 1. Raman spectra of nanosilica in epoxy. A.C Breakdown The breakdown data are presented as Weibull plots in Figure 2 and Figure 3. The addition of nanofiller has decreased the breakdown strength of the epoxy. From the second Weibull dataset, the optimum functionalised filler to disperse in epoxy is the 400 mg functionalisation, Saturating the nanosilica in the initial functionalisation process has drastically decreased the breakdown strength when dispersed in epoxy.