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|Title:||The effect of water absorption on the dielectric properties of epoxy nanocomposites|
Fothergill, John C.
Rowe, Stephen W.
|Publisher:||Institute of Electrical and Electronics Engineers (IEEE)|
|Citation:||IEEE Transactions on Dielectrics and Electrical Insulation, 2008, 15 (1), pp. 106-117|
|Abstract:||In this research, the influence of water absorption on the dielectric properties of epoxy resin and epoxy micro-composites and nano-composites filled with silica has been studied. Nanocomposites were found to absorb significantly more water than unfilled epoxy. However, the microcomposite absorbed less water than unfilled epoxy: corresponding to reduced proportion of the epoxy in this composite. The glass transition temperatures of all the samples were measured by both differential scanning calorimetry and dielectric spectroscopy. The Tg decreased as the water absorption increased and, in all cases, corresponded to a drop of approximately 20K as the humidity was increased from 0% to 100%. This implied that for all the samples, the amount of water in the resin component of the composites was almost identical. It was concluded that the extra water found in the nanocomposites was located around the surface of the nanoparticles. This was confirmed by measuring the water uptake, and the swelling and density change, as a function of humidity as water was absorbed. The water shell model, originally proposed by Lewis and developed by Tanaka, has been further developed to explain low frequency dielectric spectroscopy results in which percolation of charge carriers through overlapping water shells was shown to occur. This has been discussed in terms of a percolation model. At 100% relative humidity, water is believed to surround the nanoparticles to a depth of approximately 5 monolayers. A second layer of water is proposed that is dispersed by sufficiently concentrated to be conductive; this may extend for approximately 25 nm. If all the water had existed in a single layer surrounding a nanoparticle, this layer would have been approximately 3 to 4 nm thick at 100%. This "characteristic thickness" of water surrounding a given size of nanoparticle appeared to be independent of the concentration of nanoparticles but approximately proportional to water uptake. Filler particles that have surfaces that are functionalized to be hydrophobic considerably reduce the amount of water absorbed in nanocomposites under the same conditions of humidity. Comments are made on the possible effect on electrical aging.|
|Rights:||This is the author's final draft of the paper published as IEEE Transactions on Dielectrics and Electrical Insulation, 2008, 15 (1), pp. 106-117. Copyright © 2008 IEEE. The final version is available from http://ieeexplore.ieee.org/. Doi: 10.1109/T-DEI.2008.4446741. This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of the University of Leicester’s products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to firstname.lastname@example.org. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.|
|Appears in Collections:||Published Articles, Dept. of Engineering|
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