The effect of water absorption on the dielectric properties of epoxy nanocomposites

By C. Zou, J. Fothergill, S. Rowe. IEEE transactions on dielectrics and electrical insulation, 2008

279 citations recorded by the source corpus.

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 the reduced proportion of the epoxy in this composite. The glass transition temperatures (Tg) 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 20 K 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 with a thickness of approximately 5 monolayers. A second layer of water is proposed that is dispersed but 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.

Subfields: Biomedical Engineering, Materials Chemistry, Polymers and Plastics

View Paper: https://www.semanticscholar.org/paper/2422f0854ca69c4e83766e3d0d12ccf6e54967f3

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Citations in the corpus

Laboratory assessment and durability performance of vinyl-ester, polyester, and epoxy glass-FRP bars for concrete structures (2017, methodology): “…FRP bars made with vinyl-ester resin to determine the effect of environmental conditions (water, salts, alkalis) on their physical and mechanical properties (Mouritz et al. 2004; Wang 2005; Zou et al. 2008; Robert et al. 2009; Robert and Benmokrane 2013; Benmokrane et al. 2014, 2015, 2016b, 2016c).”
Accelerated microwave curing of fibre-reinforced thermoset polymer composites for structural applications: A review of scientific challenges (2018, background): “metallic nano-particles with high microwave absorption properties [106-109], and can also be affected by sample preparation [49, 56, 110-115], moisture [116-118], and temperature [119, 120].”
A review on the importance of nanocomposite processing to enhance electrical insulation (2011, background): “The presence of water can have additional effects on the behavior of nanocomposites, leading to changes in the dielectric properties independent of dispersion issues [20].”