The effect of dispersion on the increased relative permittivity of TiO₂/SEBS composites

Abstract

Polymer composites are currently suggested for use as improved dielectric materials in many applications. Here, the effect of particle size and dispersion on the electrical properties of composites of rutile TiO2 and poly(styrene–ethylene–butadiene–styrene) (SEBS) are investigated. Both 15 and 300 nm particles are mixed with SEBS, with amounts of sorbitan monopalmitate surfactant from 0 to 3.3 vol%, and their dielectric and mechanical properties are measured. Composites with the 300 nm TiO2 particles result in increases of 170% in relative permittivity over the pure polymer, far above those predicted by standard theories, such as Bruggeman (140%) and Yamada (114%), and improving dispersion with surfactant has little effect. The composites with 15 nm particles showed surprisingly large relative permittivity increases (350%), but improving the dispersion by the addition of any surfactant causes the relative permittivity to decrease to 240% of the pure polymer value. We suggest that the increase is due to the formation of a highly conductive layer in the polymer around the TiO2 particles.

Interfacial treatment effects on behavior of soft nano-composites for highly stretchable dielectrics

“…This notable decrease in permittivity can be explained by a change in the interphase properties of the SEBS/TiO2 composite. Similar results were concluded from a study conducted by McCarthy et al [17]. …”

“…In particular, for nanocomposites fabricated with TiO2 [17] and BaTiO3 [22], researchers found that simple mixing rules applies and the experimental results matched the theoretical ones [15,16] [24]. At low levels, an increase in filler volume fraction leads to an increase in permittivity, but to a decrease in the breakdown strength by over 50%, resulting in a decrease in the electrostatic energy density [17].…”

“…Research suggests that having higher interfacial surfaces leads to higher permittivity [17,18], and has the potential to increase permittivity by up to 100 times [20][21][22][23]. In particular, for nanocomposites fabricated with TiO2 [17] and BaTiO3 [22], researchers found that simple mixing rules applies and the experimental results matched the theoretical ones [15,16] [24].…”

“…The interface between the filler and the polymer matrix of nanocomposites can have an important effect on its mechanical and electrical properties [17,18]. The surface interaction between the filler and the polymeric matrix may also influence the dispersion process.…”

“…McCarthy et al [17] studied the effect of adding different TiO2 particle sizes in an SEBS matrix on the electrical properties of the composite using a solution cast process. Particles of 15 and 300 nm diameter were used with and without a surfactant (sorbitan monopalmitate) to enhance the dispersion of the particles in the matrix.…”