The dynamic viscoelastic behavior of polysiloxanes filled with ultrafine SiO 2 has become ever-lasting important due to its unique properties. In present article, the influence of SiO 2 treated with silane coupling agent bis(3-triethoxysilyl)tetrasulfane(TESPT) on dynamic viscoelastic properties of uncured polymethylvinylsiloxane(PMVS)/ultra fine-silica(SiO 2) composites was investigated by using an advanced rheometric expansion system(ARES) under the conditions of temperature 25 ℃, strain(γ) from 0.01% to 100% and frequency(ω) from 0.01 to 100 rad/s. The results reveal that the treated SiO 2 particles leads to the frequency-dependent storage modulus(G′) which approaches linear viscoelastic behavior in the lower frequency region. Based on an examination of the dynamic viscoelastic behavior and TEM observation, we owe these characteristics to improved dispersion of SiO 2 particles in the polymer matrix due to their surface-treatment as compared with the untreated case. On the other hand, dynamic viscoelastic behavior sensitively reflects the dispersion of SiO 2 particles with diameters from 100 to 500 nm, which further evidence the promotion of filler dispersion induced by the incorporation of TESPT.
Conductive properties of multiwalled carbon nanotubes(MWNTs) filled high-density polyethylene(HDPE) composites prepared by melt blending were studied. The results showed that as the MWNTs concents reach to 3%(mass fraction), the electrical conductivity of the composites changes from insulator to semiconductor, possessing resistivtiy of 10 10 Ω·cm. While as the MWNTs concents reach to 5%, the composites become a good conductor. The resistivity-temperature characteristic of the composites exhibits that with the increasing of the temperature, the resistivity of the composites first decreases, while increases abruptly when the temperature approaches melting point(t_m) of the matrix, indicating an existence of the negative temperature coefficient(NTC)-positive temperature coefficient(PTC) effect. It should be noted that this phenomenon can not be found in polymer-based composites filled with other conductive particles, such as carbon black, graphite, carbon fiber.
