Highly reversible and repeatable PTCR characteristics of PMMA/Ag‐coated glass bead composites based on CTE mismatch phenomena

Abstract

Positive temperature coefficient of resistivity (PTCR) behavior of poly(methyl methacrylate) PMMA/silver (Ag)‐coated glass bead composites has been investigated with reference to the conventional PMMA/carbon black (CB) composites. The PMMA/CB composites showed a sudden rise in resistivity (PTC trip) at 115°C, close to the glass transition temperature (T g, 113°C) of the PMMA. However, the PTC trip temperature (92°C) of PMMA/Ag‐coated glass bead composites was appeared well below the T g of PMMA. The room temperature resistivity and PTC trip temperature of the composites were also very much stable upon thermal cycling. Addition of 1 phr of nanoclay increased the PTC trip temperature of PMMA/CB composites to 120°C, close to the T g (118°C) of PMMA/clay nanocomposites, while PMMA/clay/Ag‐coated glass bead nanocomposites showed the PTC trip at 98°C. We proposed that the mismatch in coefficient of thermal expansion (CTE) between PMMA and glass beads played a key role that led to a disruption in continuous network structure of Ag‐coated glass beads even at a temperature well below the T g of PMMA. The decrease in dielectric permittivity of PMMA/Ag‐coated glass bead composites on increasing frequency indicated possible use of the PTC composites as dielectric material. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Positive temperature coefficient to resistively characteristics of polystyrene/nickel powder/multiwall carbon nanotubes composites

“…As observed, under 110V AC and DC application, the composites could attain ≈90°C after 125 and 150 s, respectively, which were close to the PTC trip temperature of the PS/Ni powder (40 wt%)/MWCNT (0.75 phr) composites. Thus, increase in resistivity of the composites near the PTC trip temperature led to decrease in I of the composites, and hence no further increase in temperature was observed [19–21].…”

“…As observed, under 110V AC and DC application, the composites could attain %908C after 125 and 150 s, respectively, which were close to the PTC trip temperature of the PS/Ni powder (40 wt%)/MWCNT (0.75 phr) composites. Thus, increase in resistivity of the composites near the PTC trip temperature led to decrease in I of the composites, and hence no further increase in temperature was observed [19][20][21]. Figure 7 shows the variation of dielectric permittivity (e 0 ) and dielectric loss tangent (tan d) of the PS/Ni powder (40 wt%)/MWCNT (0.75 phr) composites with frequency in a wide range (50 Hz-10 MHZ) at room temperature.…”

Pyroresistivity in conductive polymer composites: a perspective on recent advances and new applications

“…However, the correlation between PTC intensity and polymer crystallinity is not always a simple one as large PTC intensities have also been reported for amorphous CPCs. For example, Kar and Khatua reported a PTC intensity of five orders of magnitude for a PMMA composite containing 40 wt% Ag‐coated glass beads . The PTC intensity could also be tuned by physical–chemical treatments of the base polymer matrix, including, for instance, γ‐ray irradiation, plasma treatment and thermal treatment.…”

“…For example, Kar and Khatua reported a PTC intensity of five orders of magnitude for a PMMA composite containing 40 wt% Ag-coated glass beads. 40 The PTC intensity could also be tuned by physical-chemical treatments of the base polymer matrix, including, for instance, -ray irradiation, plasma treatment and thermal treatment. He et al demonstrated that -ray irradiation could modify the pyroresistive behaviour of an amorphous ethylene-propylene-diene terpolymer (EPDM)/CB composite, from showing only NTC behaviour to only PTC behaviour with a large PTC intensity (six orders of magnitude).…”

Study of Thermal Relaxation of Poly (HDDA-co-MMA) by Temperature Modulated DSC and Dielectric Spectroscopy

“…The basic limitation of TMDSC experiment lies on the low range frequency (<1 Hz) window for which the thermokinetic parameters at higher frequency cannot be probed. This limitation can be overcome by the use of broadband dielectric measurement [24,25] . Dielectric spectroscopy has been an effective technique to characterize the relaxation behavior of polymers [26,27] .…”