Positive temperature coefficient effect of polymer-carbon filler composites under self-heating evaluated quantitatively in terms of potential barrier height and width associated with tunnel current

Flexible temperature sensors based on carbon nanomaterials

Flexible temperature sensors based on carbon nanomaterials can be attached to the surface of human skin or curved surfaces directly for continuous and stable data measurements, and have attracted extensive attention in myriad areas.

Considerable different frequency dependence of dynamic tensile modulus between self-heating (Joule heat) and external heating for polymer--nickel-coated carbon fiber composites

Dynamic tensile moduli of polyethylene--nickel-coated carbon fiber (NiCF) composites with 10 and 4 vol % NiCF contents under electrical field were measured by a homemade instrument in the frequency range of 100--0.01 Hz. The drastic descent of the storage modulus of the composite with 10 vol % was verified in lower frequency range with elevating surface temperature (T(s)) by self-heating (Joule heat). The composite was cut when T(s) was beyond 108 °C. On the other hand, the measurement of the composite with 4 vol % beyond 88 °C was impossible, since T(s) did not elevate because of the disruption of current networks. Incidentally, the dynamic tensile moduli by external heating could be measured up to 130 and 115 °C for 10 and 4 vol %, respectively, but the two composites could be elongated beyond the above temperatures. Such different properties were analyzed in terms of crystal dispersions, electrical treeing, and thermal fluctuation-induced tunneling effect.

Appearance of perfect amorphous linear bulk polyethylene under applied electric field and the analysis by radial distribution function and direct tunneling effect

Without melting flow, linear ultrahigh molecular weight polyethylene (UHMWPE) provided X-ray intensity curve from only amorphous halo at 129.0 °C (surface temperature, Ts arisen by Joule heat) lower than the conventionally known melting point 145.5 °C on applying electric field to UHMWPE-nickel-coated carbon fiber (NiCF) composite. Such surprising phenomenon was analyzed by simultaneous measurements of X-ray intensity, electric current, and Ts as a function of time. The calculated radial distribution function revealed the amorphous structure with disordered chain arrangement. The appearance of such amorphous phase was arisen by the phenomenon that the transferring electrons between overlapped adjacent NiCFs by tunneling effect struck together with X-ray photons and some of the transferring electron flown out from the gap to UHMWPE matrix collided against carbon atoms of UHMWPE. The impact by the collision caused disordering chain arrangement in crystal grains.