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Unformatted text preview: JOURNAL OF MATERIALS SCIENCE 39 (2004) 4937 4939 LETTERS Time dependence of electrical resistivity under uniaxial pressures for carbon black/polymer composites WANG PENG, XU FENG, DING TIANHUAI, QIN YUANZHEN Department of Precision Instrument and Mechanology, Tsinghua University, Beijing 100084, Peoples Republic of China E-mail: email@example.com In the past several years, some composites containing dispersed conducting particles in an insulating poly- mer matrix have been studied for applications such as thermistor and pressure sensors . The electri- cal resistivity of such a composite critically depends on the volume fraction of the conducting filler parti- cles, which is well explained by the percolation the- ory . For a composite near the critical threshold, we would expect to see a negative piezoresistive effect, below a critical pressure, as well as a positive temper- ature coefficient (PTC) effect, which has been already utilized for thermistors such as self-regulating heaters and overcurrent protection devices . Recently, the time-dependent elastic properties of composites con- taining randomly dispersed particles in a polymer ma- trix have been widely studied [8, 9]. However, in the process of investigation, we found that the resistiv- ity of carbon particles/polymer composites would de- crease with time under an invariant uniaxial pressure, which is similar to a resistivity creep behavior. So, attention has been paid to this phenomenon in this paper. Room temperature vulcanized (RTV) liquid silicone rubber (SR, QD231, Beijing Chem. Plant, China) was used as a polymer matrix in our experiment. Conduc- tive carbon black (CB) powder with an average particle size 6 m (SL10, Carbon Black R&D Institute, China) was dispersed, ranging in volume between 30 and 40%. Hexane was used as solvent to mix the fillers with the rubber. Mechanical stirring along with ultrasonic vibra- tion was also used for better particle dispersion. After 4 hr of vigorous mixing, the solvent was evaporated by vacuum evaporator. The viscous mixture was molded into disks ( 6 mm 2 mm) at 45 C for 16 hr. The com- pression apparatus used for measuring the resistance change with uniaxial pressure is described in Fig. 1....
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This note was uploaded on 09/02/2010 for the course BME 314 taught by Professor Frey during the Spring '08 term at University of Texas at Austin.
- Spring '08