Effects of plasticization on the dielectric properties of poly(vinyl chloride) membranes

Electrode bodies and biosensors are engineered from membranes that often contain poly(vinyl chloride) (PVC) as the structural component. Citroflex B-6 (CF), dibutyl sebacate (DBS), dioctyl sebacate (DOS), epoxidized linseed oil (ELO), epoxidized soybean oil (ESO), ortho-nitrophenyl octyl ether (o-NPOE), and propylene glycol dioleate (PGDO) were used to plasticize the PVC membranes. After adding tridodecylamine (TDDA) and potassium tetrakis-4-chlorophenyl berate (KTpCIPB) as neutral charge carriers and negative sites, respectively, the dielectric properties of the plasticized PVC membranes were measured with a TA Instruments' DEA 2970. Using parallel plate sensors, the plasticizers were scanned at 3 degrees C min(-1) from -100 to + 100 degrees C at seven log frequencies: - 1, 0, 1, 2, 3, 4, and 5. Generally, increasing the amount of plasticizer in the membrane improved the ionic conductivity (sigma) and lowered the temperature of the tan delta peak. A positive linear correlation existed between the log sigma and the log(phr ratio) for a given temperature and frequency. The slopes and intercepts of the log sigma versus log(phr ratio) lines were linear functions of the log frequency but non-linear functions of temperature. The positive slope of the log sigma versus log(phr ratio) lines was greatest at about 0 degrees C and 10(-1) Hz, and the peak values of the slopes diminished as they shifted to higher temperatures and frequencies. The intercepts of the log sigma versus log(phr ratio) lines increased monotonously and tended to converge at the highest temperatures and frequencies. In the final analysis, the traditional phr ratios, which are associated with 200 parts of plasticizer per 100 parts of polymer, were not necessary since sufficient performance was achieved for all plasticizers at lower phr ratios.