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Electrical percolation phenomena in polymer-solvent systems

1991; Elsevier BV; Volume: 131-133; Linguagem: Inglês

10.1016/0022-3093(91)90653-n

1873-4812

James E. Anderson, Karen M. Adams, Philip R. Troyk,

Dielectric materials and actuators

In situ ac/dc electrical measurements were carried out on bulk polymers equuilibrated in controlled gaseous environments. For example, N2 saturated with water vapor (partial pressure 0) and dry N2 were blended to form a gas with intermediate partial pressure, p, where 0 >p0. Equilibration produced swollen polymers with well-defined solvent chemical potentials, (RT)ln(p/p0). One set of experiments involved polysiloxane (PDMS) equilibrated with water. methanol, ethanol and isopropanol. Water sorption, never greater than 0.1–0.25 wt%, had no apparent effect on the electrical properties of PDMS. This result matches early (about 1920–1940) reports regarding non-effects of water sorption on electrical properties of elastomers. Equilibration with C1–C3 alcohols led to significantly different results. The alcohols have higher affinity than water for PDMS; they exhibit 1–22% sorption by weight. Electrical properties vary markedly with sorption, showing characteristics of a percolation transition, Pc. The transitionoccurs at low concentrations (0.5–1.5 wt%) relative to Pc values of monomeric systems. A second set of experiments probed sorbed water effects on filter paper, taken to be a surrogate for macroporous polymer systems. Water weight-gain, i.e. sorption, followed Raoult's law and increased linearly with (p/p0). DC conductivity varied as 5 × 10−15 exp[14.7(p/p0)] − a 106 increase going from (p/p0) = 0 to (p/p0) = 1. AC measurements conformed to fixed capacitance electrically in parallel with this conductivity.