Electrical percolation phenomena in polymer-solvent systems

Abstract In situ ac/dc electrical measurements were carried out on bulk polymers equuilibrated in controlled gaseous environments. For example, N 2 saturated with water vapor (partial pressure 0 ) and dry N 2 were blended to form a gas with intermediate partial pressure, p , where 0 > p 0 . Equilibration produced swollen polymers with well-defined solvent chemical potentials, ( RT )ln( p / p 0 ). 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 C 1 –C 3 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, P c . The transitionoccurs at low concentrations (0.5–1.5 wt%) relative to P c 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 / p 0 ). DC conductivity varied as 5 × 10 −15 exp[14.7( p / p 0 )] − a 10 6 increase going from ( p / p 0 ) = 0 to ( p / p 0 ) = 1. AC measurements conformed to fixed capacitance electrically in parallel with this conductivity.