A method for determining the permeability and solubility of sulfur in poly(dimethylsiloxane) (RTV)



A method has been devised whereby the S8 permeability and solubility in silicon resin are determined by observing the reaction between sulfur vapors and silver particles within the polymer. The particles (∼10 μm diameter), which may vary between 0.1 and 100 μm in diameter, are dispersed in the polymer at a concentration up to 20% within a glass cylinder (also an aluminum container). The polymer is cured according to procedure and exposed to S8 saturated vapors at various temperatures (55°–125°C), leaving one end of the cylinder open. The Ag particles are a perfect sink for sulfur, which is consumed as soon as it reaches the reaction boundary that separates the reacted and unreacted Ag particles. Consequently, a distinct black region containing Ag2S product is left behind as the boundary advances. The line displacement, measured at time intervals for the several temperatures, is used to calculate the gas permeability in the polymer as a function of temperature on the basis of a mass transport model developed from diffusion theory. The S8 solubility in the polymer is calculated from the permeability and diffusivity. The latter is determined independently by measuring the time that the Ag2S reaction is delayed when a layer of plain polymer separates a silver surface and the sulfur environment.