AbstractA method is presented for determining the diffusivity of a gas in a polymer from the response to a step concentration change in a continuous‐flow permeation chamber. The outlined procedure has several advantages over techniques currently in use: it requires simple numerical integration rather than curve fitting; it utilizes the complete response, rather than a portion of the response which falls within the region of validity of a short‐time asympotic solution of the diffusion equation; and it is applicable both to flat membranes and cylindrical tubes. An illustration of the method is provided by the measurement of the diffusivity of sulfur dioxide in a PTFE tube at several temperatu
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