Vapor-phase moving-boundary indicator

Claim 1

In a device for monitoring the time-temperature history of an article including (a) a closed vapor-impermeable container; (b) a chamber forming one portion inside of said container; (c) an adsorptive substrate, through which vapor can permeate at measurable rate, having an indicating compound deposited on at least the outer surface thereof, said compound capable of undergoing a color response upon contact with vapor or condensed vapor specified below, and said substrate positioned inside said chamber such that the outer surface of said substrate, containing said compound, is in sealing contact with a portion of the inner surface of said chamber; (d) a source of vapor, reactive with said compound to produce a color response, within said chamber, said vapor being capable of traveling through the substrate by permeation thereof, and being constrained by said sealing contact to contact said substrate at only one portion of the observable surface of said substrate prior to traveling through said substrate in order to contact said compound on the surface of said substrate; and (e) means for providing said vapor at a given moment to the chamber; whereby a moving colored boundary is produced on the surface of the substrate during travel of the adsorbed vapor throughout the substrate, the improvement which comprises providing a polydiacetylene as said indicating compound in the form of a solution, in a solvent therefor, said solution being capable of exhibiting a visual color response upon contact with said vapor, and said vapor being soluble in said solution.