Dynamic Encoder/Decoder Based on Fiber Bragg Gratings for Optical Security System

Abstract

Thermogravimetry (TG) measurements taken at pressures ranging from 10 −1 to 10 −3 Pa are used to calculate the vapor pressure of pyromellitic dianhydride (PMDA) and 4,4 -oxidianiline (ODA). The vapor pressure calculated for PMDA is closely agrees with to those reported by Pethe et al., Elshazly and Salem. For ODA, the calculated vapor pressure fits exactly on the curve obtained by Salem. The enthalpy is also calculated. The activation energy of desorption is found to be nearly equal to the enthalpy. The adsorption and desorption rates for both PMDA and ODA at various substrate temperatures are also observed. The mean adsorption time, τ calculated for ODA is several orders of magnitude larger than that for PMDA. 1:1 doses of ODA and PMDA therefore produce imine bonds which lead to the formation of thermally unstable films.