EFFECT OF PLASTICIZER-POLYMER COMPATIBILITY ON THE RESPONSE CHARACTERISTICS OF OPTICAL THIN CO2 AND O-2 SENSING FILMS

A homologous family of dialkyl phthalates has been used to investigate the effect of plasticizer/polymer compatibility on the response chara cteristics of transparent, plastic, thin optical gas sensing films for CO2 and oxygen. Plasticizer/polymer compatibilities were determined t hrough the value of the difference in solubility parameter, i.e. Delta delta, for the plasticizer and polymer with a Delta delta value of ze ro indicating high compatibility. A strong correlation was found betwe en plasticizer/polymer compatibility and sensitivity in phenol red/eth yl cellulose CO2-sensitive films and this relationship extended to CO2 -sensitive films based on other polymers such as polystyrene and poly( methyl methacrylate). It extended also to optical O-2-sensitive films implying that the relationship is general for thin-film optical sensor s. Other results from the CO2-sensitive films in different polymers in dicated that the film sensitivity is largely independent of the polyme r matrix regardless of its inherent gas permeability, when a sufficien t quantity of compatible plasticizer is present. (C) 1998 Elsevier Sci ence B.V.