Preparation and characterization of derivatized microparticles immobilized in hydrogel membranes for optical chemical sensing based on polymer swelling

Hydrogel membranes containing aminated microparticles have been investigated for reflectance based optical sensing. The membranes were evaluated by UV/Vis spectrophotometry, for potential use in a remote distributive fiber optic chemical sensor. This work describes efforts for improving the signal and decreasing the overall response time of the membranes. The microparticles were prepared by dispersion and seeded emulsion polymerization techniques. The microparticles were derivatized to introduce pH sensitivity. The hydrogel membranes containing swellable microparticles are turbid. Scattering occurs at the microparticle-hydrogel interface and is based on refractive index changes accompanying polymer swelling. The particles swell in response to hydrogen ion concentration, causing them to reflect less light. Therefore, the membrane reflects light as a function of pH. There are many factors that control poly(VBC) particle size and distribution using dispersion polymerization. The factors that influence particle size were investigated using a factorial design experiment and systematic studies. The results indicate that increasing the solvency of the continuous phase, initiator concentration, monomer concentration, temperature and decreasing the stabilizer concentration lead to larger particle diameters. Any factor or combination of factors that enhances the solubility of the growing polymer, generally leads to increased particle diameters. Poly(vinyl alcohol), PVA, membranes containing aminated poly(vinylbenzyl chloride-co-trichlorophenyl acrylate) microparticles were prepared and characterized. The incorporation of trichlorophenyl acrylate, TCPA, in the microparticle formulation increases the hydrophilicity and increases the microporosity of the microparticles. As a result, the rate of diffusion is enhanced, producing membranes with faster response times, compared to aminated poly(VBC). Incorporating TCPA in the formulation significantly decreased the response time, but the magnitude of signal was only slightly increased. Using a seeded emulsion polymerization technique, porous 1.2 m m poly(VBC) microparticles were prepared. The particles were derivatized with diethanolamine and embedded in a PVA hydrogel and characterized. The response time of these membranes were faster than the membranes containing poly(VBC-co-TCPA). The signal change was also much larger, approximately 10 times greater. The membrane turbidity increased with increasing thickness and microparticle concentration. A decrease in signal occurred for highly crosslinked microparticles and for high ionic strength solutions