Lightly crosslinked monodisperse poly(vinylbenzylchloride-co- 2,4,5-trichlorophenylacrylate) microspheres were prepared by dispersion polymerization. Then microspheres were derivatized with various secondary amines to convert the vinylbenzylchloride to a pH sensitive amine. These microspheres were embedded in poly(vinylyalcohol) hydrogel to form a membrane. Optical sensitivity of this membrane for pH is based on refractive index changes accompanying swelling and shrinking of the polymer microspheres. The membrane appears turbid (opaque-white) because the refractive index of microspheres is greater than that of the hydrogel. 2,4,5- trichlorophenyl acrylate (TCPA) was added into the polymer formulation in order to introduce porosity and hydrophilicity to the microspheres. In the amination procedure, the large 2,4,5-trichlorophenol group is replaced by the smaller amine forming a more hydrophilic amide. This shortened the response time of the membrane from hours to a few seconds. The membrane is more turbid at short wavelengths. In addition, turbidity of the membrane increases as the pH of solution increases. There is a linear relation between microsphere concentration of the membrane and its turbidity. The range in which the membrane is sensitive to pH is from 6 to 8.5, with an apparent pK_a of 7.5.

Date Published: 9 December 1999
PDF: 8 pages
Proc. SPIE 3860, Fiber Optic Sensor Technology and Applications, (9 December 1999); doi: 10.1117/12.372961

Published in SPIE Proceedings Vol. 3860:
Fiber Optic Sensor Technology and Applications
Michael A. Marcus; Brian Culshaw, Editor(s)