An Optical Chemical Sensor Based on Polymer Swelling and Shrinking using Dithiocarbamate-Polymer Microspheres

Odeh, I.
Siam, S.
Khatib, M.
Shakhsher, Z.
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Deanship of Research and Graduate Studies, Yarmouk University, Irbid, Jordan
In this work, an optical chemical sensor based on a swelling and shrinking polymer has been developed. A dithiocarbamate functional group was attached chemically to the backbone of poly vinyl benzyl chloride which was lightly crosslinked with divinyl benzene. The derivatized polymer microspheres were dispersed in a hydrogel membrane to produce a sensing element. This modified membrane was used for sensing specific heavy metal ions, such as Hg2+. The response is based on the interaction between the metal cations with the negative charges of the deprotonated dithiocarbamate functional group, whereby the swellable polymer undergoes shrinking as a result of neutralization of the negative charges of this functional group. This complex formation of a metal cation with a dithiocarbamate functionality causes significant changes in the optical properties of the sensing element. Shrinking of the polymer microspheres resulted in a decrease in the optical transmission through the sensing membrane. This is due to the increasing difference in refractive indices between the microspheres and the dispersing hydrogel membrane. This sensor showed a good response particularly to mercury ion. There was insignificant response to H+ in the pH range 2 -13. In addition, there was no detectable response towards alkali, alkaline earth metals and other heavy metal ions such as Pb2+, Zn2+, and Cd2+.