Magnetoacoustic chemical sensors based on swellable polymer microspheres

The goal of this dissertation was to investigate chemical applications of magnetoacoustic sensors based on swellable polymer microspheres. The magnetoacoustic sensor was used to monitor viscosity of starch solution, water loading, and 2-hydroxyethyl methacrylate polymerization. Poly(vinylbenzyl chloride) (polyVBC) microspheres were prepared by suspension polymerization and then derivatized to introduce dicarboxylate groups onto the polymer backbone. Poly(vinylbenzyl chloride-trichlorophenyl acrylate) (polyVBC-TCPA) microspheres were prepared by dispersion polymerization and then derivatized to introduce amine groups onto the polymer backbone. These derivatized polymer microspheres swell and shrink with changing pH. They were entrapped in a hydrogel membrane and the membrane turbidity was investigated by UV/Vis spectrophotometry. Membrane turbidity increased with pH from 6.0 to 8.0 for entrapped aminated polyVBC-TCPA microspheres, and decreased with pH from 2.0 to 8.0 for entrapped dicarboxylated polyVBC microspheres. The change in turbidity with pH was subject to hysteresis that decreased with increasing water content of the hydrogel membrane. A magnetoelastic ribbon coated with a layer of hydrogel membrane with entrapped aminated polyVBC-TCPA or dicarboxylated polyVBC microspheres was used to monitor pH. A thin layer of polyurethane was pre-coated on the ribbon to prevent it from rusting and increase its adhesion to the pH sensitive membrane. The resonance frequency of the sensor increased as pH changed from 6.0 to 8.0 when aminated polyVBC-TCPA microspheres were used, or decreased as pH changed from 2.0 to 8.0 when dicarboxylated polyVBC microspheres were used. The magnitude of the frequency shift was linearly proportional to the particle concentration in the hydrogel membrane. Poly(vinyl alcohol) (PVA) and HYPAN hydrogels were used to make hydrogel membranes. HYPAN hydrogels are hydrophilic acrylate derivatives. They are good for magnetoacoustic sensors due to their high water content, high mechanical strength, and good adhesion to the polyurethane coated ribbon. The new magnetoacoustic sensors do not require any physical connections to the sensing elements. They are ideally suited for applications where physical connections are undesired or not possible