PMMA polymer film characterization using thickness-shear mode (TSM) quartz resonator

Poly(methyl methacrylate) (PMMA) polymer films can be used either as a chemically sensitive coating material in implementing biochemical sensors or as a waveguiding layer in guided shear-horizontal surface acoustic wave (SH-SAW) sensor platforms. Characteristic information about the viscoelastic properties of the polymer film and subsequent changes upon exposure to environmental factors is critical for the design, implementation, and analysis of these sensors. The use of the thickness shear mode (TSM) quartz resonator is proposed here to rapidly determine the mechanical properties, primarily the complex shear modulus (G=G\´+G") of relatively thin organic polymer films because of its simplicity and ability to support shear horizontal waves, which are ideal for the characterization of the complex shear modulus of thin films. Using the near-resonant electrical characteristics of the coated device, the impedance/admittance characteristics of the equivalent circuit models of both the bare and coated resonators are related to the film properties and subsequent changes in film properties, particularly the storage and loss moduli (G\´, G"). Both cured and uncured polymer films were studied under different conditions. Measurements and analyses were also performed at higher harmonics for the TSM resonance, in addition to the fundamental frequency, to inspect any frequency-dependent effects and increase the "effective" thickness of the PMMA films.