Figure 1.The schematic and principle of the polymer-coated SAW chemical sensor.As well known, polymer materials are the primary chemical selleck products interface for vapor detection. Polymers have a higher sensitivity, lower detectable limits, and better Inhibitors,Modulators,Libraries ability to operate at room temperature than metal-oxide films [5]. Thus, the so-called viscoelastic effect loading contributes mainly to SAW due to the viscoelastic nature of polymers, in addition to the mass loading from the polymer deposition [6,7]. Usually, a bulk modulus K and a shear modulus G can be used to specify the mechanical properties of a linear and isotropic polymer. They are both complex, and their real parts (G�� and K��) represent the storage moduli, where the imaginary parts (G�� and K��) represent the loss moduli.
A polymer with large shear modulus Inhibitors,Modulators,Libraries (G�� > 10 GPa) and G�� << G�� is a glassy (elastic) one. The rubbery (viscoelastic) regime is characterized by G�� �� 100 MPa, with G�� comparable to or less than G��. The glassy-rubbery polymer means that the polymer with a G�� which is 100 MPa < G�� < 10 GPa. Martin et al. first reported the response of polymer-coated SAW devices to temperature Inhibitors,Modulators,Libraries changes and polymer vapor absorption based on the perturbational approach [8]. Two different theory models were developed to predict velocity and attenuation induced by different polymer types. Grate et al. described the solubility interactions and the design of chemically selective sorbent coatings for chemical sensors and arrays in detail [9]. Kondoh et al. performed an optimization of the properties and thickness of polymers and the operating frequency theoretically [10].
Grate described the original motivation and principle behind the use of hydrogen-bond acidic polymers on chemical sensors and reviewed Inhibitors,Modulators,Libraries the types of polymer developed [11]. Yu-tang Shen et al. investigated the design rules for polymer-based ST-cut SAW sensors used in detecting organophosphorous compounds [12]. Calculations indicate that the glassy-rubbery film is most suitable in sensing application because it provides a larger AV-951 and approximately linear sensing signal. However, the previous response mechanism analysis were aimed at chemical sensors based on traditional polymer deposition techniques like spin-casting, air-brushing, or dip-coating.
Recently, some advanced techniques such as self-assembly (SEM) and molecularly imprinted (MI) technology are reported for polymer coating [13,14], in which, an active surface gold film between the sensitive film and substrate was used, the same requirement was also applicable to some simple polymer deposition reference 2 techniques like solvent evaporation. Wang et al. presented some meaningful advances in sensor response mechanism analysis considering the effect of the metal film under such case, optimal design parameters like polymer thickness, and operation frequency were extracted theoretically [15].