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Film-coating viscoelastic properties

Lipatov et al. [116,124-127] who simulated the polymeric composite behavior with a view to estimate the effect of the interphase characteristics on composite properties preferred to break the problem up into two parts. First they considered a polymer-polymer composition. The viscoelastic properties of different polymers are different. One of the polymers was represented by a cube with side a, the second polymer (the binder) coated the cube as a homogeneous film of thickness d. The concentration of d-thick layers is proportional to the specific surface area of cubes with side a, that is, the thickness d remains constant while the length of the side may vary. The calculation is based on the Takayanagi model [128]. From geometric considerations the parameters of the Takayanagi model are related with the cube side and film thickness by the formulas ... [Pg.15]

Since the transverse shear wave may penetrate the damping surface layer and the viscous liquid, additivity of the equivalent electrical elements in the BVD circuit is only valid under certain particular conditions. Martin and Frye [53] studied the impedance near resonance of polymer film coated resonators in air with a lumped-element BVD model, modified to account for the viscoelastic properties of the film. In addition to the elements shown in Fig. 12.3 to describe the quartz crystal and the liquid, L/ and Rf were added to describe the viscoelastic film overlayer. For a small... [Pg.476]

This section examines the dynamic behavior and the electrical response of a TSM resonator coated with a viscoelastic film. The elastic properties of viscoelastic materials must be described by a complex modulus. For example, the shear modulus is represented by G = G + yG", where G is the storage modulus and G" the loss modulus. Polymers are viscoelastic materials that are important for sensor applications. As described in Chapter S, polymer films are commmily aj lied as sorbent layers in gas- and liquid-sensing applications. Thus, it is important to understand how polymer-coated TSM resonators respond. [Pg.66]

Admittance-vs-frequency measurements made at several temperatures on a polyisobutylene-coated TSM resonator were fit to the equivalent-circuit model of Sections 3.1.3 and 3.1.9 to determine values of G and G for the film [66]. These extracted values are shown in Figure 4.4, along with 5-MHz values obtained from the literature for polyisobutylene having an average molecular weight of 1.56 X 10 [44]. We note excellent agreement between the extracted and literature values of G from —20°C to 60°C, and in G" from —20°C to 10°C. Above 10°C, the extracted G" values are approximately 30% higher than the literature values. These results illustrate how AW devices can be used to quantitatively evaluate the viscoelastic properties of polymer films. Similar models for other AW devices, such as the model for SAW devices coated with viscoelastic layers (Section 3.2.7 and [61]), can enable these other devices also to be used to determine modulus values. However, the pure shear motion of the TSM does simplify the model, and the evaluation of the modulus values as compared with the more complex displacements of other AW devices such as the SAW device (a comparison of the models of Section 3.1.9 for the TSM and Section 3.2.7 for the SAW demonstrates this point). [Pg.163]

FIGURE 4.7 SAW velocity and attenuation changes vs. shear wave phase shift (i) for several values of film loss parameter. The dashed line corresponds to prediction using Tiersten formula. (Reprinted with permission from Martin S. J., Frye G. C., and Senturia S. D., Dynamics and response of polymer-coated surface acoustic wave devices Effect of viscoelastic properties and film resonance, Anal. Chem., 66, 2201-2219, 1994. Copyright (1994) American Chemical Society.)... [Pg.110]

Martin S. J., Frye G. C., and Senturia S. D., Dynamics and response of polymer-coated surface acoustic wave devices Effect of viscoelastic properties and film resonance. Anal. Chem., 66, 2201-2219, 1994. [Pg.132]

Amau A, Jimenez Y, Fernandez R, Torres R, Otero M, Calvo EJ (2006) Viscoelastic characterization of electrochemically prepared conducting polymer films by impedance analysis at quartz crystal study of the surface roughness effect on the effective values of the viscoelastic properties of the coating. J Electrochem Soc 153 C455-C466... [Pg.566]

The quartz crystal microbalance (QCM) consists of a quartz crystal that is electrically driven into oscillation. The resonance frequency of the crystal is monitored. This frequency is highly dependent on any mass added to the crystal surface. Hence the mass dependence of the QCM resonance frequency can be, in air, used to weigh minute amounts of material with a sensitivity of the order of 1 ng/cm. QCM can also be coupled with electrochemistry here, the quartz crystal surface is coated with an appropriate electrode material, for example, thin film gold. This electrochemical QCM (EQCM) configuration can be used to monitor electrochemically triggered surface processes associated with the deposition (or loss) of material at the working electrode surface. However, in liquid medium the frequency shift of the QCM crystal is not solely sensitive to added mass but is also influenced by changes in the local property of the medium associated with the surface electrochemical process of interest. For example, density or viscosity variation of the medium in the electrode vicinity, in addition to variation in the viscoelastic properties of the deposited layer, can cause shifts in the resonant frequency of QCM. [Pg.624]

It has been also shown that when a thin polymer film is directly coated onto a substrate with a low modulus ( < 10 MPa), if the contact radius to layer thickness ratio is large (afh> 20), the surface layer will make a negligible contribution to the stiffness of the system and the layered solid system acts as a homogeneous half-space of substrate material while the surface and interfacial properties are governed by those of the layer [32,33]. The extension of the JKR theory to such layered bodies has two important implications. Firstly, hard and opaque materials can be coated on soft and clear substrates which deform more readily by small surface forces. Secondly, viscoelastic materials can be coated on soft elastic substrates, thereby reducing their time-dependent effects. [Pg.88]

The relative importance of the mass-loading and viscoelastic contributions to the observed acoustic sensor response is an issue that has yet to be resolved. Capitalizing on these effects to improve chemical selectivity and detection sensitivity requires further characterization of sensor response, in terms of both velocity and attenuation changes, in addition to more accurate models describing how coating-analyte interactions affect relevant film properties. [Pg.232]


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