Poly , polymer acoustics

The acoustic properties of polymers are just as for many properties strongly dependent on temperature around the glass-rubber transition the sound speed decreases rapidly from a relatively high value at T < Tg to a relatively low value at T > Tg. During this transition the absorption shows a maximum value. An example is given in Fig. 14.4, where data for a poly(metacarborane siloxane) are displayed. The measurements were made in the longitudinal mode as a function of temperature at a frequency... 

In this report we demonstrate the utility of the procedure for multiplexed data. The usefulness of the procedure for resonant data was the topic of previous publications (ii8). Using data for typical samples of amorphous polymers, poly(methyl methacrylate) (PMMA) and polycarbonate (PC), the procedure is shown to be well suited to the transition region. A Poly(vinyl chloride) (PVC) acoustical damping material is used to demonstrate the ability to change the data reduction equation (the WLF equation) parameters and their subsequent effects on the fit of the superposed data. 

Piezoelectricity links the fields of electricity and acoustics. Piezoelectric materials are key components in acoustic transducers such as microphones, loudspeakers, transmitters, burglar alarms and submarine detectors. The Curie brothers [7] in 1880 first observed the phenomenon in quartz crystals. Langevin [8] in 1916 first reported the application of piezoelectrics to acoustics. He used piezoelectric quartz crystals in an ultrasonic sending and detection system - a forerunner to present day sonar systems. Subsequently, other materials with piezoelectric properties were discovered. These included the crystal Rochelle salt [9], the ceramics lead barium titanate/zirconate (pzt) and barium titanate [10] and the polymer poly(vinylidene fluoride) [11]. Other polymers such as nylon 11 [12], poly(vinyl chloride) [13] and poly (vinyl fluoride) [14] exhibit piezoelectric behavior, but to a much smaller extent. Strain constants characterize the piezoelectric response. These relate a vector quantity, the electrical field, to a tensor quantity, the mechanical stress (or strain). In this convention, the film orientation direction is denoted by 1, the width by 2 and the thickness by 3. Thus, the piezoelectric strain constant dl3 refers to a polymer film held in the orientation direction with the electrical field applied parallel to the thickness or 3 direction. The requirements for observing piezoelectricity in materials are a non-symmetric unit cell and a net dipole movement in the structure. There are 32-point groups, but only 30 of these have non-symmetric unit cells and are therefore capable of exhibiting piezoelectricity. Further, only 10 out of these twenty point groups exhibit both piezoelectricity and pyroelectricity. The piezoelectric strain constant, d, is related to the piezoelectric stress coefficient, g, by... 

TPX has a number of unique properties and features, but it has remained a specialty engineering polymer. It has the lowest density of any plastic material 0.835 g/cw . Although crystalline, it is totally transparent due to the amorphous and crystalline phases having the same density. It has very low surface energy and outstanding optical and acoustic properties. A current growth area is in films. Mitsui has a separate tradename Opulent for films of poly 4-methyl pent-l-ene. 

When a polymer exhibits a maximum in the imaginary part of the dielectric permittivity (the loss permittivity, e") at frequencies less than 200 Hz, it becomes possible to make comparisons with the frequency dependence of shear moduli and most specifically with the loss shear modulus, G". This has been done for polypropylene diol, also called poly(oxypropy-lene), where there is reported a near perfect superposition of the frequency dependence of the normalized loss shear modulus with that of the normalized loss permittivity as reproduced in Figure 3. The acoustic absorption frequency range of interest here is 100 Hz to 10 kHz, yet present macroscopic loss shear modulus data can be determined at most up to a few hundred Hz. Nonetheless, for X -(GVGIP)32o there is a maximum in loss permittivity, e", near 3 kHz that develops on raising the temperature through the temperature range of the inverse temperature transition. With the width of the loss permittivity curve a distinct set of curves as a function of temperature become... 

A flow chart demonstrating the protocol is shown in Fig. 6. The procedure has been demonstrated for poly(3-methylthiophene) films, by analysis of frequency response as a function of time during film electropolymerization short (long) time responses represent the acoustically thin (thick) film scenario [24]. Film mass (whether or not directly accessible from A/ data) defines the product hypy, so (as shown in Fig. 6 [24]) a plot of hy versus py is a hyperbola. As film mass (polymer coverage) increases, a series of hyperbolae are generated. The acoustically thin film data (A/ and Q) define the unique solution (of the infinity of solutions on the hyperbola) for p as indicated in Fig. 6 [24] this value is projected across all the hyperbolae. 

In terms of ion and solvent transfers, polythiophenes provide some of the more complex examples of acoustic wave behavior and thus more sophisticated examples of data interpretation. In the simpler, gravimetric regime early measurements of ion, solvent, and cation ( salt ) transfer at acoustically thin poly(2,2 -bithiophene) [33] films have been shown to be typical for example, the presence of salt in reduced poly(l,4-ethylenedioxythio-phene) films is implied by a substantial contribution from cation expulsion during polymer oxidation [159]. 

The absolute value of film thickness at which one sees the shift from acoustically thin to thick behavior will depend significantly on the polymer itself, the solvent, and other physicochemical parameters, notably temperature, applied potential, and timescale. An example of the importance of the latter two control parameters is provided by a study of poly(3-hexylthiophene) films exposed to propylene carbonate [161]. Storage and loss moduli, derived from the admittance spectra, for a film held at different applied potentials (effectively, controlling charge) are shown in Fig. 26 [161]. Immediate observations are that the film is... 

To understand the transition to supersonic velocities we also make use of a description of the lattice in terms of both optical and acoustic order parameters. Here, we study a strictly ID model that is a direct map of the fPA structure. However, as far as the properties of the drifting polaron are concerned, the model is more general and quantitatively describes these properties in other polymeric systems, e.g., poly(paraphenylene vinylene) or polythiophene. In the ID model, the displacement of the lattice sites entering Equation 2.14 and Equation 2.16 is described by a single variable u . In the description of the geometry of conjugated polymers, fPA in particular, it is common to study a smoothed atomic displacement order parameter. This optical order parameter is given by... 

V.L. Finkenstadt, C.K. Liu, PH. Cooke, L.S. Liu, and J.L. Willett, Mechanical property characterization of plasticized sugar beet pulp and poly (lactic acid) green composites using acoustic emission and confocal microscopy. /. Polym. Environm. 16(1), 19-26 (2008). 

The longitudinal acoustic mode (LAM), measured by Raman spectroscopy, continues to be a powerful means of measuring the average stem length in crystalline polymers. Its application has been extended to polyethers, poly-thioether," and also polytetrafluorethylene and its oligomers. ... 

---