Polymer studies sapphire

Fig. 5.5. The electrical response of piezoelectric polymers under shock loading is studied experimentally by placing the thin PVDF element on the impact surface of a standard target, either the polymer, Kel F, z-cut quartz, or z-cut sapphire. The im-pactor is typically of the same material. The current pulse is recorded on transient digitizers with frequency responses from 250 to 1000 MHz.

The above studies have benefited from a fertile exchange with experimental groups using the Surface Force Apparatus (SFA). The SFA allows the mechanical properties of fluid Aims to be studied as a function of thickness over a range from hundreds of nanometers down to contact. The fluid is confined between two atomically flat surfaces. The most commonly used surfaces are mica, but silica, polymers, and mica coated with amorphous carbon, sapphire, or aluminum oxide have also been used. The surfaces are pressed together with a constant normal load, and the separation between them is measured using optical interferometry. The fluid can then be sheared by translating one surface... 

Miscellaneous high-pressure NMR studies of inorganic systems High-pressure NMR studies using sapphire tubes Various high-pressure studies of polymers and complex liquids High-pressure studies of liquids confined to porous media High-pressure NMR studies of solids... 

The primary photoexcitation dynamics in PDPA solutions and films in the fs to ps time domain using transient PM spectroscopy were extensively studied [182]. The PDPA polymer used was a disubstituted biphenyl derivative of frans-polyacetylene, where one of the hydrogen-substituted phenyl groups was attached to a butyl group, which is referred to as PDPA-mBu (Figure 22.25 inset) [181]. The polymer films were cast on sapphire substrates from a toluene solution the same solution was used for measuring the photoexcitation dynamics in a PDPA-mBu solution. 

EWIF has been used to study the adsorption of poly(methylmethacrylate) (PMMA) onto sapphire. Polymer molecular weights are 120,000 and 600,000 and some chains have been labelled with anthracene chromophores to allow fluorescence excitation by the optical evanescent wave. The surface excess is measured to be 1.47 mg/m. Moreover, the first moment of the monomer distribution, , can be evaluated. The observed value = 73A, is comparable to the chain radius of gyration, in good agreement with the theoretical models. The determination of higher moments of the distribution is not accessible with the present system. It would require the use of chains with molecular weights in the range 10 -10. ... 

Following the discussion of photoexcitation properties and dynamics in a-6T, the model oligomer for PT polymers, it is relatively easy now to extend the previous analysis to photoexcitations in various PT polymers. We will discuss two types of PT films an electrochemically polymerized PT (e-PT) film, in the photophysics of which defects play a major role, and a soluble PT derivative, the chemically prepared poly(3-butylthiophene) (P3BT). These films were polymerized on sapphire and KBr substrates, respectively. We also studied photoexcitations in P30T films [78], and the results were not different from those of P3BT films. 

The experimental method to assess the phase behavior is to measure the ratio of excimer to monomer intensity, la/lm- Samples of the polymer blend are cast on sapphire disks at thicknesses of the order to 10-25 pm, and the fluorescence spectra are obtained. In a study of the excimer fluorescence of poly(2-vinyl naphthalene) (P2VN) in polystyrene, the monomer emission peak at 337 nm was compared with the excimer emission peak at 398 nm [334]. The ratio of the peaks versus polystyrene molecular weight is illustrated in Fig. 5.32 (a and b). Phase separation (at 0.3 wt% P2VN addition) was observed at PS Mn of 17,500. It was noted that the results show the onset of phase separation before any visual phase separation was observed. 

To assess the scratch behavior of polymers, scratch tests are performed. A compendium of the use of variovis instruments and methods applied is given in Reference (20). Although different setups have been used for scratch studies, the basic principle relies on the use of a stylus to scratch a sur tce (2,3,21-43). The stylus can be made of materials ranging irom diamond and sapphire, to tool steel, and silicon nitrite for the case of AFM tips. It also comes with a variety of geometries including conical tips with different included angles, spherical tips of different radii, and Berkovich tip. In addition, the observation length scale and controlled experimental parameters are instrument specific. 

The surface tension of polystyrene in carbon dioxide was measured at temperatures from 170 to 210TC, within a wide range of pressures, from 500 to 2500 psi. To achieve these experimental conditions, a high-temperature and high-pressure sample cell was constructed. Briefly, the optical viewing cell consisted of a cylinder of stainless steel, which was heated by an electrical heater. The inside of the cylinder was hollow, with a diameter of 30 mm and length of 25 mm. Two optical-quality sapphire windows (Meller Optics, Inc.) are used to permit the illumination and observation of the pendant drop formed by a sample polymer melt. The setup was tested for its accuracy and reproducibility with a range of polymer-gas combinations, and the details of this study were described in a recent pubhcation [9]. 

---