Stretched sample method

Zimmerman, T. A., Monroe, E. B., Sweedler, J. V. (2008) Adapting the stretched sample method from tissue profiling to imaging. Pro-teomics, 8, 3809-3815. 

X-ray diffraction techniques can be used to establish the structure of crystalline polymers. Measurements are typically made on crystalline lamellar platelets grown from dilute solution, fibres or stretched films. Such methods have been applied to several different inorganic polymers. For example, based on measurements on stretched samples of silicone rubber, poly(dimethylsiloxane) (Me2SiO) has been shown to possess a helical conformation (Figure 8.4). ... 

Figure 7.5 Output elapsed time versus input elapsed time in the sampling method for Time-stretching (P > 1). Dashed line ideal curve, solisd line approximate curve.

H and 2H NMR have been used in styrene-butadiene rubber (SBR) with and without carbon-black fillers to estimate the values of some network parameters, namely the average network chain length N. The values obtained from both approaches were checked to make sure that they were consistent with each other and with the results of other methods [71, 72, 73]. To this purpose, a series of samples with various filler contents and/or crosslink densities were swollen with deuterated benzene. The slopes P=A/ X2-X 1) obtained on deuterated benzene in uniaxially stretched samples were measured. The slopes increase significantly with the filler content, which suggests that filler particles act as effective junction points [72, 73]. 

Early measurements of the IR-dichroism in stretched samples of LCEs have been described [16]. The dependence of the IR di-chroism of the CN-stretching mode was used to obtain the absorption coefficients and to extract the order parameter as a function of temperature. However, while these measurements yield reliable results inside the nematic phase, the sensitivity of this method turns out to be not high enough to analyze quantitatively the influence of the applied stress on the order parameter and on... 

The conductivity of PA films produced by the INS method was measured as a function of the Al/Ti ratio. No general trend was found, but the highest conductivity was achieved when the Al/Ti ratio was 4. On an iodine-doped stretched sample, the conductivity ranged between 2.2 x Kf and 4.3 x 10 S/cm. These values are twice that found for Agaki-type PA films synthesized by the solvent evacuation method. By comparison, the PA obtained using toluene as the solvent has a maximum conductivity when the Al/Ti ratio is 2 [31, 33, 35]. Researchers proposed that the properties of the INS PA are optimized at an Al/Ti ratio of 4 because the excess AlEt3 served as a solvent to stabilize the titanium catafyst. (The dielectric constant of Al t3 is 2.005, which is similar to that of toluene at 2.237.)... 

As with infrared spectra obtained by conventional sampling methods, the IR absorption bands correspond to characteristic vibrational frequencies of particular functional groups. Vapor-phase spectra do not show the effects of strong hydrogen bonding, such as the broadening of the -OH stretching peak around 3600 cm". ... 

Fig. 4a gives the temperature dependence of the electrical dc conductivity parallel c ) and perpendicular (or ) to the stretching direction of a highly stretched sample of Naarmann polyacetylene doped to maximum with iodine. The electrical conductivity of these samples varies by a factor of about 1.4-2 if measured on different pieces of the same film. Using different films prepared by the same method, the variation is much stronger for most of the samples examined, the room temperature value of o was between 20 000 S/cm and 80 000 S/cm. Some samples, however, had even higher or lower values including a sample with a > 100 000 S/cm and another one with [Pg.59]

Finally, as in macro-Raman experiments, orientation-insensitive spectra can also be calculated for spectromicroscopy. A method has been developed recently for uniaxially oriented systems and successfully tested on high-density PE rods stretched to a draw ratio of 13 and on Bombyx mori cocoon silk fibers [65]. This method has been theoretically expanded to biaxial samples using the K2 Raman invariant and has proved to be useful to determine the molecular conformation in various polymer thin films [58]. 

The method (27) can best be explained with reference to Figure 2. After stretching to 10, the force f is measured as a function of time. The strain is kept constant throughout the entire experiment. At a certain time, the sample is quenched to a temperature well below the glass-transition temperature, Tg, and cross-linked. Then the temperature is raised to the relaxation temperature, and the equilibrium force is determined. A direct comparison of the equilibrium force to the non-equilibrium stress-relaxation force can then be made. The experimental set-up is shown in Figure 4. 

One method for determining the state of cure of a mbber compound. A sample of the rubber is stretched, cooled to a temperature of around -70 °C while stretched and then released. As the temperature rises the mbber retracts and the T-50 value is the temperature at which it has lost 50% of its original elongation. The T-50 test is now obsolescent. 

Physicomechanical properties of the samples using both methods (strength of stretching and dividing) change about 3-4 % which is within the limits of permissible effect. 

Vibrational spectroscopy can help us escape from this predicament due to the exquisite sensitivity of vibrational frequencies, particularly of the OH stretch, to local molecular environments. Thus, very roughly, one can think of the infrared or Raman spectrum of liquid water as reflecting the distribution of vibrational frequencies sampled by the ensemble of molecules, which reflects the distribution of local molecular environments. This picture is oversimplified, in part as a result of the phenomenon of motional narrowing The vibrational frequencies fluctuate in time (as local molecular environments rearrange), which causes the line shape to be narrower than the distribution of frequencies [3]. Thus in principle, in addition to information about liquid structure, one can obtain information about molecular dynamics from vibrational line shapes. In practice, however, it is often hard to extract this information. Recent and important advances in ultrafast vibrational spectroscopy provide much more useful methods for probing dynamic frequency fluctuations, a process often referred to as spectral diffusion. Ultrafast vibrational spectroscopy of water has also been used to probe molecular rotation and vibrational energy relaxation. The latter process, while fundamental and important, will not be discussed in this chapter, but instead will be covered in a separate review [4],... 

X-Y stretching vibrations of octahedral molecules are thus characterized by four quantities, Ay, Ayy, 7i Y yy- The results of some sample calculations are shown in Table 6.3. Isotopic substitutions can also be considered, using the method of Section 6.9. 

ETEROAROMATics FURAN AND THIOPHENE. The chemical transformation of thiophene at high pressure has not been studied in detail. However, an infrared [441,445] study has placed the onset of the reaction at 16 GPa when the sample becomes yellow-orange and the C—H stretching modes involving sp carbon atoms are observed. This reaction threshold is lower than in benzene, as expected for the lower stability of thiophene. The infrared spectrum of the recovered sample differs from that of polythiophene, and the spectral characteristics indicate that it is probably amorphous. Also, the thiophene reaction is extremely sensitive to photochemical effects as reported by Shimizu and Matsunami [446]. Thiophene was observed to transform into a dark red material above 8 GPa when irradiated with 50 mW of the 514.5-nm Ar+ laser line. The reaction was not observed without irradiation. This material was hypothesized to be polythiophene because the same coloration is reported for polymeric films prepared by electrochemical methods, but no further characterization was carried out. 

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