Stretch alignment

The stationary red fluorescence (versus blue fluorescence see below) and fluorescence excitation spectra of Pr [76] are characterized by relatively narrow long-wavelength emission and excitation (=absorption) bands, a small blue/red intensity ratio of the excitation maxima (/380//666 = 0.5), and a small Stokes shift between the absorption and emission 0-0 bands of 180kJ mol"1 (Figure 7 top Hendricks, Butler and Siegelman [85] were the first in 1962 to report on the fluorescence of 64-kDa Pr). All three criteria are appropriate to differentiate between the helicaloid and the diverse stretched conformations of linear bilatrienes [44,47]. They confirm the proposed stretched alignment of the bilatriene chromophore in Pr (see Section I.B). The... 

This cast may be used for further processing of the conducting polymer. For instance, by stretching aligned bends of polyacetylene/porybutadiene the conductivity increase 10 fold, due to the higher state of order produced by this deformation. 

Conductivity and X-ray diffraction studies on highly conducting stretch-aligned polyacetylene samples can be fitted well by this expression, and it has been found that [175-178] ... 

Poly(arylenevinylene)s based on naphthalene (JJ7) and thiophene (118, 119) have been reported. When naphthalene was substituted for benzene in the polymer structure, the resulting conductivity for the AsFs-oxidized polymer was 10 S/cm. Orientation of the polymer via stretch alignment has not been reported. The thiophene derivative, however, was stretch aligned (118) and doped with iodine and FeCl3. Conductivities of2700 were obtained with iodine-doped samples having elongation ratios of 6. The anisotropy of the conductivity was 35. 

Disubstituted PPVs have also been explored by Martens et al. [284, 285], using x-ray and electron methods and iinstrctchcd films as well as oriented filnis. Both are obtained from spin-coated precursor films. Stretch alignment is carried out in vacuum during the initial phase of the conversion procedure above 80°C, after which conversion completes above 200°C. In the mote recent of these papers, the results for ethoxy substituents are also presented stretch-orienting has not been possible for this polymer [285],... 

From an analysis of the intensity distribution of the amorphous halo it is concluded that in maximally stretched EB-11 fibres (///o= 4.5), half of the amorphous phase is oriented at random while the other half responds to stretch-alignment and is preferentially oriented in the same direction as the oriented crystalline fraction, although with a very broad di,stribution. The increase in crystallinity upon stretching is due to nucleation of new crystallites rather than growth of preexisting ones. Similar results were arrived at in a more detailed study by means of a four-circle diffiactometer... 

Owing to the orientation present in stretch-aligned films, it has been possible to probe and analyse the dynamics of the phenyl rings, by means of inelastic neutron scattering (Sauvajol et al. [314]). 

In the United States, string cheese is usually mozzarella (sometimes with some Cheddar thrown in). The production process takes melted cheese and stretches and folds it in a single direction. This stretching aligns the proteins in the cheese, making it possible to peel off long strings of it. 

Fig. 10. Sketch of the transformations of the oriented chains during deformation, in-between are additional amorphous chains a) lamellae with some tie-molecules, b) elastic shear-deformation of lamellae imder small load and reorientation with respect to the load, c) fracture of lamellae into smaller blocks due to local stress concentration caused by tie molecules, d) stretched aligned, but not re-crystallised chains between the blocks during stretching at higher temperatures, e) some of the fibrillar arranged molecules crystallise, final stage in the case of hot stretched iPP, f) further dissolution of the blocks creating more extended chains at room temperature, g) finally, there are several strands of extended chains, not crystallised, with some amorphous regions in between, final stage in the case of cold stretched rPP.

More involved models to relate the thickness to the spinning conditions have been developed [36]. Generally, the polymer molecules within spin-coated films are relatively disordered and order has to be induced after deposition via stretch aligning or more commonly via electrical poling at elevated temperature [37]. 

In the above equation, To= lS/(kgN Eg)Lc), where Lc is the localization length. From the fitting parameter To> the localization length for the different stretched AMPSA-doped polyaniline fibers is summarized in Table 2.13. It has been reported that the localization length for an unstretched AMPSA-doped polyaniline fiber is 179 A [65]. In contrast, the localization length for the stretched fibers is between 56 and 70 A. This result indicates that the stretch alignment of the polymer chains at elevated temperatures does indeed decrease the localization length as mentioned above. 

Load Fracture. Thermoplastics, thermosets, and elastomers deform in different ways. In the case of ductile thermoplastics, as the load increases, the tangled, thread-like macromolecules become stretched, aligned, and in some cases will glide apart. The stretched areas will recoil like a spring, and this will be most pronounced at the highly stressed fracture site, which additionally warms up on... 

Alternatively, a two-stage mechanical orientation can be applied to obtain polar FLCEs (see Fig. 17 and [ 184]). A first stretching aligns the director. However,... 

In order to determine the quality and porosity of films produced by the Shirakawa method, physical measurements are intrinsically important. Specimens for stress-strain measurement and for the preparation of highly stretch-aligned films can be prepared at -78°C using a Ti(0-n-Bu)4-AlEt3(Ti = 0.3 mole/l,Al/Ti = 3.3) system with a toluene-anisole (1 3) mixture as a solvent. The films of about 100 fim thickness have a cis content of 93-5% as determined by ATRIR, a method explained in detail in Section 1.3.1. Trans and various cisitrans films are obtained by thermal isomerization of the cis films [29]. 

Figure 1.4 shows the pore size distribution of as-polymerized and various stretch-aligned films. The bulk density (0.40 g cm of the pristine film, calculated from the integrated pore volume and the fibril density (1.154 g cm [30], agrees with the value... 

Figure 1.4. Pore size distribution of as-prepared and various stretch-aligned films. Solid line, as-prepared film. Values on the...

Aubrey(37) attributed the A-B transition in peeling force to a transition from viscous to rubbery behavior in the polymer. Our mechanism is somewhat different, but there is no doubt that a variation in the relative importance of the storage and loss modulus terms in the adhesive contributes to the change in overall behavior. Pipkin(32) remarks that elastic effects are more prominent in stretching motions than in shear motions, because stretching aligns the chains better than shearing does. ... 

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