Relaxation range

Crimp. The tow is usually relaxed at this point. Relaxation is essential because it gready reduces the tendency for fibrillation and increases the dimensional stabiUty of the fiber. Relaxation also increases fiber elongation and improves dye diffusion rates. This relaxation can be done in-line on Superba equipment or in batches in an autoclave. Generally saturated steam is used because the moisture reduces the process temperatures required. Fiber shrinkage during relaxation ranges from 10 to 40% depending on the temperature used, the polymer composition used for the fiber, and the amount of prior orientation and relaxation. The amount of relaxation is also tailored to the intended apphcation of the fiber product. 

Relaxations of a-PVDF have been investigated by various methods including dielectric, dynamic mechanical, nmr, dilatometric, and piezoelectric and reviewed (3). Significant relaxation ranges are seen in the loss-modulus curve of the dynamic mechanical spectmm for a-PVDF at about 100°C (a ), 50°C (a ), —38° C (P), and —70° C (y). PVDF relaxation temperatures are rather complex because the behavior of PVDF varies with thermal or mechanical history and with the testing methodology (131). 

This model permits xR to be determined using information on the fluorescence decay in a very simple way. If unrelaxed fluorophores are excited, the decay is exponential beyond the relaxation range and, in this range, consists of two components t, and r2. These components will be simple functions of xR and t>. If we assume that emission on the short-wavelength side occurs only from the unrelaxed state and that the simultaneous loss of emitting quanta occurs due to relaxation, then the longer component, t, equals xF, and the shorter one, t2, equals 1(1/t + jxF). Unfortunately, this approach is difficult to apply when the decay is nonexponential, which is almost always the case with proteins (see Section 2.3.1.). 

With respect to water we shall conditionally extend the SWR from 10 to 300 cm this frequency region falls between the Debye relaxation range and the librational band. 

Application to Polar Biopolymers.—On the basis of the above general relationships, the classical dielectric polarization of any biomolecular system can be evaluated. In the particularly interesting case of a dilute solution of polar biopolymers with a uniform rotational diffusion coeffident a comparatively simple relation can be derived because of the fact that orientational polarization of the solute occurs far below the relaxation range of the solvent. The complex permittivity (without the contribution of background conductivity) turns out to be... 

In water/ice the LIB fraction describes the librational band, centered at 700—800 cm-1 and located near the border with the IR range. In the case of water the LIB fraction explains also the nonresonance low-frequency relaxation range. 

For low PI content blends, however, the NM-relaxation is much slower relative to the a-relaxation than the behavior observed for the homopolymer." This impression is fortified in their Abstract by the statement Finally, the terminal dynamics of PI component shows a stronger T-dependence than its segmental dynamics, and the effect is more pronounced the higher the PtBS content. As a result, the separation between the maxima of both relaxations ranges from 3 decades in pure PI and PI 50% content blends to 5 decades for 20% PI blends. ... 

Fig. 7.23 Qualitative frequency spectra of two components of dielectric permittivity e (a) and e" (b), and corresponding anisotropy of imaginary component of dielectric permittivity e"n — e" (c) and real a.c. conductivity af — (d) in the Debye relaxation range. ), v is inversion...

A TSC study of isotactic and atactic polypropylene, high density polyethylene, ethylene-propylene block copol)uners, ethylene-propylene rubbers and blends thereof [8] in the y and p relaxation range helped to identify the molecular origin of the relaxation peaks. Two 3 processes were observed in the copolymer samples, one (p,) around —5°C, the other one (Pj) at about -50°C. The former is attributed to the PP chains, while the latter is ascribed to microscopically random ethylene-propylene rubber segments. 

Upper Relaxation Range, Figures 4.55, 4.56, and 4.9 (see Sect. 4.1) show the limits and the influence of this temperature range on the dimensional stability. Initially well-annealed samples were quenched from different temperatures. Figure 4.55 shows that until quenching temperatures of 130 °C no change of the CTE (0/50) happens with increasing temperature the CTE (0/50) increases linearly until at 320 °C a saturation value is achieved. A total rise of the CTE (0/50) from —50 x 10 K to +20 x 10 is observed. At temperatures above 320 °C no further variation of the CTE occurs. 

Lower Relaxation Range. Thermal cycles which touch or include the lower relaxation range lead to a hysteresis shape of the Al/l (T) curve (see Fig. 4.57). The vertical opening of this hysteresis is of the order of Al/l = 10 . ... 

Like the effects of the upper relaxation range these effects are also strictly reversible. The effects of the upper relaxation range, however, are stable in the room temperature range, while those in the lower range relax in a relatively short time even at rather low temperatures (see Fig. 4.58). 

The experimental approaches and interpretation strategies for investigators working in the traditional impedance and dielectric analysis areas have drifted apart significantly over the years, often leading to misconceptions about assignments of frequency relaxation ranges and broader data interpretation. A combination of these two techniques in a universal broadband EIS... 

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