Absolute coil dimension

If the absolute diameter or radius of a polymer coil is known, a direct calculation of a critical concentration is possible without viscosimetric data. Common methods for the determination of absolute coil dimensions are the different light scattering methods. The critical concentration calculated from these dimensions is therefore often denoted as the critical concentration of light scattering, c ls> since the radius R (see Chap. 8) can be determined directly from static light scattering. 

Nevertheless, even the critical concentration obtained from absolute polymer coil dimensions, is only a relative value since the radii measured with scattering experiments are not equal to the hydrodynamic radii of the same polymer coils in solution. A detailed discussion on how to calculate a hydrodynamic radius is given in The critical concentration of a real coil in Chap. 8. 

Because of the relatively short displacement time or length scales typically probed by NMR diffusometry, it is particularly well suited to detect anomalies in the segment displacement behavior expected on a time scale shorter than the terminal relaxation time, that is for root mean squared displacements shorter than the random-coil dimension. All models discussed above unanimously predict such anomalies (see Tables 1-3). Therefore, considering exponents of anomalous mean squared displacement laws alone does not provide decisive answers. In order to obtain a consistent and objective picture, it is rather crucial to make sure that (i) the absolute values of the mean squared segment displacement or the time-dependent diffusion coefficient are compatible with the theory, (ii) the dependence on other experimental parameters such as the molecular weight are correctly rendered, and (iii) the values of the limiting time constants are not at variance with those derived from other techniques. 

Light scattering techniques provide absolute values for molar mass and so require no other polymer standard for calibration purposes. The molecular dimension causing scattering is related to the volume of the equivalent sphere occupied by a single polymer chain when present in solution as a random coil. 

The following examples will emphasize the importance of placing intensity data on an absolute scale, typically in the form of a differential scattering cross section dS/df2(2), in units of cm As explained in Section 7.3.1, the equivalent quantity for LS is the Rayleigh ratio [15, 66, 69], and, while the use of absolute units is not essential for the measurement of the spatial dimensions (e.g. determining the Rg of a polymer coil), it forms a valuable diagnostic tool for the detection of artifacts, to which scattering techniques are sometimes vulnerable. 

Thus, the present work results have confirmed the stated above Academician Kargin postulate. The impact toughness A of blends PET/PBT is controlled by macromolecular coil interactions, which on molecular level are reflected by structure fractal dimension. It has been shown that interaction parameter e controls the transition to both absolutely brittle (A =0,e = -0.33) and to tough (A - oo e = 0.20) fracture. 

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