6533b821fe1ef96bd127acd0

RESEARCH PRODUCT

Eine Neue Rechnung zur Röntgenkleinwinkelstreuung an Fadenmolekulen. Die Ermittlung der Segmentgestalt

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The scattering function of chain molecules in the x-ray small-angle range depends on the shape of the segments. For instance, one obtains quite different scattering curves from solutions of isotactic and syndiotactic poly(methyl methacrylate) (PMMA) in the same solvent. From several models of statistically coiled polymer chains, the scattering functions were calculated with the aid of the Monte Carlo method. Again, a considerable difference between the functions obtained is observed. If the curvature of a thread varies statistically from one point to another, the mean curvature can be determined from the scattering function. A suitable measure for the mean curvature is the persistence length; i.e., the chain length of which the end points form an angle whose average cosine is equal to 1/e. If the curvature is nonrandom, one can detect this from the scattering function. From the position and amplitude of the waves that appear one can determine the degree of preferred curvature. The mean curvature of a thread need not be connected strictly with the radius of gyration or with the statistical chain element of the coil. In real molecules the x-ray optical center line is essential for the scattering behavior. On syndiotactic PMMA in solution a preferred curvature has been found. It can be interpreted by assuming the presence of helix fragments in the coils.