Scattering polymer lamellar systems

Additional neutron scattering studies on different polymer systems could prove very important. Strobl [31,32,47,103] provides evidence that, for some polymers, lamellar crystallization is preceded by pre-ordering of the melt followed by formation of planar arrays of blocks. Investigating crystallization from the melt, Kaji and coworkers [25] find pre-ordering phenomena relating to orientational fluctuations of stiff polymer segments which, under appropriate conditions, determine phase separation prior to crystallization. 

Equation 19.11 means that the observed intensity must be multiplied by a factor q to obtain a better estimation of the periodicity in lamellar systems of semicrystalline polymers. The factor q is related to the change from the scatterers oriented at random to dispersers perfectly aligned (Fig. 19.8). This correction is implied, for instance, in the use of models of one-dimensional stacking [19]. As li iq) has been obtained from a one-dimensional model, it can be written as / (g) [19]. 

The problem of small-angle X-ray scattering of lamellar systems will be treated in the following chapters mainfy by means of biomembiane assets. Nevertheless, the concepts should generalfy ap fy to other lamellar systems, such as polymer systems. 

Small-angle x-ray scattering (SAXS) probes structural features at the mesoscopic length-scale (Section 1.9.2). It can be used to measure the radius of gyration of polymers in solution, via Eq. (1.27), which can be up to hundreds of nanometres. Semicrystalline polymers form lamellae, which are layered systems with a layer period of the order of 10 nm. Such lamellar stacks diffract x-rays at small angles, indeed they are a one-dimensional lattice, and Bragg s law can be used to determine the layer period. Furthermore, the relative intensities of the peaks depend on the distribution of amorphous and crystalline material, and this can be analysed to provide a model of the electron density profile normal to the layers. 

Ruland W (1977) The evaluation of the small-aiigle scattering of lamellar two-phase systems by means of interface distribution functions. Colloid Polym Sci 255 417- 27. Ruland W (1978) The evaluation of the small-angle scattering of anisotropic lamellar two-phase systems by means of interface distribution functions. Colloid Polym Sci 256 932-936. 

In a good approximation, the morphology of a semicrystalline polymer can be described as a lamellar two-phase system consisting of crystalline and amorphous phases with different electron densities and with sharp boundaries between them. This structure gives rise to a peak in the scattering intensity... 

Ruland W. The evalnation of the smaU-angle scattering of lamellar two-phase systems by means of interface distribution functions. Colloid Polym Sci 1977 255 417. 

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