TIT# Oriented quiescent crystallization of polyethylene studied by USAXS.
     Part 3: The evolution of crystallite stacking
AUT# Stribeck, Norbert; Almendarez Camarillo, Armando; Bayer, Rüdiger;
SOU# Macromol. Chem. Phys. (2004), submitted
LOC# xv085
CLA#
COM#
APP#
MAT#
ABS# In a series of papers the crystallization of a commercial polyethylene
     (PE) material is studied by in situ ultra small-angle X-ray scattering
     (USAXS) and it is found that placement of crystallites is predominantly a
     random car parking process delt with in the field of random sequential
     adsorption. Here we investigate the secondary effect, the generation of
     order from the chaos and characterize how lamellae agglomerate to form
     clusters. Owing to the chaotic principle, clusters are of different size
     and thus the nanostructure is, in general, heterogeneous.
     During isothermal crystallization we only find order inside sparse
     clusters of lamellae. Globally the nanostructure resembles a random
     blend of these clusters. A geometric relation couples the number fraction
     of lamellae to the size of the cluster they belong to.
     More longitudinal order is achieved, if the material is subsequently
     quenched. Amorphous gaps of favorable width act as nests in which thin
     crystals are preferentially generated (harmonic completion). Together
     with their neighboring parents they imprint excess order.
     During continuous non-isothermal crystallization we observe that clusters
     with several members are selectively built from thinner crystals. Order
     is growing in the late state of crystallization. This violation of the
     common assumption of homogeneity makes the classic notion of a distorted
     lattice (convolution polynomial, paracrystal) become restricted to a
     subset of the global crystallite thickness distribution.