Student Oral Presentation #4
SANS-Supported Liquid-Liquid Phase Separation Drives the
Inversion of Crystallization Rate from Heterogeneous Melts of
Broadly Distributed Random Ethylene Copolymers
Xuejian Chen 1 , George D. Wignall 2 , Lilin He 2 , Carlos Lopez-Barron 3 , Rufina G. Alamo 1
1
Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering,
2
ORNL, Biology and Soft Matter Division, 3 ExxonMobil Chemical Company
Abstract
Techniques aiming to control the rate of polymer crystallization have long been of industrial interest. It is known
that crystallization rate of polymer strongly depends on the initial melt state. Prior work 1 using Differential
Scanning Calorimetry (DSC) in broadly distributed (composition) random ethylene copolymers has reported an
unprecedented inversion of crystallization kinetics from heterogeneous melt with lowering temperature. The
mechanism behind this is further analyzed with detailed Small Angle Neutron Scattering (SANS) investigations
of the melt structure of a broad ethylene 1-hexene copolymer (reproduced by a copolymer blend) in a wide range
of temperatures that were reached either by heating the solid (from below) or cooling from homogeneous melt
(from above). 2 In both cases, the observed SANS signal gradually changes from a pattern consistent with a one-
phase melt (high temperature range) to a deviation toward higher intensity in the low Q region displaying
signature of a minor disperse phase in a homogeneous matrix (low melt temperature range). The latter structure
is consistent with demixing of the highly branched molecules and corroborates the postulated liquid-liquid phase
separation (LLPS) as an explanation for the inversion of crystallization kinetics observed by DSC. In the melt
approached from above, LLPS requires longer time to evolve to the same extent as in the melt approached from
below. Nevertheless, SANS gives evidence of LLPS irrespective of the path taken to approach the melt.
Figure 1. Inversion of crystallization
rate (T c,peak ) with lowering melt
temperature T melt (closed symbol).
Figure 2. Deviation of scattering
towards higher intensity in low Q
indicates LLPS in the melt.
Reference
1. Mamun A, Chen X, Alamo RG. Macromolecules, 2014;47:7958.
2. Chen X, Wignall GD, He L, Lopez-Barron C, Alamo RG. Submitted.
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