Directed Crystallization Precursor Structures in Polymers Benjamin S. Hsiao (Stony Brook University), DMR-0405432

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Directed Crystallization Precursor Structures in
PolymersBenjamin S. Hsiao (Stony Brook
University), DMR-0405432
Flow-induced crystallization has long been an
important subject in polymer processing. Varying
processing conditions can produce different
morphologies, which lead to different properties.
Recent studies indicated that the final
morphology is in fact dictated by the initial
formation of crystallization precursor structures
(i.e., shish kebabs) under flow. In this study,
factors that affect the shish-kebab formation in
entangled polymer melts are systematically
investigated, including the concept of
coil-stretch transition, chain dynamics, critical
orientation molecular weight, phase transition
during shish and kebab formations.
Several new findings of flow-induced shish-kebab
structures in polymer melts were observed. (1)
The shish entity consists of stretched chains
that can be in the amorphous, mesomorphic or
crystalline state. (2) The kebab entity mainly
arises from the crystallization of coiled chains,
which follow a diffusion-control growth process.
(Left) The shish-kebab structure with
multiple-shish in high molecular weight
polyethylene induced by shear flow. (Right) The
diffusion-controlled kebab growth rate estimated
by small-angle X-ray scattering (SAXS) data.
PRL, 2005, 94(11) 117802,1-4.
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Directed Crystallization Precursor Structures in
PolymerBenjamin S. Hsiao (Stony Brook
University), DMR-0405432
Outreach Each summer, graduate students
and post-doctoral scientists have participated in
the summer high school student research program,
sponsored by the Stony Brook University. In 2005,
four high school students were hosted in our
laboratory, all of them will compete in the Intel
Science Talent Search. The photo of PI with four
high school students, one high school teacher,
one REU student and two graduate students is
shown below.
Education This is a renewal research grant,
started in the spring of 2004. Under this grant,
one graduate student (Ms. Ling Yang) has
completed her Ph.D. thesis in 2005, two graduate
students (Mr. Feng Zuo and Mr. Jong Kahk Keum)
and one REU undergraduate student (Ms. Priya
Desai) are currently been supported. Other
scientists involved in this work include Dr.
Rajesh Somani (senior scientist), Dr. Shigeyuki
Toki (senior scientist) and Dr. Igors Sics
(beamline scientist at X27C, National Synchrotron
Light Source, Brookhaven National Laboratory)