講者：鄒海雄博士 (Dr. Andy Tsou)
演講題目：Amorphous Topology
and Plastic Deformation of Polyethylene
演講時間：9/26（五）15:30~17:00
演講地點：博雅館 103
主持人：戴子安教授
Amorphous
Topology and Plastic Deformation of Polyethylene
Andy
H. Tsou
Global
Chemical Research, ExxonMobil Chemical Company
The evolution of
polyethylene (PE) products from LDPE, HDPE, LLDPE, to mLLDPE has been a result
of catalyst innovation and discovery from peroxide, chromium, Ziegler-Natta, to
metallocene. The corresponding backbone
structures were constructed as a consequence of these catalyzed and coordinated
polymerizations ranging from short and long chain branches (SCBs and LCBs) of
various types in LDPE, linear in HDPE, inter-chain poly-dispersed SCBs of the same
type in LLDPE, to narrowly dispersed SCBs in mLLDPE. Although this structural development in PEs
leads to a continuous improvement in their mechanical toughness, it negatively
affects their blown film processability.
Fundamental studies of structural-property relationships in PE using
model polymers, molecular dynamics simulation, self-consistent field theory,
and advanced characterization methods for structural and morphology probes have
led to our understanding of the backbone structural effects on rheological and
mechanical properties of PE. In this
talk, the emphasis will be placed on the plastic deformation of polyethylene,
which contributes to their mechanical toughness, and its dependence on
amorphous topology.
A self-consistent
field theory relating the backbone structure of a polyethylene to its tie
chains, amorphous chain segments connecting the crystals, will be
reviewed. The fundamental assumptions of
this mean field theory are verified by the molecular dynamic (MD) simulation of
PE homogeneous crystal nucleation and growth.
This nucleation and growth simulation indicates that the formation of a
critical nucleus is the rate determining step and that the amorphous topological
features of tie chains and loops are relatively developed during chain-folded
nucleation. Plastic deformation of the
stack of alternating crystal and amorphous layers in PE as a function of the
amorphous chain topology is studied by another molecular dynamics simulation.
This molecular dynamics protocol to study plastic deformation has been
validated by synchrotron small and wide angle x-ray scattering examinations of
lamellar-stacks deformation in a uniaxially oriented PE. The deformation simulation revealed that, in
order to promote strain hardening for toughness enhancement in PE, short tie
chains or bridging entanglements appear to be necessary and that the strain
hardening modulus scales directly with tie chain concentration. Through the
simulation-verified self-consistent field theory and experimentally validated
MD modeling, a direct link between the backbone structure of a polyethylene and
its plastic deformation and mechanical toughness is established.
關於本次演講資訊請參考附件檔案，謝謝。
|