shear-induced crystallization of polyethylene (see heeley, morgovan, bras, dolbnya, gleeson, &...
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Shear-induced crystallization of polyethylene
(see Heeley, Morgovan, Bras, Dolbnya, Gleeson, & Ryan, Phys. Chem. Comm. (2002) 5, 158-160. Shear-induced crystallization of polyethylene studied by small- and wide-angle X-ray scattering (SAXS/WAXS) techniques)
In situ study of development of shear-induced macrostructure of PE
injection molding ––> shear flow in polymer
changes crystallization kinetics & morphology
chain alignment ––> 'shish kebab' structure
(see Heeley, Morgovan, Bras, Dolbnya, Gleeson, & Ryan, Phys. Chem. Comm. (2002) 5, 158-160. Shear-induced crystallization of polyethylene studied by small- and wide-angle X-ray scattering (SAXS/WAXS) techniques)
In situ study of development of shear-induced macrostructure of PE
synchrotron radiation using shear cell & heating stage
5 sec/frame – after shear (100 pulses/sec for 5 & 10 sec)
Shear-induced crystallization of polyethylene
crystallization temperature
Results
stacking of lamellae along shear direction
Shear-induced crystallization of polyethylene
lower MW - less orientation
shear direction
More results
invariant vs crystallization time
Shear-induced crystallization of polyethylene
Pores in polymers & carbons
(see Olivier, Lagasse, Schaeffer, Barnes, & long, Macromolecules (1996) 29, 8515-8621. SA small-angle-scattering study of the pore-orientation periodicity in porous polymer and carbon materials)
Banded spherulites ––> carbon foams
crystallized blend of maleic anhydride (MA) & polyacrylonitrile (PAN)
bands are ~ 3.5 mm in width in this system (can use SAXS)
sublimate MA & pyrolyze ––> carbon foams (98% void volume)
Pores in polymers & carbons
(see Olivier, Lagasse, Schaeffer, Barnes, & long, Macromolecules (1996) 29, 8515-8621. SA small-angle-scattering study of the pore-orientation periodicity in porous polymer and carbon materials)
Pores in polymers & carbons
(see Olivier, Lagasse, Schaeffer, Barnes, & long, Macromolecules (1996) 29, 8515-8621. SA small-angle-scattering study of the pore-orientation periodicity in porous polymer and carbon materials)
averages of intensity data around azimuth -not on absolute scale
q–4
Pores in polymers & carbons
(see Olivier, Lagasse, Schaeffer, Barnes, & long, Macromolecules (1996) 29, 8515-8621. SA small-angle-scattering study of the pore-orientation periodicity in porous polymer and carbon materials)
averages of intensity data around azimuth -not on absolute scale
q–4
sharp polymer/void interface
Pores in polymers & carbons
Pores in polymers & carbons
Plots of intensity differences from intensity averages over 22 positions
Pores in polymers & carbons
Plots of intensity differences from intensity averages over 22 positions
Plots repeat at 3 – 4 mm translation interval
Pores in polymers & carbons
Plots of sector averages of intensity vs translation position
Pores in polymers & carbons
Before pyrolysis
After pyrolysis
Pores in polymers & carbons
Observation in as-crystallized blend:
bands move when sample is rotated around growth direction
indicates rotation of crystal orientations
substantiated by high-angle x-ray studies
orthorhombic MA cells
Pores in polymers & carbons
Observation in as-crystallized blend:
bands move when sample is rotated around growth direction
indicates rotation of crystal orientations
substantiated by high-angle x-ray studies
band motion observed in pyrolyzed mat'l ––>anisotropic pore rotation
orthorhombic MA cells
Pores in polymers & carbons
band motion observed in pyrolyzed mat'l ––>anisotropic pore rotation
pore shape assumed ellipsoidal
Pores in polymers & carbons
band motion observed in pyrolyzed mat'l ––>anisotropic pore rotation
substantiated by oscillation in Porod data plots
pore shape assumed ellipsoidal
Pores in polymers & carbons
Porod constant, KP, for isotropic case
For anisotropic case
Also, for average chord length, <LV>, inside pore
vol. fact.
Pores in polymers & carbons
Porod constant, KP, for isotropic case
For anisotropic case
Pores in polymers & carbons
Porod constant, KP, for isotropic case
For anisotropic case