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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 )

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slide1

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

slide2

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

synchrotron radiation using shear cell & heating stage

5 sec/frame – after shear (100 pulses/sec for 5 & 10 sec)

crystallization temperature

slide3

Shear-induced crystallization of polyethylene

Results

stacking of lamellae along shear direction

shear

direction

lower MW - less orientation

slide4

Shear-induced crystallization of polyethylene

More results

invariant vs crystallization time

lower MW - less orientation

slide5

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)

slide6

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)

slide7

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)

q–4

averages of intensity

data around azimuth -

not on absolute scale

slide8

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)

q–4

sharp polymer/void interface

averages of intensity

data around azimuth -

not on absolute scale

slide10

Pores in polymers & carbons

Plots of intensity differences from intensity averages over 22 positions

slide11

Pores in polymers & carbons

Plots of intensity differences from intensity averages over 22 positions

Plots repeat at 3 – 4 mm translation interval

slide12

Pores in polymers & carbons

Plots of sector averages of intensity vs translation position

slide13

Pores in polymers & carbons

Before pyrolysis

After pyrolysis

slide14

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

slide15

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

slide16

Pores in polymers & carbons

band motion observed in pyrolyzed mat'l ––>

anisotropic pore rotation

pore shape assumed ellipsoidal

slide17

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

slide18

Pores in polymers & carbons

Porod constant, KP, for isotropic case

For anisotropic case

Also, for average chord length, <LV>, inside pore

vol. fact.

slide19

Pores in polymers & carbons

Porod constant, KP, for isotropic case

For anisotropic case

slide20

Pores in polymers & carbons

Porod constant, KP, for isotropic case

For anisotropic case