Transcript Optical Tweezers for Pulling Polymer Chains

Tacticity of a linear polymer chain
trans conformation
. . .breakage of covalent bonds
required to change configuration/tacticity
Isotactic:
Syndiotactic:
Atactic:
-R groups on the same side of the C-C plane
-R groups on alternating side
-R groups on either side of the C-C plane
States of polymers
Gaseous
Liquid
Solid
“melt”& solutions “glasses” semi-crystalline
decrease temperature or thermal motion
Polymer melt
polymer melt is like a bowl of spaghetti
• entanglements limit motion
• flows on long-timescales (reptation)
• elastic on short-timescales
viscoelasticity
Melts ( pure polymer “liquid”) towards crystalline solids
. . towards crystalline state
• motion frozen on scale of polymer
• segmental motion persists
… to semi-crystalline melts
crystalline/amorphous lamellae
• depends upon cooling rate
• backbone/sidegroup structure
• tacticity
100-200 Å, 40-80 PE monomers
spherulite
Some polymers do . . Some don’t (crystallise)
Crystallisation is facilitated by
• “regular” or ordered backbone structure,
• favorable interchain interactions
• lower molecular weight
Inter-chain hydrogen bonding favors
formation of semi-crystalline regions
nylon-6,6
Atactic polystyrene ?
“glasses” . . .intermediate between amorphous melts and
possible semi-crystalline states
. . . “frozen” structure precedes crystallisation, if it happens;
melt conditions
glass transition
Tg
small scale molecular motions
• limited backbone motion
• rotations, “crankshaft”
• vibrations
• flips, wags of side groups
cyrstallisation
Tm
Q4: Using complete sentences, and schematics if helpful,
contrast the chain motion of a melt of atactic
polypropylene under (a) slow temperature quench; (b)
quick temperature quench
Q5: Complete Q4 again, starting from a melt of nylon6,6
Q6: Atactic-polyvinylchloride (PVC) is amorphous, whereas
syndiotactic-PVC is partially cyrstalline. But
atactic- polyvinylalcohol is partly crystalline. Why?
Q7: Do you predict the Tm of nylon-6,6 to be higher or lower
than that of polyethylene? Why?
Polymer solutions “dilute”, semi-dilute, through to concentrated
Rheology: a study of the flow of polymer melts and solutions
(shear-thinning, die swell, energy requirements
for mold filling, design of mixers, extruders
Block copolymer solutions and
melts:
making patterned surfaces and
ordered melt morphologies
Scientists, academics < 1930s
Industrialists
1830 Charles Goodyear,: vulcanised
rubber
“A damned gooey mess”
Hevea brasiliensis + D + S
elastomeric material
1847 Christian Schonbern
Cellulose + nitric acid
cellulose nitrate
Another failed synthesis
1860 Leo Baekeland (Bakelite)
phenol-formaldehyde resin
1930s DuPont (USA) nylon, teflon
1938Dow (USA) polystyrene
1939 ICI (UK) LDPE
WWII: shortage of natural rubber!
Scientists begin to look at complex systems . . . .
1920’s Hermann Staudinger, German Physical Chemist
“long-chained molecules or macromolecules”
interacting, separate
intermediate species
e.g., Tm, flow behaviour
very long, alkane-like
but misunderstood .
flexibility