from the lcst transition to aquamelts · 2019-09-09 · from the lcst transition to aquamelts...
TRANSCRIPT
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From the LCST Transition to Aquamelts
Jens-Uwe Sommer
Insitute Theory of PolymersLeibniz-Institut für Polymerforschung DresdenHohe Straße 6, 01069 Dresden, Germany
Technische Universität (TU) Dresden, Institute for Theoretical Physics
4th Edwards Symposium/Cambridge
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“What we know is a drop, what we don't know is an ocean.”
Isaac Newton
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Miscibility: Type I
Flory Huggins Mean-Field Model:
Entropy of Translation Polymers
Interaction (MF)
for
No coexistence without translation entropy!
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Brushes in Type I Solvents
Free energy per monomer: Elasticity (de Gennes/Alexander)
Equilibrium
No phase (collapse) transition
Experimental window
No molecular clicker
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Upside down – the LCST
Various polymers (particularly water-soluble) display the opposite behavior
LCST-behavior is not restricted to water as a solvent
UCST can be very high
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LCST and type II transitions
LCST-transition is discontinuous for immobilized polymers
N. Ishida and S. Biggs, Langmuir 23, 11083 (2007)
QMB AFM
NO transition for ANY continuousfunction
Transition must be of a new type
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Type II transitions
IDEA: Negative higher order virial coefficient with positive second order. “n-cluster model”
Virial expansion in terms of c
Switches sign
P.-G. de Gennes, CRAS 313 series II, 1117 (1991)
Quantified by Afroze et al. For PNIPAm
F. Afroze, E. Nies and H. Berghmans, J. Mol. Struct. 554, 55 (2000)
Can be always mapped to a Flory-Function
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Physical and Molecular Origins
Formation of H-bonds play an essential role for water soluble polymers (PEO, PNIPAm, …)
Water is “Janus-head”: poor solvent in non-H-bond state, H-bonds provide solubility
n
(…
Hydrophobic
H-Bond
Free energy gain for H-bond with PEO
Probability to dissolve H-bond(P
H
C. Jeppesen and K. Kremer Europhys. Lett. 34, 536 (1996)
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Physical and Molecular Origins
A simple Mean Field concept for LCST
S. Berkiranov, R. Bruisma and P. Pincus Europhys. Lett. 24, 183 (1993)
Probability for H20 to have a second
monomer in its neighborhood:
Frustrated H-bond
H-bond
Phillip PincusGeneric form for type-II excess free energy
Single chain collapse
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Spiders do superior processing
C. Holland et al. Advanced Materials 24, 105 (2012)
Order of magnitude less energy to initiate fibrillation
PE
Silk
Spe
cific
wor
k of
fib
er-f
orm
atio
n
125 °C
10, 27, 40 °C
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Aquamelts
Stretching and fibrillation BEFORE crystallization
Demixing and Crystallization must be FLOW INDUCED
Inverting the processes during fiber formation in polymers
C. Holland et al. Advanced Materials 24, 105 (2012)
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Flow Induced Phase Transitions
Can miscibility of polymers depend on extension/force?
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FLIPT: A FET-OPEN project (EU)
ChrisHolland
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Theory of Polymers in Dresden
Sergii Donets
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Two Types of H-Bonds in PEO
trans conformer
trans conformer
n
(
(…
Conformation transitions
…
…
n(
(gauche
conformer
gauche conformer
Bifurcated (double) – H - bond
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Matching Scales
2.8 Å 2.9 År
r
……
n(
(
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External force changes conformation statistics
S. Donnets and JUS J. Phys. Chem. B 122, 392 (2018)
Force dipole applied to each chain
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External Force Changes H-Bonding Statistics
S. Donnets and JUS J. Phys. Chem. B 122, 392 (2018)
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Force induced phase transition
S. Donnets and JUS J. Phys. Chem. B 122, 392 (2018)
pNns
350
140
70
2 20
Pair correlation force direction
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Effective potential between two PEO chains
S. Donnets and JUS J. Phys. Chem. B 122, 392 (2018)
f f
f f
ksp
Potential of Mean Force
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Force induced phase separation assists deformation
S. Donnets and JUS J. Phys. Chem. B 122, 392 (2018)
Substantial reduction of forceto induce strong stretching.
Classical melt-spinning
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Conclusions
By harnessing the H-bond mechanism of solubility in PEO stretching inducesphase separation and even crystallization in solution far below the LCST
Complex solution properties of water-soluble polymers can be expressedby
with a type-II transition behavior
Flow-induced phase separation reduced the work for fiber formation as comparedto classical processing of semi-crystalline polymers
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Thank YOU!