Microphase Separation of Complex Block Copolymers ??????????????

1
Microphase Separation of Complex Block
Copolymers??????????????

• Feng Qiu (? ?)
• Dept. of Macromolecular Science
• Fudan University
• Shanghai, 200433, CHINA
• July 20, 2005, Peking University

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Block Copolymer (???????)
3
Order-Disorder Transition (??-????)

• ?S 1/N

Micro-phase separation (????)
4
M. Park, et al., Science, 276, 1401(1997).
5
M. Templin, et al., Science, 278, 1795(1997).
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Gyroid Phase

• http//eltweb.mit.edu/images/research/nanostructur
  es.html

A. H. Scheon, 1960s
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Diblock Copolymer Morphology

• From M. Matsen

Morphology not sensitive to chain architecture
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Phase Diagram of Diblock Copolymers
Two parameters f and ?N
Mean Field Theory
M. Matsen and W. Schick, Phys. Rev. Lett, 72,
2660(1994).
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Complex Block Copolymers

• From G. H. Fredrickson and F. S. Bates

Rich and variety chain architectures
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Triblock Copolymers (??????)
A
B
C
C
A
B
C
A
B
A
B
C
Chain Architecture
Block Sequence
Parameter space increases 18-fold
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A Challenge

• Can we effectively predict new morphologies and
  their stability?
• YES!
• Self-Consistent Field Theory

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Coarse-graining
The successive coarse-graining processes
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Chain Modeled as a Path

• q(r,s)

r(N)
r(s)
r(0)
Edwards Model
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Modified Diffusion Equation for Linear ABC
Triblock Copolymers
0 fAN (fAfB)N N
And initial condition
q similar
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Free Energy

• Mean field approximation

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SCF Equations
For linear ABC triblock Copolymers
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Fourier Space Method

• M. Matsen and W. Schick, PRL, 72, 2660(1994)

Periodic structures Known symmetry
Simplify the problem to matrix operations
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Phase Diagram of Diblock Copolymers
PS/PI, f0.37 ?N (stable) RL/RG
RHole/RLam Exp. 16-20 2.4 1.02-1.49 Theo.
14.9-20.4 2.45 1.32-1.36

• 60 basis functions
• 10-4, free energy

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Real Space Method
F. Drolet and G. H. Fredrickson, Phys. Rev.
Lett., 83, 4317(1999).
Initialize all fields randomly
Set ?(r) ?1-? A(r) - ? B(r) - ? C(r)
Solve the diffusion equations for q(r,s) and
q(r,s)
Evaluate ?A(r) , ?B(r) and ?C(r)
Update the potential fields using wAnew wAold
?(?AB?B ?AC?C ?- wAold) wBnew wBold
?(?AB?A ?BC?C ?- wBold) wCnew wCold ?(?BC?B
?AC?A ?- wCold)
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Pattern Evolution in Iterations
Free energy is lowered and finally reaches
minimum.
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2D Microphases Discovered in Linear ABC Triblocks
LAM3
HEX
CSH
TET2
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2D Microphases Discovered in Linear ABC Triblocks
LAMBD-I
HEXBD
LAMBD-II
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Phase Diagram of ABC Linear Block Copolymer
?ABN ?BCN ?ACN 55
?ABN ?BCN ?ACN 35
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Influence of Block Sequence
?AB ? ?BC ? ?AC
A
B
C
A
B
C
vs
P. Tang, F. Qiu, H. D. Zhang, Y. L. Yang, Phys.
Rev. E, 69, 031803(2004).
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Phase Diagram of ABC Linear Block Copolymer
?AB ?BC ? ?AC
A
B
C
A
C
B
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PI-PS-P2VP and PS-PI-P2VP
S. P. Gido, et al, Macromolecules, 26,
2636(1993).
Y.Mogi, et al, Macromolecules, 27, 6755(1994).
fPSfPIfP2VP?1/3, ?PI-P2VP gtgt ?PS-PI ? ?PS-P2VP
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2D Microphases Discovered in Star ABC Triblocks
LAM3
TCB
HEX3
LAMBD
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2D Microphases Discovered in Star ABC Triblocks
KP
HEX
CSH
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2D Microphases Discovered in Star ABC Triblocks
DEHT
LAMBD-I
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Phase Diagram of ABC Star Triblock
?AB ?BC ?AC 35
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Phase Diagram of ABC Star Triblock
?AB ?BC 72, ?AC 22 PS-PI-PMMA
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PS PI P2VP Star Triblock

• A. Takano et al, Macromolecules, 2004, 37, 9941

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Influence of Chain Architecture
C
A
B
C
VS
A
B
P. Tang, F. Qiu, H. D. Zhang, Y. L. Yang, J.
Phys. Chem. B, 108, 8434(2004).
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Phase Diagrams of ABC Triblocks
A
B
C
A
B
C
?AB ?BC ?AC 35
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3D Structures
A
B
C
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Conclusions

• For ABC linear triblock copolymers, seven
  microphases are found to be stable in 2D.
• When volume fractions and interaction energies of
  the three species are comparable, lamellar phases
  are the most stable phase.
• If one of the volume fractions is large,
  core-shell hexagonal, or tetragonal phase can be
  formed.
• As the interaction energies between distinct
  blocks become asymmetric, more complex
  morphologies occurs.
• Block sequence plays a profound role in the
  microphase formation.

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Conclusions

• For ABC star triblock copolymers, nine
  microphases are found to be stable in 2D.
• When the volume fractions comparable, star
  architecture is a strong topological constraint
  regulates the geometry of the microphases.
• Only when at least one of the volume fractions is
  low, the influence of the star architecture is
  not significant.

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Open Questions

• Semi-flexible chains
• Rigid chains
• Dilute solution
• Dynamics ?

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Acknowledgement
Prof. Yuliang Yang Prof. Hongdong Zhang Dr. Ping
Tang NSF of China Ministry of Science and
Technology Ministry of Education
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Thank you!