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Experimental and Theoretical Investigations on Dilute MEH-PPV Solutions

Experimental and Theoretical Investigations on Dilute MEH-PPV Solutions. 謝盛昌、陳建龍、張志偉、林信宏、 華繼中 國立中正大學化學工程系. Polymer Rheology and Molecular Simulation Lab., National Chung Cheng University, Taiwan. Conjugated polymers. Polyacetylene (PA).

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Experimental and Theoretical Investigations on Dilute MEH-PPV Solutions

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  1. Experimental and Theoretical Investigations on Dilute MEH-PPV Solutions 謝盛昌、陳建龍、張志偉、林信宏、 華繼中 國立中正大學化學工程系 Polymer Rheology and Molecular Simulation Lab., National Chung Cheng University, Taiwan

  2. Conjugated polymers Polyacetylene (PA) S. A. Chen, http://www.che.nthu.edu.tw/jacky/010422NYHU-CHE.pdf

  3. Conducting Polymers

  4. Progression of conducting polymer S. A. Chen, http://www.che.nthu.edu.tw/jacky/010422NYHU-CHE.pdf

  5. Cathode e- LUMO hv HOMO e- Anode PLED: Schematic Diagram Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.; Mackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B. Nature 347, 539 (1990).

  6. Spin-coating Casting Ink-jet printing Preparation of CP Thin Film

  7. Effect of Polymer Aggregationon Light-Emitting Properties PLED Device Performance Film Property Polymer Aggregation MEH-PPV thin film ITO Aggregation Schwartz et al. J. Phys. Chem., 104, 237 (2000).

  8. The polymer structure in solution can apparently affect the film morphology. Film Aggregation Memory Effect Solution Aggregation Macroscopic properties Microscopic properties Rheological Measurement SANS, SAXS Red Shift Molecular Dynamics S.-A. Chen et al. J. Phys. Chem., 103, 2375 (1999).

  9. SANS Study of MEH-PPV Solutions • MEH-PPV chains in chloroform are well separated and MEH-PPV chains in toluene are tied together by aggregates yielding clusters. • The aggregates present in the solution may serve as the nuclei from which the nematic domains will grow at high polymer conc. during the solvent evaporation in the spin coating process. H. L. Chen

  10. MEH-PPV/toluene c = 10 mg/ml (aged at RT for 60 days) gel MEH-PPV/toluene c = 10 mg/ml (fresh) sol Gel Formation at Constant-Temperature Annealing MEH-PPV/chloroform c = 5 mg/ml, T = 25 0C MEH-PPV/chloroform c = 5 mg/ml, T = 40 0C heating to ca. 60 oC H. L. Chen

  11. Rheological Experiments • Sample MEHPPV (Mw:86000, Aldrich); Chloroform and Toluene • Instrument Paar Physica MCR500; CC28.7 (Concentric cylinder)

  12. Annealing at const temperature Strategies for Probing Polymer Aggregation in Solutions Keeping Stationary & Isothermal Condition Precursor Solution ultrasonic & isothermal condition for a week Measuring Samples polymer viscosity vs. stationary time

  13. Constant temperature Annealing

  14. MEH-PPV in chloroform MEH-PPV in toluene 0.1 mg/ml Viscosity decrease with time The time scale for aggregate formation is about days or months)

  15. Annealing at varied temperatures t (polymer-chain orientation relaxation < ms ??)<< t (experimental measurements ~ hrs) << t (formation of polymer aggregates ~ days) Precursor Solution ultrasonic & isothermal condition for a week Measuring Samples polymer viscosity vs. varied temperature Heating Cooling Down Measuring Samples polymer viscosity vs. varied temperature

  16. Annealing at Varied Temperatures

  17. Annealing at Varied Temperatures MEH-PPV in chloroform MEH-PPV in toluene heating cooling cooling heating

  18. Proposed Aggregation Dynamics under Varied-Temperature Annealing for MEH-PPV in Chloroform More Aggregation is formed Heating process Size of polymer coils Kinetic energy of polymer After cooling state Size of polymer coilsreduce dramatically t °C Segregation less aggregation viscosity Cooling process Size of polymer coils Kinetic energy of polymer t °C Less Aggregation is formed

  19. MEH-PPV in toluene Heating: Cooling: Compact aggregation two different states of aggregation After the cooling state more aggregation viscosity

  20. Summary • Discovery of gel formation in a ‘good’ solvent (i.e., Chloroform) • Evidence of aggregate formation in both solvents based on rheological measurements in both types of annealing experiments

  21. Molecular Dynamics • Several Coarse-Grained Pictures for conjugated polymers

  22. The Rigid-Dumbbell Presentation +1 -1 Attraction +1 rc -1 Arbitrary Origin

  23. Forces Acting on A Rigid Dumbbell

  24. Linear Response Theory for Computing Zero-Shear Viscosity

  25. The Simulation Ensemble

  26. Realizations at Different Times

  27. Annealing at Constant Temperature

  28. Heating and Cooling Processes

  29. Attractive Force

  30. Conclusion • The molecular dynamics simulations are able to provide molecular insights into the dynamics of aggregate formation as well as the effect of annealing on low-shear polymer viscosity

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