For PFO, the aged PFO/toluene/nonane solution composes of the PFO-enriched phase and the isotropic phase due to the macrophase separation upon aging. The degree of microphase separation increased with increasing nonane content due to reduction of solvent quality. The PFO-enriched phase is mesomorphic, consisting of the ribbon-like aggregates. A fraction of the PFO chains/segments forming ribbon-like aggregates adopt the β-conformation, which further organize to form a layer-by-layer structure of β-phase. The promotion of gelation of PFO solution by adding nonane should be driven principally by a macrophase separation process that leads to highly interconnected domains arrested during the phase separation process. Moreover, the β-phase (Cβ) in solution can be transferred to films prepared from the solution.
For MEH-PPV, it present as components of rod-like segments in toluene solution and construct a mass fractal aggregates. However, in the MEH-PPV/toluene solution with addition of nonane, the MEH-PPV segments can be compact to form the dimmer aggregates. In solution, more aggregates formed and mesomorphic phase developed for aged MEH-PPV/toluene solution with nonane. In film at room temperature, addition of nonane can induce mesophase in cast film from fresh solution but inhibit that in cast film from aged solution. It is proposed the serious aggregation behavior in the aged solution with nonane transfers to the films and affects the formation of mesophase in the films. Upon heating, the aggregates are destroyed and the more mesophase was formed in the films. It is suggested the dimmer aggregates formed through addition of nonane and aged effect in solution are the nuclei of mesophase. After casting the film from the solution, the mesophase can be induced from the dimmer aggregates upon heating.

Catalogue
Abstract I
Catalogue II
Figure IV
Table VII
Chapter 1 Introduction 1
Chapter 2 Literature Review 2
2-1 An overview of conjugated polymers 2
2-2 Aggregation and energy transfer of conjugated polymers based on photophysical property studies 5
2-3 Most common conjugated polymer systems: PFO and MEH-PPV 12
2-3-1 Polyfluorene (PFO) 12
2-3-2 Poly[2-methoxy-5-(2’-ethylhexyloxy)- 1,4-phenylene vinylene] (MEH-PPV) 18
2-4 Gelation behavior of conjugated polymers 23
Chapter 3 Research motivation and objective 25
Chapter 4 Experimental section 27
4-1 Material and sample preparation 27
4-2 Characterizations 29
Chapter 5 Results and Discussions 30
5-1 Studies of PFO/toluene solution with addition of nonane 30
5-1-1 Photophysical properties of solution 30
5-1-2 Analysis of PFO solution structure 36
5-1-4 Photophysical properties and phases transformation of PFO films cast from the solution with and without nonane 51
5-2 Studies of MEH-PPV/toluene solution with addition of nonane 57
5-2-1 Photophysical properties of MEH-PPV solutions 57
5-2-2 Analysis of the structures of MEH-PPV solution 62
5-2-3 Photophysical properties of MEH-PPV cast films 64
5-2-4 Morphology of MEH-PPV films 67
Chapter 6 Conclusion 71
References 75

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