Nanothin films of polystyrene (PS) doped with poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) by spin-coating were researched. An Interplay between phase separation and dewetting caused by the inhibition of formation of holes with increasing concentration of MEH-PPV in polystyrene was observed in the early stages of instability. With increasing concentration of MEH-PPV, the morphology is dominated by this interplay. For low concentrations of 5%-MEH-PPV, dewetting by nucleation and growth was found as evidenced by the formation of holes with rim instability, after increasing the concentration to 15%-MEH-PPV, there was no formation of holes but rather the appearance of composition waves and later formation of droplets; with a higher concentration of 30%-MEH-PPV the surface morphology evidenced the formation of composition waves rather than the formation of holes. Under the same film thickness, composition waves are induced with increasing concentration of MEH-PPV. A short-time stepwise annealing experiment exposed the evolution of the morphological features. A residual layer measured on scratched samples by the AFM was found to be thicker for a larger concentration of MEH-PPV. The effect of film thickness was analyzed for films of 5, 10, 20 and 30 nm revealing that increasing film thickness benefits the formation of the composition waves as evidenced by the early rising of the bicontinuous pattern. For concentrations of 15%-MEH-PPV and above, The PL enhancement factor was found to decrease with film thickness revealing that the PL enhancement decreases progressively with increasing film thickness as the films move from higher instability to the formation of the composition waves. The solvent effect showed that acetone usually had a different path of instability than toluene.

Acknowledgements
Abstract……………………………………………………………………………………………………………………..I
Table of contents……………………………………………………………………………………………………...II
List of figures……………………………………………………………………………………………………………VI
List of tables…………………………………………………………………………………………………………..XIV
Chapter 1 Introduction………………………………………………………………………………………………1
Chapter 2 Literature review………………………………………………………………………………………3
2.1 Introduction…………………………………………………………………………………………………...3
2.2 Polymer thin films……………………………………………………………………………………………4
2.2.1 Spontaneous instability………………………………………………………………………………..4
2.3 Phase separation…………………………………………………………………………………………….5
2.4 Viscoelasticity………………………………………………………………………………………………….7
2.5 Hetero-junction quenching effect……………………………………………………………………8
2.6 Theory of dewetting………………………………………………………………………………………..8
2.6.1 Holes in the film…………………………………………………………………………………………10
2.6.2 Shape of the rim………………………………………………………………………………………...11
2.6.2.1 Ribbon formation…………………………………………………………………………………….12
2.6.2.2 Rim instability………………………………………………………………………………………….12
2.7 Hamaker constant………………………………………………………………………………………….12
2.8 Spinodal instability………………………………………………………………………………………..13
2.9 Spinodal decomposition………………………………………………………………………………..16
2.10 Polymer blends……………………………………………………………………………………………18
2.11 MEH-PPV…………………………………………………………………………………………………….19
Chapter 3 Experimental procedure………………………………………………………………………….20
3.1 Solvent vapor annealing………………………………………………………………………………..20
3.1.1 Materials…………………………………………………………………………………………………….20
3.2 Instruments…………………………………………………………………………………………………..23
3.2.1 The vacuum chamber…………………………………………………………………………………23
3.2.2 The spin-coater…………………………………………………………………………………………..24
3.2.2 The furnaces……………………………………………………………………………………………….26
3.2.4 Perkin Elmer spectrometer…………………………………………………………………………27
3.2.5 Atomic Force Microscope (AFM)…………………………………………………………………28
3.2.6 Fourier Transform Infrared (FTIR)……………………………………………………………….32
3.3 Sample preparation……………………………………………………………………………………….33
3.4 Experimental procedure and steps………………………………………………………………..34
Flow chart……………………………………………………………………………………………………………37
Chapter 4 Results and discussion…………………………………………………………………………….46
4.1 Overview……………………………………………………………………………………………………….46
4.2 Introduction………………………………………………………………………………………………….47
4.3 Dequenching………………………………………………………………………………………………...48
4.4 The interplay between phase separation and dewetting……………………………….52
4.4.1 The interplay as evidenced in the surface morphology…………………………..55
4.4.2 Confocal PL mapping………………………………………………………………………………66
4.5 Effect of the film thickness…………………………………………………………………………….74
4.5.1 Effect of the film thickness on low concentration of MEH-PPV (5%-MEH-PPV/PS)………………………………………………………………………………….74
4.5.2 Effect of film the thickness on middle concentration of MEH-PPV (15%-MEH-PPV/PS)………………………………………………………………………………..81
4.5.2.1 Effect of the film thickness on middle concentration of MEH-PPV (15%-MEH-PPV/PS)…………………………………………..……………………………………87
4.5.3 Effect of the film thickness on high concentration of MEH-PPV (30%-MEH-PPV/PS)………………………………………………………………………………93
4.6 Effect of a good solvent and a poor solvent on middle and high concentrations of MEH-PPV…………………………………………………………………….………………………..98
4.6.1 Effect of a good and a poor solvent on middle concentration of MEH-PPV (15%-MEH-PPV/PS)………………………………………………………………………………..97
4.6.2 Effect of a good and solvent and a poor solvent on high concentration of MEH-PPV (30%-MEH-PPV/PS)………………………………………………………………107
4.7 Effect of the switching of the solvents…………………………………………………………115
4.8 Effect of the film subjected to the in-and-out (interrupted) of the solvent vapor bath compared to the uninterrupted exposure to the solvent vapor bath……........................................................................................................127
4.9 Fourier Transform Infrared Spectrometer data…………………………………………….135
Chapter 5 Conclusions………………………………………………………………………………………………137
Chapter 6 References………………………………………………………………………………………………..139

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