Abstract
Abstract In this research, the effects of the solvent nature, concentration of solution and temperature which affect the morphology of MEH-PPV polymer chains in solution state were inquired. We discover, in spite of solvent nature and the molecular weight of MEH-PPV, the existence of aggregation phenomenon even in ultra dilute solution as the amount of molecular chains of MEH-PPV larger than 109/ml, it implicates aggregations could be a colligative property which depends only on the number of solute molecular chains. Because molecular chains’ self-assembling make the effective conjugated length increasing, therefore results in photoluminescence (PL) spectrum red shift, it implicates the aggregation has a lot of significant meaning in photophysical properties. We also discover, below the aggregated concentration region, the intensity of photoluminescence increases as the solute molecular weight increases, it implicates the intensity of photoluminescence depends on the size of luminescence particles. The affinity of solvent nature to the side chain and backbone of MEH-PPV decides the type and degree of aggregation of solvent molecular chains. Aromatic solvents such as toluene and chlorobenzene have good affinity to the backbone of MEH-PPV, so the main chains’ aggregation were forbidden attributed to the aromatic solvent filling up among the main chains, but allow the side chains’ aggregation. On the contrast, aliphatic solvents such as chloroform and tetrahydrofuran (THF), THF especially, have good affinity to the side chain of MEH-PPV, so the main chains’ aggregation proceed in the way of adamant zipper-like aggregation as the concentration of solution was increased, which could not be capable deaggregated by means of the heating process. Although when MEH-PPV was dissolved in toluene we have learned from our temperature-dependent SANS experiments which exhibits the good thermal reversibility, as heating the aggregated cluster deaggregate and as cooling the deaggregated segments aggregate again, but not include THF system due to entirely different aggregation structure.