Agglomeration controllable reprecipitation method using solvent mixture for synthesizing conductive polymer nanoparticles

Conductive polymer nanoparticles (NPs) exhibit a strong tendency to agglomerate because of strong interactions between the π electrons in the polymer. The use of a surfactant to control this agglomeration is problematic because doing so can adversely affect the characteristics of electronic devices to which the NPs are applied. By exploiting the affinity between the polymer and solvent, a modified reprecipitation method for controlling the agglomeration without the use of a surfactant was developed. The affinity between conductive polymer NPs comprising poly(3-hexylthiophene) and various solvent mixtures consisting of chloroform and ethanol was systematically tuned by varying the mixture composition. The increase in the poor solvent ratio led to the substantial increase in the agglomeration tendency. Adjusting the good solvent ratio to be within a narrow region, 70–77%, resulted in the formation of NPs with high stability and a high synthesis yield. This region corresponded to 1.4–1.7 of the relative energy difference between the polymer and solvent mixture as derived from the Hansen solubility parameters. [Figure not available: see fulltext.].