Block copolymer assisted preparation of functional nano-composites.
Date of Issue2012
School of Materials Science and Engineering
Block copolymers are widely used in the field of nanotechnology for the production of functional nanomaterials and nanocomposites. We report a technique for the synthesis of C60/polymer colloid nanocomposites in aqueous medium from a non-aqueous system via complex formation. A tri-block poly(4-vinylpyridine)-b-polyethylene-b-poly(4-vinylpyridine), P4VP8-b-PEO105-b-P4VP8 was complexed with fullerene (C60) in toluene via charge transfer complex formation, which resulted in a fullerene assembly in cluster form. A nanocomposite dispersion in aqueous solution could be obtained using an aged solution of the polymer/C60/toluene by solvent evaporation technique. However, the rate of complexation was found to be slow in toluene and took several months for unmodified fullerene (C60) to complete. Rate enhancement of the charge transfer complex formation was attempted using fullerene derivative (PCBM) instead of fullerene (C60) in toluene and THF system. The reaction was found to be typically fast in THF compared with toluene system, which allowed us to study the interaction kinetics of the reaction both qualitatively and quantitatively. Our results show that the reaction follows pseudo-first order kinetics and the P4VP units in the copolymer interact with the fullerene derivative more than two order of magnitude faster than does the small molecular model compound tert-butylpyridine. Based on this understanding, studies were carried out to enhance the rate o charge transfer complex formation of underivatized fullerene (C60) with PS-b-P4VP. Rapid assembly of C60/PS-b-P4VP composite was realized using a mixed solvent. The poor solubility of C60 in THF was overcome by first dissolving C60 in toluene before adding in THF. The complexation reaction was completed within 10 days in THF whereas negligible reaction occurs even after one month when toluene used as solvent as observed previously. Significant morphological refining was observed in C60/PS-b-P4VP complex after a solvent exchange process when the THF of was exchanged with toluene.