Fractal aggregates of polyfluorene-polyaniline triblock copolymer in solution state

We report on the aggregate structure of a symmetrical A-B-A 9,9-dialkylfluorene/2-alkylaniline "coil-rod-coil" triblock copolymer (or PF/PANI11112-b-PANI11)--consisting of 2-dodecylanilines as A blocks and 9,9-di(3,7,11-trimethyldodecyl)fluorene)s as B blocks--mixed in deuterated toluene, chloroform, and methylcyclohexane. These mixtures contain micrometer scale aggregates. Small-angle neutron scattering data indicate that the interface between the aggregates and solvents manifests surface fractal-like structure. The upper and lower limit length scales which show fractal character are of the order of > 100 and 15 nm. The surface fractal dimension D(s) varies from 2.2 to 2.8. The data show that stiff polyfluorene (PF) segments (persistence length > or = 9.5 nm, diameter approximately 2 nm) of PF/PANI11112-b-PANI11 are dissolved down to the molecular level. Photoluminescence data indicate that most PF units are isolated from both polyaniline (PANi) units and each others. Together with the scattering data, this implies that the disordered interface consists of stiff isolated PF blocks linked together via domains of associated PANi blocks.