Modulation of phase separation between spherical and rodlike molecules using geometric surfactancy.

ABSTRACT

A Dyad consisting of C(60) linked to a pi-conjugated oligomer by a propylene spacer was synthesized to explore its ability to modulate phase separation between OFTB and PCBM using differential scanning calorimetry, hot-stage polarizing optical microscopy, X-ray diffraction, and atomic force microscopy techniques. Upon thermal annealing at 10 degrees C above its T(g) for 12-48 h, the 11 blend of OFTB and PCBM resulted in a eutectic mixture. Thermal annealing of a OFTBDyadPCBM film with a 929 mass ratio at 10 degrees C above its T(g) for 12 h resulted in an amorphous film. Its AFM phase image indicated phase separation into two interspersed 30 nm amorphous domains at approximately equal fractions. Geometric surfactancy is inferred from the formation of microemulsions in analogy to widely reported traditional oil-surfactant-water systems and ternary polymer blends. In contrast, thermal annealing of a 767 film under a similar condition resulted in an amorphous film with compositional uniformity.