Phase behaviour of liquid crystalline dendronized fullerene binary mixtures

Abstract

Here we describe liquid crystalline binary mixtures of [60]fullerene with a wedge-shaped tris-(alkyl)gallate group attached via a flexible spacer, where alkyls are n carbons long (C₆₀-n). Phase behaviour was investigated as a function of blend composition. We show that the isotropization temperature is determined only by the volume fraction of the hydrocarbon moiety, irrespective of whether the material is a blend or a pure compound. Moreover, we find that above a certain fraction of the short-chain component, a transition appears from the low-temperature lamellar phase with triple layers of fullerene (L_T) to a high-temperature phase containing quadruple fullerene layers (L_Q). The L_Q phase has an isotropization temperature 50–80 K higher than the L_T phase. The behaviour of crystal melting suggests that there is a preference for the longer-chain component to occupy the outermost of the three fullerene layers of the L_T phase. The extra-large lamellar thickness observed specifically in a 6 : 4 blend of C₆₀-4 and C₆₀-16 suggests the existence of a new superlattice with a structure yet to be determined. Our studies on the liquid crystalline binary blends provide a facile way to adjust the cross-sectional ratio of C₆₀ and the hydrocarbon moiety, and deliberately tailor the desired level of cross-sectional mismatch. This in turn is likely to lead to further unusual soft matter self-assembly modes when adoption of interfacial curvature is not a solution for such a mismatch.