By means of high-resolution calorimetry, we studied thermodynamic properties of the liquid-crystal $B_4$ phase where bent-core molecules form a helical nanofilament structure. Distinctive thermal behavior characterizing the growth process of the $B_4$ phase was obtained in undergoing the phase transition with many sharp peaks, indicating a highly heterogeneous structure. It has been demonstrated that such unusual behavior is commonly seen for two types of rodlike molecules as well as for various mixture compositions. We speculate that mixture systems involve a nanoscale phase-separated structure due to the remarkable aggregation effect in the bent-core molecules and that the helical nanofilament structure independently grows in the isotropic state of rodlike molecules. We also propose that the asymmetry in viscoelastic property plays a role in yielding unusual behavior.

• Received 24 August 2011

DOI:https://doi.org/10.1103/PhysRevLett.107.237802