Abstract
A number of new states of matter have been reported in recent years for liquid crystal dimers, most notably the twist-bend nematic phase which exhibits spontaneous breaking of symmetry through the emergence of chiral structures in an achiral fluid. In this communication we report on an unsymmetrical liquid crystal dimer that exhibits a transition from the spontaneously chiral twist-bend nematic phase into a novel smectic liquid crystal phase.
Highlights
The observation of a lower temperature mesophase lacking lamellar or positional molecular order (i.e. a nematic-like mesophase),[1] later identified as the ‘twist-bend nematic’ phase (NTB),[2,3,4,5,6,7,8,9,10] has motivated a great deal of study into the properties of this intriguing state of matter by a wide range of techniques.[11,12,13,14,15,16,17,18] In a typical nematic phase rod-like molecules are orientated, on average, parallel to one another along a vector termed the director, n (Fig. 1a)
The observation of spontaneous breaking of mirror symmetry in the twist-bend nematic phase leads to the emergence of helical nano-structures in an achiral fluid;[10,45,46] questions concerning the mechanism of this phenomenon are of fundamental importance to a range of scientific disciplines,[47,48,49,50,51] and are likely to motivate further study into the NTB phase for some time to come
Transition temperatures, along with associated enthalpies and entropies were determined by differential scanning calorimetry at a heat/cool rate of 10 °C min−1 and are the mean of 10 cycles; standard deviations are given in parenthesis
Summary
The observation of a lower temperature mesophase lacking lamellar or positional molecular order (i.e. a nematic-like mesophase),[1] later identified as the ‘twist-bend nematic’ phase (NTB),[2,3,4,5,6,7,8,9,10] has motivated a great deal of study into the properties of this intriguing state of matter by a wide range of techniques.[11,12,13,14,15,16,17,18] In a typical nematic phase rod-like molecules are orientated, on average, parallel to one another along a vector termed the director, n (Fig. 1a). The identification of the mesophase immediately below the nematic as the twist-bend nematic is straightforward due to its characteristic optical textures (Fig. 3) and the shape of the peak obtained in DSC thermograms (Fig. 2).[9] As discussed by Zhu et al.,[13] small-angle X-ray scattering can be used to discriminate between the experimentally observed NTB phase and the theoretically predicted splay-bend nematic, NSB, as the electron density modulation in the former does not lead to Bragg scattering whereas it is expected to in the later.
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