Unconventional Properties in Bent-Core Nematics Exhibiting Room
Temperature Cybotactic Order
F. Vita,1,* M. Laus,2 N. Scaramuzza,3 E. Scharrer,4 E. T. Samulski,5 and O. Francescangeli1
1 Dipartimento SIMAU, Università Politecnica delle Marche and CNISM, Ancona, Italy
2 Dipartimento DISIT, Università del Piemonte Orientale “A. Avogadro” and INSTM, Alessandria, Italy
3 Dipartimento di Fisica, Università della Calabria, CNR-IPCF, Licryl Laboratory, and Centro di Eccellenza
CEMIF.CAL, Rende (CS), Italy
4 Department of Chemistry, University of Puget Sound, Tacoma, Washington, USA
5 Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina, USA
In recent years the nematic (N) phase of bent-core mesogens (BCMs) has attracted a growing interest
because of its potentially biaxial[1,2] and polar[3] nature, as well as for a series of other unconventional
properties, such as extraordinary field-induced effects.[4,5] It is now widely recognized that all of these
features result from a peculiar short-range molecular arrangement: indeed, X-ray diffraction (XRD)
experiments have demonstrated that the BCM N phase is composed of nanometer-sized clusters of
molecules (cybotactic groups),[6] exhibiting a relatively high degree of internal order, positional (smectic)
as well as orientational (biaxial, and possibly polar).
Here we provide an overview of our most recent research on this topic. In particular, we report the
structural characterization and related properties of two classes of oxadiaziole-based BCMs: a series of
low molar mass BCMs with lateral substituents[7] and a main chain liquid crystal polymer with bent-core
repeat unit.[8] Both types of compounds exhibit cybotactic order (revealed by a typical four-spot smallangle XRD pattern), which can be supercooled down to room temperature in a glassy N phase. As most
BCMs typically show the N phase at about 200 °C, lowering the working temperature range of these
compounds is an important step towards their technological exploitation. Moreover, the two materials
show other interesting properties: on the one hand, the splitting of the wide-angle XRD pattern in low
molar mass compounds, unprecedented in nematic BCMs, represents the first XRD evidence of biaxial
order, at least on the short-range length scale; on the other hand, electric measurements performed on the
polymeric compound hint at a ferroelectric-like switching response that, albeit to be definitely confirmed
by complementary techniques, is strongly supported by comparative repolarization current measurements
in the nematic and isotropic phases.
References:
[1] L.A. Madsen, T.J. Dingemans, M. Nakata, E.T. Samulski, Phys. Rev. Lett., 92 (14): 14505 (2004).
[2] B. Acharya, A. Primak, S. Kumar, Phys. Rev. Lett., 92 (14): 145506 (2004).
[3] O. Francescangeli, V. Stanic, S. I. Torgova, A. Strigazzi, N. Scaramuzza, C. Ferrero, I. P. Dolbnya,
T. M. Weiss, R. Berardi, L. Muccioli, S. Orlandi, C. Zannoni, Adv. Funct. Mater., 19: 2592–2600
(2009).
[4] O. Francescangeli, F. Vita, F. Fauth, E. T. Samulski, Phys. Rev. Lett., 107: 207801 (2011).
[5] F. Vita, I. F. Placentino, C. Ferrero, G. Singh, E. T. Samulski, O. Francescangeli, Soft Matter, 9:
6475-6481 (2013).
[6] O. Francescangeli, F. Vita, C. Ferrero, T. Dingemans, E.T. Samulski, Soft Matter, 7: 895–901 (2011).
[7] F. Speetjens, J. Lindborg, T. Tauscher, N. LaFemina, J. Nguyen, E.T. Samulski, F. Vita, O.
Francescangeli, E. Scharrer , J. Mater. Chem., 22: 22558–22564 (2012).
[8] F. Vita, K. Sparnacci, G. Panzarasa, I. F. Placentino, S. Marino, N. Scaramuzza, G. Portale, E. Di
Cola, C. Ferrero, S. I. Torgova, G. Galli, M. Laus, O. Francescangeli, ACS Macro Lett., 3: 91-95 (2014).
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* presenting author; E-mail: f.vita@univpm.it