Molecular Design of a Chiral Oligomer for Stabilizing a Ferrielectric Phase

Abstract

Appearance of ferroelectricity and antiferroelectricity in chiral tilted smectic phases is an interesting phenomenon. It is not only attractive for use in applications to fast-response displays (Goodby et al., 1991; Walba, 1995); it also attracts fundamental interest related to synclinic or anticlinic ordering of the molecules (Lagerwall & Giesselmann, 2006; Lemieux, 2007; Nishiyama, 2010). The frustration between synclinic-ferroelectricity and anticlinicantiferroelectricity in chiral smectic C phases causes temperature-induced successive phase transitions (Fukuda et al., 1994; Inui et al. 1996; Isozaki et al., 1993; Matsumoto et al., 1999; Osipov & Fukuda, 2000; Sandhya et al., 2009; Takezoe et al., 2010). When ferroelectric and antiferroelectric phases have equal free energy, intermediate ferrielectric sub-phases with a degenerated energy level can appear between ferroelectric and antiferroelectric phases. At the outset of disclosing antiferroelectric SmC*A phase in MHPOBC, three other SmC*-like phases were observed (Chandani et al., 1989a). These phases were designated as SmC*α, SmC*β, and SmC*γ in order of decreasing temperature (Chandani et al., 1989b), the SmC*β phase was regarded as the oridinary ferreoelectric SmC* phase. Gorecka et al. soon proved that SmC*γ is a ferrielectric phase (Gorecka et al., 1990). Isozaki et al. confirmed that an antiferroelectric subphase might emerge between SmC*β, and SmC*γ phases (Isozaki et al., 1992, 1993). Mach et al. reported the first direct structural observation of distinct multilayer periodicities of the subphases using resonant X-ray scattering (March et al., 1998, 1999). They confirmed three-layer and four-layer periodicities, respectively, in what they called Ferri 1 and Ferri 2 phases. Nguyen et al. identified the Ferri 1 as SmCγ* (Nguyen et al., 1994). The Ferri 2 phase was found to have antiferroelectric characteristics (Aoki et al., 1999). Later, the SmC*β of MHPOBC was identified as Ferri 2 phase (Gorecka et al., 2002). At least two ferrielectric phases consisting of three-layer and four-layer unit cells exist. Other ferrielectric subphases induced by successive phase transition have been observed. Fukuda et al. proposed that the subphases are represented as SmC*A(qT), where qT = F/(A+F) (Isozaki et al., 1993). In those equations, F denotes the number of synclinic layers in one periodicity: A represents the number of anticlinic layers in one periodicity. Figure 1 presents illustrations of antiferroelectric phase SmC*A (0), ferrielectric subphase SmC*A (1/3), antiferroelectric-like ferrielectric subphase SmC*A (1/2), and ferroelectric phase SmC*A (1). Some theoretical and experimental studies have been undertaken to explain the appearance of ferrielectric phases (Cepic & Zeks, 2001; Cepic et al., 2002; Fukuda et al., 1994; Johnson et al., 2000; Matsumoto et al., 1999; Osipov & Fukuda, 2000; Yamashita & Miyajima, 1993).