Sains Malaysiana 43(1)(2014): 145–150

Direction of Flexoelectric Polarization in Smectic C*G Phases of Chiral Smectic

Liquid Crystals

(Arah Pengutuban Fleksoelektrik dalam Fasa Smektik C*G bagi Hablur Cecair Khiral Smektik)

TENG YONG TAN & LYE HOCK ONG*

School of Physics, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia

Diserahkan: 10 Disember 2012/Diterima: 14 Mac 2013

ABSTRACT

Polarization in antiferroelectric liquid crystals has two origins: The piezoelectric polarization which is of chiral origin and the flexoelectric polarization which originates in different orientation of tilts in neighboring layers. The flexoelectric polarization is perpendicular to the tilt direction only if the structure is uniformly helicoidally modulated. In structures like SmC*F11 and SmC*F12 the flexoelectric contribution might be significant and it can be non-parallel to the piezoelectric component. Hence it may deviates the direction of polarization from the perpendicular direction significantly. The angle formed by the polarization and the tilt is therefore general and as such the basic characteristic of the SmC*G phase can be recognized. It seems that this aspect was completely overlooked in the past. In this contribution we analyze the dependence of the polarization direction on the phase structures and on the values of piezoelectric and flexoelectric coefficients in the discrete phenomenological model.

Keywords: Antiferroelectric liquid crystals; general tilt phase; multilayer structure

ABSTRAK

Pengkutuban di dalam hablur cecair antiferoelektrik berasal daripada dua sumber berikut: pengkutuban piezoelektrik yang berasal daripada sifat khiralnya dan pengkutuban fleksoelektrik yang berasal daripada 'tilt-tilt' di dalam lapisan terdekat yang berada dalam orientasi yang berbeza. Pengkutuban fleksoelektrik adalah berserenjang kepada arah 'tilt' sahaja jika struktur yang dikaji berbentuk 'kelopak bunga' yang seragam. Dalam struktur seperti Sm*F11 dan SmC*F12, penyumbangan fleksoelektrik mungkin ketara dan ia adalah tidak selari kepada komponen piezoelektrik. Maka, ia mungkin menyimpangkan arah pengkutuban daripada arah berserenjang secara ketaranya. Sudut yang dibentuk daripada pengkutuban dan 'tilt' ini adalah dikatakan secara am dan ciri asal fasa SmC*G boleh dikenal pasti. Aspek ini tidak diambil kira sebelum ini. Dalam kertas ini, kami menganalisis arah pengkutuban dalam struktur tersebut berdasarkan pergantungan nilai parameter piezoelektrik dan fleksoelektrik dengan menggunakan model fenomenologi diskrit.

Kata kunci: Fasa 'tilt' am; hablur cecair antiferoelektrik; struktur berbilang lapis

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*Pengarang untuk surat-menyurat; e-mail: onglh@usm.my