Antiferroelectric siloxane liquid crystal dimers with large molecular tilt under an applied electric field

Artikel i vetenskaplig tidskrift, 2005

The scope of the present study is the response of a series of antiferroelec. dimeric or bi-mesogenic siloxanes to an applied elec. field with focus on their pretransitional behavior and the field-induced antiferro-ferroelec. (AF-F) transition. Most of these compds. possess a mol. tilt close to 45 Deg and spontaneous polarization in the field-induced ferroelec. (F) phase in the range of 250-300 nC cm-2. In the dimers with a spacer length exceeding five carbons, a transformation from first to second order of the field-induced AF-F transition is found with temp. Several different indications for this transformation are identified and their characteristics are discussed in the framework of the existing theor. models. A large field-induced in-plane deviation of the sample optic axis was obsd. in the pretransitional region of several of the siloxane dimers and is likely due to the flexibility of the linking chains. The potential of the antiferroelec. bimesogenic siloxanes for displaying high contrast images and gray scale capability is shortly discussed. The large mol. tilt close to 45 Deg in combination with the field-induced AF-F transition of second order seems to be the most attractive features of these materials.