TWISTED HELICAL EFFECT ELECTRO-OPTICAL ELEMENT AND FERROELECTRIC LIQUID CRYSTAL COMPOSITION USED FOR THE SAME

Japanese Patent JP3768543

B2

PURPOSE: To provide a twisted helical ferroelectric liquid crystal element having high response and high contrast and to provide a ferroelectric liquid crystal compsn. to be used for the same. CONSTITUTION: A ferroelectric liquid crystal layer 15 having specified thickness is held between plural electrode plates 11, 12 at least one of which is transparent or translucent to constitute a twisted helical ferroelectric liquid crystal cell 10. By applying voltage on electrode plates 11, 12 through the layer, the optical anisotropy of the element can be changed. The ferroelectric liquid crystal which constitutes the layer shows a ferroelectric phase, while it shows a chiral nematic phase at a temp. higher than the temp. of the ferroelectric phase. In the ferroelectric phase, the pitch of natural helix of the ferroelectric liquid crystal is shorter enough than the thickness of the ferroelectric liquid crystal layer 15 of the element so that the ferroelectric liquid crystal has a helically oriented vector structure and has no stabilized surface. In the nematic phase, the pitch of natural helix of the ferroelectric liquid crystal is longer enough than the thickness of the ferroelectric liquid crystal layer 15 so that the layer 15 of the element can be easily oriented.