Spontaneous Director Rotation in Freely Suspended Ferroelectric Liquid-Crystal Films

A novel, striped texture corresponding to a continuous in-plane rotation of the molecular director on the smectic tilt cone has been observed in freely suspended ferroelectric smectic C liquid-crystal films using polarized light microscopy. It is proposed that surface splay domains at the edge of an existing film impose a cycloidal director structure on adjacent interior layers which can then flow onto the film, spontaneously forming a striped, one-dimensional π-wall array extending over several square mm. The response of the array to a slowly increased in-plane electric field is initially normal but above a threshold of E ≈ 4 V/3 mm an unexpected instability sets in and the π-walls acquire transverse ripples.