Phase transition from focal conic to cubic smectic blue phase in partially fluorinated cyano-phenyl alkyl benzoate ester doped with ultrahigh twisting power chiral dopant

Abstract

Blue phase liquid crystal (BPLC) has important applications in adaptive lenses and phase modulators due to its polarization-independent property. During our efforts for development of the new materials, we found a novel phenomenology of phase transition, from focal conic smectic to smectic blue phase in a partially fluorinated cyanophenyl alkyl benzoate ester based nematic liquid crystal (LCM-5773) doped by ultra-high twisting power [H.T.P~160 um^-1] chiral dopant (R5011/3 wt%). Polarized optical microscopy (POM) investigations revealed focal conic and fan-shaped textures typical for columnar mesophases. These focal conic domains (FCDs) are squeezed under electric field and finally at a critical electric field they undergo a dark state. When the electric field is withdrawn, the FCDs are regrown in a one dimensional array with smaller domain size. Interestingly, we have observed the domain size of the FCDs can grow several times by decreasing the cooling rate (0.02 degrees(C)/min.) ten times without any change in the phase sequence. In blue phase (BP), we have observed curved platelet texture and grain boundaries filled by small platelets, which is completely different from conventional cholesteric BP. The blue phase platelet size (PLS) also increases significantly at low cooling rates. The thermal control of FCD and PLS size has increasing demand for the construction of devices with optimal performances.