Experimental investigations of a new TGB<Subscript>C</Subscript> mesophase

We report on optical and structural X-ray studies on a smectic C twist grain boundary phase (TGB<Subscript>C</Subscript>) of a pure liquid crystalline material. It is shown that this TGB<Subscript>C</Subscript> phase, which exists over a large range of temperature, is definitely different from previously reported and predicted TGB<Subscript>C</Subscript> phases. The two main experimental features are: (i) the observation in planar geometry of an optical texture exhibiting a square grid pattern, and (ii) the detection of a broad Bragg ring in reciprocal space instead of one (TGB<Subscript>A</Subscript>) or two (TGB<Subscript>C</Subscript>) sharp rings. We suggest a few possible tracks that can be explored to understand the complex structure of this new phase. Copyright Società Italiana di Fisica, Springer-Verlag 1999