Experimental investigations of a new TGB(C) mesophase

We report on optical and structural X-ray studies on a smectic C twist grai n boundary phase (TGB(C)) of a pure liquid crystalline material. It is show n that this TGB(C) phase, which exists over a large range of temperature, i s definitely different from previously reported and predicted TGB(C) phases . The two main experimental features are: (i) the observation in planar geo metry 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(A)) or two (TGB(C)) sharp rings. We suggest a few possible tracks that can be explored to understand the complex structure of this new phase.