Probing helical structures in liquid crystals with resonant soft x-ray scattering at carbon edge*

We report the first in-situ measurement of the helical pitch in nanofilament B4 phase, using resonant soft x-ray scattering at carbon resonant edge. A strong scattering peak was observed corresponding to $\sim$100 nm periodicity in layer orientation variation. The scattering is anisotropic due to the nano-filament helical structure and bond orientation sensitivity enabled by the linearly-polarized soft x-rays. In-situ measurements of the helical pitch as a function of temperature provide unique information on the B4 structure and the nature of the B2-B4 phase transition. This approach can be extended to other helical structures in liquid crystals and beyond.