Liquid Crystalline Soft Matter
X-ray diffraction pattern from a SmA phase aligned with the layer normal (and thus the director) in the vertical direction. This gives rise to two vertically separated sharp Bragg peaks at small angles (corresponding to the smectic layer distance of about 3nm). In the horizontal direction the scattering is diffuse, reflecting the liquid-like order within each smectic layer.
Smectic liquid crystals
While the most commonly employed thermotropic liquid crystals are nematic, exhibiting long-range orientational order but only regular liquid-like, short-range, positional order, smectic liquid crystals additionally feature 1D-positional order. The molecules organize into layers with quasi-long range positional order along the layer normal direction, as witnessed by sharp Bragg peaks in an x-ray diffraction pattern. Many types of smectic phase exist, denoted SmA, SmB, SmC and so on in historical order of their discovery. The most important smectic phase in terms of applications is the SmC phase and its variations (SmCa etc.), characterized by uniform tilting of the molecules within each smectic layer.
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