Isotropic–nematic–smectic: importance of being flexible

We represent a comprehensive discussion of the effect of chain flexibility on the isotropic–nematic and nematic–smectic phase transitions, based on the notion about the individual chain conformations in the nematic phase. Our approach yields “back-of-the-envelop” explanations for several universal features of these phenomena, such as weaker IN transition and much stronger NS transition for semi-flexible chains than for rigid rods.