A diffusionless transition in a normal alkane

The normal alkanes are an interesting class of material, both in terms of their intrinsic properties and because many biological materials contain hydrocarbon domains. The normal alkanes often exhibit complicated phase behavior, with phase diagrams containing multiple solid phases. We report here a study of a curious pattern of twinned domains seen in one phase of tricosane (C23H48), which we have studied by X-ray diffraction, as well as by optical and atomic force microscopy. This pattern is seen in the rotator RV phase, a monoclinic arrangement of tricosane molecules without orientational order. Transitions between this polymorph and the orthorhombic RI rotator phase lying at higher temperatures preserve features at the molecular level, and thus represent a diffusionless, martensitic-like transformation.