Two new types of layered structures were found in binary mixtures of $n$-alkanes ranging from ${\mathrm{C}}_{122}{\mathrm{H}}_{246}$ to ${\mathrm{C}}_{294}{\mathrm{H}}_{590}$. At high temperatures a semicrystalline form is the stable phase, having a regular structure of alternating crystalline and amorphous layers. The two long-chain compounds are mixed in the crystalline layers and the amorphous layers consist of the surplus length of the longer chains. At lower temperatures a reversible transition occurs to a triple layer superlattice structure with a periodicity of up to 50 nm. These two new phases allow the existence of binary solid solutions of chains with a length ratio of up to 1.7 and a chain length difference of 100 ${\mathrm{CH}}_2$ groups.

• Received 23 November 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.4875