Rotational entropy driven separation of alkane/isoalkane mixtures in zeolite cages

(Figure Presented) Yanking chains and rattling cages: Depending on their radius of gyration, molecules either retain or lose their ability to rotate inside zeolite cages (see picture). Such differences in rotational adsorption entropy result in a preferential uptake of branched alkanes over their linear structural isomers in zeolites such as MCM-22 which allows the separation of the two types of molecules.