Abstract
Although the alkyl-bicyclohexyl-carbonitrile compounds supposed to be chemically stable, an aging behaviour was observed which strongly influences the growth of smectic B germs in the undercooled nematic phase. The aging also results in a broadening of the phase coexistence temperature ranges and in a saturating shift of phase transition temperatures with a temperature dependent dynamics. The phenomenon has been characterized by polarizing microscopy and DSC, and an experimental evidence has been given that the air atmosphere is responsible for the thermally induced ageing.