The orientational order of n-heptane molecules in the nematic phase and the smectic A (SmA) phase of the 4-heptyl-4'-cyanobiphenyl (7CB)-n-heptane binary system was investigated by H-2 NMR spectroscopy. The increase in the mobility of the alkyl chain region corresponding to an increase in the amount of n-heptane enhanced the micro-segregation of the core and the alkyl chain region and contributed to the formation of the SmA phase for this system. The actual amount of n-heptane molecule adsorbed in the SmA phase was assessed by H-2 and C-13 NMR for the coexistence state of the isotropic liquid and the SmA phase. (C) 2015 Elsevier B.V. All rights reserved.