Phase behavior of dodecane–hexadecane mixtures in bulk and confined in SBA-15

Phase behaviors of dodecane–hexadecane ( n -C 12 H 26 –C 16 H 34 , C 12 –C 16 ) binary mixtures in bulk and confined in SBA-15 (pore diameters 3.8, 9.5, and 17.2 nm) are investigated using differential scanning calorimetry. According to the thermal analysis, the bulk mixtures belong to a system of partial miscibility with two solid solutions and a eutectoid in the range of mole fraction \( x_{{{\text{C}}_{ 1 6} }} \)  = 0.1–0.8. Under confinement, phase behavior of C 12 –C 16 mixtures is distinct from the bulk. Inside pores of SBA-15 (3.8 nm), the solid mixtures has only a melting boundary. In the pores larger than 9.5 nm, phase behaviors of the mixtures show some resemblance to the bulk system. The growth of the phase diagram with the pore diameter clearly shows the size effect on the phase behavior of the confined mixtures. In comparison with those of chain length difference of pure components of two carbon atoms or less, C 12 –C 16 mixtures exhibit different phase behaviors not only in the bulk but also in the confined state.