Mesoscopic Phase Behavior of Tridecane–Tetradecane Mixtures Confined in Porous Materials: Effects of Pore Size and Pore Geometry

Phase behaviors of tridecane–tetradecane ( n -C 13 H 28 –C 14 H 30, C 13 –C 14 ) system in bulk, and confined in SBA-15 and controlled porous glass (CPG) are investigated using differential scanning calorimetry and temperature-dependent X-ray diffraction. Bulk C 13 –C 14 mixtures exhibit a complicated behavior featuring a special rotator phase R I . Adsorbed in SBA-15 with pore diameters ( d ) of 3.8 and 7.8 nm, the binary mixtures display a melting boundary of a straight line and a curve, respectively. Within SBA-15 (17.2 nm) and CPG (8.1, 31.8, 46.4, and 300 nm), the mixtures show a similar phase behavior to the bulk, especially in the larger pore CPG than 30 nm. Under confinement, the phase behavior of C 13 –C 14 mixtures varies with the pore size as well as the temperature and composition. XRD analysis reveals that the solid alkane molecules take effectively the 2D closed-packed arrangements inside pores of diameters less than 20 nm. In the large pore CPG ( d > 30 nm), the alkane molecules regain lamellar ordering in solid states. Pore geometries of SBA-15 and CPG, one-dimensional channels vs three-dimensional connected pores, may also result in much different influence on the phase behavior of the confined mixtures.