Phase transition of docosane in nanopores

Confinement effect of nanopores on phase transition of docosane ( n -C 22 H 46 , C 22 ) is studied using differential scanning calorimetry (DSC) and temperature-dependent powdered X-ray diffractions (XRD). The bulk C 22 has a stable rotator phase R I and R II . In the pores of CPGs, SBA-15, C-SBA-15, KIT-6, and MCM-41, the transition temperatures of solid–solid ( T s ) and solid–liquid ( T m ) transitions of C 22 are depressed. The depression of the transition points (Δ T s , Δ T m ) has a linear relation with the reverse diameter. However, the Δ T m values seemingly show weak relation with the polarity of the pore walls but to vary with the pore dimensionality. According to XRD analysis, C 22 confined in CPG (11.5 nm) and SBA-15 (14.4 nm) present low temperature phase and rotator phase as the bulk, but the lamellar packing of molecules is heavily disturbed in the small pores.