Suppression of the Phase Separation in Binary n-Alkane Solid Solutions by Geometrical Confinement

The crystallization of binary n-alkane solid solution n-C18H38/n-C19H40 = 90/10 (molar ratio) (abbreviated as C-18/C-19 = 90/10) and the microencapsulated counterpart (abbreviated as m-C-18/C-19 = 90/10) has been investigated by a combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). The solid-solid phase separation was obviously detected in C-18/C-19 = 90/10 by XRD, which is absent in m-C-18/C-19 = 90/10. The XRD data also show that the chain packing of m-C-18/C-19 = 90/10 is different from that of bulk C-18/C-19 = 90/10. The packing mode of m-C-18/C-19 = 90/10 molecular chains is unique; i.e., the n-alkane chains pack along the longitudinal direction and the neighboring layers interdigitate with each other, subsequently resulting in the deconstruction of lamellar ordering. The extinction of phase separation in m-C-18/C-19 = 90/10 can be understood in terms of the suppression of longitudinal chain diffusion caused by the special three-dimensional confinement effect provided by microcapsules.