Suppression of the phase separation in binary n-alkane solid solutions by geometrical confinement.

The crystallization of binary n-alkane solid solution n-C(18)H(38)/n-C(19)H(40) = 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.