Structural transformations of even-numbered n-alkanes confined in mesopores

TL;DR

This study investigates how even-numbered n-alkanes behave structurally when confined in mesopores, revealing phase sequences and new mesophases not seen in bulk states, with implications for understanding confined molecular systems.

Contribution

It provides detailed analysis of phase behavior and structural transformations of C12, C14, and C16 n-alkanes confined in mesoporous Vycor glass, highlighting new mesophases and phase sequence modifications.

Findings

C12 reproduces bulk liquid-triclinic phase sequence with hysteresis.

C16 exhibits an orthorhombic rotator mesophase absent in bulk.

C14 shows phase transition behavior dependent on cooling or heating.

Abstract

The n-alkanes C12H26, C14H30, and C16H34 have been imbibed and solidified in mesoporous Vycor glass with a mean pore diameter of 10nm. The samples have been investigated by x-ray diffractometry and calorimetric measurements. The structures and phase sequences have been determined. Apart from a reduction and the hysteresis of the melting/freezing transition, pore confined C12 reproduces the liquid-triclinic phase sequence of the bulk material, but for C16 an orthorhombic rotator mesophase appears that in the bulk state is absent for C16 but well known from odd numbered alkanes of similar length. In pore confined C14 this phase shows up on cooling but not on heating.