Quenching of lamellar ordering in an n-alkane embedded in nanopores

TL;DR

This study investigates how nonadecane molecules behave when confined in nanopores, revealing that lamellar ordering is suppressed but phase transitions remain similar to bulk, including a rotator phase.

Contribution

It demonstrates that confinement in nanopores disrupts lamellar ordering in alkanes while preserving phase transition behavior, including the emergence of a rotator phase.

Findings

Lamellar ordering is quenched in confined nonadecane.

Phase transition sequence resembles bulk behavior.

A rotator phase appears in confinement, not in bulk.

Abstract

We present an X-ray diffraction study of the normale alkane nonadecane C_{19}H_{40} embedded in nanoporous Vycor glass. The confined molecular crystal accomplishes a close-packed structure by alignment of the rod-like molecules parallel to the pore axis while sacrificing one basic principle known from the bulk state, i.e. the lamellar ordering of the molecules. Despite this disorder, the phase transitions observed in the confined solid mimic the phase behavior of the 3D unconfined crystal, though enriched by the appearance of a true rotator phase known only from longer alkane chains.