Crystallization of medium length 1-alcohols in mesoporous silicon: An X-ray diffraction study

TL;DR

This study investigates how medium-length 1-alcohols crystallize within mesoporous silicon, revealing specific orientation states and lamellar structures in 15 nm pores, with growth mechanisms similar to single-crystal formation techniques.

Contribution

It provides new insights into the crystallization behavior and orientation states of 1-alcohols in mesoporous silicon, highlighting the influence of pore size on structure formation.

Findings

Six discrete orientation states observed

Lamellar structures form in 15 nm pores

Growth mechanism resembles Bridgman technique

Abstract

The linear 1-alcohols n-C16H33OH, n-C17H35OH, n-C19H37OH have been imbibed and solidified in lined up, tubular mesopores of silicon with 10 nm and 15 nm mean diameters, respectively. X-ray diffraction measurements reveal a set of six discrete orientation states (''domains'') characterized by a perpendicular alignment of the molecules with respect to the long axis of the pores and by a four-fold symmetry about this direction, which coincides with the crystalline symmetry of the Si host. A Bragg peak series characteristic of the formation of bilayers indicates a lamellar structure of the spatially confined alcohol crystals in 15 nm pores. By contrast, no layering reflections could be detected for 10 nm pores. The growth mechanism responsible for the peculiar orientation states is attributed to a nano-scale version of the Bridgman technique of single-crystal growth, where the dominant growth direction is aligned parallelly to the long pore axes. Our observations are analogous to the growth phenomenology encountered for medium length n-alkanes confined in mesoporous silicon (Phys. Rev. E 75, 021607 (2007)) and may further elucidate why porous silicon matrices act as an effective nucleation-inducing material for protein solution crystallization.