Crystalline-to-plastic phase transitions in molecularly thin n-dotriacontane films adsorbed on solid surfaces

Cisternas, EA; Corrales, TP; del Campo, V; Soza, PA; Volkmann, UG; Bai, MJ; Taub H.; Hansen, FY

Abstract

Crystalline-to-rotator phase transitions have been widely studied in bulk hydrocarbons, in particular in normal alkanes. But few studies of these transitions deal with molecularly thin films of pure n-alkanes on solid substrates. In this work, we were able to grow dotriacontane (n-C 32H66) films without coexisting bulk particles, which allows us to isolate the contribution to the ellipsometric signal from a monolayer of molecules oriented with their long axis perpendicular to the SiO2 surface. For these submonolayer films, we found a step in the ellipsometer signal at ∼331 K, which we identify with a solid-solid phase transition. At higher coverages, we observed additional steps in the ellipsometric signal that we identify with a solid-solid phase transition in multilayer islands (∼333 K) and with the transition to the rotator phase in bulk crystallites (∼337 K), respectively. After considering three alternative explanations, we propose that the step upward in the ellipsometric signal observed at ∼331 K on heating the submonolayer film is the signature of a transition from a perpendicular monolayer phase to a denser phase in which the alkane chains contain on average one to two gauche defects per molecule. © 2009 American Institute of Physics.

Más información

Título según WOS: Crystalline-to-plastic phase transitions in molecularly thin n-dotriacontane films adsorbed on solid surfaces
Título según SCOPUS: Crystalline-to-plastic phase transitions in molecularly thin n -dotriacontane films adsorbed on solid surfaces
Título de la Revista: JOURNAL OF CHEMICAL PHYSICS
Volumen: 131
Número: 11
Editorial: AIP Publishing
Fecha de publicación: 2009
Idioma: English
URL: http://scitation.aip.org/content/aip/journal/jcp/131/11/10.1063/1.3213642
DOI:

10.1063/1.3213642

Notas: ISI, SCOPUS