title: Strings-to-Rings Transition and Antiparallel Dipole Alignment in Two-Dimensional Methanols.
abstract: Structural order emerging in the liquid state necessitates a critical degree of anisotropy of the molecules. For example, liquid crystals and Langmuir monolayers require rod- or disc-shaped and long-chain amphiphilic molecules, respectively, to break the isotropic symmetry of liquids. In this Letter we present results from molecular dynamics simulations demonstrating that in two-dimensional liquids, a significantly smaller degree of anisotropy is sufficient to allow structural organization. In fact, the condensed phase of the smallest amphiphilic molecule, methanol, confined between two, or adsorbed on, graphene sheets forms a monolayer characterized by long chains of molecules. Intrachain interactions are dominated by hydrogen bonds, whereas interchain interactions are dispersive. Upon a decrease in density toward a gaslike state, these strings are transformed into rings. The two-dimensional liquid phase of methanol undergoes another transition upon cooling; in this case, the order-disorder transition is characterized by a low-temperature phase in which the hydrogen bond dipoles of neighboring strings adopt an antiparallel orientation.
authors.affiliation: Polymat & Department of Organic Chemistry I, University of the Basque Country UPV/EHU , Avenida de Tolosa 72, 20018 San Sebastian, Spain.|IKERBASQUE, Basque Foundation for Science, Maria Diaz de Haro 3, 48013 Bilbao, Spain.
authors.forename: Ronen
authors.initials: R
authors.lastname: Zangi
authors.affiliation: School of Mathematics and Physics, University of Lincoln , Brayford Pool, Lincoln LN6 7TS, U.K.|School of Engineering and Science, Jacobs University Bremen , Campus Ring 1, 28759 Bremen, Germany.
authors.forename: Danilo
authors.initials: D
authors.lastname: Roccatano
keywords: Two-dimensional system; amphiphilic molecules; fluids under confinement; order−disorder transition; self-organization