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Strings-to-Rings Transition and Anti-parallel Dipole Alignment in Two-Dimensional Methanols

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Ronen Zangi and Danilo Roccatano

Nano Lett. 2016, DOI: 10.1021/acs.nanolett.6b00460

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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/disc-shaped and long chain amphiphilic molecules, respectively, to break the isotropic symmetry of liquids. In this paper, 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 form a monolayer characterized by long chains of molecules. Intra-chain interactions are dominated by hydrogen bonds, whereas inter-chain interactions are dispersive. Upon a decrease in density toward a gas-like 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 anti-parallel orientation.

Profile photo of Danilo Roccatano

Author: Danilo Roccatano

Danilo Roccatano received his PhD in chemistry in 1997 at the University of Rome “La Sapienza”, Italy. From 1996, he worked as a postdoc in the group of Prof. H.J.C. Berendsen at the Chemistry department of the University of Groningen in the Netherlands. In 2001, he moved back in his home country with a research associate fellowships, first at the University of Rome “La Sapienza” and later at the University of L’Aquila. In 2003, he started a position of senior research associate position in Germany at the International University Bremen. In July 2005, he was promoted to Lecturer, and, later in 2009, he got the assistant professor position in Biochemical Engineering at the same university (then renamed as Jacobs University Bremen). Since then, he is leading a computational chemistry and biochemistry group, which attracted funding and students from different Germany national research agencies (DFG, BMBF, DAAD), EU, and biotech companies (EVONIK, BASF, BRAIN). In October 2015, he started a Senior Lecturer position in the School of Mathematics and Physics of the University of Lincoln.

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