Equilibrium and dynamical characteristics of Imidazole Langmuir monolayers on graphite sheets

RODRIGUEZ, JAVIER; ELOLA, MARÍA DOLORES; LARIA, DANIEL

JOURNAL OF PHYSICAL CHEMISTRY B - (Print)

AMER CHEMICAL SOC

Lugar: Washington; Año: 2015 vol. 119 p. 9123 - 9128

1520-6106

Using molecular dynamics techniques, we examine structural and dynamical characteristics of liquid-like, Imidazole(Im) monolayers physisorbed onto a planar graphite sheet, at T = 384K. Our  simulations reveal that molecular orientations in the saturated monolayer exhibit a bistable distribution, characterized by an inner parallel arrangement of the molecules in close contact with the substrate and a slanted alignment, in those lying in adjacent, outer locations. Compared to the results  found in three dimensional, bulk phases, the analysis of the spatial correlations between sites participating in hydrogen bonding shows a clear enhancement of the intermolecular interactions, which also leads to stronger dipolar correlations. As a result, the gross structural features of the   monolayer can be cast in terms of mesoscopic domains, comprising units articulated via winding hydrogen bonds, that persist along  typical time intervals of a few tens of picoseconds.  On the dynamical side, a similar comparison of the characteristic decorrelation time for orientational motions shows a 4-fold increment.  Contrasting, the reduction of the system dimensionality leads to a larger diffusion constant. Possible substrate-induced anisotropies in the diffusive motions are also investigated.