Langmuir films of normal-alkanes on the surface of liquid mercury

Abstract

The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Kraack, H., B. M. Ocko, Peter S. Pershan, E. Sloutskin, and M. Deutsch. 2003. Langmuir films of normal-alkanes on the surface of liquid mercury.The coverage dependent phase behavior of molecular films of n-alkanes (CH 3 CH nϪ2 CH 3 , denote Cn) on mercury was studied for lengths 10рnр50, using surface tensiometry and surface x-ray diffraction methods. In contrast with Langmuir films on water, where roughly surface-normal molecular orientation is invariably found, alkanes on mercury are always oriented surface-parallel, and show no long-range in-plane order at any surface pressure. At a low coverage a two-dimensional gas phase is found, followed, upon increasing the coverage, by a single condensed layer (n р18), a sequence of single and double layers (19рnр20; nу26), or a sequence of single, double, and triple layers (22рnр24). The thermodynamical and structural properties of these layers, as determined from the measurements, are discussed.

Langmuir Films of Anthracene Derivatives on Liquid Mercury I: Symmetric Molecules

“…[8][9][10][11]13 Thus, only a brief description will be given here. The surface thermodynamics were explored using surface pressure π-molecular area A isotherms.…”

Temperature dependence of the structure of Langmuir films of normal-alkanes on liquid mercury

“…As in previous experiments, 8,9,12 the trough was cleaned carefully, and then its enclosure was flushed with a pure inert gas ͑He or N 2 ) for about 1 h. Mercury was introduced from a reservoir through a capillary under the inert atmosphere. The isotherm was then measured by stepwise deposition of measured amounts of the standard solution using a calibrated micropipette, waiting after each step until an equilibrium surface pressure was reached.…”

“…To investigate the role of the molecule's headgroup and tail interactions with the subphase in the determination of the Langmuir film's structure, we have studied the structure of Langmuir films of fatty acids, [8][9][10] alcohols, 11 and alkanes 12 on mercury, using x-ray and surface tension methods. In addition to phases with standing-up molecules, similar to those on aqueous surfaces, a variety of phases comprising surfaceparallel-oriented molecules were found, exhibiting different types of order ranging from a complete disorder to unidirectional liquid-crystal-like order to two-dimensional crystalline order.…”

“…In particular, alkanes, which lack a polar headgroup, exhibit a number of lying-down phases, all of which are found to be disordered in the surface-parallel direction and ordered only in the surface-normal direction. Clearly, the high adsorption energy of the chain onto the mercury surface, ⌬H ads Ӎ5.4 kJ/(mol of CH 2 ), 12 is the main driving force for the molecular orientation, while the interchain interaction, and the methyl-methyl headgroup interaction are too weak to induce in-plane ordering. to consist of single layer ͑SL͒, double layer ͑DL͒, and triple layer ͑TL͒ of surface-parallel molecules, depending on coverage and molecular length.…”

“…to consist of single layer ͑SL͒, double layer ͑DL͒, and triple layer ͑TL͒ of surface-parallel molecules, depending on coverage and molecular length. 12 A projection of the phase diagram at room temperature, Tϭ23°C, on the (n,) plane is given in Fig. 1, showing the lying-down phases found.…”