The Formation of Solid Monolayers of Linear Amines Adsorbed on Graphite from the Liquid

Abstract

Solid monolayer formation by all the linear amines from C6 to C16 adsorbed from their liquids to a graphite surface is demonstrated. Shorter homologues do not show such solid monolayer formation. The behavior is interpreted in terms of the competition between the alkyl chains, which favor solid monolayer formation, and the amine group, which does not. Nonylamine (C9) also shows evidence of a solid−solid phase transition in the monolayer prior to melting.

Crystalline Structures of Alkylamide Monolayers Adsorbed on the Surface of Graphite

“…For the odd amides, the low members of the series (C 5 and C 7 ) have a unit cell with pgg symmetry, and the molecules “flip” to p 2 symmetry as the chain length increases to C 9 and C 11 . This odd−even variation has also been observed before for other organic species, such as the structures of carboxylic acids and alkanes , and in the 2D melting points of amines …”

“…These weak interactions allow the influence of weak adsorbate−adsorbate interactions to be expressed and investigated. These adsorbed layers have been studied using several approaches including calorimetry, − adsorption isotherms, − X-ray and neutron scattering, − NMR, microscopy, and simulation studies . An overview of various systems and techniques used to study these physisorbed layers can be found in reviews published recently. , …”

Adsorption of Aldehydes on a Graphite Substrate: Combined Thermodynamic Study of C6−C13 Homologues with a Structural and Dynamical Study of Dodecanal

“…The two larger peaks (onset at approximately 270 and 285 K) are observed in the thermogram of the pure aldehyde alone and hence are attributed to bulk transitions (a solid−solid phase transition, typical in long-chain alkyl species, and the bulk melting point). The weaker peak at higher temperature (onset at approximately 317 K) is not present in the thermogram of the graphite nor the pure adsorbate; hence, we attribute this feature to the melting of a solid monolayer as observed for alkanes, – alcohols, , carboxylic acids, amines, amides, and other adsorbed materials confirmed by diffraction and other techniques. No additional peaks are observed that could be attributed to a solid−solid transition in the monolayer or a multilayer melting transition as seen in other systems. ,, …”

Bulk and Adsorbed Monolayer Phase Behavior of Binary Mixtures of Undecanoic Acid and Undecylamine: Catanionic Monolayers

“…Figure presents thermograms from acid/amine mixtures in the presence of graphite where the temperature region just above the bulk melting point is highlighted. The formation of solid monolayers of adsorbed pure carboxylic acids and pure amines has been reported previsously ,− , and confirmed by diffraction studies. Monolayers formed at high coverage (well above one equivalent monolayer), approximately 40 monolayers, coexist with bulk liquid.…”

“…The formation of solid monolayers that adsorb from the liquid to graphite have been observed for a wide variety of simple molecules including linear alkanes, − alcohols, − carboxylic acids, − and amines . Carboxylic acids have also been reported to adsorb solid monolayers from solution.…”