Selective adsorption at graphite/hydrocarbon interfaces

Abstract

A study was made of adsorption of n -dotriacontane and n -butanol dissolved in n -heptane onto graphitized carbon black and various ground graphites having surface areas ranging from 5 to 700 m 2 g -1 . It was established that the adsorption of n -dotriacontane by the graphites is confined entirely to the basal planes of graphite crystals. This is attributed to a remarkable fit between the hydrogen atoms attached to one side of the zig-zag carbon chain in the normal paraffins and the centres of hexagons formed by the carbon atoms in the basal planes of the substrate. The longer the chain the more contacts it can form with the graphite surface and the more strongly it is adsorbed. More detailed studies of the adsorption of n -paraffins on ground graphites have shown that they form close-packed monolayers of horizontally disposed molecules on the basal planes. There is little further adsorption after the monolayers are complete. The heat of adsorption per molecule increases uniformly with the chain length reaching very high values for the normal paraffins having more than 30 carbon atoms. The formation of the close-packed layers has been used for the measurement of the proportion of basal plane surface in different types of graphites. n -Butyl alcohol also forms closely packed monolayers, but on the polar sites of graphites, which can be used for the estimation of their area. The basal plane and polar sites act independently in adsorption and their relative proportions characterize the adsorptive properties of graphites. Examination of graphite ground in n -heptane, which consists of plates of average area of several square micrometres and average thickness of 5 nm, shows that its surface consists predominantly of basal planes having a high adsorptive capacity for n -paraffins.

Surfactant Aggregates at Rough Solid−Liquid Interfaces

“…8,9 Interactions of surfactants with metallic surfaces have become important in the production of nanoparticles. [10][11][12] Traditionally, the adsorption behavior of surfactants has been studied by depletion methods [13][14][15][16][17][18] and streaming potential techniques. 16,19 More recently, experimental efforts applying ellipsometry, [20][21][22] optical reflectometry, 23,24 electrochemical methods, 9 quartz crystal microbalances, 25 and Fourier transform infrared spectroscopy 26 have added information about the dynamic properties of surfactant adsorption.…”

Intramolecular and Lattice Melting inn-Alkane Monolayers: An Analog of Melting in Lipid Bilayers

“…Intermediate-length n-alkane molecules [CH 3 -͑CH 2 ͒ n22 CH 3 ; 20 , n , 40] adsorbed on solid substrates are of interest as prototypical systems for the interfacial behavior of more complex polymers [1][2][3] and, in their own right, as model systems for studies of lubrication [4]. Considerable progress has been made over the last 30 years in thermodynamic studies of these films [5,6]; and, more recently, in determining their structure by scanning tunneling microscopy [7,8] and diffraction techniques [9,10]. In contrast, the interfacial dynamics of these prototypical molecules is less well understood [11,12].…”

Source of Image Contrast in STM Images of Functionalized Alkanes on Graphite: A Systematic Functional Group Approach

“…[7][8][9][10] Only a single monomolecular layer of alkanes absorbs onto highly ordered pyrolytic graphite surfaces at room temperature, and the measured heat of adsorption increases uniformly with the chain length (∼0.94 kJ/mol for each methylene unit), reaching 209 kJ/mol for dotriacontane (C 32 H 66 ). 10,11 There has been some debate about whether the alkane adsorption is driven by adsorbate-substrate interactions or by lateral intermolecular interactions, but recent evidence tends to point toward the latter. 12,13 These reproducibly prepared, ordered overlayers have proven to be very amenable to study with the STM.…”