Macrocluster Formation of Alcohol on Silica Surface in Cyclohexane: Analysis of Interfacial Energy between Adsorption Layer and Bulk Solution

Abstract

Recently, we have found that alcohols adsorbed on the silica surface in non-polar liquids (cyclohexane, etc.) form ordered structures extending to several tens of nanometer through hydrogen bonding between the surface silanol groups and the adsorbed alcohols as well as between the adsorbed alcohols. We call this structure the surface molecular macrocluster. Surface forces measurement has revealed that the long range attraction appears from distances about twice of the macrocluster layer thickness. The bridging of the adsorption layers brings about the long range attraction due to the interfacial energy between the adsorption layer of molecular macroclusters and the bulk solution. In this study, the interfacial energies (γ) between the methanol adsorption layer and the bulk solution were evaluated by analyzing the long range attraction as well as pull-off force in methanol-cyclohexane binary liquid mixtures. The interfacial energy (γ) was evaluated to be 7.2 ± 0.3 mN/m, which was more than 10 times larger than that for methanol/cyclohexane interface at the phase separation (0.6 mN/m). This larger interfacial energy should be caused by the rather fixed orientation of methanol molecules at the interface due to the ordered structure of methanol molecules in a macrocluster.

Solvation forces between molecularly rough surfaces

“…They proposed that the origin of these oscillations is primarily due to the ordered layering of water molecules at mica surfaces. Similar oscillations of the solvation pressure as a function of the film thickness have been found for various polar and non-polar solvents and complex fluids [5][6][7][8][9][10][11][12][13].…”

Characteristics, Chemical Modification Processes as well as the Application of Silica and its Modified Forms

“…Additionally, the surface of the silica can contain many hydrogen, alkaline metals or hydroxyl group atoms, depending on their origins (6). Silica gel -Possibility of attaching an aromatic adsorbent to the silica gel surface (25,26) Silica gel -Adsorption at a high acetone, benzene and chloroform temperature on the surface of the silica gel (27) Silica -The adsorption of 1-propyl alcohol and isopropyl alcohol was studied, on the surface of a cyclohexane mixture with the use of FTIR spectroscopy in ATR format (28). Isothermic adsorption showed adsorption similar to the amount of each alcohol, while FTIR spectroscopy showed the presence of hydrogen connectors between the surface of the silane groups and -OH 1-propanol groups.…”

Molecular Architecture Studied by the Surface Forces Measurement

“…The oriented OH group at the interface between the adsorption layer and cyclohexane, of which the mean orientation angle is 40 ± 4°from the surface normal in the case of ethanol, should contribute to the interfacial energy and thus the long-ranged attraction. The interfacial energy between the adsorbed ethanol layer and cyclohexane is calculated to be 3.3 ± 0.6 mN/m by fitting the force profiles . Methanol, ethanol, and 1-propanol exhibit the identical mean orientation angle within the experimental error; however, the dichromic ratio of the polymer OH peak of 2-propanol is quite different from the former three.…”