Surface Induced Hydrogen-Bonded Macrocluster Formation of Methanol on Silica Surfaces

Abstract

Recently, we have succeeded in identifying the structure of the adsorption layer of ethanol on a silica surface in cyclohexane to be a hydrogen-bonded linear aggregate (polymer), which we call a surface molecular macrocluster. In this work, we studied the effect of the miscibility of liquids on the formation of the surface molecular macroclusters for confirming that this is a surface induced phenomenon. We investigated the interaction and the structure of methanol adsorbed on a silica surface in methanol-cyclohexane binary liquids by a combination of colloidal probe atomic force microscopy, adsorption excess isotherm measurement, and FTIR spectroscopy using the attenuated total reflection (ATR) mode, and compared the results with those of the ethanol-cyclohexane and 1-propanol-cyclohexane binary liquids. The former system is immiscible at methanol concentrations of ca. 8-90 mol %, and the latter two are miscible at any composition. At 0.03 mol % methanol, which is far from the critical concentration for the phase separation, the contact of the methanol macrocluster layers formed on the silica surface brought about the attraction from a distance of 42 +/- 5 nm which was similar to that observed in ethanol-cyclohexane. At a methanol concentration of 9.0 mol %, above bulk phase separation, completely different force profiles were observed. These results demonstrated that the molecular macrocluster formation was different from the wetting induced by the bulk.

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

“…The mean adsorption layer thickness t = 14.1 ± 1.4 nm thus obtained agreed well with the value calculated based on the adsorption excess isotherm measurement 13.0 ± 2.7 nm [24]. One interesting point is that the measured attraction range was 6-7 nm longer than the attraction range obtained by fitting of Eq.…”

“…The shape of this long range interaction force profiles were similar to those observed in ethanol-cyclohexane as well as in 1-propanol-cyclohexane, indicating that the long range attraction was similarly caused by the contact of opposed adsorption layers and the short range repulsion was ascribed to a steric force caused by the overlap of structured layers [20][21][22]. This was confirmed by measuring the adsorption excess amount of methanol onto the glass surfaces [24]. At methanol concentration of 0.03-0.12 mol%, the methanol adsorption layer thickness was 13.0±2.7 nm, Dashed and solid lines in black represent the van der Waals force calculated using the non-retarded Hamaker constants of 3 × 10 −21 J for glass/cyclohexane/glass and 9 × 10 −21 J for glass/methanol/glass, respectively [30].…”

“…This indicated that the interfacial energy was generated between the bulk solution and the ethanol macrocluster layer, and the contact and overlap of the adsorption layers brought about the long range attraction to reduce the interface between the ethanol adsorption layer and bulk solution. Similar molecular macrocluster and long range attraction were also found for the 1-propanol and methanol on the silica surface in cyclohexane [23,24]. This indicated that the molecular macrocluster formation induced the interfacial energy between the alcohol adsorption layer and the bulk solution even for the alcohols completely miscible with cyclohexane.…”

More room for microphase separation: An extended study on binary liquids confined in SBA-15 cylindrical pores

“…The preferential segregation of the alcohol at the surface illustrates the amphiphilic character of TBA, supported by the observation of supramolecular clusters in the bulk TBA-TOL mixtures, 21 and the higher affinity of alcohol to silica, which was demonstrated by binary gas adsorption 22 and by the formation of interfacial H-bonded alcohol clusters in alcohol-alkane mixtures in contact with hydrophilic surfaces. [23][24][25][26][27] 4…”

The interaction of patterned solutes in binary solvent mixtures

“…1, 2 The closer the mixture is to demixing coexistence, the larger the separation at which surface-induced demixing can occur. 1, 2 The closer the mixture is to demixing coexistence, the larger the separation at which surface-induced demixing can occur.…”