Adsorption Behavior of the Cetyltrimethylammonium Chloride Reverse Micelles on Porous Silica Gels

Abstract

The adsorption behavior of reverse micelles of cetyltrimethylammonium chloride (CTAC) onto porous silica gels of various pore sizes has been investigated. A decrease in the amount of CTAC in the reversed micellar bulk solution in chloroform/water added to the silica gel in a column was observed, indicating the CTAC adsorption onto the silica surface. The adsorption profile obtained showed a maximum of the adsorbed surfactant amount, where the point of surface saturation may be reached, beyond which the adsorption amount remained unchanged. The adsorption of CTAC was also dependent on the specific surface area of the silica gel used. These results suggest that a CTAC monolayer may be formed and completed on the silica surface. The adsorbed CTAC amount slightly decreased with increasing the water to surfactant molar ratio, R, in the reversed micellar bulk solution, although at R < 2 the CTAC adsorption remained constant with silica gels having larger pore diameters. Even in the presence of traces of water moisture in the bulk solution used for the CTAC adsorption, the adsorption of water on silica gel was also observed and the molar ratios, RG, of the water to surfactant adsorbed on different silica gels were almost unity, implying that the silica gel may tend to hold some of water molecules originally adsorbed on its surface. The adsorption of CTAC molecules appears to occur through the adsorbed water molecules, probably polarized at the silica surface, and a CTAC-water-silica nanointerface seems to be formed. The adsorbed water amount or RG also increased with an increase in R and on silica gels with larger pore diameters and a plateau was observed in the R range of 3 -4, beyond which an increase in RG occurred again. The water molecules present in the vicinity of the adsorbed CTAC and the silica surface may possess different properties at different R and RG values.

Adsorption Behavior of Curcumin onto Cetyltrimethylammonium Chloride Reverse Micelles Immobilized on a Glass Surface As Studied by Polarized Visible Attenuated Total Reflection Spectrometry with a Glass Slab Optical Waveguide

“…1.8 molecules nm -2 . 9 Thus, one molecule of curcumin might exist in about six molecules of CTAC in the CTAC monolayer. In summary, polarized visible ATR spectrometry with a glass SOWG revealed that curcumin adsorbed onto the CTAC reverse micelle-immobilized glass surface in two forms as shown in Fig.…”

“…[1][2][3][4][5] Fujiwara et al has intensively studied reverse micelles of cetyltrimethylammonium chloride (CTAC) and has successfully applied them for various chemiluminescence methods. [5][6][7][8] Moreover, the group has attempted the immobilization of the reverse micelles onto porous silica gels 9 as well as silica surface, where the stable structure of silica surface/water phase/CTAC/non-polar organic solvent was expected to be formed. It is assumed that the adsorption of the CTAC molecules may be caused by an electrostatic interaction between the positively charged CTAC head-groups and the silica surface covered with the water phase to form aggregates on the surface, and the CTAC hydrophobic hydrocarbon chains may orient away from the surface in the CTAC monolayer formed by the association of the surfactants.…”