I've read literature in which the rationale behind their monolayer and bilayer surfactant modification for zeolites was solely based on the external cation exchange capacity (100% and 200% ECEC for monolayer and bilayer, respectively). However, there are also procedures indicating that monolayers are generated if concentrations used are less than the critical micelle concentration (CMC). Otherwise, the bilayers are formed at concentrations > CMC.
The reported CMC for HDTMA is 2.50 mmol/L in 1:4 EtOH-Water solvent system. Using the ECEC solely (0.142 mEq/ g zeolite), a 100% and 200% ECEC modification of 6 g adsorbent in 150 mL volume using the same solvent would require me 5.7 and 11.4 mM surfactant concentration. Both concentrations are higher than the CMC. Would both 100% and 200% ECEC provide me bilayer modifications?
Marvince John Araneta
The variety of structures of zeolites and zeolite-like materials leads to certain difficulties in their description. Therefore, this is the main problem for surfactant adsorption. The greatest surfactant adsorption occurs at a concentration >CMC. Therefore, it is necessary to make a surface tension isotherm in a surfactant dispersion with zeolite and maintain the lowest surface tension when selecting the surfactant concentration.
yes, you have to take into account that not the starting but the equilibrium concentration of surfactant (after adsorption) rules the point at which you are at the adsorption isotherm.