The structure of cetyltrimethylammonium bromide (CTAB) on Cab-O-Sil (M5) silica was studied as a function of the adsorbed amount with FTIR, X-ray, and differential scanning calorimetry (DSC) techniques.  FTIR showed that the relative amount of gauche conformers decreased; powder X-ray spectroscopy showed the gradual formation of more ordered structures; and DSC showed that the enthalpies of melting and freezing increased with increased adsorbed amounts of CTAB.  These studies were consistent with the initial adsorbed surfactant being rather disorganized, a bilayer being a bit more organized, and a semi-crystalline multilayer structure building in to a monoclinic bulk-like structure with increased absorbed amount.  The enthalpies for the multilayers were fit to an exponential dependence with a constant of 1.2 mg CTAB/m2 silica, on the order of the width of a bilayer.

Transition from surface to bulk behavior: CTAB on silica

244th National Meeting (2012)

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