Silica-surfactant interface

Figure 8.4 Schematic representation of the different types of silica-surfactant interface. Solvent molecules are not shown, except for the I °S° case (triangles) dashed lines correspond to H-bonding interactions. Reproduced with permission from [5 ]. Copyright (2002) American Chemical Society...

Some surfactants aggregate at the solid-liquid interface to form micelle-like structures, which are popularly known as hemimicelles or in general solloids (surface colloids) [23-26]. There is evidence in favor of the formation of these two-dimensional surfactant aggregates of ionic surfactants at the alumina-water surface and that of nonionic surfactants at the silica-water interface [23-26]. 

Penfold et al. [62] have also used neutron reflectivity to study the adsorption (structure and composition) of the mixed anionic/nonionic surfactants of SDS and C12E6 at the hydrophilic silica-solution interface. This is rather different case to the cationic/nonionic mixtures, as the anionic SDS has no affinity for the anionic silica surface in the absence of the Ci2E6. The neutron reflectivity measurements, made by changing the isotopic labelling of the two surfactants and the solvent, show that SDS is coadsorbed at the interface in the presence of the Ci2E6 nonionic surfactant. The variations in the adsorbed amount, composition, and the structure of the adsorbed bilayer reflect the very different affinities of the two surfactants for the surface. This is shown in Fig. 7, where the adsorbed amount and composition is plotted as a function of the solution composition. 

Samoshina, Y, Nylander, T, and Lindman, B., Cationic amphiphihe polyelectrolytes and oppositely charged surfactants at the silica-aqueous interface, Langmuir, 21,4490, 2005. 

DJ Neivandt. Co-adsorption of Polyelectrolytes and Surfactants at the Silica/ Solution Interface A Spectroscopic Study. University of Melbourne, 1998. 

Lee, E. M., Thomas, R. K., Cummins, P. G., Staples, E. J., and Penfold, J. 1989. Determination of the structure of a surfactant layer adsorbed at the silica/water interface by neutron reflection. Chem. Phys. Lett. 162 196. 

Tiberg, F. and Ederth, T., Interfacial Properties of nonionic surfactants and decane microemulsions at the silica water interface. An ellipsometry and surface force study, J. Phys. Chem. B, 104, 9689-9695 (2000). 

Pagac, E. S., Prieve, D. C. and Tilton, R. D., Kinetics and mechanism of cationic surfactant adsorption and coadsorption with cationic polyelectrolyte at the silica-water interface, Langmuir, 14, 2333-2342 (1998). 

Neivandt, D. J. in Co-adsorption of poly electrolytes and surfactants at the silica-solution interface A spectroscopic study, PhD thesis. (The University of Melbourne, Melbourne), (1998). 

Figure 24-14. Off-specular X-ray reflectivity patterns showing the time-dependent growth of the first order diffraction peak for mesophase silica-surfactant films grown at the surface of a dilute acidic solution with a TMOS/CuTABr molar ratio of (a) 10.87 and (b) 7.25. At the higher TMOS/CuTABr ratio the film grows at the surface by addition of silica-coated surfactant micelles so the diffraction peak becomes narrower as the domains grow into solution, and more intense as the interface is covered. At the intermediate TMOS/Cu TABr ratio the film grows by packing at the interface of mesostructured particles formed in the bulk solution so the peak widtii does not change, but the intensity increases as the interface is covered.

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