Structure and Dynamics of Nonionic Surfactant Aggregates in Layered Materials

Overview & Synopsis

Aggregation of surfactants on solid surfaces as they are adsorbed from solution is the basis of numerous technological applications such as colloidal stabilization, ore flotation, or cleaning floors. The understanding of both the structure and the dynamics of surfactant aggregates for the development of alternative way of preparation of hybrid layered materials. For this purpose, we study the adsorption of the tri-ethylene glycol mono n-decyl ether (C10E3) nonionic surfactant onto a synthetic montmorillonite (Mt), an aluminosilicate clay mineral for organoclay preparation with important applications in materials sciences, catalysis, wastewater treatment, or as drug delivery. The aggregation mechanisms follow those observed in an analogous natural Mt, with the condensation of C10E3 in a bilayer arrangement once the surfactant self-assembles in a lamellar phase beyond the critical micelle concentration, underlining the importance of the surfactant state in solution. Solid-state 1 H nuclear magnetic resonance (NMR) at fast magic-angle spinning (MAS) and high magnetic field, combined with 1 H-13 C correlation experiments and different types of 13 C NMR experiments selectively probe mobile or rigid moieties of C10E3 in three different aggregate organizations: (i) lateral monolayer, (ii) lateral bilayer, and (iii) normal bilayer. High-resolution 1 H{ 27 Al} CP-1 H-1 H spin diffusion experiments shed light on proximities and dynamics of the dynamics of different fragments and fractions of the intercalated surfactant molecules with respect to the Mt surface. 23 Na and 1 H NMR measurements combined with complementary NMR data, at both molecular and nanometer scales, precisely pointed out the location C10E3 ethylene oxide hydrophilic group in close contact with Mt surface interacting through ion-dipole or Van der Waals interactions.