Structure and Dynamics of Nonionic Surfactant Aggregates in Layered Materials

Abstract

The 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, and floor cleaning. The understanding of both the structure and the dynamics of surfactant aggregates applies to the development of alternative ways of preparing hybrid layered materials. For this purpose, we study the adsorption of the triethylene glycol mono n-decyl ether (CE) 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 CE 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 H nuclear magnetic resonance (NMR) at fast magic-angle spinning (MAS) and high magnetic field combined withH-C correlation experiments and different types of C NMR experiments selectively probes mobile or rigid moieties of CE in three different aggregate organizations: (i) a lateral monolayer, (ii) a lateral bilayer, and (iii) a normal bilayer. High-resolution H{Al} CP-H-H spin diffusion experiments shed light on the proximities and dynamics of the different fragments and fractions of the intercalated surfactant molecules with respect to the Mt surface. Na andH NMR measurements combined with complementary NMR data, at both molecular and nanometer scales, precisely pointed out the location of the CE ethylene oxide hydrophilic group in close contact with the Mt surface interacting through ion-dipole or van der Waals interactions.

Competitive Association of Antibiotics with a Clay Mineral and Organoclay Derivatives as a Control of Their Lifetimes in the Environment

“…These layered materials show a large specific surface area, ion-exchange capacities, and outstanding hydration properties, leading to an exfoliation of the nanosheets that can even self-assemble in liquid crystalline phases. 22 − 26 Their association as holding or carrier mineral phases with pharmaceuticals and other pollutants represents a possible vector of diffusion acting as a potential “time bomb” of pollution, with an easy release or remobilization of the pollutants after a change of the environmental conditions (pH, temperature, or electrolytes) along effluents.…”

Phenolic acids interactions with clay minerals: A spotlight on the adsorption mechanisms of Gallic Acid onto montmorillonite

“…Since GA is mainly neutral at pH < pKa as explained before, its adsorption should be driven through physisorption mechanisms such as molecular interaction (ππ interaction, van der Waals forces) with the prior adsorbed molecules and by coordinative bonding through inorganic exchangeable cations located within the interlayer space and with the carboxylic moieties as both FT / IR and XRD data highlighted. A recent work stressed out the importance of ion-dipole interaction (a coordinative bonding mechanism) as the main driving force for the adsorption of nonionic surfactants (Guégan et al, 2017) onto a Mt surface and can be according to previous studies in the literature (Sonon and Thompson, 2005;Deng et al, 2006) extended to nonionic compounds and here GA in its neutral form (Fig. 7).…”

Adsorption Mechanisms of Psychoactive Drugs onto Montmorillonite

“…Moreover, the adsorption isotherms were wellfitted by the Langmuir equation in this pH condition and the E value was > 8 kJ.mol -1 ( Table 2). As a result, it is possible that a significant proportion of OXA is protonated under these pH conditions, contrary to chemical database information, or more probably that neutral OXA was intercalated through ion-dipole interaction or some other mechanism [27]. At pH = 2.5, a significant part of OXA is protonated, resulting in the possible intercalation within Na-Mt layers through cation exchange.…”