Surfactants layered double hydroxides

Adachi-Pagano, M., Forano, C. and Besse, J.-P. (2000). Delamination of layered double hydroxides by use of surfactants. J. Chem. Soc., Chem. Commun., 91. 

To summarise, amine modified layered double hydroxides have been successfully prepared via the anionic surfactant-mediated route but a considerable amormt of amino groups were protonated which hindered CO2 adsorption. After MEA extraction, the materials were exfoliated and lost their layered structure. Free amino groups were obtained through the ionic exchange between protonated amine group and ethanolamine. The CO2 adsorption capacity at 25 °C reached 1.39 mmol g and the amine efficiency was about 0.4. 

Nanoclays can be categorized into cationic and anionic types. Cationic nanoclays are based on smectite clays. An example is montmorillonite (MMT), a hydrated Al, Mg silicate that may contain cations such as Na+ and Ca++ between the anionic layers. In contrast, anionic clays contain cationic layers and anions such as Cr and in the interlayer space. Typical examples include layered double hydroxides (LDH) and hydrotalcite (HT), a mostly synthetic hydrated magnesium and aluminum carbonate salt. Whereas MMT is commonly used as a nanofiller to improve thermal, mechanical, and barrier properties, LDHs have many attractive properties that lead to application as surfactant adsorbents, biohybrid materials, antacid food formulations, acid neutralizers, and active pharmaceutical ingredients excipients [37, 13, 28, 14, 35]. 

P. C. Pavan, E. L. Crepaldi, and J. B. Valim, Sorption of anionic surfactants on layered double hydroxides. Journal of Colloid and Interface Science, 229 (2000), 346-52. 

L. Z. Qiu and B. J. Qu, Preparation and characterization of surfactant-free polystyrene/layered double hydroxide exfoliated nanocomposite via soap-free emulsion polymerization. Journal of Colloid and Interface Science, 301 (2006), 347-51. 

Crepaldi, E.L. Pavan, P.C. Valim, J.B. Anion exchange in layered double hydroxides by surfactant salt formation. 7. Mater. Chem. 2000, 10, 1337-1343. 

Soap-free emulsion polymerization (SFEP) is an ideal method for the preparation of surfactant-free polymer-LDH nanocomposites. The mechanism of SFEP involves an in situ micellization model, where the oligomeric radicals generated by the free radical reaction of an ionic initiator and styrene monomer act as surfactants and assist in forming micelles. Therefore, no surfactants are used during the emulsion polymerization process. The SFEP method has been applied to the preparation of a surfactant-free polystyrene-layered double hydroxide exfoliated nanocomposite.In a typical synthesis, 0.05 g of MgAlNOs was dispersed in 80 ml of distilled water and sonolyzed for 30 min. The mixture was charged into a 150 ml four-necked reactor equipped with a baffle stirrer, a reflux condenser, a nitrogen inlet and a septum. The temperature of the reactor was raised to 70 °C and then 5 g of styrene and 20 g of aqueous potassium persulfate (KPS) solution (0.4 wt%) were added to the reactor as... 

Kopka, FI., Beneke, K. and Lagaly, G. (1988). Anionic surfactants between double metal hydroxide layers. J. Colloid Interface Sci. 123, 427. 

It is well known that hydrolyzed polyvalent metal ions are more efficient than unhydrolyzed ions in the destabilization of colloidal dispersions. Monomeric hydrolysis species undergo condensation reactions under certain conditions, which lead to the formation of multi- or polynuclear hydroxo complexes. These reactions take place especially in solutions that are oversaturated with respect to the solubility limit of the metal hydroxide. The observed multimeric hydroxo complexes or isopolycations are assumed to be soluble kinetic intermediates in the transition that oversaturated solutions undergo in the course of precipitation of hydrous metal oxides. Previous work by Matijevic, Janauer, and Kerker (7) Fuerstenau, Somasundaran, and Fuerstenau (I) and O Melia and Stumm (12) has shown that isopolycations adsorb at interfaces. Furthermore, it has been observed that species, adsorbed at the surface, destabilize colloidal suspensions at much lower concentrations than ions that are not specifically adsorbed. Ottewill and Watanabe (13) and Somasundaran, Healy, and Fuerstenau (16) have shown that the theory of the diffuse double layer explains the destabilization of dispersions by small concentrations of surfactant ions that have a charge opposite to... 

The situation is still more complex in the presence of surfactants. Recently, a self-consistent electrostatic theory has been presented to predict disjoining pressure isotherms of aqueous thin-liquid films, surface tension, and potentials of air bubbles immersed in electrolyte solutions with nonionic surfactants [53], The proposed model combines specific adsorption of hydroxide ions at the interface with image charge and dispersion forces on ions in the diffuse double layer. These two additional ion interaction free energies are incorporated into the Boltzmann equation, and a simple model for the specific adsorption of the hydroxide ions is used for achieving the description of the ion distribution. Then, by combining this distribution with the Poisson equation for the electrostatic potential, an MPB nonlinear differential equation appears. 

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