Exfoliation anionic clays

An effective way to include a catalyst inside brucite-like layers is an LbL deposition technique [51, 52, 89, 90] exfoliated anionic clays constitute one of the components of the multilayers, while the actual electrocatalytic element possesses an opposite charge and acts as the second component of the film. This technique allows the deposition of very thin films with a homogenous and controlled disposition of the catalytic sites inside the coating. Moreover, it allows a higher number of electroactive sites to be effective in the catalytic reaction. 

Under microwave irradiation, in situ polymerization constitutes an alternative method for preparing poly(ethylene terephthalate) (PET)/layered double hydroxide (LDH) nanocomposites. LDHs are also known as anionic clays or hydrotalcite-like compounds. To overcome the lack of compatibility between PET and LDHs that contain purely inorganic anions, LDHs were modified with dodecyl sulfate prior to sample preparation. The preparation time was considerably reduced, and the inorganic filler was well dispersed and exfoliated in the polymer matrix. The nanocomposites thus obtained were thermally more stable than original PET,... 

Studies involving the use of organically modified clay particles in heterophase polymerization are rather scarce. Indeed, we are aware of only two reports that combine the emulsion or suspension polymerization approaches and ion-ex-change reaction. In one of these reports, AI BA is immobiHzed in the clay interlayer region to yield exfoliation of MMT in the PMMA matrix through suspension polymerization [135]. In another relevant study, it was demonstrated that exfoliated structures could be obtained by post-addition of an aqueous dispersion of layered silicates (either MMT or laponite) into a polymethyl methacrylate latex suspension produced in the presence of suitable cationic compounds (cationic initiator, monomer or surfactant) [136]. Since the latex particles were cationic and the clay platelets anionic, strong electrostatic forces were developed at the polymer/clay interface. 

A typical polymer-modified organoclay for the preparation of PS nanocomposites could be a PS polymer with some cationic sites to be attached to the clay surface. Polystyryl quaternary ammonium salts (PSQAS) were synthesized via three different polymerization routes anionic polymerization (AP), free radical co-polymerization (CP), and chloromethy-lation of polystyrene (CM) [67] (Table 3.6). TGA results indicated that CP-PSQAS and CM-PSQAS were thermally stable, because the C-C bonds in aromatics are much stronger than those in aliphatic compounds. The polystyryl-modified clays exhibited intercalated or partially exfoliated structures. 

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