Laponites platelets

Cryo-TEM images of spherical polystyrene latex particles stabilized by 10 wt% Laponite ciystallites (run 2 in Table 2). In b, the arrows point to a few Laponite platelets seen edge-on on the surface of the polystyrene particle. 

In the second part of this article, polymer latexes surrounded by anisotropic Laponite platelets have been successfully obtained by the two routes. It was demonstrated that the clay particles play the role of a pickering stabilizer and are capable to stabilize the composite particles whose diameter depends on the amount of Laponite initially introduced into the reactor. The higher the clay concentration, the larger the composite particle number and, therefore, the higher the polymerization rate as predicted from the emulsion polymerization theory. 

Lorthioir, C.D., Khalil, M., Wintgens, V.R., Amiel, C., 2012. Segmental motions of poly(ethylene glycol) chains adsorbed on laponite platelets in clay-based hydrogels a NMR investigation. Langmuir 28, 7859—7871. 

Similar luminescence enhancement was also observed by Yang et al. when ionic liquid 1 was added to the luminescence nanohybrid (Eu (TTA ) Lap) composed of Eu(in)-p-diketonate complexes and the synthesized clay, Laponite, dispersed in water (Fig. 7.14) [67]. The addition of 1 to the nanohybrid in water leads to a pronotmced increase in luminescence efficiency, and the absolute quantum yield of the modified nanohybrid is of 0.7, a high value that is rarely seen for luminescent nanohybrid in water. The mechanism is that the removal of the abundant protons on the Laponite platelets through a mechanism of synergic effect of ion exchange and neutralization drives the formation of Eu -p-diketonate complexes with high coordination number (Fig. 7.14). Abtmdant acidic sites exist on the surface of the... 

Figure 13.9 Example of clay encapsulation by starved-feed soap-free emulsion polymerization. The large MMT platelets are encapsulated inside dumbbell-like particles whereas small Laponite platelets are contained inside spherical latex particles. Adapted from reference 52 with permission of the American Chemical Society.

The decrease in particle size when KPS is used as initiator can be attributed to a decrease in the ionic strength of the suspension medium. Indeed, as ACPA is not water soluble, it was dissolved in 1 M sodium hydroxide solution. According to the phase diagram of Laponite dispersions in the presence of tetrasodium pyrophosphate, the Laponite platelets form aggregates under... 

A similar strategy involving Laponite or MMT platelets grafted with polymerizable organotitanate and organosilane molecules was recently reported by Voorn et al. [285, 286]. Here, starved-feed soap-free emulsion polymerization of MMA conducted in the presence of the organoclay led to clay encapsulation. However the solid content was quite low (typically around 7%). 

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. 

N. Negrete-Herrera, J.-M. Letoffe, J.-L. Putaux, L. David, E. Bourgeat-Lami, Aqueous dispersions of silane-functionalized laponite clay platelets. A first step toward the elaboration of water-based polymer/clay nanocomposites, Langmuir 2004, 20,1564-1571. 

A model poly(ethylene oxide)/laponite hybrid material, characterized by a high silicate content, was used to probe the dynamical behaviour of polymer chains at the surface with clay platelets. Such a system mimics the intercalated phases that may occur in polymer/clay nanocomposites. The segmental motions of this system were monitored over the tens of microseconds time scale by means of C and H solid-state NMR. A significant slowing down of these motions was mostly observed, as compared to the local dynamics in the amorphous phase of neat PEO. ... 

Konn C, Morel F, Beyou E, Chaumont P, Bourgeat-Lami E (2007) Nitroxide-mediated polymerization of styrene initiated from the surface of laponite clay platelets. Macromolecules 40(21) 7464—7472... 

Four types of silicate clays were obtained from Southern Clay Products (Austin, TX). Laponite-RD (LRD) is a synthetic hectorite-type clay with each platelet having a diameter of 25-30nm and a thickness of Inm (aspect ratio 25-30). Cloisite Na+ (Na-MMT) is naturally occurring sodium montmorillonite with aspect ratio of 75-100 (diameter of 75-lOOmn and thickness of Imn). Cloisite lOA (ClOA) and Cloisite 30B... 

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