Armored latexes

Fig. 19a,b. TEM of armored latexes a sealed clay on PBA template particles b sealed clay on PMMA template particles after removal of the PMMA in the core... 

In the past, many groups have tried to encapsulate clay platelets inside latex particles. This encapsulation poses some extra challenges because of the tendency of the clay platelets to form stacks and card-house structures. Most of the attempts resulted in the so-called armored latex particles, i.e. clay platelets in the surface of the latex. Recently, natural and synthetic clays were successfully encapsulated. The anisotropy of the clay resulted in non-spherical latex particles (Figs. 5 and 6), either peanut-shaped [63] or flat [64]. Clay platelets also turned out to be good stabilizing agents for inverse Pickering emulsion polymerizations [65]. 

Ma and Dai [121] reported the synthesis of polystyrene latexes armored with silica nanoparticles (10-15nm in diameter, PA-ST silica sol, Nissan Chemicals) via solids-stabilized emulsion polymerization. They used VA-086, 2,2 -azobis [2-methyl-lV-(2-hydroxyethyl)propionamide], as nonionic initiator. Whereas we found that Pickering emulsion polymerization of styrene using Ludox TM-40 and a low flux of radicals generated from potassium persulfate did not result in an armored latex, the hydroxyethyl groups probably enhance the wettability of the surface of the latex particles to promote silica adhesion. This was confirmed by a... 

Cauvin S, Colver PJ, Bon SAF (2005) Pickering stabriized miniemulsion polymerization preparation of clay armored latexes. Macromolecules 38(19) 7887-7889... 

Figure 2.7 Transmission electron micrographs of armored latexes, (a) Sealed clay on poly(butyl acrylate) template particles ...

Inverted raspberry-like morphologies (the mineral particles being located at the surface of the latex spheres) have also been discussed in Sections 4.4.2.2 and 4.4.2.4 about colloidal silica and layered silicates, respectively. These are mainly a consequence of the surfactant-like behavior of the inorganic particles in specific situations. This was clearly illustrated in a recent report by Landfester, who showed that silica or clays can be used as pickering stabilizers of miniemulsion jxjlymer-izations, resulting therefore in the formation of armored latexes, the surface of which was recovered by the small inorganic particles [99,131]. 

B. zu Putlitz, K. Landfester, H. Fischer, M. Antonietti, The generation of armored latexes and hollow inorganic shells made of clay sheets hy templating cationic miniemulsions and latexes, Adv. Mater 2001, 13, 500-503. 

Rodrigues Guimaraes T, de Camargo CT, D Agosto F, Fansalot M, Martins Dos Santos A, Bourgeat-Lami E (2014) Synthesis of multi-hollow clay-armored latexes by surfactant-free emulsion polymerization of styrene mediated by poly(ethylene oxide)-based macroRAFT/ Laponite complexes. Polym Chem 5 6611-6622... 

The present review aims to cover and discuss recent developments in the synthesis of polymer-clay nanocomposites through emulsion polymerization. The first part summarizes the research status of in situ emulsion polymerization performed in the presence of pristine or organically modified clays (either MMT or Laponite). Then, the chapter highlights work on the synthesis of clay-armored latexes through soap-free polymerization. It reports the state of the art in the field and presents recent advances in the synthesis and characterization of high solids content latexes stabilized by Laponite clay platelets, with particular attention to mechanistic aspects and properties of the film materials issued from... 

Figure 13.10 Storage modulus versus temperature obtained by dynamic mechanical analysis (DMA) of latex films obtained from (a) Laponite-armored latexes and (b) polymer-encapsulated Laponite. Adapted from reference 54 with permission of Elsevier.

Figure 13.11 (a) Synthesis scheme for synthesis of Laponite-armored latexes via... 

Laponite-armored Latexes Produced by Soap-free Emulsion Polymerization... 

Chemical formulae of the free radical initiators used for the synthesis of Laponite-armored latexes through soap-free emulsion polymerization. ... 

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