Polymer intercalation Clays

It is a common phenomenon that the intercalated-exfoliated clay coexists in the bulk and in the interface of a blend. Previous studies of polymer blend-clay systems usually show that the clay resides either at the interface [81] or in the bulk [82]. The simultaneous existence of clay layers in the interface and bulk allows two functions to be attributed to the nanoclay particles one as a compatibilizer because the clays are being accumulated at the interface, and the other as a nanofiller that can reinforce the rubber polymer and subsequently improve the mechanical properties of the compound. The firm existence of the exfoliated clay layers and an interconnected chain-like structure at the interface of CR and EPDM (as evident from Fig. 42a, b) surely affects the interfacial energy between CR and EPDM, and these arrangements seem to enhance the compatibility between the two rubbers. 

The intercalation of nano-gold into clay layers comprised two steps. The first step was the intercalation of the polymer (surfactant) into clay matrix for increasing the interlamellar space between the clay layers. The second step was the replacement of the intercalated polymer (surfactant) by Au nanoparticles by adding different amounts of nanoparticles to the polymer (surfactant)/clay composite. Both steps were performed by applying ultrasonic irradiation. The solution was sonicated at 20 kHz, 500 W. The intercalation progress was monitored as a function of time. The precipitated nano-Au/intercalated product was separated by centrifugation, washed with water and dried under vacuum overnight. After that samples were calcined in air at 800 °C for 4 h. 

The intercalation of polymer or prepolymer from the solution is described via minimum free energy principle. The driving force of polymer intercalation is the entropy from the solvent desorption. Several researchers investigated the thermodynamics properties of PCN with homo polymeric systems in a confined geometry. However, Lim et al. investigated ternary systems, and explained that the intercalation distance of poly-(methyl methacrylate) (PMMA)/organic-modified clay (OMMT) nanocomposite is larger than that for the... 

Figure 16.24 shows the schematic representation of dispersed clay particles in a polymer matrix. Conventionally dispersed clay has aggregated layers in face-to-face form. Intercalated clay composites have one or more layers of polymer inserted into the clay host gallery. Exfoliated polymer/clay nanocomposites have low clay content (lower than intercalated clay composites which have clay content -50%). It was found that 1 wt% exfoliated clay such as hectorite, montmorillonite, or fluorohectorite increases the tensile modulus of epoxy resin by 50-65%. ... 

Synthetic procedures include (a) monomer impregnation of clay followed by polymerization, (b) intercalation of monomers/polymers in clay, and (c) clay exfoliation techniques. 

The general idea underlying the preparation of layered clay-polymer intercalates follows the simple rules of ion exchange. In most cases, the synthesis involves either intercalation of a polymer from solution or a suitable monomer followed by subsequent polymerization. But for more technologically important polymers, both approaches are limited since neither a suitable monomer nor a compatible polymer host solvent system is always available. 

Conducting polymers such as PANl- or PPY-intercalated clay-type minerals are another type of ER particle material. Kim et al. synthesized PPY-intercalated montmorillonite nanocomposites through inverted emulsion pathway polymerization, and characterized its ER effect under an electric field [38]. The nanocomposites showed not only a typical ER behavior under electric fields but also the existence of a critical electrical field when the yield stress was plotted as a function of the electric field. 

XRD is a rather simple and widely used technique for the characterization of a layered-clay dispersion in a polymer matrix. WAXS analysis was used to quantify the height between adjacent silicate platelets, and subsequently to prove the widening of this distance as the matrix polymer intercalates between the galleries. Changes in the value of 20 reflect changes in the... 

Since nanoparticles in PNC are orders of magnitude smaller than conventional reinforcements, the models developed for composites are not applicable to nanocomposites. However, development of a universal model for PNC is challenging since the shape, size, and dispersion of the nanoparticles vary widely from one system to another. On the one hand, exfoliated clay provides vast surface areas of solid particles (ca. 800 m /g) with a large aspect ratio that adsorb and solidify a substantial amount of the matrix polymer, but on the other hand, the mesoscale intercalated clay stacks have a much smaller specific surface area and small aspect ratio. However, in both these cases the particle-particle and particle-matrix interactions are much more important than in conventional composites, affecting the rheological and mechanical behavior. Thus, the PNC models must include the thermodynamic interactions, often neglected for standard composites. 

Choudhaiy, S., Sengwa, R. J. (2014). Intercalated clay structures and amorphous behavior of solution cast and melt pressed poly(ethylene oxlde)-clay nanocomposites,/ Appl. Polym. Set, 131(4), DOI 10.1002/ app.39898. 

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