exfoliation (rus. эксфолиация) — Segregation of the layered filler particles into individual nanoelements in the nanocomposite material matrix.

Description

The term exfoliation is used to describe polymer-clay systems. Clay has a plate-like structure with plates of about 1 nm thick. The plates are parallel to each other and form crystallites (tactoids). There may be water molecules and metal cations in between the layers. Of most interest for the production of nanocomposites are those clay tactoids, which can desintegrate into individual nanolayers after some particular processing. The result of peeling, when the layered silicate tactoids are completely divided into separate layers, is known as exfoliation (see also delamination). To make the clay exfoliated, it should undergo some water repellent treatment and increase the distance between the plates. To achieve this, the surface of the plates shall be modified with surfactants (with resultant organoclay), or amphiphilic polymers (polyethylene oxide, block copolymers), which penetrate (intercalate) into the space between the plates. The polymer melt is mixed with a filler using an extruder, though the filled polymer can be synthesised directly from a mixture of the monomer and a filler (nanofillers).

The fully exfoliated state improves the mechanical properties of nanocomposites, such as stiffness, dimensional stability, impact resistance; increases the oxygen index, and decreases gas permeability.

Illustrations

Development of polymer/clay nanocomposite. The first stage involves generation of tactoid - polym

Development of polymer/clay nanocomposite. The first stage involves generation of tactoid - polymer closes around the organic clay agglomerates. The second stage (intercalation) involves penetration of the polymer into the interlayer space of the organic clay, causing the layers to move apart by 2-3 nm. The final stage involves exfoliation.


Authors

  • Goldt Ilya V.
  • Khokhlov Alexey R.
  • Govorun Elena N.

Sources

  1. Pinnavaia T. J., Beall G.W. Polymer-Clay Nanocomposites. — Wiley, 2000. — 370 p.
  2. LeBaron P. C., Wang Z., Pinnavaia T. J. Polymer-layered silicate nanocomposites: an overview // Appl. Clay Sci. 1999. V. 15, №1–2. P. 11–29.

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