Approaches to the manufacture of layered nanocomposites

Clay–polymer nanocomposites, resulting from industrial research, have emerged as a new class of material because a low addition of clay in a polymer matrix causes dramatic improvement in mechanical and barrier properties. They represent the low volume fraction (<4 vol.%) end of the composition range. The question now is: what will emerge from attempts to explore the high volume fraction (>60 vol.%) end? Naturally occurring materials, such as nacre, show that a combination of a high platelet content in a polymer with a layered structure is strong and tough (4–10 MPa m1/2), even if the reinforcement, aragonite in this case, is inherently brittle (∼1 MPa m1/2). This achievement of nature has inspired the synthesis of materials to mimic the nacre structure using high aspect ratio reinforcements of high elastic modulus such as smectite clay tactoids. Preliminary successes were based on layer-by-layer assembly methods and it will be interesting to find out whether sufficient order can be obtained in composites assembled by more rapid manufacturing pathways. We are interested in the factors affecting dispersion, orientation and intercalation of platelets and here we survey the strategies that have been adopted in order to create organized structures of layered nanocomposites.