surface area for polymer–filler interaction as compared to conventional composites.
From a structural point of view, polymer/clay composites can be generally classified into conventional composites and nanocomposites. In a conventional composite, the registry of the clay nanolayers is retained when mixed with the polymer, but
there is no intercalation of the polymer into the clay structure. Consequently, the
clay fraction in conventional composites plays little or no functional role and acts
mainly as a filler agent for economic considerations. Depending on the strength of
interfacial interactions between the polymer matrix and layered silicate, three
classes of polymer/clay nanocomposites are described: phase-separated (immiscible nanocomposites), intercalated nanocomposites, and delaminated (or exfoliated)
nanocomposites [43].
1. Phase-separated microcomposites are formed when the polymer is unable to
intercalate with the silicate layers. This can also be called an immiscible system,
which normally would not be regarded as a nanocomposite.
2. Intercalated nanocomposites are formed when one or a few molecular layers of
polymer are inserted into the clay galleries in a crystallographically regular
fashion, regardless of the clay-to-polymer ratio. Intercalation causes
<20–30 A ˚ separation between the silicate platelets. The result is a well-ordered
multilayer structure of alternating polymeric and inorganic layers, with a repeat
distance between them. Sometimes the silicate layers in intercalated
nanocomposites are flocculated due to hydroxylated edge–edge interaction of
the silicate layers.
3. Exfoliated nanocomposites are formed when the silicate nanolayers are individually dispersed in the polymer matrix, the average distance between the
segregated layers being dependent on the clay loading. Its ordered structure is
lost and the distance between the layers is of the order of the radius of gyration of
the polymer. In this case, the polymer separates the clay platelets by 80–100 A ˚ or
more. Exfoliated or delaminated nanocomposites show greater phase homogeneity than intercalated nanocomposites. Notice that in the exfoliated case the
surface area between organic and inorganic is increased compared with the
intercalated materials. Hence, each nanolayer in an exfoliated nanocomposite
contributes fully to interfacial interactions with the matrix. This structural
distinction is the primary reason why the exfoliated clay state is especially
effective in improving the reinforcement and other performance properties of
clay composite materials. Exfoliation may be either “ordered” or “disordered”
[44], which can be detected by X-ray diffraction (XRD) analyses.
It should be pointed out that many polymer/clay nanocomposite materials finally
result in the formation of a mixture of exfoliated and intercalated structures
[45]. The above types of nanocomposites are schematically compared with an
immiscible system in Fig. 3.
318
N.H. Tarte et al.
From a structural point of view, polymer/clay composites can be generally classified into conventional composites and nanocomposites. In a conventional composite, the registry of the clay nanolayers is retained when mixed with the polymer, but
there is no intercalation of the polymer into the clay structure. Consequently, the
clay fraction in conventional composites plays little or no functional role and acts
mainly as a filler agent for economic considerations. Depending on the strength of
interfacial interactions between the polymer matrix and layered silicate, three
classes of polymer/clay nanocomposites are described: phase-separated (immiscible nanocomposites), intercalated nanocomposites, and delaminated (or exfoliated)
nanocomposites [43].
1. Phase-separated microcomposites are formed when the polymer is unable to
intercalate with the silicate layers. This can also be called an immiscible system,
which normally would not be regarded as a nanocomposite.
2. Intercalated nanocomposites are formed when one or a few molecular layers of
polymer are inserted into the clay galleries in a crystallographically regular
fashion, regardless of the clay-to-polymer ratio. Intercalation causes
<20–30 A ˚ separation between the silicate platelets. The result is a well-ordered
multilayer structure of alternating polymeric and inorganic layers, with a repeat
distance between them. Sometimes the silicate layers in intercalated
nanocomposites are flocculated due to hydroxylated edge–edge interaction of
the silicate layers.
3. Exfoliated nanocomposites are formed when the silicate nanolayers are individually dispersed in the polymer matrix, the average distance between the
segregated layers being dependent on the clay loading. Its ordered structure is
lost and the distance between the layers is of the order of the radius of gyration of
the polymer. In this case, the polymer separates the clay platelets by 80–100 A ˚ or
more. Exfoliated or delaminated nanocomposites show greater phase homogeneity than intercalated nanocomposites. Notice that in the exfoliated case the
surface area between organic and inorganic is increased compared with the
intercalated materials. Hence, each nanolayer in an exfoliated nanocomposite
contributes fully to interfacial interactions with the matrix. This structural
distinction is the primary reason why the exfoliated clay state is especially
effective in improving the reinforcement and other performance properties of
clay composite materials. Exfoliation may be either “ordered” or “disordered”
[44], which can be detected by X-ray diffraction (XRD) analyses.
It should be pointed out that many polymer/clay nanocomposite materials finally
result in the formation of a mixture of exfoliated and intercalated structures
[45]. The above types of nanocomposites are schematically compared with an
immiscible system in Fig. 3.
318
N.H. Tarte et al.