5.3 Nanostructures Related to Compounds with Layered Structures 101
5.3.3
Polymer Composites Filled with Defoliated Phyllosilicates
Phyllosilicates are natural silicates with layered structure. Depending on the composition, these silicates are the minerals montmorillonite, hectorite, or saponite.
In contrast to the layered structures discussed previously, electrostatic and not van
der Waals forces hold the different layers of these minerals together. These minerals consist of negatively charged silicate layers, consisting of silicate tetrahedra and
aluminum or magnesium and some lithium in various quantities. Within these
layers, the bonds are covalent. These layers are approximately 1 nm thick. The
distance between two layers is 0.2 nm. In-between these negatively charged layers
are positively charged alkaline ions, in most cases sodium ions. Therefore, by
electrostatic forces, these ions hold the layered system together. The lateral size of
these platelets is in the range of a few hundred nanometers. To produce highstrength composites with a polymer matrix, these silicates need to be defoliated,
which means that the individual layers are separated.
The process of defoliating is explained in Figure 5.25. Starting material are
layered silicates (phyllosilicate).
To defoliate stacks of layered silicates, the cations in-between the layers are, in
a first step, substituted by positively charged organic molecules. This leads to a
swelling of the particle; the distance between the silicate layers increases to
Figure 5.24 Industrially produced in large scale fullerene-like MoS 2 particles intended as
friction-minimizing additive to oil or grease (Tenne, R., Weizmann Institute, Israel, private
communication 2012.).
10 nm
5.3.3
Polymer Composites Filled with Defoliated Phyllosilicates
Phyllosilicates are natural silicates with layered structure. Depending on the composition, these silicates are the minerals montmorillonite, hectorite, or saponite.
In contrast to the layered structures discussed previously, electrostatic and not van
der Waals forces hold the different layers of these minerals together. These minerals consist of negatively charged silicate layers, consisting of silicate tetrahedra and
aluminum or magnesium and some lithium in various quantities. Within these
layers, the bonds are covalent. These layers are approximately 1 nm thick. The
distance between two layers is 0.2 nm. In-between these negatively charged layers
are positively charged alkaline ions, in most cases sodium ions. Therefore, by
electrostatic forces, these ions hold the layered system together. The lateral size of
these platelets is in the range of a few hundred nanometers. To produce highstrength composites with a polymer matrix, these silicates need to be defoliated,
which means that the individual layers are separated.
The process of defoliating is explained in Figure 5.25. Starting material are
layered silicates (phyllosilicate).
To defoliate stacks of layered silicates, the cations in-between the layers are, in
a first step, substituted by positively charged organic molecules. This leads to a
swelling of the particle; the distance between the silicate layers increases to
Figure 5.24 Industrially produced in large scale fullerene-like MoS 2 particles intended as
friction-minimizing additive to oil or grease (Tenne, R., Weizmann Institute, Israel, private
communication 2012.).
10 nm