Cyclodextrins and their applications

Cyclodextrins can complexate with polymers and thus can be grafted to surfaces. Grafted layers of sliding polymers are constructed from polymers threading through ring-like molecules grafted to a surface. Such grafting mode allows the polymer chains to freely slide inside the ring-like molecules, thus providing additional degree of freedom for grafted polymers.

A cyclic molecule of a cyclodextrin consist of six to eight units of glucose. The most studied inclusion complexes in a solution are the complexes of polyethylene oxide (PEO) and cyclodextrins.

[styled_box type=”info”] Usually, a solution of PEO and cyclodextrins forms complexes comprising several cyclodextrins per chain. The behaviour of the complexes is determined by the topology of the system and thus the interactions leading to such complexes are called topological interactions.
[/styled_box] [one_half][/one_half] [one_half_last][/one_half_last]

A single sliding chain (Sliding grafted polymer layers) adopt mainly symmetric configurations (with comparable branch sizes) while grafts in dense layers are highly asymmetric so that only one branch per graft participates in the layer.

[one_half][/one_half] [one_half_last][/one_half_last]

Sliding layers on small colloids or star-like sliding micelles exhibit an intermediate behaviour where the number of longer branches participating in the corona is independent of the total number of branches (Micellization of Sliding Polymer Surfactants). This regime also exists for sliding surface-micelles comprising less chains but it is narrower.

There are three sliding regimes (Sliding grafted polymer layers) for the number of arms of a sliding star in 3D:

[list type=”triangles”]

Few chains per aggregate, q<5, average characteristics are dominated by symmetric configurations of all chains composing a star.

In the intermediate regime, 5<q<8, some of the chains adopt symmetric configurations and some chains adopt asymmetric configurations. The total number of arms is equal to 9.

In the opposite limit of many chains per aggregate, q>8, average characteristics are dominated by asymmetric configurations. This corresponds to a q-arm star.

[/list]

The behaviour of a single polymer chain grafted to a surface by several rings is different for rigid and soft surfaces. In the first case the positions of the grafting points are fixed, while for the second case they are allowed to freely slide on the surface.

A grafted sliding chain behaves like a two times shorter end-grafted chain for small extension forces, and as an end-grafted chain of the same length for large extension forces.