Structure and properties of physical and chemical supramolecular sliding gels based on α-CD/PEO polyrotaxanes
Laboratoire d’Ingénierie des Polymères pour les Hautes Technologies (LIPHT), ECPM / ULP, Université Louis Pasteur de Strasbourg, 25 rue Becquerel, 67087 Strasbourg Cedex 2, France,
Jeudi 27/11/2008, 11:00
NIMBE Bât 125, p.157, CEA-Saclay
A polyrotaxane (PR) is a macromolecular pearl necklace which consists in the stable supramolecular assembly of macrocycles onto a template polymer chain. Our group developed original routes to control the number N of pearls (α-cyclodextrins, α-CD) threaded along a poly(ethylene oxide) (PEO) chain. The effect of N on the structure and properties relationships of physical and chemical PR-based gels has been deeply studied.
Chemical gels. Chemical supramolecular sliding gels are PR-based networks with intermolecularly α-CD crosslink points. The crosslink points of such networks can slide along the template chain of the PR. The unusual physical properties of the sliding gels and their relation to the molecular structure have been studied in H2O and dimethyl sulfoxide (DMSO). In DMSO, the network has long rigid strands due to low physical intermolecular interactions and the presence of long α-CDs transient tubes. Thus, sliding gels in DMSO exhibit high swelling ratio and an unexpected rheological Zener model behaviour leading to very low viscous dissipation and underlining high relaxation ability with a single relaxation time.
Physical gels. At 20°C, a concentrated PR solution in DMSO forms a thixotropic gel due to specific interactions between α-CD. Neutron scattering experiments showed that the presence of α-CD along the PEO chain increases drastically the kinetics of the gelation. Furthermore, we demonstrated that the cohesion of the physical gel is due to the formation of α-CD nano-domains and regular isolated nano-crystallites of naked PEO segments.