Research Theme
Self-healing materials based on Cyclodextrin
Creation of photo-responsive hydrogels
To creation of hydrogels, which was switched sol state or gel state by irradiation of UV light or Vis light, we chose the α-cyclodextrin (αCD) and the Azobenezene (Azo). The hydrogel was prepared by mixing CD modified curdlan (CD-CUR) and Azo modified polyacrylic acide (pAC12Azo), indicated that CD and Azo interacted inside the hyerogel.
To investigate effect of photo stimuli on the hydrogel, we irradiated UV and Vis to the hydrogel. When UV light irradiated to the hydrogel, the hydrogel was changed in state of sol. Subsequently, When Vis light irradiated to the hydrogel, the hydrogel was changed in state of gel.
To create the redox-responsive self-healing supramolecular hydrogel, we chose the βCD as a host molecules and the ferrocene (Fc) as a guest molecules. Fc formed inclusion complexes with βCD, when Fc was reduction state. On the other hand, Fc+, which was oxidation state, dissociated inclusion complexes. The supramoleculat hydrogel was formed by mixing the Fc modified polymer and the βCD modified polymer.
The cut hydrogel pieces adhered between cut surfaces (Figure 2a).
Additionally, the self-healing performance decreased when the oxidant was coated on the cut surfaces. Subsequently, the self-healing performance recovered when the reductant was coated on the cut surfaces (Figure 2b).
(a) Readhesion experiments (b) Redox-controlled experiments of the self-healing behavior.
We successfully realized reversible sol?gel switching and a self-healing supramolecular hydrogel system consisting of the β-cyclodextrin and the ferrocene.
Nakahata, M.; Takashima, Y.; Yamaguchi H.; Harada, A., Nat. Commun. 2011, 2, 511.
Creation of preorganized hydrogels
There are two basic approaches to prepare the supramolecular polymeric materials through host?guest interactions: (1) from a mixture of host and guest polymers, and (2) from polymerization of host and guest monomers. To create high strength and short self-healing materials, we chose the method of (2).
Prior to radical copolymerization, hydrophobic guest monomers (Adamantane, Ad), which are insoluble in water, were dissolved in corresponding aqueous solutions of βCDs to form inclusion complexes. After polymerization, the homogeneous solutions yielded hydrogels (Figure 1).
The β CDAd gel(7, 6) sample immediately mends after being broken; the gel can be lifted against its own weight. The repaired β CDAd gel(7, 6) adheres strongly without a crack after crushing and dropping (Figure 2a). 1-Adamantane carboxylic acid sodium salt (AdCANa, Figure 2 b) or β CD, in aqueous solutions, were used as the competitive molecules for the β CDAd gel(7, 6). In the presence of competitive molecules on the cut surface, the gels do not adhere within 24 h. The competitive molecules inhibit the complexation between the CD and guest units on the cut surface, which function as crosslinkers to adhere the two cut gels. We successfully prepared self-healing CDguest gels crosslinked between polymer chains with inclusion complexes. The self-healing behavior exhibited by forming inclusion complexes of the free CD and guest units on the cut surfaces (Figure 2b).
