Research Theme
Self-healing materials
Tough supramolecular materials that combine rapid self-healing and recycling properties
Poly (ethyl acrylate) as the main chain, acetylated β-cyclodextrin (PAcβCD) as the host molecule, and adamantane as the guest molecule were polymerized as host and guest polymers, respectively. The polymers were mixed using a planetary ball mill with a strong mixing force (Method A shown in Figure a). As a result, the mobility of the polymer chains was improved and the material became about three times tougher than the material prepared by the conventional mixing method. In addition, the scratches on the material coated on glass after ball milling disappeared within a few seconds. Repeated ball-milling of the material after fracture allowed it to be re-formed into film again while retaining its toughness.
with reversible cross-linking
Fabrication of self-healing urethane materials using host-guest interaction
Inclusion complexes of methylated amino βCD and 1-adamantaneamine (1-AdNH2) were used to prepare HG(x) urethanes with inclusion complexes in the main chain. The amount of inclusion complexes introduced into the material affected the material's fracture energy (Gf) and self-healing properties, with HG(10) with 10 mol% methylated amino βCD and 1-AdNH2 in the polyurethane showing the highest Gf and highest repair rate, improving over HG(2.5). Host-guest interaction played an important role in Gf and self-healing properties
Preparation of self-healing elastomers consisting of reversible cross-links and their mechanical properties
In this study, host-guest interaction was chosen as a reversible cross-link. Cyclodextrin (CD) was selected as a representative host molecule. The preparation of materials consisting of reversible bonds can be done by mixing host and guest polymers or by polymerization from a mixture of host and guest monomers (see Figure a below). In this study, the method of polymerization from a mixture of host and guest monomers in Method B shown in Figure a was selected. Poly(ethylacrylate) (pEA) was selected as the polymer main chain. The pEA without cross-linking had low fracture stress and strain, while the pEA-BDA with chemical cross-linking points had high fracture stress but no improvement in strain. The pEA-PMγCD-Ad with reversible cross-linking showed interesting results, improving both fracture stress and fracture strain (see Figure b below)
with reversible cross-linking
and reversibly crosslinked pEA-PMγCD-Ad
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. 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).
Oxidation-reduction controls self-repair
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 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.
