Living matter has the ability to perceive multiple stimuli and respond accordingly. However, the integration of multiple stimuli-responsiveness in artificial materials usually causes mutual interference, which makes artificial materials work improperly. Herein, the authors develop an organic‒inorganic semi-interpenetrating network structure that is orthogonally responsive to light and magnetic fields, which is different from conventional semi-interpenetrating polymer networks.
The composite gel is prepared by the co-assembly of a photoreponsive organogelator (Azo-Ch) and superparamagnetic Fe3O4@SiO2 nanoparticles. Azo-Ch assembles into supramolecular fibers that form a gel network; Fe3O4@SiO2 nanoparticles are located in the voids of the network (Fig. 1a). In both the gel and sol states, Fe3O4@SiO2 nanoparticles can reversibly form photonic nanochains via magnetic control (Fig. 1). The authors demonstrate that smart photonic materials can be fabricated based on the orthogonal photo- and magnetic-responsiveness of the organic‒inorganic semi-interpenetrating network.
To prepare an organic‒inorganic composite gel, Azo-Ch and Fe3O4@SiO2 nanoparticles were co-assembled in cyclopentanone. SEM images showed that Fe3O4@SiO2 nanoparticles were located in the voids of the network of Azo-Ch fibers (Fig. 2b). The nanocomposite gel showed photoinduced reversible sol-gel transitions when the magnetic field was either on or off; reversible nanoparticle-to-nanochain transitions were induced by switching the magnetic field on and off in both the gel and sol states (Fig. 2b-e). The nanochains of Fe3O4@SiO2 interpenetrated with the network of Azo-Ch fibers, which is an analog of conventional semi-interpenetrating networks that are composed of crosslinked polymers with interpenetrated linear polymers. In our semi-interpenetrating network, both Azo-Ch and Fe3O4@SiO2 have sufficient space for independent structural rearrangements. Therefore, the photo- and magnetic-responsiveness of the semi-interpenetrating network is orthogonal.
Fig. 3 Applications of smart photonic gels. a Photographs of a smart window controlled by light and a magnetic field. Scale bar: 0.5 cm. b Photographs of writing and erasing a QR code on a composite gel. UV (365 nm, 30 mW·cm−2, 30 s) and visible light (530 nm, 40 mW·cm−2, 5 min) were used for writing and erasing procedures. Scale bar: 1 cm. c Photographs of composite gels with different shapes under magnetic fields with different intensities. Scale bar: 1 cm. d Schematic illustration and photographs of composite gel or sol under complex magnetic fields. Scale bar: 0.5 cm.
The authors demonstrated the potential applications of the organic-inorganic semi-interpenetrating networks. A smart window was prepared using the organic-inorganic semi-interpenetrating network; its transparency was controlled by light and magnetic fields (Fig. 3a). In addition, a rewritable pattern was fabricated. The authors wrote and erased a QR code via light irradiation (Fig. 3b). Moreover, the organic-inorganic semi-interpenetrating network can be reshaped to a square, circle, and pentagram via photoinduced reversible sol-gel transitions. The composite gels with different shapes exhibited structural colors under magnetic fields (Fig. 3c). Furthermore, the authors used different magnet assemblies to induce dynamic photonic patterns (Fig. 3d).
The authors envision that polymers in conventional (semi-)interpenetrating networks can be replaced by a variety of inorganic, organic, and composite materials, which can endow (semi-)interpenetrating networks with new properties and functions.
More details can be found in our paper "Organic‒inorganic semi-interpenetrating networks with orthogonal light- and magnetic-responsiveness for smart photonic gels" published in Nature Communications.
Link to article: https://www.nature.com/articles/s41467-023-36706-7
https://www.nature.com/articles/s41467-023-36706-7.pdf
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