| 1D magnetically responsive photonic crystals,based on the balance between long-range repulsion force and magnetic attraction force,are expected to applied in fields like magnetic control display,erasable photonic paper/ink,because of their conveniently applied external magnetic field,fast responsive rate,continuously tunable photonic bandgap,reversibly changeable structural color covering the entire visible spectrum,etc.However,the chain-like photonic structure of 1D magnetically responsive photonic crystals is not stable,which will disintegrate after withdrawing the magnetic field.Photonic nanochains are the smallest structure units of photonic crystals,they have potential applications in fields like energy-efficient displays and bragg reflectors since their highermagneticsensitivity and optical modulationresolution.Nevertheless,the reported photonic nanochains are all rigid chain structures fabricated by coating and connecting the 1D chain-like photonic structure with unresponsive materials,exhibiting only the switching effect by applying and withdrawing an external magnetic field,instead of regulating the photonic bandgap by external fields.In this paper,magnetic-temperature dual-responsive Fe3O4@PNIPAM flexible photonic nanochains are fabricated by creatively introducing temperature responsive hydrogel PNIPAM to the chain-like photonic structure.Orientation mechanism of the flexible photonic nanochains in magnetic fields and optical responsive properties in magnetic fields and temperature fields are studied.The main work is as follows:(1)The Fe3O4@PNIPAM photonic nanochains were fabricated by the combination of magnetic control assembly and UV-light initiated polymerization,and the preparation process and structure regulation mechanism were illustrated.Microstructure characterization demonstrated that the photonic nanochains arelinked by PNIPAM with a neck-connection of Fe3O4@PVP CNCs,the chains showed a natural bent state without an external magnetic field,indicating that the photonic nanochains are flexible.Chaining mechanism analysis showed that PAA forms hydrogen bond with PVP on the surface of magnetic building block CNCs and NIPAM,which is the key to accumulating NIPAM in the CNCs solvation layer,and after UV-light initiated polymerization PNIPAM coats and connects the 1D periodic structure and photonic nanochains form.The interparticle spacing,chain length and coating morphology can be regulated by the intensities of the external magnetic field,magnetic induction duration and the volume ratio of H2 O to EG in precursor solution.(2)Research on the magnetic orientation mechanism and magnetic responsive properties of Fe3O4@PNIPAM flexible photonic nanochains indicated that the orientation of the flexible photonic nanochains in the external magnetic field contains two processes,one is deflection of the chains to the direction of magnetic field with low intensities,the other is stretch of the chains along the direction of magnetic field with high intensities.The peak position remained unchanged during the orientation process,but the intensity of the diffraction peak raised with the increase of external magnetic field,and brightness increased correspondingly.The experimental data were the same as the results obtained from the physical model.Research on impact of the crosslinking degree of PNIPAM,interparticle spacing and chain length on the magnetically responsive properties of flexible photonic nanochains showed that the dependence of the diffraction peak of the photonic nanochains on external magnetic field became stronger with the increase of the chain length and the flexibility of the flexible photonic nanochains.(3)Fe3O4@PNIPAM photonic nanochains showed excellent temperature responsive properties from 8 to 40 oC,the diffraction peak position tuning range covered almost the entire visible spectrum.Cycle experiment results showed that the photonic nanochains have good repetition stability for temperature responsive properties.Furthermore,the photonic nanochains also exhibited fast responsive rate to temperature field,it tookonly 2 s for the structural color of the photonic nanochains change from red to green when shifting the external temperature from 8 oC to 40 oC.(4)Fe3O4@PNIPAM photonic nanochains have magnetic/thermally dual-responsive properties,the combination of tuning diffraction intensitiesby magnetic field and regulation of photonic bandgap by temperature endows photonic nanochains with potential applications in optical camouflage. |
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