Amphiphilic copolymer self-assembly of magnetic nanoparticles for construction of magnetically responsive photonic crystals based on steric hindrance

Abstract

Herein, a facile, simple and rapid self-assembly of magnetic colloidal nanoparticles (MCNPs) to build magnetically responsive photonic crystals (MRPCs) was devolved. A nonionic amphiphilic random copolymer poly(styrene-co-vinylpyrrolidone) P(St-co-VP) with the monomer molar ratio of 1 : 9 was used not only as an emulsifier for miniemulsion self-assembly of Fe 3 O 4 magnetic nanoclusters, but also as the coating material on the magnetic nanoclusters through itself assembly. The self-assembly of the magnetic nanocluster and the polymer coating were completed simultaneously without another polymerization process. The characterization of the MCNPs and the optical properties of the MRPCs were investigated in details. TEM showed that the MCNPs had regular spherical structures with an average diameter of 104.6 nm (RSD ¼ 13.9%, n ¼ 100). P(St-co-VP) self-assembly coating was confirmed by IR and XPS, and thermogravimetric analysis showed that the magnetite content was 76.15%. The large content of magnetite and the thin coating of the copolymer gave MCNPs the high saturated magnetization (M s ) of 52.60 emu g À1 . Under an external magnetic field, the MCNPs could assemble MRPCs instantaneously and reversibly. The structural color covered entire visible spectrum by tuning the strength of the external magnetic field. On basis of the steric hindrance from neighboring PVP stretching chains, rather than electrostatic repulsion or solvation layer to counterbalance magnetic attraction, the MRPCs could tolerate the electrolyte as high as 0.10 mol L À1 and the variance of pH from 2.0-12.0. The stability of P(St-co-VP) self-assembly coating was testified through the invariability of the structural color of MRPCs after repeated washing, as well as the recovery of structural color after removing the electrolytes.

Visualization of nonsingular defect enabling rapid control of structural color

“…The SCs afford great potential for emerging stimuli-interactive applications such as human interactive displays, sensors, and pattern encryptions (5)(6)(7). PCs based on self-assembled block copolymers (BCPs) (5) are advantageous as their periodicities and dielectric constants can be readily altered by many diverse forces such as electric (8)(9)(10)(11)(12), magnetic (13,14), thermal (7,15,16), solvating (17,18), and mechanical (19)(20)(21)(22). This reversible alteration of the SC upon external stimulation makes these PCs suitable for humaninteractive electronics where, for example, the change of body skin strain, temperature, and finger humidity can be dynamically visualized via changes in the SC of a BCP PC (6,15,19,23).…”

Photonic Crystal Palette of Binary Block Copolymer Blends for Full Visible Structural Color Encryption

“…[6,7] In addition to SCs arising from PCs based on colloidal assemblies and layer-by-layer fabricated hydrogels, [8][9][10] SCs arising from self-assembled block copolymer (BCP) PCs are of interest owing to facile and reversible alteration of both microstructures and dielectric constants of the constituent BCP domains upon various stimuli. [11,12] Many examples of such stimuli-interactive SC changes of BCP PCs are observed with electric, [13][14][15][16][17] magnetic, [18,19] solvating, [20,21] thermal, [7,22,23] and mechanical stimuli. [24][25][26][27] Development of the high performance SC of BCP PCs, however, requires a swelling agent due to the insufficient domain size, which often results in the maximum reflection of a typical BCP PC occurring in the UV region.…”