Magnetochromatic Microspheres: Rotating Photonic Crystals

Abstract

Magnetochromatic microspheres have been fabricated through instant assembly of superparamagnetic (SPM) colloidal particles inside emulsion droplets of UV curable resin followed by an immediate UV curing process to polymerize the droplets and fix the ordered structures. When dispersed in the liquid droplets, superparamagnetic Fe(3)O(4)@SiO(2) core/shell particles self-organize under the balanced interaction of repulsive and attractive forces to form one-dimensional chains, each of which contains periodically arranged particles diffracting visible light and displaying field-tunable colors. UV initiated polymerization of the oligomers of the resin fixes the periodic structures inside the droplet microspheres and retains the diffraction property. Because the superparamagnetic chains tend to align themselves along the field direction, it is very convenient to control the orientation of such photonic microspheres and, accordingly, their diffractive colors, by changing the orientation of the crystal lattice relative to the incident light using magnetic fields. The excellent stability together with the capability of fast on/off switching of the diffraction by magnetic fields makes the system suitable for applications such as color display, rewritable signage, and sensors. As a simple demonstration, we have fabricated a display unit that has on/off bistable states by embedding the magnetochromatic microspheres in a matrix that can thermally switch between solid and liquid phases.

Self-assembled colloidal structures for photonics

“…Contrast is generated by orienting the colloidal crystal side up in local regions and the carbon black side up in the remaining regions. In an alternative approach, Ge et al [60] produced anisotropic microspheres by solidifying emulsion droplets of a photocurable superparamagnetic particle suspension under a magnetic fi eld. Th e magnetic particles in this system are aligned into a chain-like structure under a magnetic fi eld and then fi xed into polymeric spheres by polymerization.…”

Bio-Inspired Photonic Structures: Prototypes, Fabrications and Devices

“…With various incident angle or observation direction, the perceived coloration is changing. Hence, it is feasible to explore novel tunable color devices by tuning orientations of the photonic structures [84][85][86]. Just like the fish neon tetra P. innesi, magnetochromatic microspheres alter their appearance by tilting the inner photonic structures with respect to the incidence (Fig.…”

Responsive photonische Kristalle

“…[68] Die periodische Partikelanordnung innerhalb der Einzelketten wurde auch in einer Untersuchung bestätigt, bei der man den Aufbau innerhalb einer Polymermatrix fixierte und ein Fragment des Komposits parallel zur Kettenrichtung herausschnitt (Abbildung 12 c). [179,180] [183,184] Um eine starke elektrostatische Abstoßung zu erzeugen, wurden den unpolaren Dispersionen Ladungskontrollreagentien wie Natriumbis(2-ethylhexyl)sulfosuccinat (AOT) zugegeben. [178] Die so erhaltenen umgekehrten Micellen mit Durchmessern von einigen Nanometern können die Energieschwelle für die Ladungstrennung auf der Partikeloberfläche herabsetzen, und sie können durch die Stabilisierung ihrer Gegenionen in den Micellen die Oberflächenladungen verstärken.…”