External Field Response and Applications of Metal Coated Hemispherical Janus Particles

Abstract

Hemispherical Janus particles that were coated with silver or nickel on the equatorial plane of hemispherical polymer microparticles were prepared and dispersed in water and the responses to AC electric and stationary magnetic fields applied were investigated. Both of the particles are so oriented that the equatorial plane is parallel to the AC electric field, owing to electric-field induced dipole orientation, which is the response proportional to the quadratic electric field. The nickel coated particles are self-assembled to make a chain-like structure aligned in the direction of the stationary magnetic field. In addition, when both AC electric and stationary magnetic fields are applied, the orientation of a nickel-coated hemispherical particle is uniquely determined in such a way that the equatorial plane is parallel to both electric and magnetic fields. Because the particle is magnetized on the plane, its direction is reversed when the magnetic field is reversed, which is the response that is proportional to the magnetic field. Utilizing these features, mirrors are fabricated that can switch the transmittance and reflectance with electric and magnetic fields. Such features of the Janus particles as to be controlled by an electric and magnetic fields will find wide applications in the fields of microoptics and microfluidics.

Mesotronics: Some New, Unusual Optical Effects

“…Based on this research, we extended our study to develop a new (to the best of our knowledge) method [94] of photonic hook-based near-field oblique illumination microscopy with super contrast subwavelength imaging. It was experimentally demonstrated [31,95] for the first time that the Janus particle [96][97][98] provides oblique illumination [99][100][101] of imaging objects by localized structured curved beams, which leads to a considerable improvement in the near-field imaging contrast without the use of immersion medium (Figure 4). One can see that the oblique illumination (illumination by PH) results in the diffracted order of +1 on the particle, which finally allows increasing the image contrast.…”

Dynamic Emissivity of Self-Assembled Magnetoresponsive Janus Particle Chain Suspensions

“…5 Prior studies have also considered single particles in suspension whose orientation alters the apparent suspension optical signature through reflected or transmitted light with limited apparent contrast. 6,7 Under the influence of a magnetic field, micrometer-scale Janus particles having iron caps will assemble into linear chains of rod-like particles and the magnetic field can then be used to dynamically reorient these rods, 8,9 as shown in Figure 1. There is a distinct advantage to this approach.…”

“…Since their first description, their use in manipulating light has been envisioned with regard to design of digital displays of physically rotating single particles in electric or magnetic fields. − This approach primarily depends on the reflection and scattering of light manipulated by the exposure of the two different faces of the particle and often requires a significant effort in designing the field as is done in e-ink displays that migrate two different colored dispersed particles in an electrode stack . Prior studies have also considered single particles in suspension whose orientation alters the apparent suspension optical signature through reflected or transmitted light with limited apparent contrast. , …”

Super-Resolution Imaging with Patchy Microspheres

“…Patchy particles are also a type of optical functional materials. For example, the mirror made of Ag-coated patchy particles can have optical responses to external electric and magnetic fields, and its optical reflectivity can be adjusted in real-time by changing the external fields [24]. Here we present the performance of super-resolution imaging in air using patchy microspheres.…”