Efficient and large scale printing of photonic crystal patterns with multicolor, multigrayscale, and fine resolution is highly desired due to its application in smart prints, sensors, and photonic devices. Here, an electric-field-assisted multicolor printing is reported based on electrically responsive and photocurable colloidal photonic crystal, which is prepared by supersaturationinduced self-assembly of SiO 2 particles in the mixture of propylene carbonate (PC) and trimethylolpropane ethoxylate triacrylate (ETPTA). This colloidal crystal suspension, named as E-ink, has tunable structural color, controllable grayscale, and instantly fixable characteristics at the same time because the SiO 2 /ETPTA-PC photonic crystal has metastable and reversible assembly as well as polymerizable features. Lithographical printing with photomask and maskless pixel printing techniques are developed respectively to efficiently prepare multicolor and high-resolution photonic patterns using a singlecomponent E-ink.
Invisible photonic crystal (PC) pattern with encrypted
and discoverable
information is potentially useful for anti-counterfeiting labels,
but it is still a big challenge to realize strict invisibility, fast
response, and convenient triggering. Here, a new kind of soaking-revealed
invisible PC pattern is fabricated by the regional coating of “ethylene
glycol–ethanol” ink on a collapsed inverse opaline macroporous
polyurethane (IOM-PU) film, followed by a quick thermal treatment.
During the above process, wet heating retains the collapsed but recoverable
IOM structure, but dry heating disables the recovery of ordered IOM
structure due to the adhesion of macropore walls, which render the
“pattern” and the “background” with different
optical responses to the solvent. In the dry state, the pattern was
invisible because both the collapsed IOM-PU film and the adhesive
PU film are colorless and transparent. Once the sample is soaked in
ethanol–water mixtures, the invisible pattern appears immediately
because only the “wet-heated” region recovers the ordered
macroporous structure and shows color, which forms a significant contrast
in color to the “dry-heated” region. Compared to the
previously invisible PC pattern, the current material has many superior
properties, such as high invisibility, large color contrast in showing,
excellent recyclability, and good toughness in bending and stretching.
The repetitive size change of the electrode over cycles, termed as mechanical breathing, is a crucial issue limiting the quality and lifetime of organic electrochromic devices. The mechanical deformation originates from the electron transport and ion intercalation in the redox active material. The dynamics of the state of charge induces drastic changes of the microstructure and properties of the host, and ultimately leads to structural disintegration at the interfaces. We quantify the breathing strain and the evolution of the mechanical properties of poly(3,4-propylenedioxythiophene) thin films in-situ using customized environmental nanoindentation. Upon oxidation, the film expands nearly 30% in volume, and the elastic modulus and hardness decrease by a factor of two. We perform theoretical modeling to understand thin film delamination from an indium tin oxide (ITO) current collector under cyclic load. We show that toughening the interface with roughened or silica-nanoparticle coated ITO surface significantly improves the cyclic performance.
In this paper, broadband microwave absorbers utilizing water-based metamaterial structure elements have been proposed and investigated. We employ water into the metamaterial structure unit-cell of the absorber as primary resonant elements such as the water-droplet, or water-tube structure. By investigating the resonant modes and the coupling between the water elements and the surrounding dielectrics, it is found the inherent multi-resonance of the proposed metamaterial structures could result in a broadband microwave absorption. For water-droplets design, 90% microwave absorption has been achieved from 7.5 GHz to 15 GHz, while for water-tube design, a much broader bandwidth from 5 GHz to 15 GHz is obtained for nearly 90% microwave absorption. The broadband absorption performance has been verified by both full wave simulation and experimental measurement. We believe the proposed broadband water-based absorber may find some applications in microwave stealth and electromagnetic compatibility technology.
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