New Multichannel Frontal Polymerization Strategy for Scaled-up Production of Robust Hydrogels

Herein, we report a new facile and safe pathway for the scaled-up production of mechanically strong and multiresponsive interpenetrating polymer network (IPN) hydrogels via multichannel frontal polymerization (multichannel FP). We designed a two-part system, of which part-1 contained high reactive monomer and could polymerize spontaneously. The polymerization of part-1 released tremendous amount of heat, subsequently initiating FP of part-2 to convert monomers to polymers without any external energy, which is flexible, cost-effective, and environmental. Multichannel FP not only allowed realization of parallel polymerization to obtain a number of hydrogels but also solved center overheating and explosion problem stemmed from a large reaction vessel. Compared with the sample prepared in bigger tubular reactor, product synthesized via multichannel FP showed more excellent thermal stability, morphology and mechanical properties. Moreover, the as-prepared IPN hydrogels exhibited chemical-, pH-, and thermal-sensitivity toward various external changes, which might broaden the applications of hydrogels in sensors

Magnetic-Directed Assembly from Janus Building Blocks to Multiplex Molecular-Analogue Photonic Crystal Structures

The predictable assembly of colloidal particles into a programmable superstructure is a challenging and vital task in chemistry and materials science. In this work, we develop an available magnetic-directed assembly strategy to construct a series of molecular-analogue photonic crystal cluster particles involving dot, line, triangle, tetrahedron, and triangular bipyramid configurations from solid–liquid Janus building blocks. These versatile multiplex molecular-analogue structural clusters containing photonic band gap, fluorescent, and magnetic information can open a new promising access to a variety of robust hierarchical microstructural particle materials

Fabrication of Reversible Phase Transition Polymer Gels toward Metal Ion Sensing

We report the synthesis of a new type of triple stimuli-responsive, i.e., thermo-, pH-, and metal ion-responsive copolymers based on poly­(<i>N</i>-vinylimidazole-<i>co</i>-methacrylic acid) (poly­(VI-<i>co</i>-MAA)) and their application as metal ion sensors. The copolymers exhibit reversible sol–gel phase transition behavior in aqueous media. The sol-to-gel transition temperature (<i>T</i>_sol–gel) can be shifted in the range of 20–80 °C, by varying monomer ratio and feeding glycerol content, by adjusting the copolymer concentration in aqueous solution, by tuning the pH of the solution, or by adding various divalent metal ions. Metal ion sensors were designed upon an inverse opal photonic film loaded with aqueous solution of poly­(VI-<i>co</i>-MAA), which allows the easy reorganization of various divalent metal ions by combining the diversity of <i>T</i>_sol–gel of the copolymers on different metal ions and flexible reflection spectra of the film. In addition, a fluorescent reversible sol–gel transition system was established by <i>in situ</i> generation of nanocrystals in the copolymer matrix. These extensions may provide the multiresponsive copolymers great flexibility for applications in biomedical, optical, and sensory fields

Design of Phosphor White Light Systems for High-Power Applications

We developed a strategy that transforms phosphor down-converting white light sources from low-power systems into efficient high-power ones. To incorporate multiple phosphors, we generalized and extended a phosphor layer model, which we term CCAMP (color correction analysis for multiple phosphors). CCAMP describes both the scattering and saturation of phosphor materials and allows modeling of different layered structures. We employed a phosphor mixture comprising YAG:Ce and K₂TiF₆:Mn⁴⁺ to illustrate the effectiveness of the model. YAG:Ce’s high density and small particle size produce a large amount of scattering, while the long (4.8 ms) photoluminescent lifetime of K₂TiF₆:Mn⁴⁺ results in saturation at high pump power. By incorporating experimental photophysical results from the phosphors, we modeled our system and chose the design suitable for high-power applications. We report the first solid-state phosphor system that creates warm white light emission at powers up to 5 kW/cm². Furthermore, at this high power, the system’s emission achieves the digital cinema initiative (DCI) requirements with a luminescence efficacy improvement of 20% over the stand-alone ceramic YAG:Ce phosphor

Quantum Dot Color-Converting Solids Operating Efficiently in the kW/cm² Regime

With rapid progress in the use of colloidal quantum dots (QDs) as light emitters, the next challenge for this field is to achieve high brightness. Unfortunately, Auger recombination militates against high emission efficiency at multiexciton excitation levels. Here, we suppress the Auger-recombination-induced photoluminescence (PL) quantum yield (QY) loss in CdSe/CdS core–shell QDs by reducing the absorption cross section at excitation wavelengths via a thin-shell design. Studies of PL vs shell thickness reveal that thin-shell QDs better retain their QY at high excitation intensities, in stark contrast to thicker-shell QDs. Ultrafast transient absorption spectroscopy confirms increased Auger recombination in thicker-shell QDs under equivalent external excitation intensities. We then further grow a thin ZnS layer on thin-shell QDs to serve as a higher conduction band barrier; this allows for better passivation and exciton confinement, while providing transparency at the excitation wavelength. Finally, we develop an isolating silica matrix that acts as a spacer between dots, greatly reducing interdot energy transfer that is otherwise responsible for PL reduction in QD films. This results in the increase of film PL QY from 20% to 65% at low excitation intensity. The combination of Auger reduction and elimination of energy transfer leads to QD film PL QY in excess of 50% and absolute power conversion efficiency of 28% at excitation powers of 1 kW/cm², the highest ever reported for QDs under intense illumination