1,721,040 research outputs found
Cooperative Assembly of Block Copolymers with Deformable Interfaces: Toward Nanostructured Particles
No full textBlock copolymers confined in emulsion droplets self-organize into polymeric particles, and cooperative self-assembly driven by deformable interfacial properties produces unprecedented structural motifs such as prolates of stacked lamellae, oblates with biomimetic nanoscale architecture, and spheres with tori or helices (see figure). Interface-mediated structural evolution provides a novel route for synthesizing functional particles with unique nanostructures
Transparent poly(ether sulfone) nanocomposite film with low thermal expansion coefficient for flexible display substrates
No full textOptically transparent poly(ether sulfone) (PES) nanocomposite films with low coefficients of thermal expansion (CTE) were synthesized for use as flexible display substrates. Boehmite (AlOOH) nanowires similar to 10 nm in diameter were synthesized and applied as fillers to reduce the CTE of the PES film. PES molecules were slightly sulfonated to enhance their compatibility with AlOOH nanowires via hydrogen bonding. The aspect ratio of the AlOOH nanowires had a significant effect on the CTE of nanocomposite films. At a fixed filler concentration of 15 wt%, the AlOOH nanowires with an aspect ratio of 100 reduced the CTE of the PES film by 73.6 % from 65.5 ppm/degrees C to 17.3 ppm/degrees C, while those with an aspect ratio of 20 reduced it only by 28 %. Although such a huge reduction of CTE was provided by AlOOH nanowires, the optical transmittance was still 96 % of the pristine PES film because the refractive indices of PES and AlOOH nanowires were the same. Introduction of AlOOH nanowires also enhanced the thermal and dimensional stabilities of the PES film.11Nsciescopu
High-speed fabrication of patterned colloidal photonic structures in centrifugal microfluidic chips
No full textIn this paper, we report a rapid and facile method for fabricating colloidal photonic crystals inside microchannels of radially symmetric microfluidic chips which were made using soft-lithography. As the suspension of monodisperse silica or polystyrene latex spheres was driven to flow through the channels under the action of centrifugal force, the colloidal spheres were quickly assembled into face centered cubic arrangement which had a few photonic stop bands. The soft-microfluidic channels and cells confined the colloidal crystals into designed patterns. The optical reflectance was modulated by the refractive-index mismatch between the colloidal particles and the solvent in the interstices between the particles. Therefore, the present microfluidic chips with built-in colloidal photonic crystals can be used as in-situ optofluidic microsensors for high throughput screening or light filters in integrated adaptive optical devices.the Creative Research
Initiative Program of the Ministry of Science and Technology and the Brain Korea 21 Program
POSTECH as the Hub of Innovative Materials Research in South Korea over the last 35 Years
No full text11Nsciescopu
Structure-Tunable Construction of Colloidal Photonic Composites via Kinetically Controlled Supramolecular Crosslinking
No full textColloidal photonic composites (CPCs) combine a unique array of colloidal particles (CPs) with a polymer matrix and exhibit intriguing optical and mechanical properties strongly depending on their structures. One-step construction of CPCs with tunable structures is crucial for enriching their properties and matching application requirements, which is highly desirable yet challenging. Here, we present a general strategy for CPC construction with tunable structures from short-range to long-range order by one-step kinetically controlling the supramolecular crosslinking between CPs and supramolecular oligomers. Importantly, the assembly process is monitored in situ and the key factors for structural regulation, i.e., the critical volume fraction of CPs and the structural transition from crystal growth to lattice compression, are disclosed, which play critical roles in obtaining CPCs with a wide range of controllable structures. The as-obtained CPCs exhibit structural colors with different angle dependencies, versatile mechanical strengths, and appealing mechanochromic and self-healing capabilities. This work provides insights into the one-step construction of structure-tunable photonic materials, opening up exciting avenues for novel solution-processable photonics. © 2022 American Chemical Society. All rights reserved.11Nsciescopu
Index-Matched Composite Colloidal Crystals of Core-shell Particles with Structural Colors and Optical Transparency
No full textWe prepared composite colloidal crystal films of core–shell nanospheres in an index-matched polystyrene matrix. Therefore, we demonstrate strong reflection colors in a thick colloidal film keeping high optical transparency. Furthermore, with no deterioration of light transmission in our index-matched composite colloidal crystals, bicolored reflective films were also successfully prepared by stacking two different colloidal crystal films. Finally, by introducing photopolymerizable resin inside colloidal crystals, we patterned composite photonic crystals through selective photopolymerization and repeated photopatterning process for multicolored films. These films may potentially be useful in reflective displays, encryption, and optical identification.2
Self-organization of colloidal nanospheres inside emulsion droplets: Higher-order clusters, supraparticles, and supraballs
No full textMonodisperse cross-linked polystyrene nanospheres were self-organized to obtain colloidal aggregates from toluene-in-water emulsion droplets employed as confining geometries. During evaporation of toluene droplets by heating, the polystyrene nanospheres were packed into higher-order clusters, supraparticles with intermediate ordering or supraballs with hexagonally ordered structures, depending on the size of the emulsion droplets, and the number of constituent polystyrene particles inside the droplets. The shrinkage of toluene droplets induced inward capillary pressure, leading to particle self-assembly into ordered spherical supraballs when a large number of polystyrene particles were contained inside the droplets. Ink-jet technology was adopted to generate monodisperse toluene droplets containing polystyrene particles, which were transformed into monodisperse supraballs after evaporation-driven self-assembly of the polystyrene nanospheres. As an alternative approach, water-in-toluene droplets were also adopted as confining geometries for the generation of supraballs. (C) 2009 Elsevier B.V. All rights reserved.This work was supported by a grant from the Creative Research
Initiative Program of the Ministry of Science & Technology for
“Complementary Hybridization of Optical and Fluidic Devices for
Integrated Optofluidic Systems.” Dr. Young-Sang Cho acknowledges
the Korea Basic Science Institute for assistances with scanning electron
microscopy. Dr. Gi-Ra Yi acknowledges the support of a KBSI
grant (N28073) and by small and medium business administration
(S1025323)
Polymeric particles with structural complexity from stable immobilized emulsions
No full textWe prepared polymeric structures with unusual complexity in surface morphology derived from photocurable emulsion droplets dispersed in an aqueous medium. The emulsion droplets a few tens of micrometers in size were stabilized with relatively small hydrophobic particles that were bound to the emulsion interfaces. The particle binding tended to immobilize the oil-in-water emulsion interface and dramatically increased the structural relaxation time of the interface deformation over a few days relative to a few milliseconds for an otherwise clean interface. In particular, perfectly immobilized emulsion drops maintained nonspherical elongated structures that were formed by shear-induced emulsification and could not be relaxed to a spherical shape. This property is useful for broad research areas ranging from crystallography and buckling phenomena to materials fabrication. The configuration of small particles on the interface and the "raspberry" shape of particle-stabilized emulsions were captured successfully by photocuring the emulsion droplets because the small bound particles immobilized the emulsion droplets. By selectively removing the small particles from the particle-covered polymeric structures, we prepared dimpled microparticles with various shapes. The dimple geometry depended on the interfacial properties or phase affinity of the small particles. The contact angle and binding energy of the particles were calculated on the basis of the dimple geometry. In addition, buckling phenomena of the particle-stabilized emulsions were observed when volatile oil was added to the photocurable resin.the Creative Research Initiative Program of the Ministry of Science & Technology for “Complementary Hybridization of
Optical and Fluidic Devices for Integrated Optofluidic Systems.”
the Brain Korea 21 Progra
High-speed fabrication of patterned colloidal photonic structures in centrifugal microfluidic chips
No full textIn this paper, we report a fast and facile method for fabricating colloidal photonic crystals inside microchannels of radially symmetric microfluidic chips. As the suspension of monodisperse silica or polystyrene latex spheres was driven to flow through the channels under the centrifugal force, the colloidal spheres were quickly assembled into face centered cubic arrangement which had photonic stop bands. The optical reflectance spectrum was modulated by the refractive-index mismatch between the colloidal particles and the solvent filled in the interstices between the particles. Therefore, the present microfluidic chips with built-in colloidal photonic crystals can be used as in-situ optofluidic microsensors for high throughput screening, light filters and biosensors in integrated adaptive optical devices
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