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- 2019
- fan-in/out devices
- polymer optical waveguide
- the Mosquito method
- space division multiplexing
- Optoelectronic Information Science and Engineering
- Keio University
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Conformational Transitions of Polymer Chains in Solutions Characterized by Fluorescence Resonance Energy Transfer
摘要： The critical overlap concentration C* is an important concept in polymer solutions and is defined as the boundary between dilute and semidilute regimes. In this study, the chain conformational changes of polystyrene (PS) with both high (Mn = 200,000 Da) and low (Mn = 13,000 Da) molecular weights in cis-decalin were compared by intrachain fluorescence resonance energy transfer (FRET). The random labeling of donor and acceptor chromophores strategy was employed for long PS chains, whereas chain-end labeling was used for short PS chains. By monitoring the spectroscopic intensity ratio between acceptor and donor, the concentration dependence on chain conformation from dilute to semidilute solutions was determined. Both long and short chains exhibit a conformational transition concentration, above which the polymer chains begin to collapse with concentration significantly. Interestingly, for randomly labeled polymer long chains, such concentration is consistent with C* determined from the viscosity result, below which only slight conformational change of polymer chain takes place. However, for the chain-end labeled short chain, the conformational transition concentration takes place earlier than C*, below which no significant polymer conformation change is observed.
关键词： viscosity,conformational transition,polymer solution,critical overlap concentration,fluorescence
更新于2025-09-23 15:23:52
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Future Scope of Silicone Polymer based Functionalized Nanocomposites for Device Packaging: A Mini Review
摘要： Organic electronic devices, such as conducting polymer and/or perovskite based solar cells are highly promising and emerging, but they are highly unstable in the presence of moisture and oxygen. It is important to protect these devices from these deterrent gases by using a suitable encapsulant and to improve the lifetime of these promising devices. “Silicone polymer” impregnated with suitable functionalized nano fillers/moisture or oxygen scavengers can be potentially used for sensitive organic device encapsulation applications, where a combined property of flexibility, thermal stability, transparency, and low moisture permeation is critical. Suitable fillers can also enhance the thermo-mechanical properties of silicone polymers, which is also important for hermitic sealing applications. Silicone polymer have a wide range of applications in electronic, mechanical, and biological industries, due to their flexibility over a broad temperature window, resiliency, transparency, superior thermal stability, resistant to aging and degradation from sunlight. This polymer also coats a surface conformally, having moisture resistance property and inertness. In this mini-review, functionalized composites based on silicone polymers, which have been developed for the potential organic device encapsulation application, has been discussed. In addition to that, future direction towards the fabrication of new functionalized nanocomposites, based on silicone polymers is also discussed briefly.
关键词： Nanocomposite,Curing,Organic devices,Functionalization,Silicone polymer
更新于2025-09-23 15:23:52
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Fighting aggregation-caused quenching and leakage of dyes in fluorescent polymer nanoparticles: universal role of counterion
摘要： Dye-loaded polymer nanoparticles (NPs) emerge as a powerful tool for bioimaging applications, owing to their exceptional brightness and controlled small size. However, aggregation-caused quenching (ACQ) and leakage of dyes at high loading remain important challenges of these nanomaterials. The use of bulky hydrophobic counterions has been recently proposed as an effective approach to minimize ACQ and dye leakage, but the role of counterion structure is still poorly understood. Here, a systematic study based on ten counterions, ranging from small hydrophilic perchlorate up to large hydrophobic tetraphenylborate derivatives, reveals how counterion nature can control encapsulation and emission of a cationic dye (rhodamine B octadecyl ester) in NPs prepared by nanoprecipitation of a biodegradable polymer, poly-lactide-co-glycolide (PLGA). We found that increase in counterion hydrophobicity enhances dye encapsulation efficiency and prevents dye adsorption at the particle surface. Cellular imaging studies revealed that ≥95% encapsulation efficiency, achieved with most hydrophobic counterions (fluorinated tetraphenylborates), is absolutely required, because non-encapsulated dye species at the NPs surface are the origin of dye leakage and strong background in cells. The size of counterions is found to be essential to prevent ACQ, where the largest species, serving as effective spacer between dyes, provide the highest fluorescence quantum yield. Moreover, we found that the most hydrophobic counterions favor dye-dye coupling inside NPs, leading to ON/OFF fluorescence switching of single particles. By contrast, less hydrophobic counterions tend to disperse dyes in the polymer matrix favoring stable emission of NPs. The obtained structure-property relationships validate the counterion-based approach as a mature concept to fight ACQ and dye leakage in the development of advanced polymeric nanomaterials with controlled optical properties.
关键词： dye-loaded polymer nanoparticles,fluorescent nanoparticles,bulky hydrophobic counterion,aggregation-caused quenching,bioimaging
更新于2025-09-23 15:23:52
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Unique Substitution Effect at 5,5′ Positions of a Fused Azobenzene-Boron Complex with N=N Double-Bond π-Conjugated System
摘要： The recent report illustrates superior optical properties, such as near infrared emission, from the polymers with the connection positions at 4,4′ positions in the fused azobenzene–boron complex (BAz). In this study, we initially demonstrate that further narrower band gap can be realized by the substituent effect with bromine groups at 5,5′ positions of BAz than that at 4,4′ positions. From the series of mechanistic studies, perturbation of the energy levels were rationally explained by the contribution difference between the inductive effect and the variable resonance effect which is correlated to the degree of electron distribution of molecular orbitals at the substituent positions. Moreover, it was found that unique electronic states, such as delocalized highest occupied molecular orbital and localized lowest unoccupied molecular orbital, should appear on the main chains of the BAz-containing copolymers with fluorene and bithiophene units according to the optical and electrochemical data and theoretical calculations. Taking advantage of property tunability and the dramatic low LUMO energy level (near ?4.0 eV) of the BAz unit, it can be said that BAz should be a conjugated building block favorable for building advanced optoelectronic devices.
关键词： azobenzene,boron,narrow band gap,conjugated polymer,low LUMO
更新于2025-09-23 15:23:52
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Chain End-Functionalized Polymer Brushes with Switchable Fluorescence Response
摘要： Herein is described the switchable fluorescence response of poly(methyl methacrylate) (PMMA) brushes. Chain end fluorescein labeled PMMA brushes are prepared by combining surface-initiated atom transfer radical polymerization (SI-ATRP) with a copper-catalyzed alkyne-azide cycloaddition (CuAAC) click reaction. Successful attachment of fluorescein is confirmed by measuring fluorescence of the as-prepared films. Utilizing co-solvency of PMMA in isopropanol-water mixtures, responsive behavior of the end-functionalized brushes is demonstrated by measuring the changes in fluorescence intensity between the swollen and collapsed states.
关键词： fluorescent polymers,polymer brushes,co-solvency,solvent responsiveness
更新于2025-09-23 15:23:52
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Graphene-Augmented Polymer Stabilization: Drastically Reduced and Temperature-Independent Threshold and Improved Contrast Liquid Crystal Device
摘要： Polymers reinforced with nano?llers, especially graphene in recent times, have continued to attract attention to realize novel materials that are cheap and also have better properties. At a di?erent level, encapsulating liquid crystals (LCs) in polymer networks not only adds mechanical strength, but could also result in device-based refractive index mismatch. Here, we describe a novel strategy combining the best of both these concepts to create graphene-incorporated polymer-stabilized LC (PSLC) devices. The presence of graphene associated with the virtual surface of the polymer network besides introducing distinct morphological changes to the polymer architecture as seen by electron microscopy brings out several advantages for the PSLC characteristics, which include 7-fold lowered critical voltage, its temperature invariance, and enhanced contrast ratio between ?eld-o? scattering/?eld-on transparent states. The results bring to fore the importance of working at very-dilute-concentration limits of the ?ller nanoparticles in augmenting the desired properties. These observations open up a new vista for polymer?graphene composites in the area of device engineering, including substrate-free smart windows.
关键词： temperature invariance,graphene,electro-optic properties,threshold voltage,polymer-stabilized liquid crystals
更新于2025-09-23 15:23:52
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Structural and Optical Properties of CeO2 Nanoparticles Synthesized by Modified Polymer Complex Method
摘要： Ceria nanoparticles (Ceria-NPs) were synthesized using a modified polymer complex method and their structural and optical properties were evaluated. The solids were heated at 550 °C and characterized using Raman, UV–Vis absorption, diffuse reflectance, X-ray photoelectron and photoluminescence spectroscopies, X-ray diffraction (XRD) and scanning and transmission electron microscopy. The primary particles obtained presented a size of ~ 10 nm. The XRD indicated that CeO2 was the only crystalline phase. From the UV–Vis and diffuse reflectance spectra, energy values of 3.8 eV and 3.4 eV were obtained, values that can be associated with band—band electronic transitions and/or with those that involve ionized states located within the gap caused by defects and isolated atoms of Ce3+. Photoluminescence spectra reiterated the existence of localized states in the gap. Raman spectra revealed the existence of peroxide (O2^2-) and superoxide (O2^-) over the surface of the ceria-NPs. The XPS results indicated that the concentrations of Ce3+ and Ce4+ were ～ 20.5% and ～79.5% respectively, and that the stoichiometry of oxygen was 1.9 per atom of Ce. The results obtained from the characterization of CeO2-NPs synthesized make it as promising material for environmental remediation, biomedicine, gas sensing and optoelectronic applications.
关键词： Modified polymer complex,Structural properties,Ceria-NPs,Optical properties,Synthesis
更新于2025-09-23 15:23:52
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Light-induced EPR study of spin-assisted charge transport in PFOT:PC61BM composite
摘要： Magnetic resonance, relaxation and dynamic parameters of polaron spins and methanfullerene radical anions, initiated by the infrared-visible-ultraviolet photons in bulk heterojunctions of the composite formed by narrow-band poly[(9,9-dioctylfluorenyl-2.7-diyl)-co-(bithiophene)] (PFOT, F8T2) copolymer and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) globules were investigated by the direct Light-Induced Electron Paramagnetic Resonance (LEPR) spectroscopy. It was shown that some of the polarons are captured by spin traps formed in the copolymer matrix due to its disordering. The number, spatial distribution and energy depth of such traps depend on the structure and morphology of composite. It is shown that the main parameters of both charge carriers are determined by the exchange interaction of the spin ensembles, as well as the energy of the photons. The formation of spin traps in the copolymer matrix and the exchange interaction between different spin packets cause the extreme sensitivity of the composite's magnetic resonance and electronic parameters to the number and energy of the initiating photons. The predominant photoinitiation of localized polarons in the copolymer matrix was demonstrated. This process is substantially accelerated when the composite is illuminated by photons with the energy lying near 1.8 and 2.7 eV. The recombination of both charge carriers can be described in terms of a bimolecular process of the second order. It was found that the contributions of polarons and methanofullerene radical anions to the effective paramagnetic susceptibility increase substantially near the photon energy of 2.6 and 2.1 eV due to the exchange interaction of these charge carriers. It is shown that the mobility of polarons varies monotonically throughout all the photon energy range, whereas the librational spin dynamics of the methanofullerene globules is substantially accelerated near the photon energy of 2.0 and 2.7 eV.
关键词： Polymer nanocomposites,Spin recombination,Transport properties,Spin interaction,Polaron,Light-induced EPR
更新于2025-09-23 15:23:52
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Low-density PMMA/MAM nanocellular polymers using low MAM contents: Production and characterization
摘要： Low-density nanocellular polymers are required to take advantage of the full potential of these materials as high efficient thermal insulators. However, their production is still a challenging task. One promising approach is the use of nanostructured polymer blends of poly(methyl methacrylate) (PMMA) and a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM), which are useful for promoting nucleation but seem to present a severe drawback, as apparently avoid low relative densities. In this work, new strategies to overcome this limitation and produce low-density nanocellular materials based on these blends are investigated. First, the effect of very low amounts of the MAM copolymer is analysed. It is detected that nanostructuration can be prevented using low copolymer contents, but nucleation is still enhanced as a result of the copolymer molecules with high CO2 affinity dispersed in the matrix, so nanocellular polymers are obtained using very low percentages of the copolymer. Second, the influence of the foaming temperature is studied. Results show that for systems in which there is not a clear nanostructuration, cells can grow more freely and smaller relative densities can be achieved. For these studies, blends of PMMA with MAM with copolymer contents from 10 wt% and as low as 0.1 wt% are used. For the first time, the production strategies proposed in this work have allowed obtaining low density (relative density 0.23) nanocellular polymers based on PMMA/MAM blends.
关键词： nanostructuration,gas dissolution foaming,PMMA,MAM,block copolymer,nanocellular polymer,nanocellular foam
更新于2025-09-23 15:23:52
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Flexible photoluminescent humidity sensing material based on electrospun PVA nanofibers comprising surface-carboxylated QDs
摘要： Flexible humidity-sensitive materials have drawn increasing attention due to their vital function in monitoring ambient humidity for tactile sensors, allowing them to approach the functionality of human skin. In this work, an electrospun polyvinyl alcohol (PVA)-based nanofiber film comprising surface-carboxylated CdSe/CdxZn1-xS quantum dots (QDs) is fabricated as a high-performance flexible humidity sensing material, based on the relationship between its photoluminescence (PL) and the humidity. The as-prepared film shows excellent PL-humidity linearity, a wide sensing range from 10% to 90% relative humidity, a relatively fast response time, good recoverability, and flexibility. The humidity sensing mechanism can be attributed to the breaking and reforming of hydrogen bonds and proton transfer occurring at the PVA-QD interfaces. This flexible humidity-sensitive material is believed to be a good candidate for humidity-sensitive components in electronic skin.
关键词： Humidity sensing,Polymer,Photoluminescence,Quantum dots
更新于2025-09-23 15:23:52