Thermal Refractive Index Research Articles

Rigid Polyimides with Thermally Activated Delayed Fluorescence for Polymer Light-Emitting Diodes with High External Quantum Efficiency up to 21 .

A series of rigid nonconjugated polyimide (PI)-based thermally activated delayed fluorescence (TADF) polymers were reported for the first time, based on a "TADF-Linker-Host" strategy. Among of which, the TADF unit contains a typical TADF luminous core structure, the "Host" unit exhibits effective conjugation length that endows polyimide with high triplet energy, and the "Linker" unit has an aliphatic ring structure to improve solubility and inhibits intramolecular charge transfer effect. All the TADF polymers exhibit high thermal stability (Tg >308.7 °C) and refractive index (1.76-1.79). Remarkably, highly-efficient polymer light-emitting diodes (PLEDs) based on the polymers are successfully realized, leading to a maximal external quantum efficiency of 21.0 % along with low efficiency roll-off. Such outstanding efficiency is amongst the state-of-the-art performance of nonconjugated PLEDs, confirming the effectiveness of structural design strategy, providing helpful and valuable guidance on the development of highly-efficient fluorescent polymer materials and PLEDs.

Carbon as a Solution for Nanocellular Foam Superinsulation

This work demonstrates the substantially improved thermal radiation blocking capability of polymer foams with the utilization of carbonaceous nanoparticles to overcome the limitation of the nanocellular foam’s thermal insulation capability to achieve superinsulation. Without carbon, the radiation heat transfer becomes extremely high through thin and transparent cell walls and struts of the low-density nanocellular foams. However, this high radiative heat transfer can be successfully reduced by incorporating multi-walled carbon nanotubes (MWCNTs). The effect of carbon on heat transfer in foams was mathematically modelled and experimentally verified. The model includes contributions of thermal transport through conduction and radiation, while convection is negligible. The effects of MWCNTs on thermal conductivity, refractive index, absorption index, dielectric permittivity and dielectric loss of the solid were studied using two examples of polystyrene/MWCNT and PMMA/MWCNT nanocomposite foams. It was found that, with carbon, the radiation blocking capability is significantly improved and nanocellular foams could achieve superinsulation level through the Knudsen effect. The optimal cellular structure at which heat transfer is minimized was investigated with the aim of manufacturing superinsulation. The foam’s total heat transfer decreased while the optimal expansion ratio increased with the filler content, which is preferable for manufacturing high performance insulation with less polymer.

Physicochemical properties of sustainable caped ZnO-Dendrimer nanocomposite with aqueous DMSO interfaces from 298.15–313.15 K

FRSA (free radical scavenging activity) of antioxidant polyphenols (APP) capped ZnO NPs is tuned with TTDMM (trimesoyl tridimethyl malonate) interfaces in aq.DMSO by modulating undesired effect of DMSO. Such action occurs on interlocuting hydrophobic and hydrophobic interactions of –CH3 groups (DMSO) with 6 terminal –CH3 groups of TTDMM tweezer respectively. The studies are supported with physiochemical contour of APP capped ZnO (c-ZnO) and c-ZnO NPs loaded TTDMM nanocomposites (cZTNCs) dispersed in aqueous (aq.) and aq.DMSO respectively to form nanocolloids. Intermolecular interactions for dispersion and stability have been explored via density (ρ), sound velocity (u), isentropic compressibility (Ks), acoustic impedance (Z), thermal expansion coefficient (β), surface tension (γ), viscosity (η), friccohesity (σ), light velocity (C) and refractive index (μri) from (298.15 to 313.15) K. The values of these structural parameters infer the impacts of APP and TTDMM on surface reengineering of nanocolloids via philicphobic domain, London dispersive forces (LDF), van der Waals forces (VWF), and hydrogen bond (HB). Besides this, the nanocolloids are not getting destructured but monodispersed and were analyzed through the said physiochemical parameters. FTIR stretching frequencies (SF) of nanocolloids have synchronized their intermolecular interactions with the surrounding medium. The unaltered surface plasmon resonance (SPR) peak for cZTNC nanocolloids inferred stability via UV/Vis spectra. The moderate negative values for Gibbs energy (ΔG), enthalpy (ΔH),entropy (ΔS), and positive activation energy (Ea) with least Ks have inferred thermodynamically and kinetically (TAK) stable cZTNC nanocolloids as the void spaces of TTDMM tweezer entrap c-ZnO NPs to a specific orientation.

A four-layer Ag-ZnO-LPFG structure for improving temperature sensitivity and coupled-wavelength transmittance stability

A novel long-period fiber grating (LPFG) with a four-layer structure is proposed, made by coating double layers of both ZnO and Ag onto a bare LPFG. Pulsed laser deposition (PLD) technology can effectively control the flatness and nanoscale thickness of ZnO film, which is conducive to achieving full energy coupling with the Ag layer and the grating. Compared with SiO2, ZnO has a higher thermal expansion coefficient and refractive index, which ensures that coated LPFG has a higher temperature sensitivity. As the fourth layer of the structure, colloidal silver is coated onto the surface of the ZnO film at an optimal thickness by a spin-coating method. The higher thermal expansion coefficient of the Ag film and a plasma resonance effect on its surface cause the temperature sensitivity to increase again. The sensitivity of the coated Ag-ZnO-LPFG structure is 1.4 times higher than that of the bare fiber. The temperature sensitivity is increased from 0.063 nm °C−1 to 0.088 nm °C−1, while retaining good linearity. We also solve the problem whereby the coating disturbs the coupled-wavelength transmittance, and by doing so, we increase the stability of the coupled-wavelength transmittance and enhance measurement accuracy.

Thermal tuning of arsenic selenide glass thin films and devices.

We present a method of post-deposition tuning of the optical properties of thin film dielectric filters and mirrors containing chalcogenide glass (ChG) layers by thermally adjusting their refractive index. A common challenge associated with the use of ChG films in practical applications is that they suffer from slight run-to-run variations in optical properties resulting from hard-to-control changes in source material and deposition conditions. These variations lead to inconsistencies in optical constants, making the fabrication of devices with prescribed optical properties challenging. In this paper, we present new work that takes advantage of the large variation of a ChG films' refractive index as a function of annealing. We have carried out extensive characterization of the thermal index tuning and thickness change of arsenic selenide (As2Se3) ChG thin films and observed refractive index changes larger than 0.1 in some cases. We show results for refractive index as a function of annealing time and temperature and propose a model to describe this behavior based on bond rearrangement. We apply thermal refractive index tuning to permanently shift the resonance of a Fabry-Perot filter and the cutoff wavelength of a Bragg reflector. The Bragg reflector, consisting of alternating As2Se3 and CaF2 layers, exhibits high reflectance across a ∼550 nm band with only five layers. Modeling results are compared with spectroscopic measurements, demonstrating good agreement.

Soluble network polymers based on trifluoropropyl‐substituted open‐cage silsesquioxane: Synthesis, properties, and application for surface modifiers

AbstractFluorinated completely condensed polyhedral oligomeric silsesquioxanes (F‐CC‐POSSs) are widely utilized as surface modifiers for polymeric materials because of their polyhedral and fluorine‐rich structures, which generate polymers with lower surface energies under molecular‐level control. In contrast, their derivatives, fluorinated incompletely condensed or open‐cage POSSs (F‐IC‐POSSs), have similarly intriguing structures, but their utilization for polymer synthesis remains undeveloped. Herein, fluorinated network polymers were prepared based on a 3,3,3‐trifluoropropyl‐substituted IC‐POSSs via hydrosilylation polymerization with isobutyl‐ and phenyl‐substituted IC‐POSS under optimized conditions. In addition to their good thermal stability and tunable refractive indices, these polymers exhibited solution processability and their casting films showed excellent optical transparency, indicating their potential for constructing fluorinated polymers. Their utilization as surface modifiers was examined by addition to poly(methylmethacrylate) (PMMA) films. Intriguingly, modified PMMA films with 2.0 and 0.5 wt% addition showed similar hydrophobicity and surface energies to the films prepared with only fluorinated network polymers.

Production of Soda Lime Glass Having Antibacterial Property for Industrial Applications.

This study was aimed to produce and characterize the first commercial glass materials with enhanced antibacterial property using conventional melting method. For this purpose, typical container glass composition that contains some specific metal ions, such as silver, strontium, and copper, was used to obtain antibacterial glass samples using classical melting method. After the melting process, antibacterial tests and migration tests were applied to the glasses, and it was found that the glass doped with 2% Ag2O was the best composition. X-rays diffractometer (XRD), thermal expansion coefficient, density, refractive index, hardness, and elastic module results showed that the glass doped with 2% Ag2O was a suitable material as a container glass. High Temperature Melting Observation System studies were performed on the produced antibacterial glass composition, and it was found that the antibacterial glass can be produced in soda lime glass furnaces without changing any furnace design and production parameters. As a result of the characterization studies, it was concluded that the produced container glass doped with silver can be a good candidate for food and pharmaceutical products where bacterial growth is absolutely undesirable.

Downscaling of sample entropy of nanofluids by carbon allotropes: A thermal lens study.

The work reported in this paper is the first attempt to delineate the molecular or particle dynamics from the thermal lens signal of carbon allotropic nanofluids (CANs), employing time series and fractal analyses. The nanofluids of multi-walled carbon nanotubes and graphene are prepared in base fluid, coconut oil, at low volume fraction and are subjected to thermal lens study. We have studied the thermal diffusivity and refractive index variations of the medium by analyzing the thermal lens (TL) signal. By segmenting the TL signal, the complex dynamics involved during its evolution is investigated through the phase portrait, fractal dimension, Hurst exponent, and sample entropy using time series and fractal analyses. The study also explains how the increase of the photothermal energy turns a system into stochastic and anti-persistent. The sample entropy (S) and refractive index analyses of the TL signal by segmenting into five regions reveal the evolution of S with the increase of enthalpy. The lowering of S in CAN along with its thermal diffusivity (50%-57% below) as a result of heat-trapping suggests the technique of downscaling sample entropy of the base fluid using carbon allotropes and thereby opening a novel method of improving the efficiency of thermal systems.

Process gas influence on microstructure and mechanical behavior of Inconel 718 fabricated via selective laser melting

The influence of process gas on porosity, microstructure, and mechanical properties of nickel-based superalloy Inconel 718 (IN718) produced via selective laser melting (SLM) was investigated. Density and surface roughness of as-built parts were similar for samples built under nitrogen and argon environments. After hot isostatic pressing (HIP) and precipitation-hardening heat treatments, argon-processed specimen had finer, more uniform grain structures, and increased room-temperature tensile failure strains (> 24%) and yield strengths (> 4%) compared with nitrogen-processed specimen. Elemental analysis showed no variation in composition or nitride precipitate concentration with environment. Larger melt pool structure and heat-treated grain size were produced under argon when laser focus shift was varied away from focal plane, while under nitrogen grain refinement was observed when focus shift is moved in the positive direction. These changes in microstructure are reflected in mechanical properties; the highest strength and ductility is achieved in argon-processed samples at the laser focal plane. To clarify the contribution of thermal conductivity, density, and refractive index of process gas to these observations, samples were built under helium and surface finish and microstructure were evaluated. It was determined that laser interaction with process byproducts is most responsible for differences in as-printed and heat-treated microstructures under each protective environment.

Preparation of Titanium-silphenylene-siloxane Hybrid Polymers with High Refractive Index, Transmittance, and Thermal Stability

Vinyl-containing titanium-silphenylene-siloxane oligomers (O1, O2, O3, and O4) with different molar ratios of titanium to silicon were successfully synthesized in high yields by nonhydrolytic sol-gel reaction, and the obtained four oligomers were further crosslinked with methylphenyl hydro-silicone oil (4) to form corresponding polymers (P1, P2, P3, and P4) by hydrosilylation reaction. Their structures were characterized with spectroscopic characterization techniques including FTIR, 1H-NMR, and Raman spectroscopy. The effect of titanium element on crosslinking behavior, thermal resistance, refractive index, transparency, thermal aging stability, glass transition temperature, and surface properties of the polymers were studied. Compared with titanium-free polymer P1, the thermal resistance, refractive index, and thermal aging stability of titanium-silphenylene-siloxane polymers (P2, P3, and P4) were significantly improved. The titanium-silphenylene-siloxane polymers achieved a high refractive index (n = 1.580–1.584) and thermostability (T5d > 500 °C). In thermal aging, the polymers exhibited superior performances with high optical transparency (~90% at 450 nm) and exhibited high thermal stability (~84% at 450 nm after thermal aging at 150 °C for 120 h). These data indicate that the polymers have potential application in optical materials such as LED encapsulants.

Resonant Wavelength Thermal Stability of Fiber Bragg Gratings Produced by Femtosecond Laser

This study is focused on the fiber Bragg gratings central resonant wavelength thermal stability, fabricated by the point-by-point inscription method, using an infrared femtosecond laser. A new methodology is proposed to analyze the refractive index decay using the central wavelength shift of fiber Bragg gratings, executing stepped and continuous annealing regimes up-to a maximum temperature of 800 °C. The obtained thermal refractive index decay follows a typical power-law function, and from the theoretical model fit to the experimental data was possible to simulate and predict the refractive index decay over a large time period, up-to 1000 years. With the proposed approach it is possible to adjust the fiber Bragg gratings pre-treatment conditions to ensure effective operation during a certain time period, at a specific working temperature, without any degradation. An experimental method to mitigate this decay is proposed, and the results demonstrate the high potential of using infrared femtosecond inscribed fiber Bragg gratings for high temperature monitoring.

Preparation and properties of high refractive index UV-cured titanium hybrid optical materials

In this study, a new synthetic route was developed to prepare UV-cured titanium hybrid optical materials. Transparent high refractive index titanium hybrid optical materials were prepared by means of non-hydrolyzed sol-gel and UV curing. The experimental results show: titanium was successfully introduced into the silicone chain in the form of Ti-O-Si chemical bonds. The materials have high light transmittance (>95%) in the visible light region, high thermal stability and tunable refractive index (1.6533–1.8145) at 486 nm. Our study provides a new ideal for preparing high refractive index UV-cured titanium hybrid optical materials for potential optical applications.

Femtosecond Laser Modification of Antimony-Containing Lithium-Aluminum-Silicate Glass and Transparent Sitall Obtained from It

The particulars of the action of a femtosecond laser beam on antimony-containing lithium-aluminum-silicate glass and the close to zero CLTE sitall obtained from this glass by heat-treatment were studied in a wide temperature range. In both the non-thermal and thermal laser action regimes local refractive index reduction is demonstrated in the laser modified regions of the sitall, reaching 0.002 in the non-thermal regime. The main reason for refractive index reduction is, by all appearances, partial amorphization of the crystal phase of β-eucryptite.

Electronic Polarizability, Optical Basicity, Thermal, Mechanical and Optical Investigations of (65B2O3–30Li2O–5Al2O3) Glasses Doped with Titanate

Titanium-doped and titanium-free lithium borate glasses were prepared using a quenching method and high-purity-grade chemical substances. Structural analysis was carried out by Fourier transform infrared (FT-IR) spectroscopy and mechanical measurement. The states of the produced glasses were examined by x-ray diffraction, and the density (ρ) and molar volume (Vm) were determined. The Makishima–Mackenzie model was applied for the prepared glasses. FT-IR confirmed that the concentration of [BO4] was greater than that of [BO3] structural units. These variations confirmed that the compactness of the lithium borate network increased as the concentration of (TiO2/B2O3) increased. The longitudinal (vL) and shear (vT) velocities of the samples with varying concentrations of (TiO2/B2O3) were found to increase, along with the elastic moduli. The thermal stability, energy gap, and refractive index of the prepared glasses increased as the concentration of (TiO2/B2O3) was increased.

Pulse compression in graphene-clad microfiber as a saturable absorber in mode-locked fiber lasers: modeling and analysis

In this paper, the outstanding influence of self-phase modulation (SPM) induced by thermal nonlinear refractive index (TNRI) in graphene-clad microfiber on laser pulse width, during the mode-locking process, is demonstrated for the first time. To meet the requirements, analytical relations for effective absorption coefficient of graphene-clad microfiber (GCM), thermal nonlinear refractive index and self-phase-modulation parameter are presented. Improvement on pulse compression process by optimizing the GCM parameters such as microfiber diameter and graphene length is studied by the aid of Haus master equation.

Synthesis and characterization of 9,9‐bis(4‐hydroxyphenyl and 4‐aminophenyl)dibenzofluorenes: Novel fluorene‐based monomers

ABSTRACTTwo novel 9,9‐difunctionalized fluorene‐type monomers, 9,9‐bis(4‐hydroxyphenyl‐ and 4‐aminophenyl)‐2,3:6,7‐dibenzofluorenes, are synthesized by the reaction of dibenzenzofluorenone with phenol and aniline. These monomers are used for the preparation of polyester and polyimide as the typical polymers to evaluate the property change such as thermal stability caused by the benzene rings fused to the fluorene skeleton with keeping good solubility, in comparison with the polymers derived from simple fluorenone. In fact, these two new polymers have the fairly enhanced thermal stability and refractive index value along with satisfactory solubility in organic solvents, enough to emphasize the fusion effect. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2602–2605

Physicochemical properties of ether-functionalized ionic liquids [CnOC2mim][Gly] (n = 1–5)

A novel ionic liquid 1-ethoxyethyl-3-methylimidazolium glycine ([C2OC2mim][Gly]) was prepared and characterized by 1H NMR spectroscopy, 13C NMR spectroscopy, elemental analysis and thermogravimetric analysis. The density, surface tension and refractive index of [C2OC2mim][Gly] were measured in T = (288.15–328.15) K using the standard addition method. Based on experimental data, physicochemical properties molar volume, parachor, surface tension, the molar surface Gibbs energy, the molar vaporization enthalpy, thermal expansion coefficients, molar refraction and refractive index of the homologues [CnOC2mim][Gly] (n = 1–5) were predicted using semiempirical methods. The predicted values were in good agreement within an order of magnitude with the experimental ones.

Preparation and properties of high refractive index ZrO2 nano-hybrid materials

In this study, a new synthetic route was developed to prepare ZrO2 nano-hybrid materials. Polymer matrix containing S and Br elements was prepared by means of thiol-epoxy click chemistry. Transparent high refractive index ZrO2 nano-hybrid materials were prepared by means of sol-gel preparation and segmental heat curing. The experimental results show: ZrO2 particles were successfully synthesized and homogeneously dispersed at the nanometer scale into the polymer matrix, the materials had high light transmittance (>85%) in the visible light region, high thermal stability and tunable refractive index (1.6494–1.7021) at 486 nm. Our study provides a new ideal for preparing high refractive index ZrO2 nano-hybrid materials for potential optical applications.

Synthesis of Silphenylene-Containing Siloxane Resins Exhibiting Strong Hydrophobicity and High Water Vapor Barriers

The novel phenylenedisilane, 1,4-bis(dimethoxyphenylsilyl)benzene (BDMPD), was successfully synthesized via the reaction between trimethoxyphenylsilane (TMPS) and a Grignard reagent originating from 1,4-dibromobenzene. In comparison to common Grignard reactions, this process was a facile one-pot method. 1H NMR spectroscopy, FT-IR measurements, and elemental analysis confirmed the predicted structure of BDMPD. In addition, vinyl-terminated polysiloxanes containing silphenylene units (VPSSP), which were hydrolytically copolymerized from BDMPD, TMPS, and divinyltetramethyldisiloxane, exhibited excellent thermal stabilities (T10%: 502 °C, Rw%: 76.86 beyond 700 °C) and suitable refractive indices (1.542). Furthermore, water contact angle and water vapor permeability tests confirmed that the fully cured siloxane resins containing VPSSP-based silphenylene units exhibited strong hydrophobicity (water contact angle: 119°) and superior water vapor barrier properties, thereby indicating their potential to serve as strong waterproof coatings for moisture-proof applications or as adhesives for use in immersed equipment.

Fifth- and third- order nonlinear optical responses of olive oil blended with natural turmeric dye using z-scan technique

In this study, nonlinear optical responses of olive oil as a pure material and also blended with turmeric powder at different concentrations are demonstrated using z-scan technique. This material is found to be a novel natural nonlinear medium with large nonlinear refractive index. The modified Newton-Raphson method was used to solve the formula obtained from Gaussian Decomposition method for transmission of beam light in z-scan technique. It shows a negative third order nonlinear refractive index (n2) on the order of 10−7cm2/w under irradiation of maximum 50 mw continuous wave (CW) He-Ne laser at 632.8 nm wavelength. The third order nonlinear susceptibility (χ3) of olive oil was calculated on the order of 10−5 (esu). The fifth order nonlinear refractive index (n4) of this oil was calculated positive and on the order of 10−9cm4w2 for the first time according to the authors' knowledge. It is worth noting that the fifth order nonlinear susceptibility occurs at lower intensity with regards to other nonlinear materials. The thermal nonlinear refractive index of the olive oil is also calculated for pure olive oil and different concentrations of olive oil blended with turmeric.