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Understanding the Microscopic Behavior of Binary Mixtures of Ionic Liquids Through Various Spectroscopic Techniques
摘要： In recent times it has been shown that certain binary mixture of pure ionic liquids having appropriate chemical composition can behave like a new chemical entity. However, current knowledge about the microscopic behavior of these interesting systems is rather limited. The present study is undertaken with an objective to understand the microscopic behavior in terms of intermolecular interaction, structure and dynamics of these systems. In the present study, few (IL+IL) mixtures are chosen with a common cation and a variation of anion. The investigations are also carried out by taking individual pure ILs so that the difference in behavior between pure IL and (IL+IL) mixtures are understood. Initially the systems have been investigated by studying the thermophysical properties of the concerned mixtures. Synergistic effect between combining pure ILs through photochromism has also been studied. These mixtures have been investigated further through steady state and time resolved fluorescence spectroscopy, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR) and fluorescence correlation spectroscopy (FCS). Interestingly, time-resolved fluorescence data also pointed out that (IL+IL) mixtures are not only spatially heterogeneous but they are dynamically heterogeneous too. EPR measurements have suggested that the micro-polarity (ET(30)) of (IL+IL) mixture is close to aliphatic polyalcohol. Measurements of translational diffusion coefficients of the diffusing species through NMR and FCS studies have provided idea about the nano-structural organization within (IL+IL) binary mixtures. The analysis of data essentially reveals that the mixtures of ILs that are used in the current study do not behave like a non-ideal solution. The behavior of the IL mixtures is observed to be more like quasi-ideal type.
关键词： thermophysical properties,binary mixtures,EPR,FCS,fluorescence spectroscopy,NMR,Ionic liquids,photochromism,spectroscopic techniques
更新于2025-09-23 15:21:01
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Design of Thermophysical Properties Test System by Laser Point Heat Source Method
摘要： Laser is widely used in material thermophysical properties testing because of its good test accuracy and test efficiency. However, due to the high market price of laser flash devices, their promotion space is limited. Based on the unsteady heat transfer model of a laser point heat source, the enantiomorphous heat source theory was introduced to modify the influence of an adiabatic boundary on the temperature rise of a measuring point. The thermal conductivity and thermal diffusivity of isotropic materials were calculated by numerical analysis combined with computer programming. A thermophysical property test system was developed, and the thermophysical properties of blast furnace firebrick, marble, and diatomite brick were studied. The results showed that the maximum repeatable accuracy error was 4.75%, and the maximum relative deviation from the reference value was 2.04%. The effective test range of the device was that the thermal conductivity was less than 3 W∕(m ? K). Compared with the laser flash method, the device does not require high test-time accuracy and data collection instantaneity in terms of test principles. Therefore, the device can use a general-level laser generator, temperature sensor, timer, data collector, and so on, and the hardware cost is greatly reduced.
关键词： thermophysical properties,thermal diffusivity,test system,thermal conductivity,laser point heat source
更新于2025-09-23 15:19:57
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Thermophysical Properties of Silicon-Carbide-Based Ceramic Composite Materials Obtained by Spark Plasma Sintering (SPS)
摘要： The factors influencing the thermal conductivity of SiC-based ceramic composite materials obtained by the spark plasma sintering technology with relative density 99% and B4C, AlN, Si3N4, Y2O3, Al2O3, and HfB2 as additives are examined. The thermophysical properties were determined in the temperature range 20 – 1300°C: specific heat, thermal diffusivity, and thermal conductivity of composites. The thermal diffusivity and specific heat were measured by the laser-spark method. The measurements of specific heat are supplemented by measurements performed with a DSC and adiabatic calorimeter. The thermal conductivity is calculated using data on the thermal diffusivity, specific heat, and density.
关键词： laser flash method,specific heat,adiabatic calorimeter,thermal conductivity,ceramic composite materials,thermal diffusivity,thermophysical properties,differential scanning calorimetry (DSC)
更新于2025-09-19 17:15:36
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Thermophysical properties of methacrylic polymer films with guest-host and side-chain azobenzene
摘要： The methacrylic polymer films containing azobenzenes with different peripheral substituents in the form of side-chain (P) and guest-host (A) systems were thermally investigated. The azo polymers with thicknesses below 1 μm were deposited on glass substrates using spin coating method. Photothermal radiometry (PTR) and scanning thermal microscopy (SThM) were used for determination of thermophysical properties of polymer samples. The topography of studied compounds was examined by atomic force microscopy (AFM). The results showed the influence of peripheral substituents as well as that of the polymer system on the thermophysical properties of studied azo polymers. Thermal diffusivity (α) extracted from PTR measurements is between 5.56 10-8 m2s-1 and 11.3?10-8 m2s-1 for A samples, 2.76 10-8 m2s-1 and 7.62?10-8 m2s-1 for P samples depending on the substituent. Likewise, thermal effusivity (ε) changes from 474 Ws1/2m-2K-1 to 532 Ws1/2m-2K-1 for A, and from 473 Ws1/2m-2K-1 to 564 Ws1/2m-2K-1 for P samples. The volumetric heat capacity (Cv) and in-depth thermal conductivity (κ) were calculated on the base of PTR results. Local κ obtained from SThM measurements is between 0.15 Wm-1K-1 and 0.22 Wm-1K-1 due to different substituents and polymer system. Thermal studies performed in this work provide valuable information for engineers designing azobenzene polymer thin films based devices and supplement the knowledge of their thermal behavior in the system.
关键词： polymer,nanomaterials,thermophysical properties,thin films,azobenzenes
更新于2025-09-09 09:28:46