Huaiyu Ye

First-principles study of the effect of functional groups on polyaniline backbone

We present a first-principles density functional theory study focused on how the chemical and electronic properties of polyaniline are adjusted by introducing suitable substituents on a polymer backbone. Analyses of the obtained energy barriers, reaction energies and minimum energy paths indicate that the chemical reactivity of the polyaniline derivatives is significantly enhanced by protonic acid doping of the substituted materials. Further study of the density of states at the Fermi level, band gap, HOMO and LUMO shows that both the unprotonated and protonated states of these polyanilines are altered to different degrees depending on the functional group. We also note that changes in both the chemical and electronic properties are very sensitive to the polarity and size of the functional group. It is worth noting that these changes do not substantially alter the inherent chemical and electronic properties of polyaniline. Our results demonstrate that introducing different functional groups on a polymer backbone is an effective approach to obtain tailored conductive polymers with desirable properties while retaining their intrinsic properties, such as conductivity.

Density-Functional Calculation of Methane Adsorption on Graphenes

The adsorption behaviors of methane adsorbed on different graphenes (pristine, and B-, N-, P-, and Al-doped monolayer and multilayer) are analyzed using density-functional theory. The results demonstrate that the sensing performance of graphene as a methane sensor strongly depends on the selection of dopants and the number of layers. The adsorption energy on monolayer P-doped or Al-doped graphene shows about one order of magnitude higher than that with other dopants. In addition, graphenes doped with different impurities show different responses to the charge transfer. A further analysis indicates that the multilayer structure has a positive effect on the adsorption energy on the pristine, B-doped, and N-doped graphene, while the P-doped or Al-doped graphene shows a significant decrease with the increase in the number of layers. Moreover, the multilayer structure has a minor effect on the charge transfer. Based on the combined effects on the adsorption energy and the charge transfer, Al-doped monolayer graphene is the optimal candidate for methane sensing.

Functionalization-induced changes in the structural and physical properties of amorphous polyaniline: a first-principles and molecular dynamics study

In this paper, we present a first-principles and molecular dynamics study to delineate the functionalization-induced changes in the local structure and the physical properties of amorphous polyaniline. The results of radial distribution function (RDF) demonstrate that introducing -SO3−Na+ groups at phenyl rings leads to the structural changes in both the intrachain and interchain ordering of polyaniline at shorter distances (≤5u2009Å). An unique RDF feature in 1.8–2.1u2009Å regions is usually observed in both the interchain and intrachain RDF profiles of the -SO3−Na+ substituted polymer (i.e. Na-SPANI). Comparative studies of the atom-atom pairs, bond structures, torsion angles and three-dimensional structures show that EB-PANI has much better intrachain ordering than that of Na-SPANI. In addition, investigation of the band gap, density of states (DOS), and absorption spectra indicates that the derivatization at ring do not substantially alter the inherent electronic properties but greatly change the optical properties of polyaniline. Furthermore, the computed diffusion coefficient of water in Na-SPANI is smaller than that of EB-PANI. On the other hand, the Na-SPANI shows a larger density than that of EB-PANI. The computed RDF profiles, band gaps, absorption spectra, and diffusion coefficients are in quantitative agreement with the experimental data.

Numerical modeling of thermal performance: Natural convection and radiation of solid state lighting

The increased electrical currents used to drive light emitting diode (LED) cause significant heat generation in the solid state lighting (SSL) system. As the temperature will directly affect the maximum light output, quality, reliability and the life time of the SSL system, thermal management is a key design aspect in terms of cost and performance. Particularly for consumer SSL system, natural convection cooling is cheaper and more reliable than the forced air cooling heat sinks. Although with less efficiency, natural convection heat sink is a good compromise between economy and thermal performance of SSL systems. In this work, the thermal performance of two geometrically different passive heat sink designs for consumer SSL applications is numerically simulated. The heat sink performance is simulated for two orientations: LED up and LED down orientation. Simulation runs for the two designs at the two orientations, in order to investigate the thermal performance of the heat sinks with natural convection cooling. Meanwhile, the radiation effect is considered. With passive cooling, the natural convection plays an important role, and results show that if free ambient air flow is blocked by the heat sink design and the performance reduces considerably. Furthermore, the volume of free air in the luminaire is expected to have significant impact to the heat sink thermal performance. Therefore, the thermal performance for different volumes of luminaire enclosures is also investigated in this work. To analyze the modeling results, a straightforward calculation of the thermal resistance between the LED junction and the environment is applied. In the results, the thermal resistances of LED junction to environment decreases but the air velocity gradually increases with the increasing luminaire volume. In conclusion, although more study is needed for validation of the optimal volume and shape for natural convection, the results in this work can already be used to guide the design of luminaires. In future work, the simulation on real model of bulb or luminaires will be applied to investigate what extend designs based on natural convection and radiation principles can be exploited to manage the LED junction temperature.

Sorption and Diffusion of Water Vapor and Carbon Dioxide in Sulfonated Polyaniline as Chemical Sensing Materials.

A hybrid quantum mechanics (QM)/molecular dynamics (MD) simulation is performed to investigate the effect of an ionizable group (–SO3−Na+) on polyaniline as gas sensing materials. Polymers considered for this work include emeraldine base of polyaniline (EB-PANI) and its derivatives (Na-SPANI (I), (II) and (III)) whose rings are partly monosubstituted by –SO3−Na+. The hybrid simulation results show that the adsorption energy, Mulliken charge and band gap of analytes (CO2 and H2O) in polyaniline are relatively sensitive to the position and the amounts of –SO3−Na+, and these parameters would affect the sensitivity of Na-SPANI/EB-PANI towards CO2. The sensitivity of Na-SPANI (III)/EB-PANI towards CO2 can be greatly improved by two orders of magnitude, which is in agreement with the experimental study. In addition, we also demonstrate that introducing –SO3−Na+ groups at the rings can notably affect the gas transport properties of polyaniline. Comparative studies indicate that the effect of ionizable group on polyaniline as gas sensing materials for the polar gas molecule (H2O) is more significant than that for the nonpolar gas molecule (CO2). These findings contribute in the functionalization-induced variations of the material properties of polyaniline for CO2 sensing and the design of new polyaniline with desired sensing properties.

Thermal analysis of phosphor in high brightness LED

The drive to increased electrical currents input to achieve high lumen for Light Emitting Diode (LED) hasled to a series of thermal problems. Hence, thermal management for solid-state lighting (SSL) is a key design parameter as the temperature will directly affect the maximum light output, quality, reliability of the solid state lighting and the life time. Two of the major heat sources in LED package has been identify to be die and phosphor. Many thermal researches clear show the thermal behavior in LED package. But the phosphor efficiency in LED and its performance is still under discussion because it is more complex to separate the original light and converted light in LED. In this work,a group of experiment is executed to check the thermal effect of phosphors in LED and to distinguish the light from LED die or from phosphor. In addition, a numerical simulation is achieved with the efficiency of LED die and phosphor according to thermal analysis.

A novel lifetime prediction for integrated LED lamps by electronic-thermal simulation

In this paper, an integrated LED lamp with an electrolytic capacitor-free driver is considered to study the coupling effects of both LED and driver’s degradations on lamp’s lifetime. An electrolytic capacitor-less buck-boost driver is used. The physics of failure (PoF) based electronic thermal simulation is carried out to simulate the lamp’s lifetime in three different scenarios: Scenario 1 considers LED degradation only, Scenario 2 considers the driver degradation only, and Scenario 3 considers both degradations from LED and driver simultaneously. When these two degradations are both considered, the lamp’s lifetime is reduced by about 22% compared to the initial target of 25,000h. The results of Scenario 1 and 3 are close to each other. Scenario 2 gives erroneous results in terms of luminous flux as the LED’s degradation over time is not taken into consideration. This implies that LED’s degradation must be taken into considerations when LED and driver’s lifetimes are comparable.

Arsenic Phosphorus Monolayer: A Promising Candidate for H 2 S Sensor and NO Degradation With High Sensitivity and Selectivity

The sensing behaviors of arsenic phosphorus (AsP) for nitric oxide (NO) and hydrogen sulfide (H₂S) are investigated by means of the density functional theory and the nonequilibrium Green’s function method. The calculated adsorption energy and charge transfer of H₂S molecule on silicon-doped AsP (Si-AsP) are 0.352 eV and 0.106 <inline-formula> <tex-math notation=LaTeX>

Nitrogen Dioxide Gas Sensor Based on Monolayer SnS: A First-Principle Study

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First-Principles Study of Nitric Oxide Sensor Based on Blue Phosphorus Monolayer

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