Thermal Conductivity Prediction Model for Composite Thermal Interface Materials Using Copper Metal Foam

In the previous research, we prototyped the TIC in which a conventional TIM composed of silicone resin and filler was filled in pores of copper foam, and measured its thermal conductivity by a steady-state method. In addition, the effective thermal conductivity of TIC was predicted by Bhattacharya’s equation and Boomsma’s equation. As a result, it was reported that the experimental value and the predicted value match within 0.7 W/(m·K) by modifying the thermal conductivity of copper to 120 W/(m·K) in the Boomsma’s equation. The issue of that was to investigate the cause of the decrease in thermal conductivity of copper to 120 W/(m·K). In this paper, the effective thermal conductivity of TIC was predicted using the WP structure instead of the Kelvin structure, which is the basis of the Bhattacharya’s equation and Boomsma’s equation. As the result, it was clarified that the effective thermal conductivity predicted by the three-dimensional thermal conductivity calculation model based on the WP structure is more accurate than that predicted by the Kelvin model. And it was found that the experimental value and the predicted value match in the range of 0.4 W/(m·K) by considering the TIC surface structure without modifying the thermal conductivity of copper.

Lessons Learned in Protein Precipitation Using a Membrane Emulsification Technique to Produce Reversible and Uniform Microbeads

The effects of the manufacturing process and the regeneration of Shirasu porous glass (SPG) membranes were investigated on the reproducibility of protein precipitants, termed protein microbeads. Intravenous immunoglobulin (IVIG) was selected as a model protein to produce its microbeads in seven different cases. The results showed that the hydrophobically modified SPG membrane produced finer microbeads than the hydrophilic SPG membrane, but this was inconsistent when using the general regeneration method. Its reproducibility was determined to be mostly dependent on rinsing the SPG membrane prior to the modification and on the protein concentration used for emulsification. The higher concentration could foul and plug the membrane during protein release and thus the membrane must be washed thoroughly before hydrophobic modification. Moreover, the membrane regenerated by silicone resin dissolved in ethanol had better reproducibility than silicone resin dissolved in water. On the other hand, rinsing the protein precipitant with cold ethanol after the emulsification was not favorable and induced protein aggregation. With the addition of trehalose, the purity of the IVIG microbeads was almost the same as before microbeadification. Therefore, the regeneration method, protein concentration, and its stabilizer are key to the success of protein emulsification and precipitation using the SPG membrane.

Observation of Highly Durable Silicone Resin for Encapsulating AlGaN-Based UVB Light-Emitting Diodes

In this paper, we report an AlN-based ceramic lead frame (LF) with encapsulating silicone between the surface of an AlGaN-based ultraviolet-B light-emitting diode (UVB-LED) chip and a quartz glass cover; the light output power (LOP) of this structure was 13.8% greater than that of the corresponding packaging structure without encapsulating silicone. Another packaging structure in which the silicone fully filled the cavity of the AlN-based ceramic LF included covering with quartz glass; in this case, the enhancement of the LOP was 11.7%. Reliability tests performed over a period of 3500 h at a forward current (If) of 100 mA revealed that the LOPs of these two silicone-containing packaging types decreased to 45.3 and 48.6%, respectively, of their initial values. The different degradation rates of these UVB-LEDs were not, however, correlated with the appearance of cracks in the encapsulating silicone during long-term operation. Excluding any possible mechanisms responsible for degradation within the UVB-LED chips, we suggest that the hermetic cover should be removed to avoid the appearance of cracks. Moreover, the main mechanism responsible for the slow degradation rates of LOPs in these proposed packaging structures involves the encapsulated silicone, after cracks have appeared, undergoing further deterioration by the UVB irradiation.

Synthesis and characteristic applications of silicon resins for the modifying agent in heat conduction

Heat energy retention and dissipation have become key points of global smart textiles in recent years. This study describes the designing of silicon resin by using a sol–gel process, which acts as the modifying agent for siloxane substrate. The modifying agent was effectively blocked by silicon resin mixed with the ethylene or aluminum bond group, to control the molecular weight. Advanced polymer chromatography confirmed that the number average molecular weight (Mn) of silicon resin is 41,301 g mol−1, the weight average molecular weight (Mw) is 47,982 g mol−1, and the molecular weight distribution is 1.1617, which is relatively narrow. When the addition of vinyl groups is 5%, the silicone resin Mn decreases to 18,906 g mol−1 and Mw decreases to 28,641 g mol−1. When the addition of aluminum bond groups is 5%, the silicone resin Mn decreases to 17,497 g mol−1 and Mw decreases to 27,114 g mol−1. The result of thermogravimetric analysis shows that the pyrolysis temperature rises from 265.43°C to 266.17°C after the ethylene is added to the silicon resin, and the index of heat tolerance increases from 179.14°C to 191.38°C. After the addition of aluminum bond groups, the pyrolysis temperature rises from 265.43°C to 309.37°C, and the index of heat tolerance increases from 179.14°C to 193.09°C, meaning the silicone resin has higher thermal stability.

Research on Resin Used for Impregnating Polyimide Fiber Paper-Based Composite Materials

In this paper, a resin with high adhesion, easy curing, good flexibility, and high temperature resistance was prepared from polyimide fiber paper. First, in order to improve the toughness and curability of impregnating resin, epoxy resin was modified by addition of vinyl silicone resin. Subsequently, ternary resin with high temperature stability was obtained by polyimide resin addition. Among the investigated conditions, the optimal additive amount of vinyl silicone resin and polyimide resin was 30% and 5%, respectively. The prepared ternary resin has better toughness, crosslinking degree, high temperature stability (5% mass loss at 339.2 °C) and no obvious glass transition at high temperature. Finally, the polyimide fiber paper-based composite material was impregnated with modified epoxy resin and ternary resin, respectively. The results shows that the paper-based composite material impregnated with modified epoxy resin has a better fiber bonding degree, a smooth surface, and contact angle could reach up to 148.71°. Meanwhile, the paper-based composite material impregnated with ternary resin has good high temperature resistance, and the tensile index of the paper-based composite material could reach up to 35.1 N·m/g at 200 °C.

Optical Performance and Moisture Stability Enhancement of Flexible Luminescent Films Based on Quantum-Dot/Epoxy Composite Particles

Quantum dots (QDs) have been widely applied in luminescent sources due to their strong optical characteristics. However, a moisture environment causes their quenching, leading to an inferior optical performance in commercial applications. In this study, based on the high moisture resistance of epoxy resin, a novel epoxy/QDs composite particle structure was proposed to solve this issue. Flexible luminescent films could be obtained by packaging composite particles in silicone resin, combining the hydrophobicity of epoxy resin and the flexibility of PDMS simultaneously. The photoluminescence and light extraction were improved due to the scattering properties of the structure of composite particles, which was caused by the refractive index mismatch between the epoxy and silicone resin. Compared to the QD/silicone film under similar lighting conditions, the proposed flexible film demonstrated increased light efficiency as well as high moisture stability. The results revealed that a light-emitting diode (LED) device using the composite particle flexible (CPF) structure obtained a 34.2% performance enhancement in luminous efficiency as well as a 32% improvement in color conversion efficiency compared to those of devices with QD/silicone film (QSF) structure. Furthermore, the CPF structure exhibited strong thermal and moisture stability against extreme ambient conditions of 85 °C and 85% relative humidity simultaneously. The normalized luminous flux degradation of devices embedded in CPF and QSF structures after aging for 118 h were ~20.2% and ~43.8%, respectively. The satisfactory performance of the CPF structure in terms of optical and moisture stability shows its great potential value in flexible commercial QD-based LED displays and lighting applications.

Miniaturization of Respiratory Measurement System in Artificial Ventilator for Small Animal Experiments to Reduce Dead Space and Its Application to Lung Elasticity Evaluation

A respiratory measurement system composed of pressure and airflow sensors was introduced to precisely control the respiratory condition during animal experiments. The flow sensor was a hot-wire thermal airflow meter with a directional detection and airflow temperature change compensation function based on MEMS technology, and the pressure sensor was a commercially available one also produced by MEMS. The artificial dead space in the system was minimized to the value of 0.11 mL by integrating the two sensors on the same plate (26.0 mm × 15.0 mm). A balloon made of a silicone resin with a hardness of A30 was utilized as the simulated lung system and applied to the elasticity evaluation of the respiratory system in a living rat. The inside of the respiratory system was normally pressurized without damage, and we confirmed that the developed system was able to evaluate the elasticity of the lung tissue in the rat by using the pressure value obtained at the quasi-static conditions in the case of the ventilation in the animal experiments.