THERMOPHYSICAL PROPERTIES OF NANOSTRUCTURED MATERIALS

As electronic devices become smaller in size, thermal management challenge for various applications must be solved for enhanced system performance and reliability. Without appropriate thermal conductivity to dissipate excess heat, the system overall performance and reliability will be compromised. For high power electronic applications, local heat flux can be on the order of kW/cm2, highly thermally conductive materials are preferred to effectively dissipate heat generated inside system. On the other hand, materials with low thermal conductivity are desired to prevent thermal short-circuit, for example, in thermoelectric applications. This dissertation investigates thermal properties of nanostructured materials, in which the approach of using additives in the base material to tailor the effective thermal conductivity of composite material. For power systems, Wax-BN composite exhibits in-plane thermal conductivity of 3.14 W/mK, which is 12 time enhancement compared to that of pristine wax. Moreover, an improved 11.3-13.3 MV/m breakdown voltage of Wax-BN composite was achieved. For optoelectronic systems, a thermally conductive, electrically insulating and optically transparent nanopaper using a bilayer design structure with BN and cellulose nanofiber (CNF) was proposed. An optical transparency (70%) and in-plane thermal conductivity (0.76 W/m/K) were successfully achieved with BN-CNF nanopaper. For lithium ion battery energy storage system, BN-coated separator results in Coulombic efficiency stabilizing at 92% over 100 cycles compared to 18% for pristine separator under 0.5 mA/cm2 current density condition. BN-coated separator reduced lithium dendrite by creating a more homogeneous thermal environment. In extreme high temperature applications, certain substrate for example glass suffers from poor thermal management properties, which greatly limits the system performance. With BN coated thin film glass push the maximum operating temperature to 1000 ⁰C compared to that of 700 ⁰C for normal glass, indicating enhanced thermal management capability of substrate. Bi2Te3 material properties modification with external magnetic field has also been explored. Inside magnetic field, cross-plane thermal conductivity of Bi2Te3 is predicted to experience 3.3% drop. The TEC numerical simulation indicates Bi2Te3 exhibit 1.7 ⁰C enhancement inside magnetic field. Material thermal conductivity modification has been demonstrated as a promising approach to enhance thermal management capability in electronic systems