| In recent decades, with the rapid development of nanotechnology, microelectronics and mechanical systems (mems) and many new technologies, materials’low-dimensional development trend is catching on and has obtained wide applications in traditional industrial sectors and high-tech areas. Thermophysical properties of two dimensional thin films are different from buck materials, which are caused by size effects, fabrication process, microstructure, impurities and defects. The rapid progress of thin films’research and application, plus research of micro/nano-size heat transfer, deepens the research of thermophysical properties and its measuring apparatus of thin films materials, in which the characteristics of thin films and its relationship to chemical component and microstructure have become focus topics.By using a nanosecond laser, nanosecond response MCT infrared detector and high speed oscilloscope, laser flash method is utilized to construct an apparatus to measure the thermal diffusivity of thin films. Integreating thermal expansion component, a multifunctional apparatus measuring thermphysical properties of thin films is developed. The apparatus can measure three different kinds of thin films with thickness1-500microns in the temperature range-50～300℃. By utilizing this apparatus, SEM, TEM and other charactrizaion method, the thermophysical properties of polyimide composite films, anodic alumina films and polyethelene nanowire arrays films related to its microstructure and other influencial effects are researched.Polyimide (PI) films has got wide spread applications due to its excellent properties and PI based composite films using ceramic nanoparticles to modify its properties have become a hot subject. A new test model has been developed to simplify the pretreatment procedure and improve the precision of semi-transparent sample such as PI films tested by laser flash method. Thermophysical properties of Pi/Silica composite films with different silica content and PI/C films are investigated. Specific heat of composite films comply with addition principle of composite materials. Thermal expansion decreases with the addition of silica nanoparticles to suppress the extension of polyer molecular chains. The thermal conductivity of composite films increases with temperature increasing, which means the thermal conductivity behavior of PI films does not change with the addition of silica nanoparticles. Themal conductivity of PI increases from0.17W/(m-K) to0.64W/(m-K) after20wt%silica is added. Thermal conductivity of PI composite films increases with increase of silica content and is much higher than values predicted by composite materials prediction models, which indicates the prediction models for bulk composite materials may not apply to thin films’thermal conductivity prediction because of the aggregation of nanoparticles.Anodic alumina films are widely used as bio-sensors, fabrication templates and thermal control coatings in aeroplanes. Anodic alumina films with thickness of900nm-5μm are grown from aluminum foil by anodic oxidation. Thermal properties of anodic films in temperature range220～480K are researched. The film with thiner thickness has more porosity, which explains thermal diffusivity increases with thickness increasing. Thermal conductivity of film with2.5μm thickness is1.22W/(m-K) at220K,1.4W/(m-K) at RT and1.71W/(m-K) at480K which is much lower than bulk alumina material. This temperature dependence is coherent with calculated results of minimum thermal conductivity model. The comparison results show that non-steady method is more suitable for measurement of thermal conductivity around room temperature range.Polymers can have larger thermal conductivity by stretching polymer’s moleculars. High-density polyethylene (HDPE) nanowire arrays with diameter of100nm and200nm and low-density polyethylene (LDPE) nanowire arrays with diameter of200nm are fabricated by using a nanoporous template wetting technique, which have a room thermal conductivity of10and2.2W/(m-K) respectively, which are about2orders of magnitude higher than their bulk counterparts. Estimated thermal conductivity of a single HDPE nanowire and LDPE nanowire is as high as26.5W/(m-K) and5W/(m-K) respectively at room temperature. This enhancement may be attributed to transformation from ramdom orientation to high chain orientation of the nanowire arrays. |
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