Thermal Conductivity Measurement Of Polyvinyl Alcohol Thin Film Using Harmonic Method

Polymer thin films are widely used in the micro-electronics industry due to their outstanding chemical,physical properties and high stability.But the heat dissipation problems caused by their low thermal conductivity reduce the lifetime,work efficiency and reliability of the devices.Accurate measurement and improvement of the thermal conductivity are of great significance to promote the further development of micro-electronics industry.It is difficult to measure the thermal conductivity of these films compared with bulk materials owing to their small thickness and low mechanical strength.In our study,we choose the harmonic method.Harmonic method(also named 3-Omega method)is a widely used method for measuring the thermal conductivity and volumetric heat capacity of solid,liquid,thin films and porous materials.3-Omega method enjoys the advantages of simplicity,low cost and small experiment error.In the first part of the research,we designed and built the 3-Omega experiment platform.After that,we measured the thermal conductivity of a variety of standard materials(such as silicon,silica,Pyrex7740,deionized water,glycol)to verify the accuracy of the platform.The results showed that the error of the platform was acceptable(~6%).The thermal conductivity of polymers is very low due to the phonon scattering,which stems from the amorphous arrangement and tanglement of polymer chains.Recent studies showed that single chains and ultra-drawn nanofibers of polymer possessed high thermal conductivity(~100 W/(m·K)).It implied that polymers had the prospect to be an alternative of metals to solve the heat dissipation problems in microelectronic devices.Electrospinning is one of the ways to fabricate nanofiber films,which is simple and easily operative.The prepared thin nanofiber films are of high porosity,small diameters and uniformity.In our research,we employed a new model,the bidirectional asymmetric heat transfer model,to measure the thermal conductivity of polyethylene film(0.42 W/(m·K)),which was in concordance with others.Results showed that the used model was of high veracity and feasibility.After that,we selected polyvinyl alcohol(PVA)as the experiment materials to produce electrospinning film and measured the effective thermal conductivity of the film.The effective thermal conductivity of the film was 0.7 W/(m·K),which was twice higher than that of spinning-coating film.The ordered structures would increase the thermal conductivity of films by reducing the phonon scatterings.The results indicated that the nanofiber films prepared using electrospinning method showed high effective thermal conductivity.Our study paves the way to enhance the thermal conductivity of polymers.