Time-Resolved and Micro-Scale Measurement of Thermal Property for Intermolecular Dynamics Using an Infrared Laser

This paper describes a time-resolved measurement of thermal property in microscale during reaction process of a polymer by using an infrared (IR) laser. Polymer and gel-like material, so-called macromolecules, have diversity in its structure and intermolecular association, and recent development of measurement and control technique in micro- and nano-scale has open up new possibilities for the property design in the materials, including the control of thermophysical properties. The heat conduction process in macromolecules is affected by the internal structure or intermolecular association of the material. Thus, the intermolecular dynamics of polymer can be reflected in time-resolved information of the thermal conductivity or thermal diffusivity. A measurement system of the thermal diffusivity in time-resolved and non-contact manner based on the forced Rayleigh scattering method (FRSM) has been developed. This system can be applied for a changing process of a wide variety of polymer material because of employing a CO2 laser with the infrared wavelength of 10.6 μm. Also, it is possible to measure micro-scale property. In the present study, the measurement area is set at 500 μm in diameter. By using the IR-FRSM system, an investigation of the relationship between intermolecular dynamics of macromolecules and energy transfer can be conducted through the time-resolved data of the thermal diffusivity. As samples, crosslinking processes of a polysaccharide aqueous solution and an ultraviolet curable polymer are measured; variations in molecular interactions caused by hydrogen and covalent bonding occur, respectively. Time evolution of the measured thermal property from the IR-FRSM system clearly indicates the difference in bonding modes of macromolecules. According to the time-resolved measurement results, the validity of the IR-FRSM for a versatile instrument of intermolecular dynamics of macromolecules is demonstrated.