Micro-Scale Thermal Imaging of Organic and Polymeric Materials with Cooled and Uncooled Infrared Cameras

The emissivity corrected thermal imaging combined with a real-time direct imposed-signal system on the freezing of biological cells is presented, which makes it possible to visualize the exothermic latent heat at a minus temperature. The applicability of the uncooled micro bolometer (thermal detector) to the micro-scale thermal analysis on the phase transitions of organic and polymeric materials is discussed in comparison with the photon detector, equipped with the optics originally designed. 1. Introduction Noncontact thermal imaging methods are preferred in the characterization of materials in the increasing number of applications. Creating and monitoring thermal distributions with a spatial resolution of ~10？μm is required, in particular, for the materials developed in the energy saving and renewable technology [1]. A recent advance in IR detectors arrays provides the enhanced applications [2]. Thermal imaging applied to the materials’ characterization in a micro-scale is summarized with actual imaging results of organic, polymeric, and biological materials, using a cooled and an un-cooled infrared cameras equipped with the optics originally designed in this study. Examples of microscale thermal analysis and the lock-in thermography are presented. The latent heat generation and dissipation at minus temperatures during the freezing of biological cells are visualized that clarifies the thermal diffusion effect on crystallization and the vitrification [3–7]. On-lamellae thermal analysis of n-alkane visualizes the early stage of anisotropic lamella formation and the difference of thermal propagation in crystallizations and the rotator phase transitions [8]. The crystallization front of polymeric spherulite of poly(ethylene oxide) visualizes the temperature rise of ~100？mK [9]. The basic results of lock-in thermography visualize the phase and amplitude image using a method of modulated spot heating with a diode laser that generates a thermal wave inside the specimen [10, 11]. A promising application of micro-bolometer sensor is additionally introduced [12]. 2. Approach and Techniques In order to visualize the material’s thermal phenomena with a spatial resolution ~10？μm and in a time scale ~10？ms, the following techniques have been developed. The measurement is done preferably under the dynamic temperature field such as a constant rate heating/cooling and a temperature modulation. 2.1. Optics Materials for optics suitable to the mid- and long-wave infrared cameras are chosen, respectively. Spatial resolutions 4.3？μm (calculated at ？μm, λ: wavelength) and