Microthermal analysis

Abstract: We have used a platinum/10% rhodium resistance thermal probe to image variations in thermal conductivity or diffusivity at micron resolution and to perform localized calorimetry. The probe is used as an active device that acts both as a highly localized heat source and detector; by generating and detecting evanescent temperature waves, we may control the maximum depth of sample that is imaged. Earlier work has shown that subsurface images of metal particles buried in a polymer matrix are consistent with computer simulations of heat flows and temperature profiles, predicting that a 1 μm radius probe in air will give a lateral resolution of ∼200 nm near the surface, with a depth detection of a few μm. We have a special interest in polymer blends, and we present zero‐frequency mode and temperature‐modulation mode thermal images of some immiscible blends in which the image contrast arises from differences in thermal conductivity/diffusivity between single polymer domains. The behavior of domains is observed in real time as the blends are subjected to a slow temperature rise. We have also achieved localized differential thermal analysis of a number of polymers, and recorded events such as glass transitions, meltings, recrystallizations, and thermal decomposition within volumes of material estimated at a few μm3. This opens the way forward towards calorimetric imaging, by which it should be possible to distinguish between different regions undergoing either reversible or irreversible changes as the temperature is varied.

Abstract: We have used a miniaturized Wollaston wire resistive thermometer as a probe to record infrared absorption spectra of polymeric samples by detecting photothermally induced temperature fluctuations at the sample surface. This method opens the way to absorption Fourier transform infrared spectroscopy/microscopy with a spatial resolution that is no longer diffraction limited, but is determined instead by the size of the contact between probe and sample. At present, this is on the order of a few hundred nanometers. The thermal probe, of a type used in scanning thermal microscopy and microthermal analysis, allows us to detect the photothermal response of a specimen exposed to the beam of a Fourier transform infrared spectrometer and heated thereby. The signal from this probe measures the resulting temperature fluctuations, and thus provides an interferogram which replaces the interferogram normally obtained by means of direct detection of the IR transmitted by a sample.

Abstract: Morphological studies were performed on a polymer blend, used as a friction bearing, consisting of polyamide 6.6 (80%), poly-(tetrafluoroethylene) (18%), and silicone oil (2%). Raman imaging, FT-IR imaging, scanning electron microscopy with energy-dispersive X-ray spectrometry, and microthermal analysis determined the distribution of poly(tetrafluoroethylene) clusters in the polyamide matrix. Each characterization method allows qualitative identification of the main components and provides information about cluster size and distribution. It is proved that poly(tetrafluoroethylene) clusters of 10 to 30 μm are randomly distributed in a polyamide matrix and that silicone oil can be found at the cluster matrix interface. The good agreement that was obtained in our investigations indicates high reliability of the results since all applied methods are based on different chemical and physical properties. This combined approach revealed information about the morphology of the blend for a better understanding of its working principle and enhanced knowledge for its processing. A comparison of the different methods employed in this study highlights their advantages and limitations for polymer analyses.