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Homogeneous crystal nucleation in polyamide 66 (PA 66) was studied by a combination of atomic-force microscopy (AFM) and fast-scanning chip calorimetry (FSC), with a specific experimental setup all...

An isothermal study was performed on 1.25 μm thin layers of PC61BM, a benchmark acceptor for organic photovoltaics. Using fast scanning chip calorimetry allowed for a scanning rate of 30 000 K·s–1, ensuring that all non-isothermal effects were avoided. The effect of isothermal treatments above and far below the glass transition was investigated. It was proven that PC61BM can crystallize below its glass transition, a behavior seen before for several organic glasses. Isothermal treatments as far as ca. 100 K below the glass transition lead to an initial enthalpic relaxation process around the glass transition, which over time gives rise to crystals melting around 300 °C. These observations show a remarkable similarity with the two-step nucleation mechanism documented in the literature. A standard crystallization process was observed for treatments above the glass transition. By combining chip calorimetry pretreatments with atomic force microscopy, different crystal morphologies were visualized for these two...

Smart detection systems for explosive sensors are designed both to detect explosives in the air at trace level and identify the threat for a specific response. Following this need we have succeeded in using microthermal analysis to sensitively identify and discriminate between RDX and PETN explosive vapors at trace level. Once the explosive vapor is trapped in a porous material, heating the material at a fast rate of 3000 K/s up to 350 °C will result in a thermal pattern specifically corresponding to the explosive and its interaction with the porous material. The explosive signatures obtained make it possible to simultaneously identify the presence and the nature of the explosive vapor in just a few milliseconds. Therefore, this also allows the development of multitarget devices using porous material for capturing the vapor combined with microthermal analysis for fast detection and identification. So far it is the first time that chip calorimetry has been used to characterize and identify explosives in vapor state.

It was reported that glass transition temperature (Tg) measured by differential alternating current (ac) chip calorimetry showed little thickness dependence for polymer films. Here we demonstrate the detection of Tg in thin films by ac-chip calorimeter and show that Tg is decreased as the thickness is reduced for oligomers and star-shaped polymers, as compared with their long linear analogues. The deviation range is a few to more than ten Kelvin. Such a depression in Tg is quite pronounced for ac-chip calorimetric measurement at a high frequency of 10 Hz. We argue that the perturbation in the increased interfacial free volume for spin-cast oligomers and dendrimers is the major reason for increasing segmental dynamics for ultrathin films.

The crystallization rate of polyamide 11 has been quantified in a wide temperature range between 320 and 450 K, using fast scanning chip calorimetry and differential scanning calorimetry. Different...