Calibration of a Rapid Heat-Cool Differential Scanning Calorimeter & Application to Nanofibres and Nanocomposites

Abstract

Rapid Heat-Cool DSC (RHC) is a form of fast scanning calorimetry (FSC), currently still in the research phase. The principle is identical to conventional heat flux DSC. Using an infrared heater and a liquid nitrogen cooling system allows maintaining heating rates and cooling rates up to 2000°C/min. These high rates allow simulating the parameters of industrial production methods, enabling a qualitative and quantitative investigation. DSC experiments are usually conducted at the rates used during calibration. For RHC this is often not the case, by using different rates, transitions will shift to higher or lower temperatures, due to a change of thermal lag of the system. This can also lead to suppressing kinetic effects, such as reorganisation and crystallization. The thermal lag not only becomes more important when working at high rates, the same happens when using a higher mass than the one calibrated for. Standard calibrations do not account for these effects.
The German Society for Thermal Analysis, GEFTA (Gesellshaft für Thermische Analyse), proposed a more rigorous calibration procedure for FSC's. In this masterthesis, a modified procedure was experimentally developed for the RHC apparatus. Instead of a standard primary calibration with indium, a four point calibration is conducted, covering a large temperature range. Based on experimental data, a thermal lag correction model has been designed to account for the rate and sample mass used in experiments. Additionally, a symmetry check of the system using liquid crystal standards is presented. Other standard reference materials were used to evaluate the heat capacity calibration. In each step of the calibration procedure, a comparison of results in both T1 and T4P mode are presented.
In the second part of this masterthesis, the application of RHC to nanofibres and nanocomposites is researched. The nanofibres were produced using electrospinning, a technique which allows to spin fibres with diameters in the nanometer-range. Four different types of nanofibres were used, amongst which poly(?-caprolactone) fibres. Two types of PCL based nanocomposites have also been studied. These materials are used to show what the capabilities of RHC are, and to demonstrate the need for an improved calibration. For further investigation of the nanofibres, SEM images were made. These show that the fibre mats used are far from perfect. Apart from nanofibres, submicron and even microfibres are present. The latter two represent a relatively large mass percentage of the entire sample.
Fibres spun on silicon wafers show more perfection. These individual fibres were examined with Atomic Force Microscopy. Although complex, the measurements proved to be feasible. A micro-thermal analysis option allows heating the probe, giving qualitative information regarding the melting transition.

Date of Award	25 Jun 2010
Original language	English
Supervisor	Guy Van Assche (Promotor) & Linda Beenaerts (Promotor)