Differential Scanning Calorimetry
As a technique Differential Scanning Calorimetry (DSC) has been extensively used for the characterisation of the thermal properties of all types of materials, including metals, ceramics, polymers and composites.. Typical resultant graphs of the energy flow versus temperature or time can be easily used to identify a number of endothermal or exothermal transitions occurring in materials and parameters can be identified such as glass transition temperature (Tg), crystallisation temperature (Tc), melting temperature (Tm) and the heat of cure. A number of methods could be used, under isothermal conditions, constant heating rate (typically at 10 or 20°C/min), modulated temperature (which overall is a much slower rate of heating), and recently Hyper-DSC (which operates at very high heating rates >100°C/min).
The Perkin-Elmer Diamond DSC is a unique power-compensation DSC, offering sensitivity and insights into materials processes. It is designed where the sample and reference pans are heated by two independent furnaces embedded in a temperature-controlled heat sink. This allows sophisticated analysis when performing the direct measurement of heat flow into or out of a sample The power compensation DSC design leads to sharper peaks and high sensitivity. Additionally, benefits include true isothermal operation, modulated temperature DSC (StepScan) technique and HyperDSC™ for dramatic enhancements in sensitivity, as well as greater productivity.
Features Of Diamond DSC Include:
- Unique power-compensation design
- Highest caloric accuracy
- Superior signal resolution and sensitivity
- Multiple cooling options for a temperature range of -170 °C to 725 °C
- HyperDSC™, the leading fast scan DSC technique
- StepScan, for Modulated Temperature DSC
Examples Of Work Undertaken At The Institute
DSC has been extensively used for the characterisation of the thermal properties of polymers and composites for biomedical applications. DSC can also be used to assess the effect of incomplete curing of materials as shown in Figures 1 and 2 comparing the thermograms of the first heating cycles for bone cements cured at room temperature and at 37°C. As can be observed, in both the BCRT and BC37 there appears to be a low glass transition that is in the range of 40-60°C indicated by an endothermic inflection (upwards) in both thermograms. At temperatures above the transitions, both materials underwent exothermic peaks (characterised by a downward inflection in the thermograms) that reached a maximum at around 112 and 115°C for BCRT and BC37 respectively. If the curing is not complete during the initial setting of the bone cements, unreacted residual monomers trapped within the polymerised chains are released as the temperature increases above Tg, and therefore undergo further reactions. Figure 2 shows the second heating curve and, as can be seen, in all materials there was an absence of the residual exothermic peak and a clear Tg inflection showing that the heating process during the first cycle allowed the unreacted residual monomer to undergo further curing. DSC has also been used to investigate the kinetics of fast setting inorganic based calcium phosphate cements as shown in Figure 3. Three typical isothermal DSC measurements showing the normalised heat flow of the exothermic setting reaction against reaction time for a specific powder liquid ratio and three retardant concentrations.