Part 2. How To: Create Kinetic Model with Diffusion Control for Curing (DSC Curing with Diffusion Control)
If the glass-transition appears during the cross-linkage of a thermoset, then the reaction is separated into two domains that are dominated by different mechanisms: The part taking place far above glass-transition depends on the chemical reaction and can be described by the Arrhenius relation. In the part below glass-transition diffusion controlled mechanisms dominate the reaction behavior. Therefore, the reaction rate around the glass-transition is influenced by both processes.
That's why the kinetic model has to be expanded by the special diffusion control algorithms in order to take into account the change of the material behavior.
In this "How To:", two single-step kinetic models for DSC data will be created:
- preliminary kinetic model without diffusion control,
- final kinetic model with partial diffusion control.
In this system kinetic mechanism changes when sample temperature crosses glass transition temperature.
We will start by loading a sample data project included in Kinetics Neo, will then create a preliminary kinetics model, will then add the diffusion control mechamism in order to have the final model.
- Data type: DSC Curing (Differential Scanning Calorimetry with Diffusion Control)
- Project file: DSC_Diff_Control_Epoxy_Data.kinx
2. Open Sample Data DSC Curing project.
Click on "Open" in the menu on the left side, then select "Samples". The Kinetics Neo samples directory will be opened in Windows Explorer.
Select directory "DSC_Diff_Control_Epoxy".
4. In the tree panel select Glass transition Data and check if the glass transition data are present and fit is created.
11. Switch to Conversion and check the checkbox Diffusion control. Three additional parameters appear in the parameter list for this reaction step. The default values for these additional parameters are usually not too far away from the optimum parameters.
These Parameters K, C1 and C2 are the parameters from WLF (Williams-Landel-Ferry) equations, which is used for the calculation of diffusion coefficient near glass transition temperature.
The curing of epoxy resin containing the crossing of glass temperature and sample temperature, can be described by the kinetic model with diffusion control. Diffusion near glass transition temperature is described by WLF (Williams-Landel-Ferry) equation.