Chemorheology
Use the Chemorheology node to model changes in the polymer viscosity using the chemoviscosity model that relates the viscosity to the degree of cure (conversion) and temperature.
Transport Properties
Viscosity factor
Select Castro–Macosko or Percolation model to calculate the viscosity factor αc.
The following parameters are required for the Castro–Macosko model:
•
 Gel point . The default is 1.
•
 Model constant c1. The default is 0.
•
 Model constant c2. The default is 0.
The following parameters are required for the Percolation model:
•
 Gel point . The default is 1.
•
 Percolation exponent p. The default is 0.
Compute effective transport properties
From the Chemorheology node, it is possible to generate the viscosity for the cured material. Select Compute effective transport properties check box to select the viscosity model that describes the temperature, shear rate, and cure dependencies.
When Compute effective transport properties check box is selected, the following predefined viscosity models are available: Newtonian, Power law, and Cross.
The parameters for the selected model can either be specified by a Fluid material, or by a User defined expression
The following parameters are required for the Newtonian:
•
Dynamic viscosity μ
The following parameters are required for the Power law:
•
 Fluid consistency coefficient m
•
 Flow behavior index n
•
 Lower shear rate limit
•
 Reference shear rate
For the Cross model, the following parameters are required:
•
 Zero shear rate viscosity μ0
•
 Infinite shear rate viscosity μinf
•
 Power index n
•
 Critical stress τtr
Thermal Function
The polymer viscosity has a strong dependency on the temperature. Thus, the apparent viscosity is modified using factor αT. The thermal effects are activated with five options: None, Arrhenius, Williams–Landel–Ferry (WLF), Exponential, and User defined.
•
When the default, None, is kept, the shift function αT is set to unity and the viscosity is not modified.
•
For Arrhenius enter values or expressions for these properties:
-
 Reference temperature T0
-
 Activation energy Q
•
For Williams–Landel–Ferry enter values or expressions for these properties:
-
 Calibration temperature TWLF
-
 WLF constant 1 C1WLF
-
 WLF constant 2 C2WLF
•
For Exponential enter values or expressions for these properties:
-
 Reference temperature T0
-
 Temperature sensitivity b
•
For User defined enter the expressions for αT
Material Generation
Create/Update Cured Material () option can be selected when Compute effective transport properties check box is selected. When you click it, a new material will be created under Materials. It contains the material parameters required for selected viscosity model. The name of this material is Cured Material.
For this type of Materials to work correctly, it is important that you do not edit the generated nodes manually. By clicking the Create/Update Cured Material button again, you can reset the generated node.
See also
•
Non-Newtonian Flow
•
Materials in the Materials chapter in the COMSOL Multiphysics Reference Manual.