DHR/AR Rheometer: Setting Up a Flow Temperature Ramp Test

In this topic
Overview
Test Setup

Overview

Ramping the temperature during a flow test is a fast test method to determine the temperature dependence of a material’s viscosity. In a flow temperature ramp, the temperature is varied continuously and the instantaneous viscosity is recorded.

Equilibrium flow has to be reached first before ramping the temperature, therefore, it is better to start at an elevated temperature, and ramp the temperature from high to low. The ramp rate has to be slow enough to reduce temperature gradients in the sample to a minimum.

Evolving materials are usually characterized in an oscillation temperature ramp test. However, it is possible to measure the viscosity in flow while approaching the gel point. Since a applying a constant shear rate would disrupt the forming network, it is better to do this type of experiment applying a constant stress.

Test Setup

To select a Flow Temperature Ramp test, select Flow > Temperature Ramp. See Using Experimental Procedures for additional information on selecting test types.

To set up a Flow Temperature Ramp test, set the following parameters.

Environmental Control

Select the following environmental control parameters:

Start temperature: The temperature range is dependent on the configuration of your instrument and the installed environment control system. The initial and end temperature, as well as the temperature increment, are dependent on the transition(s) being evaluated. The initial and final temperatures should bracket the entire range of interest. Enter the desired start test temperature or select one of the following options from the drop-down list:
Select Use entered value to use the value you entered in the Start temperature field for this step.
Select Inherit set point to maintain the previously-specified temperature at the start of this step.
Select Start from current to use the current temperature conditions at the start of this step.
Wait for temperature: Select this option to wait until the entered temperature is reached before beginning the test. If you wish to begin data collection, while achieving the temperature, disable this option.
Soak time: Enter the amount of time the sample will be held at the initial temperature.
Ramp rate: Enter the desired rate of thermal change that the sample material will undergo during the test.
End temperature: Enter the desired final test temperature.
Soak time after ramp: Enter the length of time the sample will be held at the end temperature.
Estimated time to complete: Displays an approximate length of time, based on the parameters entered, that the experiment will run.

Test Parameters

Set up the following test parameters:

Select between Torque, Stress, Velocity or Shear rate. This test can be run using either torque/stress or velocity/strain rate as the controlling variable.
Torque: The torque is defined as the torque to be applied by the motor at each measurement. This value is used to extract the torque M_s applied to the sample during the measurement. The torque should be selected to be within the linear viscoelastic range of the sample, and still provide a large enough signal to ensure good data.
Stress: The stress is defined as the stress to be applied to the sample at each measurement. This value is determined from the sample torque M_s applied to the sample during the measurement and the sample geometry and dimensions. The stress can be selected to simulate real-life end-use conditions, or it can be a value selected to be within the linear viscoelastic range of the sample, and still provide a large enough signal to ensure good data.
Velocity: The velocity is defined as the velocity to be applied to the sample by the motor at each measurement. The angular velocity should be selected to be within the linear viscoelastic range of the sample, and still provide a large enough signal to ensure good data.
Shear rate: The shear rate is defined as the shear rate applied to the sample at each measurement. This value is used, along with the sample geometry and dimensions, to calculate the peak angular deflection to be applied to the sample during the measurement. The shear rate can be selected to simulate real-life end-use conditions, or it can be a value selected to be within the linear viscoelastic range of the sample, and still provide a large enough signal to ensure good data.
Enter the desired data Sampling parameters:
Number of points: The number of points determines the total number of values collected during the specified range. This includes both the initial and final value.
Sampling interval: The value entered in this field defines the time interval between recorded data points.

Controlled Rate Advanced

Select desired Motor mode (Velocity, Shear rate only): Choose between Auto, Soft, Medium, and Stiff, depending on the sample stiffness. As a rule of thumb, leave this option set to Auto. Matching the mode to the stiffness of your sample may increase the quality of your data.

Data Acquisition

There are additional data collection options that can be adjusted to control how data is obtained and what additional information is collected during the measurement.

End of step: The default behavior is set to zero the torque. However, in certain situations, for example a ramp up followed by a ramp down, select maintain final torque/velocity. Note that the final ramp value will be maintained through any environmental control block in the subsequent step.

There is also an option to zero the velocity, which might be useful when measuring low viscosity fluids where just zeroing the torque would not slow the velocity quickly enough prior to the next step starting.

Save image: Select to store images of the test within the data file for future recall when using the Camera accessory.

Save image every: Specify the collection rate for time-based experiments. Select the minimum time in seconds between images. An image is stored with the next test point when the time between images has elapsed.

Step Termination

TRIOS Software allows you to define conditions in which a step is halted ahead of its normal termination conditions (Limit checking). You can use this to ensure that, for instance, the instrument does not over speed or apply excessive strains.

Rather than running a step for a certain amount of time, you may wish to run it until stable data is obtained. You can set an Equilibrium limit (such as the viscosity value becoming constant when running a single shear with time) that will stop the currently active test.