We present a detailed protocol outlining how to perform nonlinear oscillatory shear rheology on soft materials, and how to run the SPP-LAOS analysis to understand the responses as a sequence of physical processes.
This method can help answer key questions in the field of soft matter, such as the correlation between macroscopic and microscopic responses. The main advantage of the method is it can quantify the viscoelastic properties of materials throughout a rheological experiment in contrast to the traditional methods that provides average information. Though this method can provide insight into polymeric materials, it can also apply to other systems, such as colloidal gels and glasses and biological materials.
Work with a Rheometer that can perform stain control measurements. First, attach the upper and lower drive geometries. For the lower fixture, use a 50 mm plate.
Use a two degree cone for the upper fixture. Next, zero the gap, calibrate the measurements, and set the temperature. Once these steps are completed, open the gap in the geometries from zero to allow the loading material to be tested.
Move on to get the material for testing. In this case, it is polyethylene oxide in DMSO, with red dye for demonstration. With a spatula, load the material onto the top of the bottom geometry.
Ensure that no air bubbles are entrained in the sample in the Rheometer. Work with the measuring systems, set to trim gap. Use a square-ended spatula at the end of the geometry to gently trim excess material.
Return to the measurement gap, before continuing. Run the sinusoidal oscillatory shear test using software. Navigate to My Apps.
Find and open Large Amplitude Oscillatory Shear. Next, go to the measurement box. There, click the strain variable.
Enter the initial and final value for a strain amplitude sweep. 1 and 4000 percent respectively. Specify the imposed frequency.
Also, set the total number of strain amplitudes in the chosen range to 16. Check the Get waveform box to collect transient responses. Click the Start button to start the experiments.
Data will be displayed during the course of the approximately five minute run. The Rheometer can also be used for arbitrarily defined deformations. In an external file create a list of strain values to define the function to be applied.
Go to the Rheometry software and click on My Apps. And click on the waveform sign generator. In the measurement box, click on strain.
From there, click on Edit. In the value list, paste the pre-determined strain values from the external file. Specify the number of points entered, the point duration and the time to adjust the imposed frequency.
When done, check the Get Waveform box of the top. Then click the Start button to begin the experiment. Measurement data will appear on the monitor as the experiment proceeds.
These data are for a Xanthan Gum solution under oscillatory shear tests. These non-linear stress strain curves indicate that a sequence of physical processes take place within the material. Sequence of physical processes and analysis software determines the transient moduli that signals the elastic and viscous properties of materials.
Their evolution reveals behavior under large amplitude oscillatory shearing. Here, the instance of maximum elasticity are nearly constant across amplitudes. A plot of this maximum elasticity observed during large amplitude oscillatory shearing and the dynamic moduli across the range of amplitudes reveals a clear correspondence with the linear regimes storage modulus.
The elastic strain determined by the sequence of physical processes software at the instance of maximum elasticity is approximately 16 percent, even when the applied strain is as large as 4000 percent. Here is a sequence of physical processes undergone by the Xanthan Gum solution. In the Viscoplastic regime, analysis indicates zero elasticity.
As the shear rate decreases, the solution stiffens indicating that its structure reforms. Once sufficient strain is acquired, there is a rapid transition from elastic to viscous behavior. After yielding, the response returns to the Viscoplastic deformation regime and the sequences occurs in the opposite direction.
After its development, this technique pave the way for researchers in the field of soft matter rheology, to further explore transient structure property processing relationships.
