Introduction
The Immobilization Cell is used with the Kinexus rotational rheometer to characterize the rheological properties of a paint or coating while it is dried on a substrate. Such a test is useful to determine the effects of
- Solids content
- Porosity of the coating substrate
- Thickness of the coating substrate
- Water retention additives
- Applied pressure drop
on the rheological properties of a material.
Figure 1 shows the Immobilization Cell system.
A measurement is made by placing the sample on a substrate positioned on a porous sintered disk and a vacuum applied below to initiate the dewatering process. An upper geometry (cone or plate) of up to 45 mm in diameter can be used, and real-time measurements made in rotation (viscometry) to characterize the sample’s immobilization kinetics, or oscillation to detect changes in the viscoelastic properties.
Measurement Parameters
In the following, the rheological properties of a wall paint were measured during drying. Table 1 details the measurement parameters.
Table 1: Measurement Parameters
| Device | Kinexus ultra+ rotational rheometer |
| Type of test | Oscillation, time sweep |
| Geometry | PP40 (plate/plate, diameter: 40 mm) |
| Gap at measurement start | 1 mm |
| Normal force during measurement | 0.5 N |
| Frequency | 1 Hz |
| Shear StrainStrain describes a deformation of a material, which is loaded mechanically by an external force or stress. Rubber compounds show creep properties, if a static load is applied.strain | 0.5% |
Remarks on:
Selection of the shear StrainStrain describes a deformation of a material, which is loaded mechanically by an external force or stress. Rubber compounds show creep properties, if a static load is applied.strain: The shear StrainStrain describes a deformation of a material, which is loaded mechanically by an external force or stress. Rubber compounds show creep properties, if a static load is applied.strain of 0.5% was selected because it is in the Linear Viscoelastic Region (LVER)In the LVER, applied stresses are insufficient to cause structural breakdown (yielding) of the structure and hence important micro-structural properties are being measured.linear viscoelastic region (Linear Viscoelastic Region (LVER)In the LVER, applied stresses are insufficient to cause structural breakdown (yielding) of the structure and hence important micro-structural properties are being measured.LVER) and so does not lead to a breakdown of the sample´s structure. This was determined by means of an amplitude sweep experiment (results not displayed). Of course, the sample changes during the measurement because it is drying, so that its Linear Viscoelastic Region (LVER)In the LVER, applied stresses are insufficient to cause structural breakdown (yielding) of the structure and hence important micro-structural properties are being measured.LVER may also change. A look at the harmonic distortion curve revealed that the sample remained in the Linear Viscoelastic Region (LVER)In the LVER, applied stresses are insufficient to cause structural breakdown (yielding) of the structure and hence important micro-structural properties are being measured.LVER during the entire measurement.
The normal force applied during the measurement: A gap of 1 mm was chosen for the test, but to make allowance for the shrinkage that was expected from the drying of the sample, a small normal force was applied to ensure contact was maintained between the upper plate and the sample with the change in gap during the test. This technique prevented the sample from being ejected as maintaining a normal force resulted in the reduction in gap size matching the sample’s shrinking.
LVER – Linear Viscoelastic Range
- The Linear Viscoelastic Region (LVER)In the LVER, applied stresses are insufficient to cause structural breakdown (yielding) of the structure and hence important micro-structural properties are being measured.LVER is the amplitude range where StrainStrain describes a deformation of a material, which is loaded mechanically by an external force or stress. Rubber compounds show creep properties, if a static load is applied.strain and StressStress is defined as a level of force applied on a sample with a well-defined cross section. (Stress = force/area). Samples having a circular or rectangular cross section can be compressed or stretched. Elastic materials like rubber can be stretched up to 5 to 10 times their original length.stress are proportional.
- In the Linear Viscoelastic Region (LVER)In the LVER, applied stresses are insufficient to cause structural breakdown (yielding) of the structure and hence important micro-structural properties are being measured.LVER, the applied stresses (or strains) are insufficient to cause structural breakdown of the structure and hence microstructural properties are being measured.
Harmonic Distortion
Within the Linear Viscoelastic Region (LVER)In the LVER, applied stresses are insufficient to cause structural breakdown (yielding) of the structure and hence important micro-structural properties are being measured.LVER, input oscillation frequency is the same as the output oscillation frequency. Beyond the Linear Viscoelastic Region (LVER)In the LVER, applied stresses are insufficient to cause structural breakdown (yielding) of the structure and hence important micro-structural properties are being measured.LVER, we get harmonic distortion. The input oscillation breaks down to higher (i.e., harmonic) frequency responses. As the StrainStrain describes a deformation of a material, which is loaded mechanically by an external force or stress. Rubber compounds show creep properties, if a static load is applied.strain goes out of the Linear Viscoelastic Region (LVER)In the LVER, applied stresses are insufficient to cause structural breakdown (yielding) of the structure and hence important micro-structural properties are being measured.LVER, the harmonic distortion increases. It can be easily displayed in the NETZSCH rSpace software.
Measurement Results
Figure 2 displays the complex stiffness and the gap measured during drying of the wall paint.
After a 1-minute equilibration in which an oscillation was applied without vacuum, the pump was switched on and dewatering of the paint began. This resulted in a three–decade increase in the Complex ModulusThe complex modulus consists of two components, the storage and the loss moduli. The storage modulus (or Young’s modulus) describes the stiffness and the loss modulus describes the damping (or viscoelastic) behavior of the corresponding sample using the method of Dynamic Mechanical Analysis (DMA). complex modulus. Complex stiffness and gap during paint drying 2(stiffness) within 11 minutes, while the sample shrank by more than 10%. After this time, the Complex ModulusThe complex modulus consists of two components, the storage and the loss moduli. The storage modulus (or Young’s modulus) describes the stiffness and the loss modulus describes the damping (or viscoelastic) behavior of the corresponding sample using the method of Dynamic Mechanical Analysis (DMA). complex modulus as well as the gap plateaued, indicating the end of the drying process.
A demonstration of setting up the Immobilization Cell can be seen in this video: How to use the immobilization cell