FT-Rheology of emulsions
|Figure 1: Examples for emulsions and polymer blends in daily use.|
|Figure 2: Emulsions under rest (left), under nonlinear shear (centre) and after nonlinear shearing, at rest again, droplet breakup occured (right).|
The size and size distribution of these globular domains strongly affect both the processing and the mechanical properties of final products.
To this end, significant efforts were done in the last decades in order to quantitatively measure and control the morphology of blends through different non invasive measurement techniques e.g. with direct microscopical optical methods, light scattering, rheological experiments etc.
Within this regard a new methodology for the estimation of droplet size distribution was recently proposed, based on the so-called Fourier Transform Rheology (FTR), see also FT-Rheology at our homepage. FTR is an oscillatory shear experiment with large amplitude oscillatory shear (LAOS). The response is no longer linear but consists of an overlay of the excitation frequency and its higher harmonics. The intensity and the phase of the overtones include information about the droplet size distribution with known interfacial tension or vice versa.
|Figure 3: Commercial emulsion under nonlinear oscillatory shear LAOS. The record was the 147th overtone in the spectra.|
The high sensitivity of LAOS measurements on highly filled emulsions (figure 3) will be used to calculate the desired quantities droplet size distribution respectively interfacial tension.