Giovedì 22 aprile 2010 alle ore 15.00 nell’aula DICM (aula del Dipartimento di Ingegneria Chimica),
la Dott. ssa Kathrin Reinheimer
Technische Chemie und Polymerchemie
Karlsruher Institut of Technology (KIT)
76131 Karlsruhe (D)
terrà il seminario dal titolo:
FOURIER TRANSFORM RHEOLOGY: A NEW APPROACH TO PROBE INDUSTRIAL EMULSIONS
Emulsions are ubiquitous in polymer industry, in food processing, in pharmacology, and in cosmetics. They are a class of materials in which two or more constituents are blended together to create a new material able to tailor the properties of a “composite” material without resorting to expensive chemical synthesis. The typical microstructure of a dilute emulsion at rest consists of spherical droplets immersed in a continuous matrix. The size and size distribution of these globular domains strongly affect both the processing and the mechanical properties of final products. Thus, development of experimental techniques for the characterization of blend morphology through rheological measurements could be an appealing opportunity. Rheology is the study of the materials response when subjected to flow. The schematic setup of a typical rheological experiment is the shear rheometer: two plates with a sample in between. One plate gives the strain deformation in terms of an oscillatory excitation with a sinusoidal waveform and the other plate measures the stress response of the sample in between:
The rheological properties of a material can be either elastic (i.e. the stress response is in phase with the strain deformation), viscous (the stress response is in phase with the derivative of the strain deformation) or a combination of both of them (viscoelastic materials). These characteristics can be expressed by the moduli G’ (elastic modulus) and G’’ (viscous modulus) in the linear regime (that is for Small Amplitude Oscillations: SAOS).
Here, the rheological behaviour of polymer blends is investigated when samples are subjected to large amplitude oscillatory shear (LAOS) experiences and stress signal is analyzed by exploiting an innovative theoretical procedure named as Fourier Transform Rheology (FTR): stress response is no longer a simple harmonic signal but consists of an overlay of the excitation frequency and its higher harmonics. It was indeed found that the intensity and the phase of the overtones may give information about the droplet size morphology and other physical properties of the emulsion.