Title Promoter Affiliations Abstract "Investigation of lubricating fluids with combined rheological and rheo-optical techniques" "Christian Clasen" "Sustainable Materials Processing and Recycling (SeMPeR), Soft Matter, Rheology and Technology (SMaRT)" "This PhD aims at understanding the role of polymeric additives in lubricants on the rheological behaviour and lubricating properties. While the rheological properties of lubricants can and have been accessed in the past with standard rheological investigation tools, it is in particular the high shear behaviour that is relevant for most applications that is, however, often outside the deformation rate range that can be applied with commercial rheometers. Within this project, the material functions of lubricants will be accessed via the (rheo)-optical investigation of flow-birefringence and -dichroism of model lubrication fluids, utilising a novel flow cell that enables the simultaneous determination of the rheo-mechanical and rho-optical material functions over variating gap distances in a lubrication flow field" "Novel tools for the determination of second normal stress differences in complex fluids" "Christian Clasen" "Soft Matter, Rheology and Technology (SMaRT)" "Within this PhD thesis the specific interplay of nano-particles and short chain polymers in high shear flow fields will be investigated in order to optimise lubrication properties in sustainable and energy efficient applications. The determination of the full stress tensor, in particular second normal stress differences, requires the development of novel measurement techniques, that utilise the observation of stress induced interfacial deformations with sophisticated (rheo-)optical techniques to be developed within this thesis work." "Inclusions in yield stress or highly shear-thinning dispersions" "Pavlik Lettinga" "Soft Matter and Biophysics" "We want to study both experimentally and theoretically, micro- versus macro-rheological effects in the structural evolution of particle suspensions as affected by the motion of spherical inclusions. Gravity field exerts a pressure on the inclusions which may induce motion, depending on the local rheological properties, and modification of the dynamic behavior of the suspension. The effect of the inclusions on the microstructural evolution of the suspension during macroscopic flow and after flow cessation will be studied, whereby structure may evolve or not until yield stress recovery. The study will include the influence of the macroscopic rheological behavior of the suspension, while particle shape (from spheres to rods or platelets) and interparticle potential will be varied. For the experimental study, we will use model systems consisting of suspensions of particles of well-defined size, shape and interaction potential, as well as systems which are relevant for applications in the food industry (e.g. suspensions of protein or fat particles).  Rheology and rheo-optical techniques will be used, in particular following developments in FZ Juelich and other experts in the field involved in the DiStruc project. Experimental results will be compared to theoretical predictions whenever possible, also in interaction with other groups." "Supramolecular Polymeric Solutions in Shear and Extensional Flows" "Christian Clasen" "Surface and Interface Engineered Materials, Soft Matter, Rheology and Technology Section" "The behaviour of transient polymer networks in strong flows is poorly understood.Those transient polymer networks are candidates for, e.g. self-healing and recyclable materials, easily tunable viscosity modifiers, and stimuli-responsive materials with applications in foodstuff, coatings, cost-efficient processes or biomedical areas.To explore their potential and define strategies for designing novel materials amenable to contemporary needs, a fundamental understanding of their very complex and diverse multi-scale supramolecular structure and dynamics is needed.The thesis aims to contribute to the understanding of metal-ligand bonded polymeric solutions with respect to non-equilibrium structures and strong flows.With this purpose in mind, the behaviour under large deformation was studied employing rheometry, such as orthogonal superposition rheology, capillary break-up, rheo-optics, and a toolbox of molecular characterisation techniques.The behaviour of telechelic polymers during capillary break-up was studied.To this aim, a framework towards more accurate capillary break-up measurements was developed.It was found that the metal-ligand bonds withstand the strong flow fields and do not break.Moreover, the average number of assemblies in solution was determined as a function of polymer concentration, metal cation nature, and metal cation concentration.The largest effective molecular weight is obtained at stoichiometric concentration, whereas a cation excess will decrease the average number of assemblies, depending on the binding constant.A rheological device capable of performing orthogonal superposition measurements was re-developed.The working principle was demonstrated by comparing linear and branched worm-like micelles.The response of supramolecular hydrogels to shear as well as the equilibration after cessation of flow was studied shining light onto the responsiveness of transient polymer networks.Non-monotonic stress relaxation after cessation of shear flow was revealed.The increase in stress is associated with the redistribution of energy after the flow has stopped.When broken bonds are re-established after flow cessation, the released energy is partly used to locally increase the elastic energy by the formation of deformed domains.If shear has induced order such that these elastic domains are partly aligned, the re-establishing of bonds gives rise to an increase of the overall stress.Furthermore, a transition from predominantly intramolecular to predominantly intermolecular bonds under shear is indicated by an increase of the orthogonal storage modulus, failure of the Cox-Merz rule, and an increase in stress during uniaxial extensional flow.Whereas the increase in plateau modulus as well as the stress increase at intermediate Hencky strains could be linked to non-linear stretching of elastically active chains, the failure of the Cox-Merz rule points towards flow induced structure formation.At the same time, a shear induced reduction of the bond lifetime is observed, causing shear thinning, despite the enhanced structure.The findings will pave the way towards a clearer understanding of supramolecular structures, and the introduced techniques will open new avenues of inquiry to study complex materials."