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TY - THES AU - Petrunin, Alexander V. TI - Charged microgels and hollow microgels in concentrated binary suspensions PB - RWTH Aachen University VL - Dissertation CY - Aachen M1 - RWTH-2025-08260 SP - 1 Online-Ressource : Illustrationen PY - 2025 N1 - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University N1 - Dissertation, RWTH Aachen University, 2025 AB - Microgels are a class of soft colloidal particles widely used both as a model system in condensed matter physics and as versatile functional materials in practical applications. The advances in the synthesis protocols made it possible to obtain microgels with a desired electrical charge and complex internal architectures. The presence of charges and complex internal architectures, such as in hollow microgels with a central cavity, can dramatically influence how a microgel behaves in a concentrated suspension, i.e. if it deswells, deforms or interpenetrates its neighbors. These responses influence the phase behavior, optical properties and viscoelasticity of the suspensions. In this thesis, binary mixtures of microgels with different charges and internal architectures are realized to investigate the interplay of microgel structure, response to crowding and bulk properties of the mixtures. Small-angle neutron scattering with contrast variation was used to resolve the form factors of individual microgels in concentrated suspensions, whereas small-angle X-ray scattering and shear rheology were used to analyze the microstructure and bulk viscoelasticity of the suspensions, respectively. It is demonstrated that the dominating response of a microgel to crowding depends on its charge as well on the charge of the surrounding microgels. When the microgel and its surroundings have a similar charge, osmotic deswelling is the main response mechanism. Conversely, when the microgel has a much larger charge than its surroundings, the deswelling is suppressed and instead the deformation at contact (faceting) becomes important. In the case when the microgel and its surroundings are oppositely-charged, electrostatic attraction and counter-ion release lead to formation of inter-microgel complexes (clusters), where the particles are strongly compressed independently of concentration. In the case of the hollow microgels, it is already known from the literature that strong osmotic deswelling and buckling occur in concentrated suspensions. The focus of the thesis is thus to identify the influence of the hollow microgels on phase behavior and rheology of binary mixtures with regular microgels. It is found that the hollow microgels shift the freezing and melting points of the binary mixtures to higher generalized volume fractions and eventually suppress the crystallization completely. The microstructure of the fluid phase is barely affected by the hollow microgels, whereas colloidal crystals form much slower and have more defects. The dynamical arrest (glass transition) is also shifted to higher generalized volume fractions, and the shear moduli in the glassy state are weaker due to the cavity of the hollow microgels. In the steady shear flow, the cavity leads to a stronger distortion of the microstructure and suppression of shear-induced crystallization. Finally, the transient rheological response is strongly modified by even the small amounts of hollow “defects”, favoring more brittle and delayed yielding. Overall, the results showcase the power of using binary mixtures to answer several open questions about the behavior of microgels with specific functions in crowded environments. These findings are crucial to use microgels as model soft colloids to address the fundamental questions about phase transitions or flow of complex fluids, as well as to formulate the design rules for functional materials based on soft colloidal building blocks like biosensors, cell scaffolds or separation membranes. LB - PUB:(DE-HGF)11 DO - DOI:10.18154/RWTH-2025-08260 UR - https://publications.rwth-aachen.de/record/1019227 ER -