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| Book/Dissertation / PhD Thesis | PUBDB-2026-02068 |
; ; ;
2026
Verlag Deutsches Elektronen-Synchrotron DESY
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2026-02068
Report No.: DESY-THESIS-2026-011
Abstract: The structure and dynamics of four different colloidal systems are investigated usingcoherent X-ray scattering methods. The static structure of the samples is studied us-ing Small Angle X-ray Scattering (SAXS), while the dynamics are probed using X-rayPhoton Correlation Spectroscopy (XPCS). First, correlations of structure and dynamicsare investigated in dense hard-sphere and charge-stabilized systems. The studied hardspheres cover fluid to glassy states with increasing volume fraction, while the studiedcharge-stabilized samples are all in fluid, including supercooled, states. The timescalesof higher-order correlations are investigated using a novel time correlation function gC ,tracking the time evolution of the cross-correlation function C from X-ray Cross Corre-lation Analysis (XCCA). For both systems, the local order within the sample is found tobecome disproportionately more long-lived when the system approaches the glass transi-tion. For the charge-stabilized particles, cross-correlations between neighbor shells wereinvestigated using XCCA. The fifth Fourier coefficient (l = 5) dominated at the highestvolume fraction, which could be a fingerprint of alternating shells of icosahedral and do-decahedral symmetry, as were predicted in simulation studies.The structure and dynamics of concentrated silica-PNIPAm (poly-N-isopropylacrylamide)nanogels is studied as a function of hydrostatic pressure up to 3500 bar. Upon increasingpressure and depending on the initial particle volume fraction, a transition from a liquidor glass state to a colloidal gel is observed for pressures p ≈ 1500 bar at a temperatureof 293 K. The observed behavior of the dynamics is similar to temperature-dependentstudies. Time-dependent analysis of the dynamics after pressure increase shows ageing inglass and gel samples which is absent in the liquid state. This indicates stress-dominateddynamics upon pressure changes that equilibrate after few 100 s.The dynamics of dilute, polyethylene glycol-coated gold nanoparticles in water are inves-tigated as a function of pressure from 0 to 6000 bar and as a function of temperature from260 to 293 K. No change of particle size is observed with varying pressure or temperature,indicating that the previously observed compression of the ligands at high concentrationswith increasing pressure is a crowding effect. For both the pressure- and the temperature-dependent measurements, the extracted viscosity of water follows the expectation fromprevious studies. This demonstrates the feasibility of measuring aqueous systems withlengthscales shorter than 40 nm and viscosities of η ≈ 1 Pas using XPCS. Additional mea-surements using the newly developed TEMPUS detector show how event-based detectorsgive access to shorter timescales that cannot be resolved with conventional detectors.
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