Book/Dissertation / PhD Thesis

PUBDB-2022-00714

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Higher-Order Correlations in Complex Liquids

Dartsch, M. (Corresponding author)Extern* ; Gruebel, G. (Thesis advisor)XFEL.EU*DESY* ; Pearson, A. (Thesis advisor)Extern*XFEL.EU*EMBL*

2022
Verlag Deutsches Elektronen-Synchrotron DESY Hamburg

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Please use a persistent id in citations: doi:10.3204/PUBDB-2022-00714

Report No.: DESY-THESIS-2022-003

Abstract: Colloidal dispersions show a peculiar rheological behavior known as shear-thinning,that is the viscosity of a sample decreases with increasing shear rate. In thiswork the underlying structural changes that lead to this effect are studied byusing samples consisting of polyacrylate-coated silica nanoparticles dispersed inpolyethylene glycol-200. The silica particles are synthesized using a modifiedStöber method and samples with volume fractions between $\phi$ = 0.22 and $\phi$ = 0.53are prepared.The experiments performed in this thesis utilize a setup combining a cone-platerheometer with a small-angle x-ray scattering (SAXS) setup. In this way rheological and structural properties of the samples can be measured simultaneously.Data collected from the SAXS measurements are evaluated further using x-raycross-correlation analysis (XCCA) in order to study higher-order correlations andlocal symmetries.It is shown that under shear the highly concentrated nanoparticle dispersionsform structures with hexagonal symmetry which can be interpreted as layersof hexagonal close-packed spheres. From XCCA the sixth Fourier coefficient ofthe cross-correlation function can be used as an order parameter to quantify thedegree of local hexagonal order. In the regime of intermediate shear rates thedegree of hexagonal order is correlated with the magnitude of the shear rate. Anincrease of the shear rate corresponds to an increase of local hexagonal order.Since the viscosity is decreasing with increasing shear rate it can be concludedthat a higher degree of local order minimizes internal friction of the sample, andtherefore lowers its viscosity.

Note: Dissertation, Universität Hamburg, 2022

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Contributing Institute(s):

1. Coherent X-ray Scattering (FS-CXS)

Research Program(s):

1. 633 - Life Sciences – Building Blocks of Life: Structure and Function (POF4-633) (POF4-633)
2. 6G3 - PETRA III (DESY) (POF4-6G3) (POF4-6G3)

Experiment(s):

1. PETRA Beamline P10 (PETRA III)

Appears in the scientific report 2022

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Database coverage:

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