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| Home > Publications database > Structure and Dynamics of Complex Liquids - The Phase Behaviour of Silica-PNIPAm Nanogels |
| Home > Publications database > Structure and Dynamics of Complex Liquids - The Phase Behaviour of Silica-PNIPAm Nanogels |
| Book/Report/Dissertation / PhD Thesis | PUBDB-2019-04870 |
; ;
2019
Verlag Deutsches Elektronen-Synchrotron
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2019-04870
Report No.: DESY-THESIS-2019-032
Abstract: In this thesis, the structure and dynamics of highly concentrated core-shell nanogel particlescomposed of a silica core and a poly(N-isoproylacrylamide) (PNIPAm) shell suspendedin water are studied. The particles were synthesised with dierent core-to-shell size ratiosand prepared at various concentrations with volume fractions e between approximately0:004 and 2. X-ray photon correlation spectroscopy (XPCS) enables to follow the dynamical,small-angle X-ray scattering (SAXS) the structural changes of the thermo-responsivenanogel particles which undergo a volume phase transition at a so-called lower criticalsolution temperature (LCST) of 32C. All samples were studied in a broad temperaturerange around the LCST with approximately 15C < T < 45C and the main focus is ondensely-packed systems.For a system with e = 0:55, the structural relaxation time c was found to decreasewith increasing temperature. Above the LCST, the structural relaxation time initiallycontinues to decrease. The eect is accompanied by a transition from stretched to compressedexponential behaviour of the intensity autocorrelation functions, which could bedetermined by analysing the intensity autocorrelation functions. Upon further heating asudden slowing down at a critical temperature Tc 37C. In parallel, the q-dependenceof the relaxation time shows an anomalous change from c / q3 to c / q1. Theresults reveal a temperature-induced transition from swollen repulsive particles with polymerdriven dynamics at lower temperatures T < Tc towards a colloidal gel composed ofcollapsed attractive particles. The transition of structure and dynamics shows a distinctdependency on the eective particle volume fraction. Below a critical concentration notransition upon heating was found.The de-swelling behaviour of the PNIPam nanogel was inuenced with the additionof Trimethylamine N-oxide (TMAO) to the concentrated particle suspension. With increasingTMAO concentration, a shift of the LCST towards lower temperatures and apreferential hydrophobic state could be determined.With all results a full phase diagram of a silica-PNIPAm core-shell system is presentedas a function of temperature and concentration. It spans from dilute suspensions toan eective volume fraction of more than ninety percent covering two liquid phases, astructural rearrangement phase and a colloidal gel phase.
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