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Nanoclay interaction with charged species: from fundamentals to functional materials

Defense Thèse de doctorat : Univ. Genève, 2018 - Sc. 5222 - 2018/06/04
Abstract In this thesis, interaction of layered double hydroxide (LDH) nanoparticles with various charged species were investigated. Moreover, functional materials with enzymatic activities were prepared. While the Chapter 1 represents the introduction, experimental background and outline of the thesis, the Chapter 2 focuses on ion specific effect on colloidal stability and charging properties of the LDH material. It was observed that different monovalent salts influence the electrophoretic mobilities and the colloidal stability of LDH nanoparticles in a different extent. The main reason for this phenomenon is the variation of the counter-ion hydration, as it had been predicted by the Hofmeister series. Multivalent ions showed more pronounced effect on charging and aggregation of LDHs according to the Schulze-Hardy rule. However, such ion specific effects were more pronounced than predicted by these theories due to strong adsorption of the counter-ions on the surface of the LDH particles. In the Chapter 3, the influence of a copolymer adsorption on the colloidal behavior of LDH was studied. Coating was performed at various ionic strengths to clarify the nature of interparticle interactions. The negatively charged copolymer was able to induce charge neutralization followed eventually by significant charge inversion of the LDHs. This charge reversal led to increased surface charge density and to stable dispersions even at elevated salt concentrations. Interaction of LDH platelets with oppositely charged latex spheres was probed in mobility measurements and by dynamic light scattering in the Chapter 4. In this case, LDH behaves as a polyelectrolyte and strongly adsorbs on the surface of the latex particles causing charge inversion. Charge neutralization occurred at a certain value of LDH dose inducing rapid particle aggregation in the dispersion. Aggregation in these samples was faster than the diffusion-limited aggregation, which was a proof of additional attractive force (patch-charge force). Latex particles were coated by two types of LDHs with a different anion intercalated among layers, however, this difference did not influence the outcome of the experiments. Preparation of LDH-DNA hybrid nanocomposite was performed in the Chapter 5. Two different approaches were examined, namely, adsorption due to the opposite charge of the support and the guest molecule and covalent bonding after functionalization of the support and activation of the DNA. Successful immobilization was proved by IR spectroscopy and SEM-EDX measurements. Chapter 6 concerns functionalization of LDH clay with biocompatible polyelectrolyte, heparin. It was able to induce charge inversion, which corresponds to typical U-shaped stability curves. In comparison to the bare particles, the coated ones exhibited multiple times improved colloidal stability. Difference in the morphology of the bare and coated nanoparticles was not observed. This was the initial step towards preparation of enzymatically active, highly stable, functional material. The two final chapters with results (Chapter 7 and Chapter 8) are focused on the preparation of functional materials. Namely, superoxide dismutase (SOD) and horseradish peroxidase (HRP) were adsorbed separately on LDH platelets. LDH-SOD was afterwards coated with heparin in order to make the material resistant against salt-induced aggregation. While for HRP immobilization, heparin adsorption had to be performed initially, in order to introduce sufficient negative charge to the particles, which enables successful enzyme adsorption via electrostatic interaction (HRP has a net positive charge at neutral pH). Importantly, both enzymes kept their native conformation, which was reflected as a preserved enzymatic activity upon immobilization. Materials were also stable at elevated ionic strength (above 150 mM, which is the one in blood) and changes in morphology of the particles upon functionalization were not observed. The last chapter of the present thesis is concerned with the conclusions of the work.
Keywords Layered double hydroxideSODHRPColloidal stability
URN: urn:nbn:ch:unige-1059525
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PAVLOVIC, Marko. Nanoclay interaction with charged species: from fundamentals to functional materials. Université de Genève. Thèse, 2018. https://archive-ouverte.unige.ch/unige:105952

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Deposited on : 2018-06-27

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