Authors: Jun Xiang
Source: Knowledge UdeS (Institutional Deposit of the University of Sherbrooke) (article, 2018-01-01)
Field: Materials Science — Materials Chemistry

Study of upconversion nanoparticle/polymer hybrid materials: from nanovectors to thin films Abstract: The research carried out in this thesis involves the design, synthesis, and investigation of three new types of hybrid materials based on polymers and upconversion nanoparticles (UCNP). These materials are sensitive to near-infrared light (NIR) because UCNP can absorb light with a wavelength of 980 nm then emit light in the visible and ultraviolet (UV) light region. For the first two systems studied, their potential application as a drug nanovector whose release is triggered by NIR radiation is demonstrated. As for the other system in the form of a thin film, it demonstrates that the layer-by-layer assembly is an effective method for organizing UCNP in a film together with gold nanoparticles (AuNP). The obtained results validate the proposed new strategies or methodologies, which are general and offer new perspectives in the development and exploration of UCNP/polymer hybrid materials applications. In the first project (Chapter 1), the self-assembly of an amphiphilic diblock copolymer on the surface of UCNP is carried out to form a micelle with single UCNP encapsulation inside. Using surface-initiated atom transfer radical polymerization, UCNP is covered by the diblock copolymer with poly(4,5-dimethoxy-2-nitrobenzyl methacrylate) (PNB) as the inner and hydrophobic block and poly(methoxy polyethylene glycol monomethacrylate) (POEG) as the outer and hydrophilic block. Under 980 nm laser exposure, the UV light emitted by the UCNP is absorbed by PNB, resulting in the cleavage of o-nitrobenzyl groups and formation of carboxylic acid groups. The increased hydrophilicity of the copolymer resulting from the photochemical reaction triggered by the NIR light disturbs the nanovector and thus leads to the release of doxorubicin (DOX). In the second project (Chapter 2), UCNP are complexed with a UV-labile polyelectrolyte by electrostatic interaction between charges of opposite sign, which allows the covering of each UCNP by a polymer layer. A charged model drug, fluorescein (FLU), is encapsulated in the polyelectrolyte layer via a co-assembly process. Also, under the 980 nm laser irradiation, the UV light emitted by the UCNP is absorbed by photolytic side groups of the polyelectrolyte, resulting in cleavage of o-nitrobenzyl groups and formation of carboxylic acid groups. As a result, a portion of the positive charges carried by the polyelectrolyte is converted to negative charges, and this inversion disrupts the balance between the charged components and leads to the release of FLU molecules. In the last project (Chapter 3), the layer-by-layer method is used to assemble UCNP into a thin film in a controlled manner, in particular by adjusting the deposition order of four UCNP/polyelectrolyte bilayers and four AuNP/polyelectrolyte bilayers. The extinction spectra and the upconversion emission spectra of these plasmonic and NIR-sensitive hybrid thin films reveal that the spatial organization determined by the deposition sequences influences the interaction between these two types of nanoparticles and thus their optical properties. Nanoparticle ; Materials science ; Polymer ; Thin film ; Nanotechnology ; Composite material Luminescence Properties of Advanced Materials ; Nuclear materials and radiation effects ; Thermal and Kinetic Analysis