Auto-assemblée de sphères colloïdales à travers des cycles de sédimentation inversée

L'hyperuniformité est un concept relativement récent, utilisé afin de comprendre et de prédire les propriétés photoniques de matériaux désordonnés. Motivés par la perspective de fabriquer des systèmes hyperuniformes désordonnés au moyen d'un processuss pouvant etre reproduit a une échelle industrielle, nous forcons de facon périodique une suspension de sphères colloidales a travers des cycles de sédimentation inversée. La caractérisation de la dynamique et de la structure du système implique differentes techniques adaptées a la taille des particules et aux propriétés de la suspension. Nous analysons la pertinence de chaque technique quant a l'évaluation de l'hyperuniformité d'un système. Nous détectons et suivons des particles de borosilice de facon individuelle afin de caractériser leurs propriétés dynamiques. Nous trouvons une forte anisotropie dans la dynamique de ces suspensions, ainsi qu'une transition dynamique a un temps d'attente caractéristique. L'anisotropie peut etre annulée en introduisant une nouvelle direction de sédimentation. La dynamique de suspensions de particules de silice est examinée via une technique appelée Differential Dynamic Microscopy. Nous observons une augmentation du coefficient de diffusion des particules a un temps d'attente caractéristique, dépendant du temps d'attente. Finalement, nous étudions la structure de ces suspensions a travers la diffusion statique de la lumière aux angles faibles. Nous observons un changement du facteur de structure des suspensions, au meme temps caractéristique mesuré en Differential Dynamic Microscopy.Hyperuniformity is a relatively recent concept that has been increasingly used to understand and predict the photonic properties of disordered materials. Motivated by the perspective of generating disordered hyperuniform system through a new and scalable process; we periodically drive three-dimensional suspensions of colloidal spheres through reversed cycles of sedimentation. The size of colloids chosen is kept to a micrometric scale to keep a focus on potential application in photonics. The characterization of the dynamics and structure of the system involves different techniques, adapted to the nature and properties of the particles and the suspending media. The extent to which each of these techniques can provide information about the hyperuniformity of the system is assessed. We use particle tracking to study the dynamics of the suspensions of borosilicate particles. We find a strong anisotropy in the suspensions dynamics, as well as a dynamical transition at a characteristic wait time. This anisotropy can be cancelled by allowing another sedimentation direction in the system. The dynamics of the suspensions of the silica particles are examined using Differential Dynamic Microscopy. We observe an increase of the diffusion coefficient of the particles at a characteristic wait time that is concentration-dependent. We then investigate the structure of these suspensions through Low Angle Static Light Scattering. We observe a change in the structure factor of the suspensions, which occurs at the same characteristic wait time measured through Differential Dynamic Microscopy

Presentation1_Reliable particle sizing in vaccine formulations using advanced dynamic light scattering.PDF

Understanding the impact of lipid nanoparticle size on immunogenicity represents an important step for enabling the rapid development of novel vaccines against known or emergent diseases. Dynamic light scattering, also known as quasi-elastic light scattering or photon correlation spectroscopy, has established itself as an optimal analytical method to determine particle size due to its in-situ approach and fast measurements. However, its application to many systems of industrial relevance has been hindered due to artifacts arising from multiple scattering. Result interpretation becomes severely compromised depending on the concentration of the system and the size of the particles. In this context, strong sample dilution is often required, bringing additional uncertainties to the formulation development process. Here, we show how advanced dynamic light scattering technology can filter out multiple scattering from the signal and yield fully accurate sizing measurements regardless of the sample concentration. We illustrate this in a comparative study with standard dynamic light scattering using polystyrene beads as model suspension as well as a concentrated commercial lipid nanoparticle adjuvant (AddaVax™).</p