Dissertation

Linking Microgel Particle Properties to Filtration Behavior Through Microscopic Observations

de Aguiar, Izabella Bouhid

2019

Overview

Soft particles are present in our daily lives and differently from their hard counterparts, they can change conformation and composition when experience an external source of stress. This specific characteristic of soft particles can make it more challenging to predict their behavior in processes such as filtration and centrifugation. More information on the specific behavior of soft particles under external stress is still lacking on current literature and can be useful to different areas of application.The aim of this thesis is to provide information that will contribute to the understanding of soft particle behavior under pressure such as in pore clogging and cake formation in membrane processes. We use micrometer-sized microgels as model particles in this work due to their tunability and ease of production. Also, using micrometer-sized microgels we can consider colloidal interactions negligible, what simplifies our system and allows us to focus on individual particle behavior.In the first two experimental chapters (Chapters 2 and 3), we focus on microgel packings (static conditions). The packings were produced by osmotic stress with controlled, varying applied pressure.In Chapter 2, we focus on the collective behavior of microgels in packings in static conditions and we describe the behavior of the microgel packings in term of wellknown polymeric theories such as the Flory-Rhener theory. We found that suspensions of dextran microgels start to resist compression at volume fractions close to random close packing of hard spheres with the same size distribution. For volume fractions between random close packing and 1, the resistance increases similarly to that of a dextran solution of the same concentration. From image analysis followed that microgels are deformed but internal concentration remains the same. At volume fractions ‘higher than 1’, microgels are forced to expel solvent and deswell.In Chapter 3, we explore our observation from Chapter 2 that individual particles will respond to stress in different ways according to the applied pressure. For that we use microgel packings containing a mixture of fluorescent and non-fluorescent microgels with an excess of non-fluorescent microgels. We observe the packing using fluorescence microscopy and are able to observe single fluorescent particles surrounded by non-fluorescent particles (non-visible). We found that both deswelling and deformation occur simultaneously when soft particles are under pressure and we describe a theory to predict their behavior according to the pressure applied to the system.In Chapters 4 and 5, we use microfluidic devices to observe the behavior of soft particles in dynamic systems.In Chapter 4, we focus on the collective behavior of particles. For that we use a microcentrifuge coupled with an optical microscope to investigate the reversibility of soft particle deposits according to the applied force. We found that, for the particles used, total reversibility of deposits is possible as long as there is water available for particle reswelling. Also in Chapter 4, we use microfluidic devices composed of an array of parallel channels as a model membrane for filtration experiments.

• Publisher: ProQuest Dissertations & Theses
• Subject: Behavior / Deformation / Emulsion polymerization / Environmental engineering / Food / Hemodialysis / Medicine / Membrane separation / Microscopy / Milk / Osmosis / Particle size / Phase transitions / Polymer chemistry / Polymers / Pore size / Sludge / Spheres / Water treatment
• ISBN: 9798380569682