Osmotic Pressure of Microgel Suspensions

Abstract

Microgels are used in applications ranging from optics to medicine. Due to their ubiquity, a better understanding of their mechanical properties is desired. In these systems, the softness of individual constituents plays a pivotal role in the overall system behavior. For instance, the hallmark of crystallization and arrest in systems of soft spheres may occur at volume fractions differing from those of hard spheres. In other systems, these transitions turn out to qualitatively match hard sphere behavior. We seek to better understand the role of individual particle softness on the overall behavior of the system. To achieve this, we need to determine the single particle modulus. The goal of the project is to determine the bulk modulus of microgel suspensions, by exerting a predetermined external osmotic pressure on microgels, and study the change in modulus as the system undergoes a phase transition. Since usual osmotic pressure measurement equipment is not designed for long time measurements, a new protocol of sample preparation, measurement, and sample collection is needed. The work presented in this undergraduate thesis is focused on tackling and successfully addressing the set-up, calibration, and testing of a membrane osmometer, along with the sample preparation needed for this set of experiments. We have developed a protocol for measurment involving preparation of reference samples, calibration, sample preparation, and sample recovery. We have also established limitations of the equipment in relation to these samples. Finally, we present preliminary results to assess experimental set-up validity as proof-of-principle of the technique.