PhD Defense for Scott Fenton


Thursday, March 2, 2023 - 11:00am to 2:00pm


ESB Room 1001 ; Zoom Link:
Title:  Characterizing the Phase Behavior of Thermoresposive Colloidal Dispersions to Enable Thermokinetic Processing of Colloidal Gels


Colloids are used to form processable soft solids that are ubiquitous in everyday materials like foods, industrial building materials, coatings and biomedical products. However, despite their prevalence, there is limited understanding of their phase behavior and processing, especially for colloidal systems where interparticle interactions are thermoresponsive.  Therefore, to build toward a comprehensive understanding of colloidal materials, we first use a model thermoreversible colloidal system to develop new methods to precisely establish locations of non-equilibrium states, like colloidal gels and glasses, to generate a comprehensive colloidal phase diagram and to elucidate the underlying combination of mechanisms that lead to the emergence of gelation. Our method employs systematically varied quenches of the colloidal fluid over a range of volume fractions to identify minimal conditions for gel solidification. The method is applied to experimental and simulated systems to test its generality toward attraction potentials of varied shape. Using structural and rheological characterization, we show that all gels incorporate elements of percolation, phase separation and glassy arrest, where the quench path sets their interplay and determines the shape of the gelation boundary. We find that the slope of the gelation boundary corresponds to the dominant gelation mechanism, and its location approximately scales with the equilibrium fluid critical point. These results are insensitive to potential shape, suggesting that this interplay of mechanisms is applicable to a wide range of colloidal systems. Next, we use our new understanding of colloidal phase behavior to elucidate how programmed quenches to the gelled state can be used to effectively tailor gel structure and mechanics. Specifically, we look at how changing the quench rate from the fluid phase into the gel region can be used to vary the gels elastic by over two orders of magnitude.  These results suggest that to control the structure and mechanics of gels, an important dimensionless parameter to consider is the ratio of the timescale of the thermal quench relative to the timescale for phase separation. We then demonstrate the usefulness of our new understanding of colloidal gel phase behavior and processing by using our model colloidal system to develop a new technique for templating porous polymeric materials.

Event Type: 

General Event