[CCoE Notice] Cullen College Dissertation Defense Announcement - Diego Soetrisno_ChBE

[Hutchinson, Inez A]

[Dissertation Defense Announcement at the Cullen College of Engineering]

Extensional Rheology of Colloidal Particles and Polymer Mixtures



Diego Soetrisno



Monday, November 20, 2023;   10:00 AM - 12:00PM

Room: Agrawal Eng. Research Building (AERB), Room 126



TEAMS:

       Meeting ID: 237 151 734 550

Passcode: qUw93K



Committee Chair:
Jacinta Conrad, PhD

Committee Members:

Ramanan Krishnamoorti, Ph.D. | Alamgir Karim, Ph.D. | Behrooz Ferdowsi, Ph.D. |

Vivek Sharma, Ph.D

Abstract

Extensional deformation is ubiquitous in industrial processes involving extrusion, spraying, and roll-coating of products formulated with colloid-polymer mixtures, which are often used to manufacture materials ranging from consumer products to devices for energy applications. The processability of these products is typically qualitatively expressed in terms of “sprayability”, “stringiness”, or “printability”, which are correlated with their extensional material properties. Quantifying these extensional response and understanding how they change with polymer content and macromolecular properties can inform a better physical picture on how formulation affects material performances.



Here, we study the extensional flow properties via the pinch-off dynamics of dense colloidal suspensions (volume fraction Φ ≥ 0.40) with non-adsorbing polymer using a dripping-onto-substrate (DoS) protocol. We use a methacrylate copolymer particles with dimethylacrylamide copolymer brushes suspended in refractive index and density matched 80% (w/w) glycerol in water with NaCl added to screen electrostatic repulsion. We add polyacrylamide polymers of different molecular weights to induce depletion interactions. We characterize the extensional properties by calculating the extensional relaxation time λE and filament lifespan tf from the capillary-driven pinching dynamics. The addition of polymer delays and modifies the pinch-off dynamics of the dense suspensions depending on the size of the polymer. The concentration dependence of λE follows the polymer size, and the presence of particles did not affect λE when scaled with free volume polymer concentration normalized with the overlap concentration c/c*. These results provide insight into the role of polymer size in the extensional rheology of colloid-polymer mixtures, which represent simplified models of suspensions used in practical applications.

[Engineered For What's Next]


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