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<span style="font-family: "Times New Roman", serif; font-size: 12pt; line-height: 150%;"><img alt="Dissertation Defense Announcement at the Cullen College of Engineering" id="x_Picture_x0020_3" style="width: 6.25in; height: 1.7812in; margin-top: 0px; margin-bottom: 0px;" data-outlook-trace="F:1|T:1" src="cid:image005.jpg@01D845D5.17B10F60"></span></p>
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<span style="font-family: "Times New Roman", serif; font-size: 16pt; line-height: 150%; color: red;"><b>Extensional Rheology of Colloidal Particles and Polymer Mixtures</b></span></p>
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<span style="font-family: "Times New Roman", serif; font-size: 12pt; line-height: 150%;"> </span></p>
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<span style="font-family: "Times New Roman", serif; font-size: 13.5pt; line-height: 150%; color: black;"><b>Diego Soetrisno</b></span></p>
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<span style="font-family: "Times New Roman", serif; font-size: 13.5pt;"><b> </b></span></p>
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<span style="font-family: "Times New Roman", serif; color: black;">Monday, November 20, 2023; 10:00 AM - 12:00PM</span></p>
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<b>Room: </b>Agrawal Eng. Research Building (AERB), Room 126</span></p>
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<span style="font-family: "Times New Roman", serif; color: black;"><b> </b></span></p>
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<span style="font-family: "Times New Roman", serif; color: black;"><b>TEAMS</b>:</span></p>
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<span style="font-family: "Times New Roman", serif; color: black;"> </span><span style="color: black;">
</span><span style="font-family: "Times New Roman", serif; color: black;">Meeting ID: 237 151 734 550</span></p>
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<span style="font-family: "Times New Roman", serif; color: black;">Passcode: </span>
<span style="font-family: "Times New Roman", serif; color: rgb(37, 36, 36);">qUw93K</span></p>
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<span style="font-family: "Times New Roman", serif; color: black;"><b>Committee Chair:</b><br>
Jacinta Conrad, PhD</span></p>
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<span style="font-family: "Times New Roman", serif; color: black;"><b>Committee Members:</b></span></p>
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<span style="font-family: "Times New Roman", serif; color: black;">Ramanan Krishnamoorti, Ph.D.
<b>| </b>Alamgir Karim, Ph.D. <b>|</b> Behrooz Ferdowsi, Ph.D. <b>|</b></span></p>
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<span style="font-family: "Times New Roman", serif; color: black;">Vivek Sharma, Ph.D</span></p>
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<span style="font-family: "Times New Roman", serif; font-size: 12pt; line-height: 150%; color: rgb(200, 16, 46);"><b>Abstract</b></span></p>
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<span style="font-family: "Times New Roman", serif; color: black;">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.</span></p>
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<span style="font-family: "Times New Roman", serif; color: black;"> </span></p>
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<span style="font-family: "Times New Roman", serif; color: black;">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 λ<sub>E</sub> and filament lifespan t<sub>f</sub> 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 λ<sub>E</sub> follows the polymer size, and the presence of particles did not affect λ<sub>E</sub> 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.</span></p>
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