Skip to main content

2D Soft Particle Clogging: A Hard Problem

Mia Morrell is a sophomore majoring in Physics. She was awarded a Spring 2018 Conference Grant which she used to attend the American Physical Society Meeting in Los Angeles.

When shaking parmesan cheese on your pizza, have you mused in frustration why the cheese always seems to clog up in the holes of its container? Have you ever clogged a toilet and wondered what led to this most unfortunate form of humiliation? Or on a more serious note, have you contemplated the arterial clotting of human blood cells in the early phases of a stroke?

Our plexiglass hopper chamber displaying hydrogel particles in a clogged state.
These questions have fascinated me ever since I was introduced to soft matter physics upon my freshman year at Emory. During my time in Emory University’s Weeks lab, which focuses on soft matter and complex systems, I have studied soft particle clogging in two dimensions, devising experiments which can be applied to the previously cited situations of blood clots, parmesan cheese flow, and toilet clogs.

The clogging behavior of hard particles such as sand has been a popular subject of study for the past sixty years.[1] Simulations of pedestrians (modeled as hard particles) leaving a room through a single door have shown that increasing the speed at which people rush towards the door leads to increased clogging frequency (that is, people get stuck in the door!).[2] This celebrated phenomenon is known as the “faster is slower” principle. People are usually modeled as hard particles, because any “deformation” of a person will result in injury.

Our plexiglass chamber, which can be angled to vary the speed at which the hydrogel particles rush towards the chamber exit slit
I wondered whether forcing a system of soft particles such as cheese, blood cells or any other deformable material through a small opening lead to increased or decreased clogging. Would soft particles display the same “faster is slower” principle? Would allowing soft particles to wiggle around slightly once a clog was formed dislodge the clog?

A hydrogel bead. We place 200 of these soft, deformable polyacrylamide spheres into our hopper chamber.
To answer these questions, my PI Eric Weeks and I devised an ongoing series of experiments using a plexiglass chamber in which we placed soft polyacrylamide hydrogel beads. The chamber has a small exit slit of adjustable width through which we allow the hydrogels to flow. We can adjust the speed at which the hydrogel particles rush towards the exit slit by angling the hopper, therefore varying the driving force of gravity upon the hydrogel particles. The chamber is also outfitted with an eccentric rotating mass motor which can apply vibrations to the hopper system to test whether we can dislodge hydrogel clogs by causing the particles to wiggle around.

The eccentric rotating mass (ERM) motor used to make the hydrogel particles wiggle during clog formation.

With this experimental setup, we found that when the hydrogels flow faster towards the exit slit, clogging occurs less frequently. This result contradicts the “faster is slower” phenomenon and is most likely due to the soft hydrogels’ ability to deform and squeeze through the exit slit, as opposed to hard particles, which cannot be deformed. We also found that allowing the hydrogels to wiggle around during clog formation does not dislodge clogs but contributes to increased clogging frequency. We are currently investigating the roots of this phenomenon.

I recently presented these findings at the 2018 APS March Meeting in Los Angeles, CA. I attended the Jamming and Clogging session, where I was able to share my research with experts in the field including Dr. Bob Behringer of Duke University and Dr. Douglas Durian of UPenn, both whose work I deeply admire. I received plenty of ideas concerning new directions for my investigation of soft particle clogging, including high-speed video analysis, which I am currently applying. I am so grateful for Emory University’s continual support of my research and cannot emphasize the importance of Emory’s role in fostering my intellectual and professional development enough. Thank you, Emory!


Visit the Undergraduate Research Programs website to learn more about applying for Conference Grants. 




[1]  W. A. Beverloo, H. A. Leniger, and J. van de Velde, The flow of granular solids through orifices, Chem. Eng. Sci., 15, 260–269 (1961).
[2] D. Helbing, I. Farkas, and T. Vicsek, Simulating dynamical features of escape panic, Nature, 407, 487–490 (2000).

Comments

Popular posts from this blog

Why Research Wednesday: Aamna's Story

Aamna Soniwala is a sophomore majoring in Human Health (on the pre-dental track) with a minor in Sociology. URP's Research Ambassador Arielle Segal had the pleasure of interviewing Aamna about her research experiences. Here it is:  What research do you do on campus? How long have you been doing it? “I work under Dr. K.M. Venkat Narayan with Dr. Jithin Varghese in the Hubert Department of Global Health at Rollins – specifically within the Emory Global Diabetes Research Center. I started during my second semester of my first year, researching global health equity in diabetes precision medicine.” How did you get started in your research? “I took HLTH 210 last spring, and Dr. Narayan was one of our asynchronous guest lecturers. I felt that I resonated with his values and research, so I reached out to him and started working with a post-doctoral fellow, Dr. Varghese.” How has research impacted your undergraduate career? “Research has allowed me to grow as a critical thinker and problem

A Whole New World of Research

Monica Vemulapalli is a junior majoring in Neuroscience and Behavioral Biology. She was awarded a Spring 2019 Conference Grant which she used to attend the Experimental Biology Conference . When I found out that my first ever research conference was going to be in my hometown of Orlando, Florida, I was excited! I knew that having an unfamiliar event happen at a very familiar place would make me less anxious. However, the conference turned out to be less stressful and more interesting than I ever thought. I attended  Experimental Biology (EB)  and   presented  my very first research poster , a memory that I will definitely cherish forever.

Why Research Wednesday: Katelyn King

  Katelyn King is a senior at Emory’s College of Arts and Sciences, majoring in Biology and minoring in Global Health, Culture & Society. Her research area is on c ancer biology, and she investigates the effects of knocking out anti-apoptotic genes on drug efficacy in multiple myeloma.   Her collegiate research journey started the summer after her first year. She was accepted into the NIH-NIDDK Short-Term Research Experience for Underrepresented Persons (STEP-UP) program and was tasked with finding a mentor. She reached out to Oxford Professor Dr. Taliaferro-Smith because SHE was interested in her triple-negative breast cancer (TNBC) research. After a brief informational interview, Dr. Taliaferro-Smith invited Katelyn to join her lab! During the 10-week program, SHE studied the effects of genetic modifications in TNBC. She offered to continue her position on the project throughout the academic year as an Oxford Research Scholar. She has since had the opportunity to conduct rese