Researching How Gravity Impacts Gel Materials Including Tests in Space

Safa Jamali

MIE Assistant Professor Safa Jamali is principal investigator for a recent $500K NSF grant, which will consist of research on how gravity impacts gel-like systems. Jamali hopes to better understand how the different particles that make up a gel system interact under different conditions.

Titled, “Bimodal Colloidal Assembly, Coarsening and Failure: Decoupling Sedimentation and Particle Size Effects,” the work will be done in collaboration with Ali Mohraz from University of California, Irvine.

Gels belong to a larger class of materials called “soft materials” that include also different polymers and plastics, as well as many biological materials, Jamali explained. Everything from TVs to cars have some form of soft materials in them, and the science of soft matter and how they react to other materials has become increasingly critical over the past few decades.

“It’s important to think about how they’re formed, how you can fabricate those materials, and how they behave over time,” he said. “We know much more about classical materials such as metals and fluids. But we don’t know as much about soft materials and particulate systems [and gels].”

Gel is specifically a difficult material to define, Jamali added. For example, it is both a liquid and a solid: it sits somewhere in between. Furthermore, gels are being used in numerous types of everyday necessities. Gels are naturally present in many foods, hand sanitizers, consumer products such as shampoos and lotions, and are used as carriers for targeted delivery of medicines. However, these gels behave in a complex form to mechanical stimuli, so it is very important to understand how they will respond to certain types of processes or other additives.

“The problem with the particles that make up a gel is that on the ground, on Earth, everything is subject to gravitational force,” Jamali said. “So, if I wanted to study how these particles behave, or to track them under a microscope, gravitational force complicates it. In many examples such as in shampoos, or in biological systems, we have several particles that each behave differently to gravitational force. Now, how do these individual behaviors affect the properties of a gel? I don’t know, because of gravity.”

Through the NSF grant, researchers will be able to send the same materials being studied on Earth into space, to the International Space Station (ISS) to test how they behave in presence of other particles without gravitational force. That way, the role of gravity can be ruled out on what researchers see with anything from shampoos to hand sanitizers.

Along with the micro-gravity experiments aboard ISS, there will be computer simulations and control ground experiments performed, Jamali explained.

“What can you do in space, that still benefits life on Earth,” he said. “We’re taking a step back, using fundamental science, to widely benefit society in many applications.”

From shampoo to crude oil

There are myriad applications for colloidal gels, including consumer products, biomedical needs, and even in large industries such as oil.

With shampoos and lotions, those products will have expiration dates, Jamali said. That expiration date is chosen because the constructors within the gel will fall apart.

“It does happen naturally,” he said. “Gravity is trying to make them collapse, and sooner or later it will.”

But no one wants to have shampoo that eventually gets to the stage where it flows similar to water out of the bottle, Jamali added.

With medicines, gel tablets are being more commonly used for dosages.

“When you swallow that gel, the product dissolves in your body and a drug is released slowly over a certain period of time,” he said. “If I can understand exactly how that gel forms, understand it’s properties, then we can better understand the release time, and correspondingly make a gel carrier that is designed to release the medicine over a certain period of time, which is an important biomedical application.”

Additionally, crude oil is a gel. When crude oil is clogged in the pipelines of deepwater extraction rigs, it can cost hundreds of millions of dollars to shut down an operation for clean up, Jamali said.

“If I can understand how [those clogs] form, then I can know how to prevent them, or make them form the way I want them to, and we can potentially prevent those events.”

Abstract Source: NSF

A wide range of natural and artificial materials are composed of different components – such as particles and polymer molecules – dispersed in a fluid. Examples are personal care products, food, and inks. Physical properties and function of these products, along with their shelf-life and consumer perception, depend on the behavior of these components. Designing materials with specific desired properties, therefore, requires a better understanding of how these particles and polymers interact under different conditions. Of particular interest are gel-like systems where particle size variations can lead to product failure. This award will combine computer simulations and terrestrial experiments, along with experiments onboard the International Space Station. The goal is to examine the effect of gravity on these gels and to investigate the size variation effects on final properties of such materials. Such findings could benefit several industries and will also help opening new avenues of fundamental research. A series of outreach activities are proposed to enhance the participation of traditionally underrepresented groups in STEM fields.

In this project, we will study the physics of colloidal gelation, coarsening and phase-separation in bimodal attractive colloidal suspensions, in which the size difference between the two particle populations is appreciable. This size disparity can cause selective gravitational settling in one hand, and heterogeneous clustering where large particles serve as nuclei for aggregation of small colloids in another hand, leading to coarsening and failure of the gels. The role of particle size difference in coarsening and eventual failure of colloidal gels will be probed by decoupling the role of gravitational forces and inter-particle interactions. The ultimate goal is to explore the role of particle composition (ratio of small to large particles) as well as the range of interactions between the particles in mediating gelation, coarsening, and [gravitational] failure. An integrated effort, with detailed study of the physical phenomena through computational/theoretical platforms in conjunction with control ground experiments in addition to essential micro-gravity experiments will be performed. The cohesive integration of theory, computation and experiments with and without gravity will enable us to systematically decouple the roles of gravity and particle size disparity in mediating gelation, coarsening, and failure, paving the way for the development of a theoretical framework to better understand attractive colloidal systems in real-world applications.

This award reflects NSF’s statutory mission and has been deemed worthy of support through evaluation using the Foundation’s intellectual merit and broader impacts review criteria.

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Related Departments:Mechanical & Industrial Engineering