News & Notes - Science Education
Always working to enhance the polymer content on our website, AGPA is developing a new section of the website that will highlight the exciting, valuable research of the faculty in the College of Polymer Science and Polymer Engineering. This new feature will include videos from inside the research labs and interviews with research faculty, their graduate students, and their research associates. I will keep you updated on the developments of this new endeavor. In the short term, I will entice you to visit this future section by providing brief descriptions of this research. The first research faculty I would like to present to you is Dr. Shi-Qing Wang, Professor of Polymer Science. The following description from Dr. Wang gives you a glimpse into his research lab. If you are not very familiar with polymers, I advise viewing the "What are Polymers?" PowerPoint for a basic understanding of polymers.
Polymeric materials, more commonly known as plastics and rubbers, are everywhere: from milk jugs and grocery bags to automobile/aircraft tires and prescription glasses. To make these products, the polymers are heated into the liquid state and squeezed into different forms. This heating and squeezing is called polymer processing. In this liquid state, one can think of the polymer material as a bowl of spaghetti where the long polymer chains cannot cross through each other, but have to go around one another. Indeed, the polymers, also known as macromolecules, could take a long time to move around each other, so long that polymeric liquids are unable to flow during processing. So what do the polymers do? They break up like solids do. This solid-like failure was difficult to observe previously because, in contrast to ordinary solids, the failed sample eventually heals after a period of resting.
So discovery of such natural phenomena at The University of Akron in Dr. Wang's lab actually came as a BIG SURPRISE. Liquids are usually thought of as substances capable of conforming to any arbitrary shapes, but the nature of polymer liquids was forgotten. Polymer liquids are viscoelastic, which means they respond elastically at short times when the long chain molecules are unable to move very far (think of a rubber ball), and they flow at long times (think of a ball of glue putty that flattens over time). During processing, the time to wait for the polymers to flow is not available. The polymers are forced to flow and they respond "violently", undergoing solid-like failure. To look for evidence of such behavior, the team under Dr. Wang's direction, developed an effective particle-tracking velocimetric (PTV) method based on home-video technology. The PTV observations of the failure behavior violated the understanding of polymers discussed in contemporary textbooks. Evidence of solid-like failures of polymeric liquids is available on Dr. Wang's homepage and on YouTube at http://www.youtube.com/user/polymerrheology. In the first 8 seconds of the movie, "Shear banding upon yielding in entangled polymers" on YouTube, the originally expected behavior of homogeneous shear is observed. However, the sample suffered a visible breakdown around 9 seconds, and was unable to return to homogeneous flow. This result was quite unexpected.
Additional research is necessary to understand this polymer behavior. The new knowledge will be useful for improved, efficient polymer processing at faster speeds and lower energy costs.
- Carin Helfer, Assistant Director, Science Education Outreach