Polymers are among the most widely manufactured materials in the world and are used in a wide range of products, including films and fibers. The properties of these polymers are controlled the presence of long- chain branches, such as molecules with one branch (a “star”) or two branches (an “H”). One of the most sensitive ways to characterize the type of branching is through their flow properties or “rheology” in simple oscillating, or vibrating deformations. We have shown that for a complex mixture of branched structures, such as the the mixture represented by the chromatographic trace on the top figure, we can predict the corresponding rheology, shown in the bottom figure, where the lines are predictions. This ability to predict these curves helps industry determine which polymers will be most easily shaped into products. Fingerprinting Polymers Using Rheology Ronald G. Larson, University of Michigan Ann Arbor, DMR

The field of rheology is strategically important to a wide variety of industries, including the food, pharmaceuticals, and consumer product industries, as well as to suppliers of parts for automobiles, electronic equipment, and others. Providing training for industrial scientists working in rheology is particularly important, as job descriptions change in fast-moving industries. Ron Larson was co-teacher of a short course, held in Amherst, MA, May 30-31, He taught on polymer rheology, drawing from the latest work in the field, including work performed under the NSF grant. Larson also gave an invited lecture to some 30 scientists, some of them linked in by videoconferencing, at Dow Chemical company on June 5, Teaching Rheology to Industrialist Scientists Ronald G. Larson, University of Michigan Ann Arbor, DMR Classroom training at short course on rheology, “ARC2013,” organized by Henning Winter, May 30-31, Co-taught by Winter, Larson, and Jonathan Rothstein. Image from

The best work in the area of polymer rheology is now done through worldwide collaborations, which our group participates in. Larson was asked to summarize the state of the field recently in a Perspective article for the leading journal Science, read broadly by the entire worldwide scientific community. A figure from that work is reprinted here. Figure: This shows the types of molecular motion that occur in molten polymers that are entangled with each other, so they are forced to move along their own contour, represented by a tube-like region in the figure. A. Linear, or unbranched polymers moves by sliding. B. star polymer cannot slide and so fluctuates to escape the tube. C. Commercial polymers are mixtures of linear and branched polymers. Taken from R.G. Larson, Science, 333: Perspective: “Predicting the Flow of Real Polymers.” Training Industrialists in Rheology Ronald G. Larson, University of Michigan Ann Arbor, DMR