The proposed research aims to achieve three objectives: (A) carefully examining the previous results to identify potential sources of technical error and scientific ambiguity; (B) removing experimental difficulties to verify whether the new emerging picture would still hold in absence of any artifacts that have caused controversies in the literature; (C) building on the newly available understanding to further probe the nature of disintegration of chain entanglement network due to external deformation. Specifically, many current findings have not been proved to beyond doubt and cannot form the new phenomenological foundation for polymer rheology unless improved experiments are carried out. These experiments include (i) interrogation of strain-induced chain disentanglement under circumstances where the sample at the edge of a shear cell would not suffer fracture and (ii) flow birefringence measurements in absence of any inclusions such as solid particles that have been suspected by de Gennes to be the source of shear banding. Single-molecule imaging velocimetry is proposed as an effective method to probe velocity field in entangled systems without any foreign particles and to directly determine whether shear inhomogeneity would arise from flow-induced polymer migration or from non-uniform chain disentanglement. Finally, in anticipation of potential implications for polymer processing, particle-tracking velocimetric technique will be applied to examine effect of chain disentanglement in pressure-driven flow and related phenomena.
NON-TECHNICAL SUMMARY:
Each year, more than two hundred billion pounds of plastic and rubber materials are made into consumer products in this country. Such a huge volume typically flows in a manner similar to pouring honey or squeezing tooth paste. How the various polymeric materials flow under different processing conditions is a subject of both academic and economic importance. The fruits of the proposed studies could alter our long-held knowledge about polymer flow and transform the contents of existing textbooks on the subject. Current scientific findings and proposed research offer new hope that could eventually give the domestic market a cutting edge in the global competition and innovation for more efficient production of petroleum-based consumer goods of higher quality. Ultimately, the outcome of the proposed work could directly impact the R&D directions in the plastic and rubber industries. The impact of this investigation is clearly going beyond the border of the United State, as the emerging new picture begins to be discussed in classroom and recorded for video streaming on the world wide web at http://eres.avs.uakron.edu/eres/coursepass.aspx?cid=647. The visualization-intensive nature of the research also makes it attractive materials for youngsters in middle and high schools, making science intuitive, observational and straightforward to perceive.
The NSF support has allowed us to carry out scientific research that has transformed the way we think about how several hundred billion pounds of plastics and rubbers are made yearly into the familiar products including milk bottle, plastic grocery bags, computer frames, garden hoses, automobile tires, etc. Our findings confirm that this special class of polymeric liquids behaves very differently from the common liquids such as water, syrup, honey. For the first time, we know for sure these polymers are more like the yogurt when heated to the molten state for shaping. Such understanding represents a shift of the scientific paradigm and could potentially result in practical guiding to process the hundred billion pounds of polymeric materials in an energy-saving and cost-effective manner. Specifically, our research shows how and why molecular properties of polymers such as the molecular weight determine whether there would be difficulties during manufacturing of automobile tires, in fiber spinning of polyesters, in shaping of polyethylene pipes and polypropylene containers. On the theoretical side, our work challenges the existing theoretical model that simplified a real polymeric material to a level where some essential physics might not have been captured. As a consequently, a new conceptual picture has emerged to suggest that a polymer in its liquid state should be viewed as a three dimensional fishing net where all the constituent chain-like molecules are mutually and temporarily connected to one another, and such a polymer "breaks" during external deformation in a manner reminiscent of mechanical failure of tofu or gelatin. In short, the outcome of the NSF supported research is going to form the core of a new textbook on the subject and re-draw the boundary of knowledge in this crucial area of research vital to the national economy.
