Can Nanoscale Inclusions Effectively Reduce the Viscosity and Modulus of Polymer Melts?

Michigan State University, East Lansing MI

Investigators

Abstract

Proposal Title: Can Nanoscale Inclusions Effectively Reduce the Viscosity and Modulus of Polymer Melts? Proposal Number: CTS-0400840 Principal Investigator: Michael E. Mackay Institution: Michigan State University In this project, the flow and physical properties of a suspension or slurry is being investigated. However, the particles are smaller than the fluids molecules in which they are dispersed and this produces unusual effects. We have found that nanoparticles with a size of order 5-10 nm suspended in a polymeric liquid with molecules of size 15-40 nm produce a liquid that has a viscosity lower than the neat polymeric liquid itself. A viscosity reduction is at odds with Einsteins century old prediction that Brownian particles increase the viscosity of liquids. Indeed all observations suggest that a viscosity increase is always present in particulate suspensions. A recent publication on this effect is in press in the journal Nature Materials. Since the particles are so small it is believed they influence the dynamics of the polymeric liquid on a local scale. The nanoparticles apparently increase the free volume in the polymeric liquid as well as confine the polymer molecules to produce the viscosity decrease. Further, contemporary methods to quantify entanglements suggest no change in the entanglement density. It is the purpose of this work to further elucidate the phenomenon and resolve this quandary. A recent discovery, included in the preliminary results, is that very chemically different nanoparticle (polyethylene). polymer (polystyrene) systems can be molecularly dispersed as long as the particle is smaller than the polymer. The polyethylene. polystyrene system is a model phase separating system and it has been discovered that changing the molecular topology of one component into a particle-like conformation affects its solubility and stability in a polymeric liquid. This is a unique result, not fully understood at present and represents one aspect of the proposed research. This could create a new class of molecular alloys. Further research will be conducted with fullerenes, as a model system whose size is much smaller than available nanoparticles, and single wall carbon nanotubes, as a model system to introduce a new particulate geometry. These systems will be utilized to generalize the viscosity reduction effect. We will use a variety of techniques in the proposed work to measure the dispersion of the nanoparticles as well the state of the suspending fluids. chain-like molecules. These techniques include: rheological characterization, thermal analysis, mechanical testing, electron optics evaluation and small angle neutron scattering. All this instrumentation exists in the group, is on campus or is available at Argonne National Laboratory. Graduate and undergraduate students in the research group will be exposed to these results and in some cases will gather results together as we have done when performing neutron scattering. There are three females and three males in the research group and through teamwork participation of an underrepresented group will broaden their learning experience. Dissemination of these results will be presented through the scientific literature and conferences as well as through undergraduate and graduate level lectures. The principal investigator sets aside one lecture every semester in the introductory (sophomore) course he teaches to introduce his research to the students. This lecture is well received and gives students an introduction to the research process as well as the results of research. The proposed research is unique and is at odds to contemporary observations. Inclusion of this topic in the research lecture will demonstrate how science and engineering is continuously evolving and not stagnant. Many underrepresented students attend this lecture and immediately after, as well as for many months thereafter, they show interest in research and wish to undertake research with the principal investigator or other professors.