This research helps provide a fundamental understanding of polymer dynamics in the presence of nanoparticles using a coordinated experimental and theoretical approach. This Materials World Network team from the University of Pennsylvania and Durham University has considerable experience in polymer nancomposites and dynamic properties, and is working together in exploring polymer diffusion and rheology in these fascinating and complex materials. This team recently found a dramatic example of how polymers behave differently in the presence of nanoparticles, wherein polymer diffusion first slowed and then recovered with the addition of nanoparticles. Research efforts are focusing on three aspects of polymer nanocomposite dynamics. (1) Establishing the underlying mechanism of polymer diffusion in nanocomposites. A variety of studies are underway that explore the impact of nanoparticle / polymer interactions, nanoparticle orientation, relative size of the polymer and nanoparticle diameter, and nanoparticle shape. (2) Relating the polymer and nanoparticle diffusion studies to rheological measurements including linear viscoelastic measurements, zero-shear viscosity, plateau modulus and relaxation times. Polymer diffusion and polymer rheology are intimately related through fundamental relaxation parameters, so our goal is to reconcile these two measures of polymer dynamics in polymer nanocomposites. (3) Refining and extending our theoretical description of the polymer dynamics in the presence of nanoparticles. One critical extension is to adjust the monomeric friction coefficient near the particles to evaluate the importance of enthalpic interactions on diffusion.

The research team is well-positioned for groundbreaking insights into the physics of polymer nanocomposites that are likely to have a positive impact on the emerging industry of polymer nanocomposites. Interactions include meetings, bi-monthly teleconferences, monthly reports, data sharing via a secure website, regular international trips, and remote access to experimental equipment. This project also addresses the needs of women in science and engineering by establishing professional problem-solving groups for women faculty and graduate students as a means to collectively address the challenges and opportunities in science and engineering careers. Furthermore, undergraduates from both the University of Pennsylvania and Durham University participate in the research activities as well as consider the business aspects of launching new materials.

This Materials World Network research is supported by the DMR Polymers Program and the DMR Office of Special Programs.

Project Report

This award funded an international, multidisciplinary team to investigate how large molecules, namely polymers, behave in the presence of nanoparticles. Specifically, we measure the diffusion rate of polymers within a polymer / nanoparticle mixture. Previously, the study of polymer motion was limited to cases with much larger particles or much smaller particles (solvents), but the new availability of nanoparticles enables the study of polymers and particles of comparable size. Our most significant scientific contribution has been the introduction of a new term, the confinement parameter, to describe the extent to which polymer motion is hindered by the presence of nanoparticles. The confinement parameter is the average distance between spherical nanoparticles divided by the size of the polymer molecule. Using this confinement parameter, we found universal behavior of the reduced diffusion coefficient. We have tested the universality of this parameter by probing a range of polymer sizes, nanoparticle sizes, and polymer-nanoparticle attractions. This fundamental finding is being used by theorists working to predict how nanoparticles perturb polymers and is inspiring the next generation of experimental studies that involve soft spherical nanoparticles. We have also explored how cylindrical nanoparticles perturb polymer dynamics. In contrast to the spherical nanoparticle, the diffusion coefficient of polymers goes through a minimum as the concentration of nanoparticles increases. While the underlying origin of this finding remains unknown, we have measured how temperature impacts the observation and simulated polymer statics and dynamics near cylindrical nanoparticles. The temperature dependence of the polymer diffusion coefficient suggests that the polymer dynamics are captured by established concepts of free volume in the polymer melts. This award is acknowledged in 9 publications and has been featured in more than 15 invited talks at major scientific meetings, universities, and companies. Including with our international partner at the University of Sheffield (United Kingdom), this project has involved 2 undergraduate students (Ehrich, Oake), 2 masters degree students (Hao, Metkus), 5 doctoral students (Bird, Gam, Hore, Lin, Tung), 2 postdoctoral scholars (Choi, Seitz), 1 government lab collaborator (Hore), and 1 industrial collaborator (Meth). This group of trainees includes 6 women. To facilitate our international collaboration we have held more than 25 teleconferences and completed more that 12 international exchanges.

Agency
National Science Foundation (NSF)
Institute
Division of Materials Research (DMR)
Application #
0908449
Program Officer
Andrew J. Lovinger
Project Start
Project End
Budget Start
2009-08-01
Budget End
2013-01-31
Support Year
Fiscal Year
2009
Total Cost
$480,000
Indirect Cost
Name
University of Pennsylvania
Department
Type
DUNS #
City
Philadelphia
State
PA
Country
United States
Zip Code
19104