October 2, 2008
Nanoscale Polymers Don’t Play By the Rules
U.S. scientists have discovered polystyrenes, when reduced to nanoscale, don't function under the laws of fundamental polymer physics.
"Although applications for nanoscale polymer flow are being widely investigated, the underlying, fundamental polymer physics is not," said University of Illinois Professor William King. "Understanding the way a polymer flows during nanoscale molding or imprinting processes is essential for designing new, nanoscale manufacturing processes.
King and colleagues at Trinity College in Dublin, Ireland, have reported polymer squeeze flow measurements made at unprecedented short length scales.
"We found an unexpected increase in the squeeze flow of thin films when the film thickness was smaller than 100 nanometers," King said. "This seemed backwards. Normally, you would expect the polymer to become harder and harder to press into thinner films."
The effect was more pronounced in polymers of higher molecular weight, King said. "We expected the viscosity to increase with increasing molecular weight, but we found the opposite to be true when the films were thin enough."
King says the findings suggest polymer flow during nanoscale manufacturing may be enhanced by selecting polymers of higher molecular weight.
The study appears in the online journal Science Express.