By Josh Perry, Editor
[email protected]

Researchers from the University of Delaware (Newark, Del.), the Max Planck Institute for Polymer Research (Mainz, Germany), Princeton (N.J.) University, and the University of Trento (Italy) have revealed details about the surface mobility, glass transition temperature and elastic modulus of polymer nanoparticles.

In this illustration, arrows indicate the vibrational activity of particles studied by UD researchers, while the graph shows the frequencies of this vibration.
(University of Delaware)

According to a report from Delaware, the researchers used Brillouin light spectroscopy, which explores the molecular properties of nanoparticles through vibration. The study examined how vibrations, and thus properties, changed at different temperatures.

“The research team found that polystyrene nanoparticles start to experience the thermal transition at 343 Kelvin (158°F), known as the softening temperature, below a glass transition temperature of 372 K (210°F) of the nanoparticles, just short of the temperature of boiling water,” the article explained. “When heated to this point, the nanoparticles don’t vibrate—they stand completely still.”

Researchers demonstrated that the temperature activated a mobile surface layer in the nanoparticle that caused the particles to increasingly interact with each other.

The research was recently published in Nature Communications. The abstract stated:

“Measuring polymer surface dynamics remains a formidable challenge of critical importance to applications ranging from pressure-sensitive adhesives to nanopatterning, where interfacial mobility is key to performance.

“Here, we introduce a methodology of Brillouin light spectroscopy to reveal polymer surface mobility via nanoparticle vibrations. By measuring the temperature-dependent vibrational modes of polystyrene nanoparticles, we identify the glass-transition temperature and calculate the elastic modulus of individual nanoparticles as a function of particle size and chemistry.

“Evidence of surface mobility is inferred from the first observation of a softening temperature, where the temperature dependence of the fundamental vibrational frequency of the nanoparticles reverses slope below the glass-transition temperature.

“Beyond the fundamental vibrational modes given by the shape and elasticity of the nanoparticles, another mode, termed the interaction-induced mode, was found to be related to the active particle–particle adhesion and dependent on the thermal behavior of nanoparticles.”