Researchers from University of Delaware identified mechanical properties of nanoparticles that can be used to create novel products
Materials made with polymer nanoparticles possess the capability to develop novel products. However, several of the properties of nanoparticles are not yet understood. Now, a team of researchers from Max Planck Institute (MPI) for Polymer Research in Germany, Princeton University, and the University of Trento, led by Hojin Kim, a graduate student in chemical and biomolecular engineering at the University of Delaware, identified new mechanical properties of polymer nanoparticles. The findings that include properties such as surface mobility, glass transition temperature, and elastic modulus, were published in the journal Nature Communications on July 25, 2018.
The team was directed by MPI Prof. George Fytas and used Brillouin light spectroscopy, a technique that examines the vibrations of microscopic nanoparticles to describe their molecular properties. The team analyzed the vibration between each nanoparticle to understand the change in their mechanical properties at different temperatures. The characteristics of polymer nanoparticles are distinguishable from those of larger particles of the same material as nanostructure and small size of the particles provide different mechanical properties.
Polymer nanoparticles are flexible at the glass transition temperature as they soften from a stiff texture to a soft one. This is owing to ease in activation of polymer mobility at small particle surfaces. The team found that thermal transition in polystyrene nanoparticles occurs at 343 Kelvin, which is known as the softening temperature. This temperature is below a glass transition temperature of 372 K of the nanoparticles. Nanoparticles do not vibrate when heated at this point and stand completely still.
Such phenomenon was not evident previously and the team found evidence to suggest that this temperature activates a highly mobile surface layer in the nanoparticle. When particles are heated up between their softening temperature and glass transition temperature, the interaction between the particles increase. Previous researches proposed that glass transition temperature drops with decrease in particle size, owing to the differences in particle mobility. However, these researches failed to directly observe the phenomenon. In the current research, the team studied interactions between the nanoparticles to identify their elastic modulus.