Thanks to modern chemical-physical synthesis techniques, it is possible to produce, today, colloidal particles, or particles of a thousandth of a millimeter, of countless shapes and materials.

Among these are microgels, soft microscopic objects made entirely of polymeric material, so versatile that they are used as much in basic research as for a large number of practical applications.

A new study conducted by researchers of the Department of Physics in collaboration with Cnr-Isc, Institute of Complex Systems of the National Research Council and the University of Lund (Sweden), investigates how the temperature and concentration of microgels influence the structure and collective dynamics of particles, and the final properties of the material they compose. The results of the research are published in the journal Nature Communications.

"The great attraction of these elastic spheres," explains Lorenzo Rovigatti from Sapienza Department of Physics, "is given by the possibility to change almost instantly some of their microscopic properties, such as size or softness, varying macroscopic parameters such as temperature or pH of the sample."

Microgels are used in many sectors ranging from the conservation of cultural heritage to nanotechnologies, from the food industry to the field of biomedical. Nevertheless, the microscopic mechanisms underlying the interaction between these particles are still unclear.

The combined analysis of the results, obtained by the researchers with experiments and computer simulations, has allowed to demonstrate how the predictions of the models applied in the past to describe the interaction between microgel (based on the classical theory of elasticity formulated at the end of the 800) lead to conclusions incompatible with experimental evidence.

The international collaboration has therefore developed a new "multi-elastic" model that, unlike the previous one, is based on the microscopic structure of the microgels and is able to quantitatively describe the experimental results at way that will lead to a much deeper knowledge of these systems.

"Microgels," explains Emanuela Zaccarelli, Sapienza and Cnr-Isc, "are essential components for studying phenomena such as the formation of glass or crystals, but are used in many industrial processes, from the synthesis of new materials to the development of innovative drugs. Yet, despite being used in theoretical contexts in which it is essential to know the microscopic properties of the particles that make up the system, up to now this knowledge has been incomplete or even based on incorrect assumptions."

"Our work," concludes Lorenzo Rovigatti, "establishes a new point of reference for future studies aimed at the full understanding of the behavior of these objects, so promising from the technological point of view."

References:

A new look at effective interactions between microgel particles - Maxime J. Bergman, Nicoletta Gnan, Marc Obiols-Rabasa, Janne-Mieke Meijer, Lorenzo Rovigatti, Emanuela Zaccarelli & Peter Schurtenberger - Nature Communications volume 9, Article number: 5039 (2018) DOI: 10.1038/s41467-018-07332-5

Further Information

Lorenzo Rovigatti
Department of Physics, Sapienza University of Rome
lorenzo.rovigatti@uniroma1.it

Emanuela Zaccarelli
Department of Physics, Sapienza University of Rome
Cnr-Isc – Institute of Complex Systems of the National Research Council
emanuela.zaccarelli@roma1.infn.it