"Through the Years with Nanomaterials - Investigation of Phenomena at Interfaces" Rastko Joksimovic

Seminar by Dr. Rastko Joksimovic, Tohoku University

Date:     Wednesday, July 29, 2014
Time      14:00 - 15:00 (incl. Q&A)
Venue:  B503, Center Building

Rastko Joksimovic, Ph.D.

Tohoku University

Biography:

Dr. Rastko Joksimovic received his BSc in Science and Engineering from the Ecole Polytechnique in Paris in 2007 and a MSc in Environmental Engineering from Stanford University in 2008. He pursued then a PhD in Physical Chemistry specializing in Colloid Chemistry at the Technical University of Berlin in the group of Prof. Michael Gradzielski. His thesis titled “Synthesis and functionalization of silica nanoparticles and their interactions with polymers and human cells” was successfully defended on October 1, 2012. He is currently a postdoctoral fellow at the WPI-AIMR (Advanced Institute of Materials Research) at Tohoku University in Sendai in the group of Prof. Kazue Kurihara. The main field of investigation of the group is interface science, with a focus on surface forces and tribology. His research concerns the nanotribological properties of inorganic nanoparticle dispersions investigated, among others, by the Surface Forces Apparatus.

Seminar Title: 
"Through the Years with Nanomaterials _ Investigation of Phenomena at Interfaces"

Seminar Abstract:

In a first part, the results obtained during my research time at the TU Berlin will be covered. Silica nanoparticles were synthesized following several routes and the particles obtained were thoroughly compared, especially in terms of their monodispersity and sphericity. The surface of the silica particles was functionalized with amino groups and covered with small silver beads. Another topic was the interaction with soft matter, more precisely polymers. We investigated the adsorption on the particle surface of poly(ethylene oxide), especially by means of Small Angle Neutron Scattering (SANS), and observed the effect of the polymer chain length. We were also interested in the interaction with living matter, namely human cells (macrophages). We investigated the cytotoxicity of the particles and also their uptake into the cell by fluorescence microscopy.

A project bridging the PhD research and postdoc was the investigation of the segregation between small DNA strands (400bp) and silica nanoparticles. Peculiar patterns were formed after the drying of droplets containing both compounds. The patterns were observed by SEM and the segregation evidenced by fluorescence microscopy.

The postdoc research at Tohoku University, Sendai, deals with the normal forces between mica surfaces confining dispersions of ceria nanoparticles measured by the Surface Force Apparatus (SFA). The nanoparticles (ca. 6 nm) have a cubic shape and are coated by decanoic acid. A long-range repulsion was observed for the first compression, whereas it was absent subsequently, indicating that the adsorbed nanoparticles are rearranging forming a dense structure consisting in a monolayer or a double layer of particles. Resonance shear measurements were performed and the confined particle layers were shown to significantly reduce the friction compared to the mica-mica contact. Those results are contributing to the understanding of the processing of nanoparticles into thin films and to the implementation of nanomaterials in tribology.