Seminar Program - Series - Dr Emmanouil Glynos #Day 1

Abstract

Many physical properties of polymers, such as glass transition, wetting, structural relaxation, mechanical properties, and dynamics are influenced by interactions between the macromolecules and external interfaces [1]. In this talk, I will discuss the role of macromolecular architecture, and in particular the star-shaped architecture, on the structure and dynamics of the polymers close to surfaces and interfaces. I will provide evidence that the behavior of polymer at the vicinity of an interface can be tailored, in a very controllable manner, not by changing the monomer or the interface chemistry, but simply by changing the macromolecular architecture and in particular through changes of the molecular characteristics (number of arms and arm length) of star-shaped polymers. In the first part of the talk I will show that star-shaped polystyrene (SPS) molecules exhibit notably different wetting properties than their linear analogues (linear polystyrene, LPS) [2-4]. In particularly the equilibrium contact angles of macroscopic droplets of SPS, on oxidized silicon substrates, may be as much as one order of magnitude smaller than that of LPS droplets on the same substrates. Unlike linear chains, the wetting of SPS macromolecules is determined by the competition between their enhanced adsorption onto surfaces with increasing functionality (number of arms, f), and an opposing soft steric entopic repulsion with increasing f that limits their ability to adsorbed and closely “pack” onto surfaces. In the second part of the talk, I will show how the aforementioned competing effects in the interfacial properties of SPS are manifested on the glass transition [5,6], glassy structural relaxation [7,8], and surface dynamics [9] in SPS supported films. Experiments and molecular dynamic simulations do show evidence of ordered organization of the molecules in the form of layers, in a manner identical to soft colloid particles.

[1] S. Napolianto, E. Glynos, N. B. Tito; Reports on Progress in Physics 2017, 80, 036602

[2] E. Glynos, B. Frieberg, P.F. Green; Physical Review Letters 2011, 107, 118303

[3] E. Glynos, A. Chremos, B. Frieberg, G. Sakellariou, P.F. Green; Macromolecules 2014, 47, 1137

[4] P.F. Green, E. Glynos, B. Frieberg; MRS Communication 2015, 5, 423

[5] E. Glynos et al.; Physical Review Letters 2011, 106, 128301

[6] E. Glynos et al.; Macromolecules 2015, 48, 2305

[7] B. Frieberg, E. Glynos, P. F. Green; Physical Review Letters 2012, 108, 268304

[8] B. Frieberg, E. Glynos, M. Stathouraki, G. Sakellariou, P. F. Green; Macromolecules 2018, 50, 3719

[9] E. Glynos et al.; Physical Review Letters 2017, 11, 227801

Speakers Short CV

Dr Emmanouil Glynos is a Research Scientist at the Institute of the Electronic Structure and Laser (IESL) of the Foundation for Research and Technology-Hellas (FORTH). He received his Bachelor in Physics from the University of Patras in 2003 and a PhD in 2007 in Materials Science in the core subject of Polymer Physics from the University of Edinburgh. After graduation, he joined as a postdoctoral research fellow the University of Michigan, working on the effect of macromolecular architecture on the physical properties of polymers at surfaces and interfaces. In 2012 he was appointed as a Research Investigator at the University of Michigan at the Center for Solar and Thermal Energy Conversion were his research focused in addressing important scientific challenges associated with the structure-property relation of organic photovoltaics and the correlation of the polymer active layers morphology to the overall performance of these systems. From 2017 to 2018, he was a Stavros Niarchos Research Fellow at FORTH/IESL in 2017-2018. The main objective of his current research at IESL/FORTH is to develop a fundamental understanding of, and controlling via macromolecular engineering, the structure and properties of nanostructured soft-materials that can be used as solid electrolytes in lithium-metal batteries and electrochromic devices, and as active layers in organic photovoltaics.