[institut] SCL seminar (povodom izbora u zvanje istraživač saradnik), Miljan Dašić, četvrtak 18. maj u 12:00

[Igor Stankovic]

Поштоване колегинице и колеге,

Позивам вас на семинар Лабораторије за примену рачунара у науци Центра 
за изучавање комплексних система који ће у четвртак 18. маја у 12:00 у 
читаоници "Др Драган Поповић" Института за физику у Београду одржати 
Миљан Дашић (Лабораторија за примену рачунара у науци, Институт за 
физику Београд) поводом предстојећег избора у звање истраживач сарадник. 
Наслов семинара је:

Dear colleagues,

You are invited to the SCL seminar of the Center for the Study of 
Complex Systems, which will be held on Thursday, May 18th 2017 at 12:00 
in the library reading room “Dr. Dragan Popović" of the Institute of 
Physics Belgrade. The talk will be given by Miljan Dašić (Scientific 
Computing Laboratory, Center for the Study of Complex Systems, Institute 
of Physics Belgrade). The title of the talk is:

Modelling the behaviour of confined dipolar helices and ionic liquids

Апстракт предавања:

Abstract of the talk:

This talk has two distinct parts related to my research until now. The 
first part is concerned with dipolar particles in cylindrical 
confinement. We have been analyzing self-assembly of hard shperes with 
permanent dipole moment under cylindrical confinement, i.e., dipolar 
helices made up of hard spheres [1]. Such structures are relevant 
objects in biological systems. We observe a complex dependence of 
cohesive energy on surface packing fraction and dipole moment 
distribution. As far as single helices are concerned, the lowest 
cohesive energy is achieved at the highest surface packing fraction. 
Besides, a striking non-monotonic behavior is reported for the cohesive 
energy as a function of the surface packing fraction. For multiple 
helices, we discover a new phase, markedly having higher cohesive 
energy. This phase is referred to as ZZ tube consisting of stacked crown 
rings, resulting in a local triangular arrangement with densely packed 
filaments parallel to the tube axis.

The second part of the talk is dealing with ionic liquids under 
confinement and shear. We present an approach for simulating mesoscopic 
phenomena related to lubrication with ionic liquids [2]. We have 
implemented a coarse grain molecular dynamics (MD) description of an 
ionic liquid as a lubricant which can expand into lateral reservoirs. 
Ionic liquid (IL) consists of an equal number of cations and anions, 
represented as coarse-grained particles charged with elementary charge, 
which are placed between fcc (111) plates. Interactions in our system 
include non-bonded Lennard-Jones and Coulombic potentials. Our geometry 
allows a variable confinement gap and a variable amount of lubricant in 
the gap. Ions are initially randomly placed inside the gap and they are 
equilibrated. We observe that IL confined between solid surfaces 
features alternating positive and negative ionic layers. We observe 
nonmonotonic dependence of the normal force (acting on the top plate) on 
plate-to-plate distance. At small plate-to-plate distances we observe a 
steep rise of that normal force. This is an interesting behaviour that 
could be exploited for preventing solid–solid contact and wear. The 
shear simulation results have revealed two distinct regimes of 
lubrication: elasto-hydrodynamic regime under low loads and lubrication 
regime with low and velocity-independent specific friction, under high 
loads.

References:
[1] I. Stanković, M. Dašić and R. Messina, “Structure and Cohesive 
Energy of Dipolar Helices”, Soft Matter (2016)
[2] K. Gkagkas, V. Ponnuchamy, M. Dašić, I. Stanković, Molecular 
dynamics investigation of model ionic liquid lubricant for automotive 
applications, Tribology International (2016)

Срдачан поздрав,

Yours sincerely,

Игор Станковић / Igor Stanković