Author: Vladislav Ivanistsev

Soaked to the skin: tuning ionic liquids for electrochemical devices

A post in JPhys+ about our recent article: Researchers at the Universities of Santiago de Compostela, A Coruña, Tartu, Stratchclyde and Cambridge, shed light on the structure of the electrified interface in mixtures of contaminated ionic liquids in their recently published JPCM letter.

https://jphysplus.iop.org/2016/10/28/soaked-to-the-skin-tuning-ionic-liquids-for-electrochemical-devices/

The article is published here: http://iopscience.iop.org/article/10.1088/0953-8984/28/46/464001

P.S. This publication became possible thanks to the COST CM1206.

P.P.S. Finally they have corrected the authors names!

 

pdf optimisation

While preparing an online report for the PUT1107 project, I encountered a limit for uploaded pdf-files as low as 3 Mb. Thus, I was forced to reduce the pdf-file size to this limit as follows:

1. I merged a set of articles into one files: pdftk 1.pdf 2.pdf 3.pdf output set.pdf

2. Then I reduced the size of the resulting file: gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=out.pdf set.pdf

The size was reduced by more than 50% with almost the same visual quality.

STSM to Trieste: Simulation of surface charge effect on the sliding friction of a nanoconfined ionic liquid

The interest towards using ionic liquids as lubricants has been increasing since ca. 2012 [1]. It was demonstrated that the interfacial structures in ionic liquids control the nanoscale friction. Experimental (see refs in [1]) and several computational studies [2–5] revealed that lubricity varies with the number and lateral structure of confined ion layers, which in turn are dependent on the applied potential. This opens a possibility of electrochemical control of friction, in other words a “Tantalizing prospect of tunning friction on small dimensions without changing surfaces with a self-replenish­ing layer, and could be easily integrated into niche situations, … because ionic liquids are cheaper than existing nonconducting molecular lubricants” (see refs in [1]). At the same time it was shown that the restructuring of the potential dependent interfacial structure happens in ionic liquids on a regular manner [6,7]. Therefore, there is a direct relation between various interfacial properties through the potential dependent interfacial structure [8]. For instance, it has not been marked in the literature that the potential dependent friction force [9–11] is proportional to the potential dependent capacitance [12–14]. The understanding of this structure-based relationship can help in controlling of the nanoscale friction in ionic liquids by a potential-tuned ionic lubricant layer.

During this STSM visit, we have initiated a comprehensive study: formulated a hypothesis, prepared a research plan, and obtained preliminary results. The later reveal a proportionality between potential dependent capacitance and friction force. Such structure-based relationship can be of use in controlling of the nanoscale friction in ionic liquids by an applied potential. Further work should verify the generic mechanism of the electrotunable lubricity and capacity. In the future study we plan to perform a detailed atomistic simulation to enable comparison between specific computational and experimental data.

This research was supported by a short term scientific mission funded by COST action MP1303.

References:

[1] R. Hayes, G.G. Warr, R. Atkin, Structure and Nanostructure in Ionic Liquids, Chem. Rev. 115 (2015) 6357–6426.

[2] R. Capozza, A. Vanossi, A. Benassi, E. Tosatti, Squeezout phenomena and boundary layer formation of a model ionic liquid under confinement and charging, J. Chem. Phys. 142 (2015) 64707.

[3] R. Capozza, A. Benassi, A. Vanossi, E. Tosatti, Electrical charging effects on the sliding friction of a model nano-confined ionic liquid, The Journal of Chemical Physics. 143 (2015) 144703.

[4] O.Y. Fajardo, F. Bresme, A.A. Kornyshev, M. Urbakh, Electrotunable Lubricity with Ionic Liquid Nanoscale Films, Sci. Rep. 5 (2015) 7698.

[5] O.Y. Fajardo, F. Bresme, A.A. Kornyshev, M. Urbakh, Electrotunable Friction with Ionic Liquid Lubricants: How Important Is the Molecular Structure of the Ions?, The Journal of Physical Chemistry Letters. 6 (2015) 3998–4004.

[6] V. Ivaništšev, K. Kirchner, T. Kirchner, M.V. Fedorov, Restructuring of the electrical double layer in ionic liquids upon charging, J. Phys.: Condens. Matter. 27 (2015) 102101.

[7] V. Ivaništšev, S. O’Connor, M.V. Fedorov, Poly(a)morphic portrait of the electrical double layer in ionic liquids, Electrochem. Commun. 48 (2014) 61–64.

[8] M.V. Fedorov, A.A. Kornyshev, Ionic liquids at electrified interfaces, Chem. Rev. 114 (2014) 2978–3036.

[9] J. Sweeney, F. Hausen, R. Hayes, G.B. Webber, F. Endres, M.W. Rutland, R. Bennewitz, R. Atkin, Control of Nanoscale Friction on Gold in an Ionic Liquid by a Potential-Dependent Ionic Lubricant Layer, Phys. Rev. Lett. 109 (2012) 155502.

[10] H. Li, R.J. Wood, M.W. Rutland, R. Atkin, An ionic liquid lubricant enables su­perlubricity to be “switched on” in situ using an electrical potential, Chem. Com­mun. 50 (2014) 4368–4370.

[11] H. Li, M.W. Rutland, R. Atkin, Ionic Liquid Lubrication: Influence of Ion Structure, Surface Potential and Sliding Velocity, Phys. Chem. Chem. Phys. 15 (2013) 14616–14623.

[12] M. Drüschler, N. Borisenko, J. Wallauer, C. Winter, B. Huber, F. Endres, B. Roling, New insights into the interface between a single-crystalline metal elec­trode and an extremely pure ionic liquid: slow interfacial processes and the influ­ence of temperature on interfacial dynamics, Phys. Chem. Chem. Phys. 14 (2012) 5090–5099.

[13] R. Atkin, N. Borisenko, M. Drüschler, S.Z. El Abedin, F. Endres, R. Hayes, B. Huber, B. Roling, An in situ STM/AFM and impedance spectroscopy study of the extremely pure 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophos­phate/Au(111) interface: potential dependent solvation layers and the herringbone reconstruction, Phys. Chem. Chem. Phys. 13 (2011) 6849.

[14] R. Costa, C.M. Pereira, A.F. Silva, Charge Storage on Ionic Liquid Electric Double Layer: The Role of the Electrode Material, Electrochim. Acta. 167 (2015) 421–428.

Taming the equations in Libreoffice

Working on large documents with many equations in a word processor is a torture. In my case, booklets of chemistry problems require a lot of work. For certain reason I prefer to use LibreOffice. When is needed to reformat all equations in a document the following macro is very useful:

Sub FormulaFontSizeChanger

o = ThisComponent.getEmbeddedObjects()

fontSize = 12

fontFamily = “Arial”

For i = 0 to o.count-1

if (not IsNull(o(i))) and (not IsNull(o(i).Model)) then

o(i).Model.TopMargin = 0

o(i).Model.BottomMargin = 0

o(i).Model.LeftMargin = 0

o(i).Model.RightMargin = 0

o(i).Model.BaseFontHeight = fontSize

o(i).Model.FontNameVariables = fontFamily

o(i).Model.FontVariablesIsItalic = 1

o(i).Model.FontNameFunctions = fontFamily

o(i).Model.FontNameNumbers = fontFamily

o(i).Model.FontNameText = fontFamily

o(i).Component.BaseFontHeight = fontSize

o(i).ExtendedControlOverEmbeddedObject.update()

endif

Next i

End Sub

 

P.S. The script might be useful also when writing a thesis with a lot of chemistry inside and many Zotero references. LaTeX might not be so comfortable, and in Word one is still limited with few math fonts.

STSM to Vienna: MD simulations of ionic liquid mixtures with polarizable force fi elds

Generic force fields are widely used in molecular level computations. However, in real physical systems, the magnitude and localization of the charges are variable due to the interatomic polarization and the molecular dynamics. There are two ways to take these into account: (i) to reduce the atomic charges to non-integer values or (ii) to include polarizableforces.

In this STSM the latter method was used adding Drude oscillators to the system to add the polarizability to the particles. The polarizable force fields (FFs) developed by the group of Prof. Schroder where used to simulate the mixtures of ionic liquids with classical molecular dynamics. Namely mixture of [EMIm][BF4] and [EMIm]I was used. For comparison, the same system with non-polarizable FFs and the system of pure [EMIm][BF4] using polarizable FFs were simulated.

The main problem with classical MD simulations of ions is that the viscosity is overestimated which comes from the fact of imprecise non-bonding interactions. The polarizable FFs estimate it better and taken from the simulations the diffusion constant for the same system with polarizable FFs was much higher than for non-polarizable (1.03 A2/ns and 0.48 A2/ns respectively for cations). The system of pure [EMIm][BF4] showed that iodine affects the movement of ions as the diffusion constant differs by 10% (1.15 A2/ns for cations in pure system). All in all, the polarizable FFs improves the system and adding the small amount of iodine does not change the diffusion nor the structure that much.

Comp. perspective on the supercaps

In the recent years, a significant progress has been achieved in the modeling of realistic porous carbon electrodes [J. C. Palmer and K. E. Gubbins, Micropor. Mesopor. Mat., 154, 24–37 (2012).], simulations under constant potential conditions [D. T. Limmer et al., Phys. Rev. Lett., 111, 106102 (2013).], description of the electrode material electronic structure [E. Paek, A. J. Pak, and G. S. Hwang, J. Electrochem. Soc., 160, A1–A10 (2013).], and ion packing relation to the capacitance [S. Kondrat, C. R. Pérez, V. Presser, Y. Gogotsi, and A. A. Kornyshev, Energy Environ. Sci., 5, 6474–6479 (2012).]. Let us turn the readers’ attention to two aspects of the theoretical predicted relation between the ion size and the pore size, suggesting higher capacitance values for certain pore sizes. First, the molecular dynamics and density functional theory simulations do confirm the theory in case of slit-pore models with rigorously defined width [D. Jiang and J. Wu, J. Phys. Chem. Lett., 4, 1260–1267 (2013).] & [G. Feng, S. Li, V. Presser, and P. T. Cummings, J. Phys. Chem. Lett., 4, 3367–3376 (2013).]. Therefore, the theory suggests that some electrode materials with a certain pore distribution the capacitance is higher due to specific ion packing. Yet, as has been elegantly pointed by Cummings and co-workers [G. Feng, S. Li, V. Presser, and P. T. Cummings, J. Phys. Chem. Lett., 4, 3367–3376 (2013).], due to a wide distribution of pore sizes in the real electrode material this effect might not at all affect the experimentally measured capacitance. Second, as noted above, the capacitance is greatly determined by the electronic structure of the electrode material. The state-of-the-art molecular dynamics studies do not yet include the electronic structure into account [M. V. Fedorov and A. A. Kornyshev, Chem. Rev., 114, 2978–3036 (2014).]. The situation is about to change in the future, for example with the help of ab initio molecular dynamics [M. Salanne, Phys. Chem. Chem. Phys., 17, 14270–14279 (2015).].

Note, the following text appeared in the artile: E. Tee, I. Tallo, T. Thomberg, A. Jänes, E. Lust, J. Electrochem. Soc. 163 (2016) A1317–A1325. See at http://jes.ecsdl.org/content/163/7/A1317.abstract (DOI: 10.1149/2.0931607jes)

Travel tips

Summer is a great time for research visits, schools as well as vacations. Here is my check list for a safe trip from 2016.

  • Passport, ID card and driving license (and a secure place for these documents)
  • A bottle of water (stay hydrated)
  • Snacks or meal replacement bars for sustenance during the trip
  • Cough drops
  • Wet wipes and napkins
  • Something to read or listen (headphones)
  • A notebook or something to write on
  • A scarf or something to protect your neck from cold
  • A cap or something to close your face while sleeping
  • Sunglasses
  • Compression socks
  • Lightweight and water-resistant pair of shoes
  • Some coins and some cash
  • A universal adapter

Here is what I would like to add to the list in 2023 (thanks to chatGPT for ideas):

  • A portable charger or power bank to keep your devices charged
  • Hand sanitizer or disinfecting wipes to keep your hands and surfaces clean
  • An extra set of clothes or a change of underwear in case of unexpected delays or lost luggage
  • Maps or a guidebook for your destination to help you navigate and plan your trip
  • A medical mask!

size limits of email boxes

Email is an essential part of the work. Sometimes the box gets full, thus preventing the work. With gmail there is a trick how to find and delete large emails that occupy most of the space. To search for attachments greater than 5 Mb search “size:5000000”.

Installing Gromacs and Lammps

FFTW:

./configure –enable-float –enable-shared –enable-sse2
make -j N
make install

===

Gromacs:

$ tar xvfz gromacs-x.y.z.tar.gz
$ ls
gromacs-x.y.z
$ mkdir build
$ cd build
$ cmake ../gromacs-x.y.z -DCMAKE_INSTALL_PREFIX=/home/yourUser/opt/gromacs.x.y.z -DGMX_CPU_ACCELERATION=SSE2 -DGMX_SIMD=SSE2
$ make -j N
$ make install

===

LAMMPS:

$ git clone git://git.lammps.org/lammps-ro.git LAMMPS
$ make yes-molecule
$ make mpi

===

To the .bashrc add:

#Gromacs

source /home/yourUser/opt/gromacs.x.y.z/bin/GMXRC
#or source /your/installation/prefix/here/bin/GMXRC

#LAMMPS
export LD_LIBRARY_PATH=~/LAMMPS/src:$LD_LIBRARY_PATH
export PATH=~/LAMMPS/src:$PATH