Molecular Simula-on studies of Organic salts inside carbon nanopores Harsha Dissanayake Dr. Francisco R. Hung Dr. Joshua D.

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1 Molecular Simula-on studies of Organic salts inside carbon nanopores Harsha Dissanayake Dr. Francisco R. Hung Dr. Joshua D. Monk Ramesh Singh Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA, USA

2 What are Ionic liquids? An ionic liquid is a salt in liquid phase at room temperature. Made up of ions and have ionic bonds. Posses low vapor pressure and are moderate or low electric conductors. Highly tunable properies; ILs could be formed by varying caions, anions. 1,3 dimethylimidazolium chloride [DMIM+][Cl ] Vast number of applicaions due to disinct properies in many fields such as Organic chemistry, Engineering, Electro chemistry, Catalysis and Physical chemistry. (Solvents, electrolytes, etc)

3 Importance of Ionic Liquids(IL s) IL s can be synthesized to possess fluorescent, magneic and many other qualiies according to necessity. Ionic liquids can be synthesized from safe, FDA approved compounds; therefore could be used in Bio medical applicaions. Nanomaterials with fluorescent proper-es can be used to label Issues and cells for biomedical imaging Nanomaterials with magne-c proper-es can be used in cancer treatment (magneic hyperthermia). Aber acaching them to cancer cells, the paient can be exposed to a safe magne-c field and the heat generated by the magneic nanoparicles will destroy the respecive cancer cells that they are acached to. Image courtesy of the Warner group [PF 6ˉ ] 1 butyl 2,3 methylimidazolium hexafluorophosphate, [bm 2 im + ][PF 6ˉ ]

4 Why molecular simulaion? The properies of ionic liquids confined inside nanopores can be very different from what we see in day to day usage (bulk systems). It is extremely difficult to extract experimental data regarding such systems Molecular dynamics (MD) simulaion is a very useful technique in such cases to give insights to experimental scienists and to complement their observaions regarding properies and characterisics of molecules at nanolevel.

5 Overview of simula-on methods TIME /s 10 0 (ms)10-3 (µs)10-6 (ns)10-9 (ps)10-12 (fs)10-15 Atomistic simulation methods Semi-empirical methods Ab initio methods Mesoscale methods tight-binding MNDO, INDO/S Lattice Monte Carlo Brownian dynamics Dissipative particle dynamics Monte Carlo Molecular dynamics Continuum Methods (nm) (µm) LENGTH/meters

6 Molecular dynamics: a quick introduc-on In molecular dynamics (MD), we follow the posiions and velociies of each molecule in Ime by solving Newton s equaions of moion: i=1,2,3, N U = inter/intra molecular potenial (i.e., interacions between atoms) r i = posiion vector of atom i F i = force acing over atom i m i = mass of atom i In MD these equations are integrated numerically to obtain the time evolution of the system 6

7 Pair Poten-als: Large, Flexible Mols. Total pair energy breaks into a sum of terms: DNA U str stretch U bend bend U tors torsion U disp dispersion (van der Waals) U elec electrostaic U pol polarizaion 7

8 System to be studied 1,3 dimethylimidazolium chloride [DMIM+][Cl ] Molar mass mols/gram MulI walled carbon nanotube hcp:// tokyo.ac.jp/~maruyama/agallery/ nanotubes/mwnt.gif In my summer project I will be invesigaion various properies of the ionic liquid [DMIM+][Cl ] when it is confined in a muli walled carbon nanotube. I will be using Gromacs MD sobware to perform MD simulaions of [DMIM+][Cl ] Maolin Sha, Guozhong Wu, Haiping Fang, Guanglai Zhu, and Yusheng Liu J. Phys. Chem. C, 2008, 112 (47), DOI: /jp Publica?on Date (Web): 30 October 2008

9 [DMIM+][Cl ] molecules inserted into carbon nanotube System without [Cl ] atoms

10 IniIal configuraion Minimized Energy state Melted state The [Cl ] ion has not been depicted for visualizaion purposes.

11 Density Density 10 per. Mov. Avg.(Density) rmsd rmsd 10 per. Mov. Avg. (rmsd) rdf rdf 10 per. Mov. Avg.(rdf) Aber running the system under bath condiions for approximately 10ns we can extract the data and analyze it to understand the molecular level properies and characterisics of the system. This informaion can be useful to experimentalists.

12 End

13 Molecular dynamics: Introduc-on MD simula5ons are similar to real experiments In a basic MD simulaion program: Prepare the sample : IniIal energy (or temperature) Number of paricles N Box size (N/L 3 = density) Force field equaions, parameters Time step dt for integraing equaions of moion IniIalize posiions and velociies of all paricles Do the experimental measurement : Compute forces on all paricles Integrate Newton s equaions (F = ma) Update paricle posiions and velociies Calculate instantaneous properies Stop aber iteraing t max steps Repeat unil we reach an appropriate simulated Ime 13