MolecularSimula-onstudiesofOrganicsaltsinsidecarbonnanopores

HarshaDissanayakeDr.FranciscoR.HungDr.JoshuaD.Monk

RameshSingh

CainDepartmentofChemicalEngineering,LouisianaStateUniversity,

BatonRouge,LA,USA

WhatareIonicliquids?

•  Anionicliquidisasaltinliquidphaseatroomtemperature.

•  Madeupofionsandhaveionicbonds.

•  Posseslowvaporpressureandaremoderateorlowelectricconductors.

•  HighlytunableproperIes;109‐1018ILscouldbeformedbyvaryingcaIons,anions.

•  VastnumberofapplicaIonsduetodisInctproperIesinmanyfieldssuchasOrganicchemistry,Engineering,Electrochemistry,CatalysisandPhysicalchemistry.(Solvents,electrolytes,etc)

1,3‐dimethylimidazoliumchloride[DMIM+][Cl‐]

ImportanceofIonicLiquids(IL’s)

IL’scanbesynthesizedtopossessfluorescent,magneIcandmanyotherqualiIesaccordingtonecessity.

Ionicliquidscanbesynthesizedfromsafe,FDA‐approvedcompounds;thereforecouldbeusedinBio‐medicalapplicaIons.

ImagecourtesyoftheWarnergroup

1‐butyl‐2,3‐methylimidazoliumhexafluorophosphate,[bm2im+][PF6ˉ]

[PF6ˉ]

•  Nanomaterialswithfluorescentproper-escanbeusedtolabelIssuesandcellsforbiomedicalimaging

•  Nanomaterialswithmagne-cproper-escanbeusedincancertreatment(magneIchyperthermia).Aberacachingthemtocancercells,thepaIentcanbeexposedtoasafemagne-cfieldandtheheatgeneratedbythemagneIcnanoparIcleswilldestroytherespecIvecancercellsthattheyareacachedto.

•  TheproperIesofionicliquidsconfinedinsidenanoporescanbeverydifferentfromwhatweseeindaytodayusage(bulksystems).

•  Itisextremelydifficulttoextractexperimentaldataregardingsuchsystems

•  Moleculardynamics(MD)simulaIonisaveryusefultechniqueinsuchcasestogiveinsightstoexperimentalscienIstsandtocomplementtheirobservaIonsregardingproperIesandcharacterisIcsofmoleculesatnanolevel.

WhymolecularsimulaIon?

5

10-15

10-12

10-9

10-6

10-3

100

10-10 10-9 10-8 10-7 10-6 10-5 10-4 (nm) (µm)

(fs)

(ps)

(ns)

(µs)

(ms)

LENGTH/meters

TIME/s

Mesoscale methods

Semi-empirical methods

Ab initio methods

Monte Carlo Molecular dynamics

tight-binding MNDO, INDO/S

Continuum

Lattice Monte Carlo Brownian dynamics

Methods

Overviewofsimula-onmethods

Atomistic simulation methods

Dissipative particle dynamics

Moleculardynamics:aquickintroduc-on

• Inmoleculardynamics(MD),wefollowtheposiIonsandvelociIesofeachmoleculeinImebysolvingNewton’sequaIonsofmoIon:

i=1,2,3,…N

U=inter/intra‐molecularpotenIal(i.e.,interacIonsbetweenatoms)ri=posiIonvectorofatomiFi=forceacIngoveratomimi=massofatomi

6

•  In MD these equations are integrated numerically to obtain the time evolution of the system

PairPoten-als:Large,FlexibleMols.

•  Totalpairenergybreaksintoasumofterms:

DNA

•  Ustr‐stretch

•  Ubend‐bend

•  Utors‐torsion

•  Udisp‐dispersion(vanderWaals)

•  Uelec‐electrostaIc

•  Upol‐polarizaIon

7

Systemtobestudied

1,3‐dimethylimidazoliumchloride[DMIM+][Cl‐]Molarmass‐132.5mols/gram

MaolinSha,GuozhongWu,HaipingFang,GuanglaiZhu,andYushengLiuJ.Phys.Chem.C,2008,112(47),18584‐18587•DOI:10.1021/jp8079183•Publica?onDate(Web):30October2008

•  InmysummerprojectIwillbeinvesIgaIonvariousproperIesoftheionicliquid[DMIM+][Cl‐]whenitisconfinedinamulI‐walledcarbonnanotube.

•  IwillbeusingGromacsMDsobwaretoperformMDsimulaIonsof[DMIM+][Cl‐]

MulI‐walledcarbonnanotubehcp://www.photon.t.u‐tokyo.ac.jp/~maruyama/agallery/nanotubes/mwnt.gif

[DMIM+][Cl‐]moleculesinsertedintocarbonnanotube

Systemwithout[Cl‐]atoms

IniIalconfiguraIon

MinimizedEnergystate

Meltedstate

The[Cl‐]ionhasnotbeendepictedforvisualizaIonpurposes.

0

200

400

600

800

Density

Density

10per.Mov.Avg.(Density)

00.20.40.60.81

1.2

070

014

00

2100

28

00

3500

42

00

4900

56

00

6300

70

00

7700

rmsd

rmsd

10per.Mov.Avg.(rmsd)

0

0.5

1

1.5

2

2.5

3

3.5

4

00.07

80.15

60.23

40.31

20.39

0.46

80.54

60.62

40.70

20.78

0.85

80.93

61.01

41.09

21.17

1.24

81.32

61.40

41.48

2

rdf

rdf

10per.Mov.Avg.(rdf)

AberrunningthesystemunderbathcondiIonsforapproximately10nswecanextractthedataandanalyzeittounderstandthemolecular‐levelproperIesandcharacterisIcsofthesystem.ThisinformaIoncanbeusefultoexperimentalists.

End

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Moleculardynamics:Introduc-on

•  MDsimula5onsaresimilartorealexperiments

•  InabasicMDsimulaIonprogram:

•  ‘Preparethesample’:

•  IniIalenergy(ortemperature)

•  NumberofparIclesN

•  Boxsize(N/L3=density)•  ForcefieldequaIons,parameters

•  TimestepdtforintegraIngequaIonsofmoIon

•  IniIalizeposiIonsandvelociIesofallparIcles•  ‘Dotheexperimentalmeasurement’:

•  ComputeforcesonallparIcles

•  IntegrateNewton’sequaIons(F=ma)

•  UpdateparIcleposiIonsandvelociIes•  CalculateinstantaneousproperIes•  StopaberiteraIngtmaxsteps

RepeatunIlwereachanappropriate‘simulatedIme’