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
13
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’
