NMR of liquid crystal dendrimers

248 Pages·2017·9.575 MB·English

by  Carlos Rodrigues da Cruz, João L. Figueirinhas, Pedro J. Sebastião

NMR of Liquid
Crystal Dendrimers

Pan Stanford Series on Renewable Energy — Volume 2
NMR of Liquid
Crystal Dendrimers
Carlos R. Cruz
editors
João L. Figueirinhas
Preben Maegaard
Anna Krenz Pedro J. Sebastião
Wolfgang Palz
The Rise of Modern Wind Energy
Wind Power
for the World
October4,2016 13:5 PSPBook-9inx6in 00-NMR-Dendrimers-Prelims
Publishedby
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October4,2016 13:5 PSPBook-9inx6in 00-NMR-Dendrimers-Prelims
Contents
Preface ix
1 Introduction 1
1.1 Dendrimers 1
1.2 NMRofLiquidCrystalsandLiquidCrystal
Dendrimers 5
2 LiquidCrystals 9
2.1 LiquidCrystals 9
2.2 MesophasesofThermotropicLiquidCrystals 15
2.2.1 NematicPhases 15
2.2.2 SmecticPhases 20
2.2.3 ColumnarPhases 25
3 MolecularStructuresofLiquid-CrystallineDendrimers 29
3.1 Introduction 29
3.2 Side-ChainLiquid-CrystallineDendrimers 31
3.2.1 PAMAM-andPPI-BasedLiquid-Crystalline
Dendrimers 33
3.2.2 Silicon-ContainingLiquid-Crystalline
Dendrimers 38
3.2.2.1 Carbosilane-baseddendrimers 38
3.2.2.2 Siloxane-baseddendrimers 42
3.2.2.3 Carbosilazane-baseddendrimers 45
3.3 Main-ChainLiquid-CrystallineDendrimers 46
3.4 Shape-PersistentLiquid-CrystallineDendrimers 51
3.5 SupramolecularDendromesogens 51
3.6 OtherLiquid-CrystallineDendrimerStructures 56
3.7 Summary 58
October4,2016 13:5 PSPBook-9inx6in 00-NMR-Dendrimers-Prelims
vi Contents
4 FundamentalsofNuclearMagneticResonance 61
4.1 Introduction 61
4.2 NuclearParamagnetism 63
4.2.1 NuclearSpin 63
4.2.2 NuclearMagnetization 65
4.2.3 InteractionwithanExternalField 66
4.3 DynamicsofNoninteractingSpins:Bloch’sEquations 67
4.3.1 MotionofaMagneticMoment 67
4.3.2 Bloch’sEquations 68
4.3.3 InteractionwithanOscillatingMagnetic
Induction 69
4.3.4 GeneratingB1andReadingM⊥ 70
4.4 TheNuclearSpinHamiltonian 71
4.4.1 ReducedSpinHamiltonianinHigh-FieldNMR
Spectroscopy 72
4.4.2 ReducedSpinHamiltonianinHigh-FieldNMR
SpectroscopyofIsotropicLiquidsandGases 74
4.4.3 SelectionRulesandTransitionProbabilities 74
4.4.4 EnergySpectrumoftheNuclearSpin
HamiltonianinHigh-FieldNMRSpectroscopy 75
4.4.4.1 Energyspectrumofasystemofn
interactingspins 76
4.5 DynamicsofInteractingSpins 78
4.5.1 TheDensityMatrix 78
4.5.1.1 Timeevolutionofthedensitymatrix:
theLiouville/vonNeumannequation 79
4.5.1.2 Thedensitymatrixinthermodynamic
equilibrium 80
4.6 PulsedNuclearMagneticResonance 81
4.6.1 DetectionoftheNMRObservable 81
4.6.2 TimeEvolutionoftheDensityMatrixunderRF
Pulses 82
5 NMRSpectroscopyofAnisotropicFluidSystems:Theoryand
Experiment 85
5.1 Introduction 85
5.2 NuclearSpinHamiltonianforNMRofAnisotropic
FluidSystems 86
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Contents vii
5.3 AveragedSecond-RankTensorialQuantitiesand
OrderParameters 88
5.4 DeterminationofHigh-FieldNMRAbsorptionSpectra
forSelectedSpinSystems 90
5.4.1 NMRSpectrumfromTwoInteractingIdentical
Spin1/2ParticlesSubjectedtotheSame
ChemicalShift 90
5.4.2 NMRSpectrumfromOneSpin1Particle
SubjectedtoQuadrupolarInteractionandthe
ChemicalShift 95
5.5 QuantumMechanicalAnalysisofSelectedNMRPulse
Sequences 97
5.5.1 SpinSystemSubjectedtoaSingleπ/2RFPulse
inResonance 97
5.5.2 SolidEchoPulseSequence 100
5.6 ExperimentalDetails 102
6 NMRRelaxationandMolecularDynamics:Theory 105
6.1 GeneralConcepts 105
6.2 RelaxationRates 108
6.2.1 Spin–LatticeRelaxationinAlignedSystems 112
6.3 RelaxationMechanisms 113
6.3.1 IsotropicRotations 113
6.3.2 Rotations/Reorientations 116
6.3.3 MolecularTranslationalSelf-Diffusion 118
6.3.3.1 Collectivemotions 119
6.3.3.2 Cross-relaxation 123
7 NMRRelaxometryandMolecularDynamics:Experimental
Techniques 127
7.1 InversionRecovery 127
7.2 FastFieldCycling 128
7.3 ExperimentalSetups 131
8 NMRSpectroscopyofLiquidCrystalDendrimers 133
8.1 NMRofLCDendrimersandtheInvestigationofthe
BiaxialNematicPhase 133
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viii Contents
8.1.1 BiaxialNematicOrderingandNMR
Spectroscopy 133
8.1.2 OrganosiloxaneTetrapodes 137
8.1.3 ExperimentalProcedures 141
8.1.3.1 90◦rotation 142
8.1.3.2 Continuousrotation 145
8.1.4 ExperimentalResultsandSpectraSimulations 146
8.1.4.1 90◦rotationtechniqueandspectraofa
staticdistributionofnematicdomains 146
8.1.4.2 Continuous-rotationtechniqueand
theeffectofslowmotions 147
8.1.5 DiscussionoftheSpectraSimulationResults 152
8.2 ComparisonwithTetrapodes’MonomersandOther
Main-ChainLCDendrimers 156
9 NMRRelaxometryofLiquidCrystalDendrimers:
ExperimentalResults 161
9.1 Liquid-CrystallineDendrimersInvestigatedbyNMR
Relaxometry 161
9.1.1 End-OnOrganosiloxaneTetrapodeswith
StrongTerminalDipoles 165
9.1.2 OrganosiloxaneTetrapodeswithLaterally
AttachedMesogens 172
9.1.3 OrganosiloxaneOctopodeswithLaterally
AttachedMesogens 182
9.1.4 PAMAMLiquid-CrystallineDendrimersof
Generations1and3 188
9.2 TheInfluenceofDendrimers’Structureonthe
MolecularDynamics 198
Bibliography 203
Index 223
October4,2016 13:5 PSPBook-9inx6in 00-NMR-Dendrimers-Prelims
Preface
This book, about nuclear magnetic resonance (NMR) studies on
liquid crystal dendrimers, is expected to be useful for researchers
and graduate students in the fields of dendrimers, liquid crystals,
andNMR.Besidesageneralpresentationofthestructuralproperties
ofliquidcrystaldendrimers’mesophases,thetheoreticalprinciples
and experimental techniques of NMR, typically used for the study
of these systems, are explained in an accessible way to graduate
studentsofphysics,chemistry,andmaterialsscience.Applicationsof
thesetechniquesinspecificexperimentalstudiesarealsopresented.
Most of the experimental work on NMR spectroscopy and
relaxation of liquid crystal dendrimers described herein was done
intheframeworkofcollaborationsbetweentheauthorsandseveral
colleagues. The investigations carried out by these chemists and
physicistswereessentialtotheaccomplishmentoftheresultsthat
werepublishedintheliteratureandcited,particularlyinChapters
8 and 9. These achievements were possible, in a great part, due
to the participation in two Marie Curie European projects funded
by the European Commission,LCDD,Supermolecular Liquid Crystal
Dendrimers (HPRN-CT-2000-00016) and Dendreamers: Functional
Liquid Crystalline Dendrimers, Synthesis of New Materials, Resource
for New Applications (FP7-PEOPLE-2007-1-1-ITN 215884), and
theprojectFromMolecularOrderandDynamicstoBiaxialNematic
Phases(PTDC/FIS/65037/2006),fundedbythePortugueseScience
and Technology Foundation, FCT. The authors are grateful to the
institutions that provided financial support to these projects and,
above all, to those who took part in the investigations—all the
Marie Curie fellows, young researchers, and the respective team
leaders. Some of these colleagues are co-authors of the cited
works, others are members of the teams participating in the