Matthew Alan Lohr

221 Pages·2014·6.86 MB·English

MICROSTRUCTURE AND PHASE BEHAVIOR IN
COLLOIDS AND LIQUID CRYSTALS
Matthew Alan Lohr
A DISSERTATION
in
Physics and Astronomy
PresentedtotheFacultiesoftheUniversityofPennsylvania
in
PartialFulfillmentoftheRequirements fortheDegreeofDoctorofPhilosophy
2014
ArjunG.Yodh,ProfessorofPhysicsandAstronomy
Supervisor ofDissertation
RandallD.Kamien,ProfessorofPhysicsandAstronomy
GraduateGroupChairperson
Dissertation Committee
RandallD.Kamien,ProfessorofPhysicsandAstronomy
PeterJ.Collings,AdjunctProfessorofPhysicsandAstronomy
KathleenJ.Stebe,ProfessorofChemicalandBiomolecular Engineering
GaryM.Bernstein, ProfessorofPhysicsandAstronomy
Dedication
Dedicated tomywife,Melissa.
Thankyouforourlifetogether.
ii
Acknowledgements
Thisworkwouldn’texistwithouttheconstantsupport ofmanypeopleovermanyyears.
My wife, Melissa, has been extremely important in keeping me sane, fed, groomed and
grounded throughout my graduate studies. When I was writing my undergraduate thesis, she
walked into my room and noticed I had been so distracted by writing that I had let a bottle of
detergent spill into the middle of the floor. My functionality during the writing of this thesis
dissertation is largely due to her. More importantly, she makes me happier than I could ever
imagine.
Myadvisor, Prof. ArjunYodh, hasbeenagreatmentorwhohasbeenverysupportive when
Ibecamefrustratedwithmyresearch. Duringmygraduateschoolvisits,Iaskedeveryprofessor
I met what they thought the worst thing about their department was. Many had clever and cir-
cuitousanswers(“Wedon’thaveenoughgraduatestudents!”). Arjunwastheonlyonewhogave
meastraightforward answer of, “What? No, there’s nothing wrong withPenn. Youshould just
comehere.” Ihave sincelearned such frankness isanimportant partofbeing agood communi-
cator, and Ihope that his sincere, direct, patient and good-natured advice has molded meinto a
betterscientist.
My family, currently spread across the country and globe, has been a constant source of
love and support throughout mylifeand academic career. Myparents, beyond being extremely
supportive through my young and adult life, have always been thoughtful about my gifts and
values, pushing me towards a fulfilling career while always encouraging my interests (be they
science, music, theater, or beer). Though Ilove all my siblings equally, I have to give a special
shout-out in this thesis to my brother Mike, a fellow scientist who has constantly encouraged
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metochallenge myintellectual limitsand, toquoteMr. EdwardAbbey,“SubverttheDominant
Paradigm.”
The Yodh Soft Matter Group is full of awesome people who also happen to be great scien-
tists. Tomyfellow graduate students, DanChen, OniBasu, PeterYunker, (Matt) Gratale, Zoey
Davidson, and Wei-Shao Wei; to our postdocs, Zexin Zhang, Ke Chen, Tim Still, Ye Xu, and
Joonwoo Jeong; andtoour academic collaborators, Prof. KevinAptowicz andProf. PiotrHab-
das: youallhavemadethisgroupafunplacetopursueone’sPh. D,andIowealmosteverything
Ilearnedingraduateschooltothelotofyou. Icouldnothavehopedforabettergroupofpeople
toworkwithovertheseyears,andIhopetocontinue collaborating withallofyouinthefuture.
Beyondmyimmediategroup,Ihavehadsomegreatcollaborators inandaroundPenn,with-
out whom my work would be boring and incomplete. ToAhmed Alsayed, Marcello Cavarello,
MohammedGharbi, Prof. Kathleen StebeandProf. PeterCollings, thankyouforallyourwork
sharing your experimental expertise and valuable insight into sometimes mysterious and tem-
peramental materials. To Bryan Chen, Prof. Randall Kamien, Daniel Beller, Carl Goodrich,
and Daniel Sussman, thank you for performing complex derivations and simulations to support
my results, for taking the time to patiently explain finer points of various theories, and, most
importantly, forsharingyourscotchwithme.
Speaking of Penn, I have to give credit to the Penn Physics department. Ever since I first
visited Penn back when I wasdeciding where to go for graduate school, itwas clear to methat
this was a department full of well-rounded and interesting people. I am proud to have been a
partofit,andI’mgladforallofthefriendsI’vemadethere. Also,Ihavetothankthestaffofthe
LRSMformakingitawelcomingbuilding tovisiteveryday.
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I never could have imagined that a close-knit group of open, friendly, passionate people
would be interested in the same squishy things I thought were cool. So Ihave to thank the soft
matter community at large. Though I will be stepping into a career in industry research and
development, I hope to stay in touch, and can’t wait to see the great new work you all produce
onself-assembly, phasebehavior, andnonlinear phenomena.
I am extremely grateful for the opportunities I have had to pursue undergraduate research,
so I have to thank Prof. Peter Schiffer, Prof. Daniel Lathrop, Prof. Diane Henderson, Dr.
Charles Doumalin, and Dr. Masafumi Fukuto, as well as the NSF’s REU program, for getting
me involved in interesting research early on. I still draw on things I learned from your labs to
thisveryday.
I finally have to thank the city of Philadelphia for being an interesting and affordable place
to live, and the perfect place for a budding scientist to spend formative years. Also, need to
thankmycatLeela(anativeofUniversityCity,foundcrouchedunderacaroutsideDRLbymy
friendsandcolleaguesPeterYunkerandErinBuckley)forbeingthesweetestpetanymancould
askfor,andcomforting meduringthemorestrenuous periods ofmygraduate career.
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ABSTRACT
MICROSTRUCTURE AND PHASE BEHAVIOR IN COLLOIDS AND
LIQUID CRYSTALS
MatthewAlanLohr
ArjunG. Yodh
Thisthesis describes our investigation of microstructure and phase behavior in colloids and
liquid crystals. The first set of experiments explores the phase behavior of helical packings of
thermoresponsive microspheres inside glass capillaries as a function of volume fraction. Sta-
ble helical packings are observed with long-range orientational order. Some of these packings
evolve abruptly to disordered states as the volume fraction is reduced. We quantify these tran-
sitions using correlation functions and susceptibilities of the orientational order parameter, 𝜓 .
6
Theemergence ofcoexisting metastable packings, aswellascoexisting ordered and disordered
states, is also observed. These findings support the notion of phase-transition-like behavior in
thisclassofquasi-one-dimensional systems.
The second set of experiments investigates cross-over behavior from glasses with attrac-
tive interactions to sparse gel-like states. In particular, the vibrational modes of quasi-two-
dimensional disordered colloidal packings ofhardcolloidal spheres withshort-range attractions
aremeasuredasafunction ofpackingfraction. Acrossoverfromglassytosparsegel-like states
is indicated by an excess of low-frequency phonon modes. This change in vibrational mode
distribution is found to arise from highly localized vibrations that tend to involve individual
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and/or small clusters of particles with few local bonds. These mode behaviors and correspond-
ing structural insights may serve as a useful signature for glass-gel transitions in wider classes
ofattractivepackings.
A third set of experiments explores the director structures of aqueous lyotropic chromonic
liquidcrystal(LCLC)filmscreatedonsquarelatticecylindrical-micropost substrates. Thestruc-
tures are manipulated by modulating the concentration-dependent elastic properties of LCLCs
viadrying. NematicLCLCfilmsexhibitpreferred bistable alignmentalong thediagonals ofthe
micropost lattice. ColumnarLCLCfilmsformtwodistinct director anddefectconfigurations: a
diagonally aligned director pattern withlocal squares ofdefects, andanoff-diagonal configura-
tion with zig-zag defects. We suggest that the formation of these patterns is tied to the relative
free energy costs of splay and bend deformations in the precursor nematic films. The observed
nematicandcolumnarconfigurationsareunderstoodnumericallyusingaLandau-deGennesfree
energymodel. Thisworkprovidesfirstexamplesofquasi-2DmicropatterningofLCfilmsinthe
columnar phase and the first micropatterning of lyotropic LC films in general; the work also
demonstrates alignment and configuration switching of typically difficult-to-align LCLC films
viabulkelasticproperties.
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Contents
Dedication ii
Acknowledgements iii
Abstract vi
ListofFigures xxxii
1 Introduction 1
1.1 StructureandMeltingofHelicalPackings . . . . . . . . . . . . . . . . . . . . 3
1.2 VibrationalSignatures ofGel-likeandGlassyColloidalPackings . . . . . . . . 6
1.3 Microscopic OrderingofLyotropic ChromonicLiquidCrystals . . . . . . . . . 9
1.4 Organization ofThesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2 HelicalPackingsandPhaseTransformationsofSoftSpheresinCylinders 13
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 ContextualandTheoretical Background . . . . . . . . . . . . . . . . . . . . . 15
2.2.1 HelicalPackingStructures . . . . . . . . . . . . . . . . . . . . . . . . 15
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2.2.2 Transformations ofHelicalStructures . . . . . . . . . . . . . . . . . . 19
2.2.3 PhaseTransitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.3.1 PhaseTransitions, LongRangeOrderandDimensionality . . 22
2.3 ExperimentalMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.1 pNIPAmmicrospheres . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.1.1 pNIPAmSynthesisandFluorescent Functionalization . . . . 29
2.3.1.2 pNIPAmParticleDiameterCharacterization . . . . . . . . . 30
2.3.2 MicrotubeGeometryandSampleConfiguration . . . . . . . . . . . . . 32
2.3.3 Fluorescence ConfocalMicroscopy . . . . . . . . . . . . . . . . . . . 33
2.3.3.1 Background onConfocalMicroscopy . . . . . . . . . . . . . 34
2.3.3.2 AdvantagesandDisadvantages ofTSMandCLSM . . . . . 36
2.4 ResultsandAnalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.4.1 Characterization of3DStructure . . . . . . . . . . . . . . . . . . . . . 38
2.4.2 Long-RangeOrientational OrderinAchiralPackings . . . . . . . . . . 43
2.4.3 TheoreticalModelforLong-RangeOrientationalOrderinHelicalPackings 45
2.4.4 Orientational Order Parameter, Susceptibility, and Evidence of a Phase
TransitioninExperiment . . . . . . . . . . . . . . . . . . . . . . . . . 49
2.4.5 StructuralTransformations inChiralPackings . . . . . . . . . . . . . . 53
2.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3 Low-FrequencyModesasaHallmark ofStructural Crossovers inQuasi-2D Dense
AttractiveColloidalPackings 56
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
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3.2 ContextualandTheoretical Background . . . . . . . . . . . . . . . . . . . . . 57
3.2.1 AttractiveGlasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.2.2 Gels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.2.3 DifferencesbetweenGelsandAttractiveGlasses . . . . . . . . . . . . 60
3.2.4 PhononsinDisordered Solids . . . . . . . . . . . . . . . . . . . . . . 61
3.2.4.1 Conventional Low-Frequency Phonon Behavior: The Debye
Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.2.4.2 Low-FrequencyPhononsinDisorderedSolids . . . . . . . . 62
3.3 ExperimentalandAnalytical Methods . . . . . . . . . . . . . . . . . . . . . . 65
3.3.1 SamplePreparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.3.1.1 IssuesFormingQuasi-2DThermalAttractiveMonolayers . . 65
3.3.1.2 NovelMonolayerSpreading FromLutidineWetting . . . . . 67
3.3.1.3 TemperatureStability . . . . . . . . . . . . . . . . . . . . . 69
3.3.1.4 MonolayerFormation . . . . . . . . . . . . . . . . . . . . . 71
3.3.2 vDOSCalculation fromParticleTrajectories . . . . . . . . . . . . . . 71
3.3.3 AnalyticalConsiderations forvDOScalculations . . . . . . . . . . . . 74
3.4 ResultsandDiscussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.4.1 Conventional Structural Characteristics ofAttractiveMonolayers . . . 76
3.4.2 vDOSShapeasaSignatureofStructuralTransition . . . . . . . . . . . 80
3.4.2.1 ComparisonofvDOSinDensePackingtoSimulations . . . 82
3.4.3 Localization ofLow-FrequencyModes . . . . . . . . . . . . . . . . . 85
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