Flow of Quasi-two-dimensional Emulsions: Clogging, Avalanches, and Dynamics Open Access

Hong, Xia (2017)

Permanent URL: https://etd.library.emory.edu/concern/etds/dn39x2409?locale=en
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Abstract

Abstract

Flow of Quasi-two-dimensional Emulsions: Clogging, Avalanches, and Dynamics

By Xia Hong

We experimentally study the flow of oil-in-water emulsion droplets in a quasi-two- dimensional system. Due to surfactants coating the droplets, they easily deform and slide past each other, approximating frictionless and soft disks. Similar experiments were done in granular material [1-9] and it is exciting to see both similarities and disagreement between prior results and our new findings.

In Chap. 4, by flowing emulsion using gravity, droplets have chances to clog at the hopper exit. By varying the hopper width, the transition from clogging to unclogging is observed. This clogging at the hopper exit requires a narrow hopper opening that is slightly larger than the droplet diameter and no observation of large arch at the hopper exit. Prior studies with frictional disks found long arch formation and cloggings at the hopper exit with significantly larger hopper openings [1]. However, our simulation work shows the importance of gravity and softness that is leading to the change in the clogging probability.

Chap. 5 uses syringe pump to drive the droplets flowing through a hopper. In this system there is no permanent clogging, unlike gravity driven hopper flow, due to the continuous pumping. The droplets would eventually exit the hopper due to the

pressure build-up in the system. There are three types of very different flow behaviors observed. At the lowest flow rates, the droplets exit the hopper via intermittent avalanches. At the highest flow rates, the droplets exit continuously. The transition is a fairly smooth function of the mean strain rate. This is remarkable because emulsion system is frictionless while friction is crucial in granular material to have avalanche [1-3]. However, there is little or no dependence of the flow behavior on the area fraction of the system.

Chap. 6 is inflating oil droplet into the emulsion in an open chamber to study its dynamic response. We examine both monodisperse and bidisperse sample with a large range of packing fraction. The mean flow is well defined like simple fluid. But the fluctuation of velocity increases as the packing fraction gets further above jamming regardless of the polydispersity of emulsions.

Table of Contents

Contents

AbstractCoverPage .............................. i

CoverPage ................................... ii

Acknowledgments................................ iii

Dedication.................................... vi

TableofContents................................ vii

ListofFigures.................................. ix

ListofTables.................................. xii

CitationstoPreviouslyPublishedWork ................... xiii

1 Introduction 1

  1. 1.1 SoftMaterialsandJamming....................... 1

  2. 1.2 FlowofSoftMaterials .......................... 6

    1.2.1 Emulsion ............................. 8

    1.2.2 FlowofEmulsion......................... 12

    2 Experimental Apparatus and Procedures 16
  3. 2.1 MakingMicrofluidicDevice ....................... 16
  4. 2.2 MakingDroplets ............................. 20
  5. 2.3 MakingChambersandLoadingSamples ................ 26
  6. 2.4 PumpingandImaging .......................... 29
  1. 3 Analytical Method 32

    1. 3.1 EmulsionIdentification.......................... 33

    2. 3.2 EmulsionTrackingandVelocity..................... 37

    3. 3.3 T1Events................................. 38

      3.3.1 NeighborExchange........................ 39

      3.3.2 StrainMethod........................... 40

    4. 3.4 ForceandStress.............................. 41

      3.4.1 ForceOntheBoundary ..................... 43

    5. 3.5 Visualization ............................... 44

  1. 4 Clogging of Oil Droplets in 2D Hopper 45

    1. 4.1 Introduction................................ 45

    2. 4.2 ExperimentalMethods .......................... 48

    3. 4.3 PhysicsofFlowingEmulsions ...................... 52

    4. 4.4 Results................................... 57

      4.4.1 CasesofNoClogging....................... 57

      4.4.2 CasesofClogging......................... 60

      4.4.3 CrystallineEffect ......................... 67

    5. 4.5 DiscussionandConclusion........................ 68

  2. 5 Avalanches of Rearrangements in 2D Emulsion Hopper Flow 73

    1. 5.1 Introduction................................ 73

    2. 5.2 ExperimentalMethod........................... 75

      5.2.1 SamplesandSampleChambers ................. 75

      5.2.2 ControlParameters........................ 77

    3. 5.3 ResultsandDiscussion .......................... 79

    4. 5.4 Conclusions ................................ 92

  3. 6 Dynamic Response to Local Perturbations 98

    1. 6.1 Introduction................................ 98

    2. 6.2 ExperimentalMethods .......................... 101

      6.2.1 Samples .............................. 101

      6.2.2 ControlParameters........................ 106

    3. 6.3 ResultsandDiscussion .......................... 110

      6.3.1 MeanFlow ............................ 110

      6.3.2 VelocityFluctuation ....................... 116

      6.3.3 LocalStructure .......................... 122

    4. 6.4 ConclusionandOutlook ......................... 129

7 Summary 133

7.1 SummaryofThesis ............................ 133

7.2 ImpactandOutlook ........................... 137

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