M<scp>ICROSTRUCTURAL</scp> E<scp>VOLUTION IN</scp> P<scp>OLYMER</scp> B<scp>LENDS</scp>

Tucker, Charles L.; Moldenaers, Paula

doi:10.1146/annurev.fluid.34.082301.144051

Cited by 380 publications

(230 citation statements)

References 100 publications

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“…[3][4][5][6] The behavior of drops and blends in bulk flow has been reviewed various times. [7][8][9][10][11] In microfluidic applications, however, where the drop diameter is typically in the order of the channel height, the flow behavior can be significantly altered by the presence of channel walls. An example includes the behavior of blends and single drops undergoing shear flow in a confined system.…”

Section: Introductionmentioning

confidence: 99%

Boundary-integral method for drop deformation between parallel plates

Janssen

Anderson

2007

Physics of Fluids

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A new boundary-integral method is proposed to study the deformation of drops between two parallel walls. The free-space Green's functions are extended to obey the no-slip condition at the walls. The current formulation is limited to drops with viscosity equal to the matrix fluid, but can be extended to study the effect of nonunit viscosity ratio systems. With this method, the influence of the capillary number and the degree of confinement on drop deformation is investigated. Results for small capillary are compared with small-deformation theory and large capillary results with recent experiments. In both cases, an excellent match is observed. Drops undergoing shear flow deform stronger and align themselves more in the flow direction as the distance between the walls becomes smaller relative to the drop size. Furthermore, the shapes of the drops start to divert significantly from the normal ellipsoidal shapes found, as they show more pointed tips closer to the walls. The transient deformation behavior for more confined systems shows that the drops stretch out to a maximum value, and they slowly retract again to a steady situation. For larger capillary numbers even damped, oscillatory behavior is observed. Investigating the critical capillary number reveals that a minimum is found at a mediocre degree of confinement, after which the critical capillary number increases again to values even larger than the unconfined system. The breakup mode also makes a significant change as it goes from binary to ternary breakup, where the breakup occurs as the drop is retracting.

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Section: Introductionmentioning

confidence: 99%

Boundary-integral method for drop deformation between parallel plates

Janssen

Anderson

2007

Physics of Fluids

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“…1 Since the pioneering research of Taylor, 2 many theoretical and numerical studies describing the Newtonian droplet behavior in bulk flow have been developed and reviewed, showing all good agreement with experimental results. [3][4][5][6] In the past decade, the use of microfluidic devices and applications in processing industries has grown to a large extent. 7,8 Many of these applications consider multiphase systems, for instance, to create dispersions with a desired droplet-size distribution.…”

Section: Introductionmentioning

confidence: 99%

Microconfined equiviscous droplet deformation: Comparison of experimental and numerical results

et al. 2008

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The dynamics of confined droplets in shear flow is investigated using computational and experimental techniques for a viscosity ratio of unity. Numerical calculations, using a boundary integral method ͑BIM͒ in which the Green's functions are modified to include wall effects, are quantitatively compared with the results of confined droplet experiments performed in a counter-rotating parallel plate device. For a viscosity ratio of unity, it is experimentally seen that confinement induces a sigmoidal droplet shape during shear flow. Contrary to other models, this modified BIM model is capable of predicting the correct droplet shape during startup and steady state. The model also predicts an increase in droplet deformation and more orientation toward the flow direction with increasing degree of confinement, which is all experimentally confirmed. For highly confined droplets, oscillatory behavior is seen upon startup of flow, characterized by an overshoot in droplet length followed by droplet retraction. Finally, in the case of a viscosity ratio of unity, a minor effect of confinement on the critical capillary number is observed both numerically and experimentally.

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“…36,37,44,46 The free volume size is evaluated as V f ¼ (4/3)pR 3 . The fractional free volume or the free volume content (F v ) is calculated as…”

Section: Positron Annihilation Lifetime Measurementsmentioning

confidence: 99%

“…Thus, the structure and thermodynamics of internal interfaces between different polymers determine many practically important properties of blends. 2 When a blend just begins to separate into one rich and the other poor domains, the width of the interface is much broader than the molecular size of the polymer; 3 in other words, smaller the width of the interface, more entanglements are formed across these interfaces which improves the mechanical properties of the blend system. 4,5 Theoretical descriptions, conversely, are quite different to describe interfaces between two unmixed domains.…”

Section: Introductionmentioning

confidence: 99%

A new insight into interface widths in binary polymer blends based on ortho‐positronium lifetime studies

Ramya

Ranganathaiah

2012

J of Applied Polymer Sci

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The interface widths in two immiscible polymer blend (Poly vinyl chloride (PVC)/Polystyrene (PS)) and PVC/Ethylene Vinyl Acetate (EVA) are determined experimentally using hydrodynamic interaction approach through free volume measurement by positron annihilation lifetime spectroscopy. For comparison, the same study is performed in a miscible blend (Styrene Acrylonitrile (SAN)/Poly Methyl Methacrylate (PMMA)). The interfacial width (Dl) is evaluated from the hydrodynamic interaction (a) based on Kirkwood-Risemann theory and friction coefficient from Stokes equation. Friction at the interface of a binary blend evidences how close the surfaces of the polymer chains come or stay apart which in turn depends on the type of force/interaction at the interface. In this work, we define interface width from a different perspective of Flory-Huggins interaction approach. Measured composition dependent interface widths in the three blends studied clearly demonstrate the sensitivity of the present method. In miscible blend, high friction at the interface results in stronger hydrodynamic interaction and hence smaller interface widths (0.36-1.97 Å ), whereas weak or no interaction in immiscible blends produce wider widths (2.81-25.0 Å ).

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MICROSTRUCTURAL EVOLUTION IN POLYMER BLENDS

Cited by 380 publications

References 100 publications

Boundary-integral method for drop deformation between parallel plates

Boundary-integral method for drop deformation between parallel plates

Microconfined equiviscous droplet deformation: Comparison of experimental and numerical results

A new insight into interface widths in binary polymer blends based on ortho‐positronium lifetime studies

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