Single Droplet Break-up in Controlled Mixed Flows

Boonen, Eva; Puyvelde, Peter Van; Moldenaers, Paula

doi:10.1021/am100389x

Cited by 9 publications

(3 citation statements)

References 45 publications

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“…The lower viscosity polymer will encapsulate the higher viscosity polymer at a low shear rate. [32][33][34] According to Fig. 1, as the h* of PMMA is lower than that of PVDF, the PMMA will encapsulate the PVDF.…”

Section: Resultsmentioning

confidence: 99%

Advanced dielectric polymer nanocomposites by constructing a ternary continuous structure in polymer blends containing poly(methyl methacrylate) (PMMA) modified carbon nanotubes

Zhao¹,

Cao²,

Zhao³

et al. 2014

J. Mater. Chem. A

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A nanocomposite with ultra-low percolation threshold and high dielectric performance is prepared by controlling the localization of multiwalled carbon nanotubes (MWNTs) in one phase of a ternary continuous polymer blend system through melt processing. Polystyrene (PS), poly(vinylidene fluoride) (PVDF), and poly(methyl methacrylate) (PMMA) can form a ternary continuous structure when the volume fractions of PS, PVDF and PMMA are 70 vol%, 20 vol%, and 10 vol%, respectively. The PS is a continuous matrix (sea-phase) whereas the other two phases are interconnected threads (the PVDF is situated as the core while the PMMA is the shell, and the thickness of the PMMA shell is about 1 mm). Adding PMMA could improve the compatibility between the PS and PVDF components. Selective distribution of MWNTs in the PMMA shell is achieved through a combination of PMMA modified MWNTs and appropriate processing procedures. The composite shows an ultra-low percolation threshold of ca.0.3 wt%. When the weight fraction of PMMA modified MWNTs is 0.4 wt%, the dielectric constant of the composite is as high as 182 (at 100 Hz), which is about 60 times higher than that of a pure PS matrix.The composite's dielectric properties have excellent temperature stability. This approach can provide a new and low-cost route to design high-performance dielectric materials with ultra-low percolation thresholds.

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Section: Resultsmentioning

confidence: 99%

Advanced dielectric polymer nanocomposites by constructing a ternary continuous structure in polymer blends containing poly(methyl methacrylate) (PMMA) modified carbon nanotubes

Zhao¹,

Cao²,

Zhao³

et al. 2014

J. Mater. Chem. A

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“…Additional passes of the emulsion through the colloid mill allow the drop size to be further reduced. While drop breakage in simple shear or Couette flow has been well studied (Cristini et al, 2003;Zhao, 2007;Renardy et al, 2002;Grace, 1982;Boonen et al, 2010), drop breakage mechanisms in colloid mills are not well understood. Common practice is to assume simple or extensional shear flow, in which drops break due to capillary instability when the ratio of the viscous stress to the interfacial tension force crosses a critical value (Wieringa et al, 1996;King and Keswani, 1994;Almeida-Rivera and Bongers, 2012).…”

Section: Introductionmentioning

confidence: 99%

Prediction of emulsion drop size distributions in colloid mills

Maindarkar

Dubbelboer

Meuldijk

et al. 2014

Chemical Engineering Science

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Developed a population balance equation model for emulsification in colloid mill. Derived the function for drop breakage frequency in simple shear flow. Proposed a new daughter drop distribution function for capillary drop breakage. Used a viscosity model to predict the emulsion viscosity at high shear rates. Demonstrated good agreement between measured and predicted drop size distributions. Colloid mills are the most common emulsification devices used in industry for products with high oil content. Drop breakage occurs when the emulsion is flowed through a small gap between rotor and stator under laminar shear conditions. In this paper, we have developed the first full population balance equation (PBE) model for colloid mills and used the model to better understand the relevant drop breakage mechanisms. The PBE model accounted for both drop breakage and coalescence and generated predictions of the drop size distribution after each pass of the emulsion through the colloid mill. Drops were assumed to break due to capillary instability with the distribution of drop sizes resulting from each breakage event studied in detail. A viscosity model was developed to predict the emulsion viscosity as function of the oil fraction and the high shear rates commonly used. Nonlinear optimization was used to estimate adjustable parameters in the breakage and coalescence functions to minimize the least-squares difference between predicted and measured drop size distributions for high oil-to-surfactant emulsions. We concluded that experimentally observed drop volume distributions could not be predicted with daughter drop distribution functions reported in the literature. Improved predictions were obtained using a new bimodal distribution function which captured drop breakage into multiple, nearly uniform daughter drops with a large number of small satellite drops. We also investigated model extensibility for changes in the oil fraction, emulsion flow rate and rotor speed.Published by Elsevier Ltd.

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“…In studies of multicomponent polymer blends of more than two phases, papers dedicated to this subject have shown that the morphology resulting from the competition between drops collision under flow followed by coalescence/encapsulation or drop breakup depends mainly on the interfacial and rheological properties. , The final droplet size distribution, under mixing, results from the balance between the present phenomena . Recently, the effect of compatibilization on the deformation and breakup of drops in stepwise increasing shear flow has been investigated…”

Section: Introductionmentioning

confidence: 99%

2D Encapsulation in Multiphase Polymers: Role of Viscoelastic, Geometrical and Interfacial Properties

2011

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The aim of the present work has been to gain a fundamental understanding of the mechanisms governing encapsulation in the multiphase systems as a blend or multilayer structures. The model systems chosen for this study are based on (i) Newtonian poly(dimethylsiloxane) polymers of varying molar masses and (ii) high molecular weight, viscoelastic, and compatible pair polymers of PVDF and PMMA. The same approach was applied to functionalized polymers to investigate the effect of physicochemical affinity on two pairs of asymmetrical reactive polymers based on PE-GMA (glycidyl methacrylate)/PVDF-g-MA (maleic anhydride) and a PE/PVDF as a reference. The linear viscoelastic and surface properties of the neat and bilayer model systems structures have been investigated. The optical obeservations of the encapsulation kinetic of two drops were recorded using a homemade device. Specific experiments were carried out to follow up the kinetic of encapsulation, and the results were rationalized as a function of the effect of the viscosity, elasticity ratios, drop geometry, the interfacial tension, and the physicochemical affinity. Throughout all the experiment, the mechanisms were purposed for each system and discussed based on the theories of molecular forces or Brownian motion governing diffusion and Ostwald ripening, in contrast to the theories of coalescence. The viscosity ratio coupled to the drop geometry of the material was found to be a key parameter and that it has to be linked to the interfacial tension and spreading parameters. Furthermore, the encapsulation appeared to be hindered by the interdiffusion process in the case of compatible pair system despite their elasticity and surface tension contrast. Finally, the encapsulation kinetic could be reduced or eliminated by the creation of a copolymer at the interface for a reactive system. The results obtained by the optical investigation of two drops corroborated the rheological data of the bilayer systems. Hence, the obtained results rendered it possible to decouple the influence of the viscoelastic parameters to flow, interfacial tension, thereby highlighting a number of macroscopic effects that were governed by the interdiffusion or reaction of macromolecular chains at the interface to give a better understanding of encapsulation phenomenon in multiphase systems.

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Single Droplet Break-up in Controlled Mixed Flows

Cited by 9 publications

References 45 publications

Advanced dielectric polymer nanocomposites by constructing a ternary continuous structure in polymer blends containing poly(methyl methacrylate) (PMMA) modified carbon nanotubes

Advanced dielectric polymer nanocomposites by constructing a ternary continuous structure in polymer blends containing poly(methyl methacrylate) (PMMA) modified carbon nanotubes

Prediction of emulsion drop size distributions in colloid mills

2D Encapsulation in Multiphase Polymers: Role of Viscoelastic, Geometrical and Interfacial Properties

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