Pressure–deformation relations of elasto-capillary drops (droploons) on capillaries

Ginot, Gaël; Kratz, Felix; Walzel, Friedrich; Farago, Jean; Kierfeld, Jan; Höhler, Reinhard; Drenckhan, Wiebke

doi:10.1039/d1sm01109j

Cited by 11 publications

(14 citation statements)

References 48 publications

(93 reference statements)

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“…In general, the stress state of the evolving inhomogeneous membrane of such a capsule is very complex and depends on the mechanical properties of the membrane, the time-and radius-dependent stress tensor of such thick membranes, 51 the initial, stress-free state, and the mechanical connection to the needle. 52 Therefore, an accurate evaluation of the membrane elastic modulus is not possible. However, the existence of the elastic properties of the capsule can be tested in our setup shown in Figure 1 by changing the capsule volume and measuring the corresponding pressure changes.…”

Section: Discussionmentioning

confidence: 99%

Pressure Changes Across a Membrane Formed by Coacervation of Oppositely Charged Polymer–Surfactant Systems

Keshavarzi,

Reising,

Mahmoudvand

et al. 2024

Langmuir

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We investigate the mass transfer and membrane growth processes during capsule formation by the interaction of the biopolymer xanthan gum with C n TAB surfactants. When a drop of xanthan gum polymer solution is added to the surfactant solution, a membrane is formed by coacervation. It encapsulates the polymer drop in the surfactant solution. The underlying mechanisms and dynamic processes during capsule formation are not yet understood in detail. Therefore, we characterized the polymer−surfactant complex formation during coacervation by measuring the surface tension and surface elasticity at the solution−air interface for different surfactant chain lengths and concentrations. The adsorption behavior of the mixed polymer− surfactant system at the solution−air interface supports the understanding of observed trends during the capsule formation. We further measured the change in capsule pressure over time and simultaneously imaged the membrane growth via confocal microscopy. The cross-linking and shrinkage during the membrane formation by coacervation leads to an increasing tensile stress in the elastic membrane, resulting in a rapid pressure rise. Afterward, the pressure gradually decreases and the capsule shrinks as water diffuses out. This is not only due to the initial capsule overpressure but also due to osmosis caused by the higher ionic strength of the surfactant solution outside the capsule compared to the polymer solution inside the capsule. The influence of polymer concentration and surfactant type and concentration on the pressure changes and the membrane structure are studied in this work, providing detailed insights into the dynamic membrane formation process by coacervation. This knowledge can be used to produce capsules with tailored membrane properties and to develop a suitable encapsulation protocol in technological applications. The obtained insights into the mass transfer of water across the capsule membrane are important for future usage in separation techniques and the food industry and allow us to better predict the capsule time stability.

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Section: Discussionmentioning

confidence: 99%

Pressure Changes Across a Membrane Formed by Coacervation of Oppositely Charged Polymer–Surfactant Systems

Keshavarzi,

Reising,

Mahmoudvand

et al. 2024

Langmuir

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“…A detailed follow-up of the bubble growth kinetics using a high-speed camera in the limit where it is limited by the interfacial rheology, seems a promising prospect for this work, since it could open the way to a new characterization of the interfacial rheology of surfactants in a nearly spherical geometry. Indeed, it has been recently shown that "Capillary pressure Elastometry", which consists in analyzing the quasi-static pressure-deformation curves for a bubble in this type of geometry, allows to analyse the elastic properties of interfaces [35]. The simple model proposed here should allow to extend the field of application of "Capillary pressure Elastometry" to the dynamic response of interfaces.…”

Section: Discussionmentioning

confidence: 99%

Unstable growth of bubbles from a constriction

Grosjean¹,

Lorenceau²

2022

Preprint

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Bubbles and droplets are ubiquitous in many areas of engineering, including microfluidics where they can serve as microreactors for screening of chemical reactions. They are often formed out of a constriction (a microfluidic channel or a cylindrical tube) by blowing a given volume of gas into a liquid phase. It is obviously crucial to be able to control their size, which is not always easy due to the coupling between the volume of the bubble and the gas pressure induced by the Laplace law. In this paper, we examine the size and formation dynamics of soap bubbles blown from a cylindrical tube, which is the paradigm geometry for bubble and droplet formation. To do so, one end of the tube is closed by a soap film, while the other end is connected to a large reservoir of variable volume filled with gas. To inflate the gas in the bubble, we reduce the volume of the reservoir, which mimics air inflation through the lung diaphragm or the flow-rate driven bubble formation in microfluidics geometry such as flow-focusing. As the volume of the reservoir decreases, the gas pressure increases, the soap film curves and takes the form of a spherical cap with an increasingly smaller radius of curvature. This quasi-static process continues until a critical pressure is reached for which the bubble is quasi-hemispherical. Beyond this pressure, the film undergoes a rapid topological transformation and swells very rapidly (in less than a hundred ms) until it reaches its final volume. We describe this instability in particular by showing that this unstable regime appears when a dimensionless number -whose expression we specify -reaches a critical value. Using a quasi-static model that we solve analytically, we predict the bubble growth dynamics and the final height of the bubble produced for any reservoir volume and constriction size.

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“…The transition to solid elasticity then gives rise to deviatoric anisotropic stresses, which can no longer be taken into account as an effective isotropic and homogeneous surface tension γ eff obtained by solving the usual Young–Laplace equation. 17,27,29–33,41–44…”

Section: Methodsmentioning

confidence: 99%

“…The dilational investigations are performed combining shape analysis and pressure measurements 27 of a bubble held by a needle in solution during sinusoidal or linear volume changes. The dilational response of the interface being rapidly non-linear, we apply for the first time the method of general stress decomposition (GSD) [28][29][30] to polyelectrolyte multilayers.…”

Section: Introductionmentioning

confidence: 99%

Interfacial rheology of linearly growing polyelectrolyte multilayers at the water–air interface: from liquid to solid viscoelasticity

Pivard,

Jacomine,

Kratz

et al. 2024

Soft Matter

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Pressure–deformation relations of elasto-capillary drops (droploons) on capillaries

Abstract: An increasing number of multi-phase systems exploit complex interfaces with interfacial stresses of multiple origins. Despite growing efforts, simple and reliable experimental characterisation of the interfacial properties remains a challenge,...

Cited by 11 publications

References 48 publications

Pressure Changes Across a Membrane Formed by Coacervation of Oppositely Charged Polymer–Surfactant Systems

Pressure Changes Across a Membrane Formed by Coacervation of Oppositely Charged Polymer–Surfactant Systems

Unstable growth of bubbles from a constriction

Interfacial rheology of linearly growing polyelectrolyte multilayers at the water–air interface: from liquid to solid viscoelasticity

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