Effect of disjoining pressure on the drainage and relaxation dynamics of liquid films with mobile interfaces

Tabakova, S.; Danov, Krassimir D.

doi:10.1016/j.jcis.2009.03.084

Cited by 24 publications

(19 citation statements)

References 48 publications

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“…In practice, however, there is usually a typical distance h 0 below which particle surfaces interact not only via the fluid, but also through a direct particleparticle force. This interaction can have various physical origins, among which direct contacts between asperities of rough solid surfaces [22,23,24,25] or repulsion between charged or polymeric surfactant molecules at the bubble or droplet surface [29]. Our present focus is not necessarily to capture any of the details of such effects, but rather to represent their common feature: a strong steric repulsion that works on the particle surfaces in parallel to the viscous force (Fig.1 a1).…”

Section: Internal Dynamics: Particle Interactionmentioning

confidence: 99%

Internal relaxation time in immersed particulate materials

Rognon¹,

Einav²,

Gay³

2010

Phys. Rev. E

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We study the dynamics of the solid to liquid transition for a model material made of elastic particles immersed in a viscous fluid. The interaction between particle surfaces includes their viscous lubrication, a sharp repulsion when they get closer than a tuned steric length and their elastic deflection induced by those two forces. We use Soft Dynamics to simulate the dynamics of this material when it experiences a step increase in the shear stress and a constant normal stress. We observe a long creep phase before a substantial flow eventually establishes. We find that the typical creep time relies on an internal relaxation process, namely the separation of two particles driven by the applied stress and resisted by the viscous friction. This mechanism should be relevant for granular pastes, living cells, emulsions and wet foams.

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Section: Internal Dynamics: Particle Interactionmentioning

confidence: 99%

Internal relaxation time in immersed particulate materials

Rognon¹,

Einav²,

Gay³

2010

Phys. Rev. E

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“…Similarly to the long-wavelength model [3]- [6], the velocity and pressure are developed in asymptotic expansions on the coordinate z = O(ε), that is explained in details in [12] and [9].…”

Section: Modeling Of the Film Dynamicsmentioning

confidence: 99%

“…For the zero order term of the longitudinal velocity and film thickness, a dynamic system is obtained from the Navier-Stokes equations together with the kinematic and dynamic boundary conditions on the interfaces [6], [12], [9]: where u = (u, v) is the longitudinal velocity, ∇ = ∂ ∂ x , ∂ ∂ y is the plane gradient, T = −P + T is the film stress tensor with P = −0.5σ h∇ 2 hI + 0.5(∇h) 2 I − ∇h ⊗ ∇h , as pressure tensor and T = 2µh (∇ · u) I + 0.5 ∇u + (∇u) T as viscous stress tensor, Π is the disjoining pressure and I is the identity tensor.…”

Section: Modeling Of the Film Dynamicsmentioning

confidence: 99%

“…In general, the disjoining pressure is represented as a sum of attractive and repulsive counterparts as discussed in [9]:…”

Section: Modeling Of the Film Dynamicsmentioning

confidence: 99%

“…In the case of a laterally bounded film by a solid boundary, the dynamics of a planar film is studied numerically in [7], [8] and [9]. In the last work, the electrostatic and steric repulsive components are included into the disjoining pressure.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Dynamics and Stability of Free Thin Films

Tabakova¹,

Todorov²,

Christov³

2010

AIP Conference Proceedings

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The modeling of the free thin film dynamics and stability is usually performed in the framework of the extended lubrication approach, including inertial, viscous, capillary and intermolecular van-der-Waals forces. For films with mobile surfaces, this approach leads to a system of nonlinear PDE for the film thickness and lateral velocities. In the present work the 1D variant of this system is studied numerically in the case of a laterally bounded free film by a frame, with a prescribed wetting angle. A linear and non-linear stability analysis of this problem is performed and their results generalize the stability results obtained for periodic free films by other authors. It is shown that the film rupture can be caused either by the non-existence of a static film shape or by the instability of an existing static shape. It is found that the static film shapes are always stable when subjected to symmetrical disturbances, but can be unstable if asymmetrical disturbances are imposed on them. The latter fact depends on the wetting angle in combination with the action of the van-der-Waals attraction and of the surface tension.

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Foamability of aqueous solutions: Role of surfactant type and concentration

Petkova

Tcholakova

Chenkova

et al. 2020

Advances in Colloid and Interface Science

155

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In this paper we study the main surface characteristics which control the foamability of solutions of various surfactants. Systematic series of experiments with anionic, cationic and nonionic surfactants with different head groups and chain lengths are performed in a wide concentration range, from 0.001 mM to 100 mM. The electrolyte (NaCl) concentration is also varied from 0 up to 100 mM. For all surfactants studied, three regions in the dependence of the foamability, V A , on the logarithm of surfactant concentration, lgC S , are observed. In Region 1, V A is very low and depends weakly on C S . In Region 2, V A increases steeply with C S . In Region 3, V A reaches a plateau. To analyse these results, the dynamic and equilibrium surface tensions of the foamed solutions are measured. A key new element in our interpretation of the foaming data is that we use the surface tension measurements to determine the dependence of the main surface properties (surfactant adsorption, surface coverage and surface elasticity) on the surface age of the bubbles. In this way we interpret the results from the foaming tests by considering the properties of the dynamic adsorption layers, formed during foaming. The performed analysis reveals a large qualitative difference between the nonionic and ionic surfactants with respect to their foaming profiles. The data for the nonionic and ionic surfactants merge around two master curves when plotted as a function of the surface coverage, the surface mobility factor, or the Gibbs elasticity of the dynamic adsorption layers. This difference between the ionic and nonionic surfactants is explained with the important contribution of the electrostatic repulsion between the foam film surfaces for the ionic surfactants which stabilizes the dynamic foam films even at moderate surface coverage and at relatively high ionic strength (up to 100 mM). In contrast, the films formed from solutions of nonionic surfactants are stabilized via steric repulsion which becomes sufficiently high to prevent bubble coalescence only at rather high surface coverage (> 90 %) which corresponds to related high Gibbs elasticity (> 150 mN/m) and low surface mobility of the dynamic adsorption layers. Mechanistic explanations of all observed trends are provided and some important similarities and differences with the process of emulsification are outlined.

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Effect of disjoining pressure on the drainage and relaxation dynamics of liquid films with mobile interfaces

Cited by 24 publications

References 48 publications

Internal relaxation time in immersed particulate materials

Internal relaxation time in immersed particulate materials

Dynamics and Stability of Free Thin Films

Foamability of aqueous solutions: Role of surfactant type and concentration

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