Anderson, P.D.

Fischer, P.

Sagis, L.M.C.

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Eur. Phys. J. Special Topics 222, 1–5 (2013)© EDP Sciences, Springer-Verlag 2013DOI: 10.1140/epjst/e2013-01821-4THE EUROPEANPHYSICAL JOURNALSPECIAL TOPICSEditorialDynamics of complex fluid-fluid interfacesExperiments, theory, and simulationL.M.C. Sagis1,2,a, P. Fischer3, and P.D. Anderson4,51 Food Physics Group, Wageningen University, Bomenweg 2, 6703 HD Wageningen,The Netherlands2 Polymer Physics, Department of Materials, ETH Zurich, Wolfgang-Pauli-Str. 10,8093 Zurich, Switzerland3 Institute of Food, Nutrition and Health, ETH Zurich, Schmelzbergstrasse 9, 8092 Zurich,Switzerland4 Department of Mechanical Engineering, Eindhoven University of Technology,5600MB Eindhoven, The Netherlands5 Institute for Complex Molecular Systems, Eindhoven University of Technology,5600MB Eindhoven, The NetherlandsReceived 16 April 2013 / Received in final form 23 April 2013Published online 17 June 2013A complex interface is deﬁned as an interface in which the adsorbed species formmesophases, such as 2d gels, 2d glass phases, 2d dispersions, 2d (liquid) crystallinephases, or 2d composite structures. Such interfacial mesophases can be formed by, forexample, proteins, protein aggregates, protein-polysaccharide complexes, amphiphilicpolymers, mixtures of immiscible lipids, or amphiphilic colloidal particles [1]. Complexinterfaces are found in emulsions for food and personal care applications, vesicles andmicrocapsules for controlled delivery purposes, biological systems such as red bloodcells or lung alveoli, or protective biodegradable coatings. In recent years numer-ous articles have appeared focusing on the determination of dynamic properties ofcomplex ﬂuid-ﬂuid interfaces, and on exploring the eﬀects of those properties on themacroscopic behaviour of multiphase materials [1].In contrast to complex interfaces, simple interfaces are those stabilised by lowmolecular weight surfactants, which do not order in mesophases. Their response toshear deformations tends to be linear even at relatively high deformation rates, and ispredominantly viscous. Simple interfaces often have very low surface shear viscosities( 10−6Ns/m). For multiphase materials with simple interfaces surface tension tendsto be the only surface property with a discernable eﬀect on the macroscopic dynamicbehaviour of the material.For materials with complex ﬂuid-ﬂuid interfaces, additional surface propertiessuch as their surface shear and dilatational moduli, or bending rigidities, may aﬀecttheir dynamic behaviour, and the eﬀect of these properties may even dominate theeﬀects of surface tension. For example, surface shear and dilatational moduli are animportant factor in the stability of foam [2] and emulsions [1,3–6], they aﬀect thea e-mail: leonard.sagis@wur.nl2 The European Physical Journal Special Topicsamplitude of surface waves in free surface ﬂows [7–9] (important in coating ﬂowsor ﬁlm extrusion processes), they inﬂuence the breakup of liquid jets or droplets[10,11], and they aﬀect the wetting behaviour of thin ﬁlms on solid surfaces [12], orthe dynamic behaviour of lung alveoli [13]. The dynamic behaviour of water-in-wateremulsions, such as vesicles and phase-separated biopolymer solutions, is aﬀected bythe bending rigidity [1,14–20] and permeability [20,21] of their interfaces. In contrastto simple interfaces, the response of complex interfaces to a perturbation is oftenhighly nonlinear. This nonlinear response is the result of changes in the structure ofthe interface. Examples of this behaviour are the shear thinning behaviour (a decreasein rheological properties for increasing (rate of) deformation) observed in interfacesstabilised by colloidal particles [22–28]. Similar strain thinning behaviour was alsoobserved in interfaces stabilised by protein ﬁbrils [29]. Some of these ﬁbrils appearto have the ability to form liquid crystalline phases, after adsorption at the interface[29–33]. Above their isoelectric point they are negatively charged and can be cross-linked by divalent ions [34], so they also have the potential to form highly cross-linkedisotropic elastic networks at interfaces. When interfaces, stabilised by either a liquidcrystalline phase or an isotropic network of these ﬁbrils, are deformed in a surfaceshear experiment, the ﬁbrils tend to align with the direction of ﬂow, reducing thesurface shear properties.The determination of surface properties of complex ﬂuid-ﬂuid interfaces (in par-ticular the surface rheological ones), and the modelling of their eﬀect on the dynamicbehaviour of multiphase materials is the main focus of this issue. Javadi et al. [35]discuss recent advances in the characterisation of dilatational rheological propertiesof interfaces using bubble pressure, drop proﬁle, and capillary pressure tensiometry.One of the issues raised by Javadi et al. [35] at the end of their contribution is theproper generalisation of the Young-Laplace equation typically used for the analysisof tensiometry experiments, to dynamic conditions. The contribution by Sagis [36]discusses how such generalisations can be derived within the framework of non-equilibrium thermodynamics.In droplet or bubble based oscillatory tensiometry methods the surface dilata-tional modulus is usually expressed in terms of a dynamic surface tension, and theusefulness of this concept is discussed by Sagis [37], based on an analysis of the gen-eralised surface momentum balance. This analysis shows that for complex interfacesthe response to a deformation contains not only contributions from changes in surfacetension, but may also include contributions from in-plane and out-of-plane deviatoricstresses, inertial stresses, and contributions from the bending rigidity of the inter-face. For establishing the dominant contributions in the response a testing protocolis suggested, which includes frequency, amplitude, and droplet radius variations.In their contribution Ru¨hs et al. [38] discuss how mass transfer can interfere withthe determination of surface rheological properties, of interfaces stabilised by globularprotein monomers, and protein ﬁbrils. In a follow-up discussion Sagis et al. [39] discusshow deformations of elastic membranes can induce adsorption of globular proteins atthe interface. Both papers are illustrations of the coupling of in-plane momentumtransfer and mass transfer between the interface and the adjoining bulk phases, oftenobserved in complex interfaces. Suggestions on how to deal with this coupling on anexperimental as well as theoretical level are provided in both contributions.The issue continues with a contribution by Fischer [40], with an overview of recentexperiments on surface rheological characterisation of interfaces stabilised by mixturesof proteins and polysaccharides. In spite of their practical relevance (such mixturesare for example frequently encountered in food emulsions or foam) such interfaceshave received relatively little attention in the literature.In their contribution Verwijlen et al. [41] discuss a novel geometry that can bemounted on a rotational rheometer, and can be used to determine surface dilatationalCharacterization of Complex Fluid-Fluid Interfaces 3properties. This geometry (a variation of the double-wall-ring geometry [11,42], orig-inally developed for the determination of surface shear properties) subjects the inter-face to a mixed ﬂow ﬁeld, and can be used as an alternative to tensiometric methods.Advantages and limitations of this new geometry are discussed [41].In their response to a deformation complex ﬂuid-ﬂuid interfaces share many com-monalities with viscoelastic bulk phases. The surface shear and dilatational moduliare basically the 2d equivalents of the shear and bulk modulus of a three dimen-sional bulk phase. It is a well-known fact that in bulk phases shear deformations cangenerate normal stresses (the ﬁrst and second normal stress diﬀerence). A recentlydeveloped constitutive model for the extra stress tensor of an interface stabilised byrod-like particles [43,44], predicts the existence of normal stresses also for interfacessubjected to shear deformations. These stresses are in-plane, perpendicular to thedirection of ﬂow. The existence of such normal stresses has so far not been conﬁrmedby experiments, and the contribution by Sagis [45] suggests a possible experimen-tal setup for measuring these stresses, combining a shear band device mounted in aLangmuir trough, with a nano-force transducer.As we noted earlier in this paper, complex interfaces often have a highly nonlinearresponse to deformations, even at low deformation (rates). There are however very fewconstitutive equations available in the literature, capable of describing this nonlinearbehavior properly [1]. In his contribution Sagis [46] discusses the derivation of suchequations within the framework of nonequilibrium thermodynamics (NET). Severalframeworks are reviewed (classical irreversible thermodynamics, extended irreversiblethermodynamics, extended rational thermodynamics, and GENERIC) with respectto the type of constitutive models that can be constructed within these frameworks,and advantages and limitations of each of the frameworks are discussed. Emphasisis on the derivation of structural models, i.e. models in which the response of aninterface to an applied deformation is linked directly to the time evolution of itsmicrostructure (described by one or more structural variables, of a scalar, vectorial,or tensorial nature). Structural models have been used widely and successfully inmodelling the nonlinear rheology of complex bulk phases, such as polymer melts andsolutions, liquid crystalline phases, or biopolymer solutions [47–49]. For modellinginterfacial behaviour only a few examples of such models currently exist [50–54].The next two contributions in this issue discuss the use of mesoscopic nonequilib-rium thermodynamics (MNET) to model transfer processes in complex multiphasematerials. Santamaria et al. [55] discuss the use of MNET for modelling diﬀusionand adsorption processes in porous materials with narrow irregularly shaped pores.Lervik and Kjelstrup [56] apply MNET to modelling active transport of calcium ionsthrough cell walls.The contribution by Glavatskiy and Bedeaux [57] discusses the validity of the localequilibrium assumption for interfaces in multiphase materials, by comparing a macro-scopic description of such materials that incorporates surface excess densities, with alocal nonequilibrium square gradient model. They show that these two descriptionsare consistent, which justiﬁes treating the interface as a separate thermodynamic sys-tem in local equilibrium with its surroundings. This assumption forms the basis ofmany NET descriptions for multiphase materials.The ﬁnal three contributions to this issue discuss numerical methods to simulatethe dynamics of multiphase materials with complex interfaces. Kru¨ger et al. [58] dis-cuss hybrid simulation methods that combine a lattice Boltzmann solver for the ﬂowin the bulk phases with, for example, an immersed boundary method (applied to thesimulation of vesicles and capsules), or a molecular dynamics algorithm (applied tothe simulation of interfaces stabilised by nanoparticles). Park et al. [59] discuss simu-lations of the behaviour of droplets stabilised by insoluble surfactants in microﬂuidicsdevices, using a diﬀuse-interface method, in which the Navier-Stokes/Cahn-Hilliard4 The European Physical Journal Special Topicsequations and a surfactant conservation equation are solved by a ﬁnite elementmethod, along with a grid deformation method. The issue closes with a contributionby Gross and Reusken [60] who discuss simulations of multiphase problems based onsharp-interface methods, and illustrate these methods for rising droplets with a cleaninterface model, and spherical droplets in a Poisseuille ﬂow with a Boussinesq-Scriveninterface model.To summarise, the collection of papers presented in this issue cover recent advancesin the areas of experimental characterisation, theoretical modelling, and simulation ofthe dynamic behaviour of complex ﬂuid-ﬂuid interfaces. Some pertinent issues of thisﬁeld have been addressed (such as how to deal with the highly nonlinear response ofinterfaces to an applied deformation, or the coupling of in-plane momentum transferwith mass transfer between the bulk phase and interface), and solutions for thesewere suggested. We believe the ﬁeld of surface dynamics will greatly beneﬁt from acloser integration of experiments, theory, and simulation work.References1. L.M.C. Sagis, Rev. Mod. Phys. 83, 1367 (2011)2. R. Prud’homme, S. Khan, eds., Foams: Theory, Measurements, Applications (MarcelDekker, New York, 1996)3. M.A. Bos, T. van Vliet, Adv. Colloid Interface Sci. 91, 37 (2001)4. B.S. Murray, Curr. Opinion Colloid Interface Sci. 7, 426 (2002)5. P. Fischer, P. Erni, Curr. Opinion Colloid Interface Sci. 12, 196 (2007)6. P. Erni, H.A. Jerri, K. Wong, A. Parker, Soft Matter 8, 6958 (2012)7. T.F. Swean, Appl. Mech. Rev. 47, S173 (1994)8. Z.D. Chen, X.D. Chen, J.J.J. Chen, Chem. Eng. Sci. 52, 3265 (1997)9. F. Monroy, F. Ortega, R.G. Rubio, M.G. Velarde, Adv. Colloid Interface Sci. 134-135,175 (2007)10. D.B. Jones, A.P.J. Middelberg, AIChE J. 49, 1533 (2003)11. O. Regev, S. Vandebril, E. Zussman, C. Clasen, Polymer 51, 2611 (2010)12. D.A. Edwards, A. Oron, J. Fluid. Mech. 298, 287 (1995)13. S.M.I. Saad, A.W. Neumann, E.J. Acosta, Colloids Surfaces A 354, 34 (2010)14. J.B.A.F. Smeulders, C. Blom, J. Mellema, Phys. Rev. A. 42, 3483 (1990)15. J.B.A.F. Smeulders, C. Blom, J. Mellema, Phys. Rev. A. 46, 7708 (1992)16. K.H. de Haas, G.J. Ruiter, J. Mellema, Phys. Rev. E 52, 1891 (1995)17. E. Scholten, L.M.C. Sagis, E. van der Linden, J. Phys. Chem. B 108, 12164 (2004)18. E. Scholten, L.M.C. Sagis, E. van der Linden, Macromolecules 38, 3515 (2005)19. E. Scholten, L.M.C. Sagis, E. van der Linden, J. Phys. Chem. B 110, 3250 (2006)20. L.M.C. Sagis, J. Controlled Release 131, 5 (2008)21. E. Scholten, J. Sprakel, L.M.C. Sagis, E. van der Linden, Biomacromolecules 7, 339(2006)22. S. Reynaert, P. Moldenaers, J. Vermant, Phys. Chem. Chem. Phys. 9, 6463 (2007)23. K. Masschaele, J. Fransaer, J. Vermant, J. Rheol. 53, 1437 (2009)24. F. Ravera, E. Santini, G. Loglio, M. Ferrari, L. Liggieri, J. Phys. Chem. B 110, 19543(2006)25. F. Ravera, M. Ferrari, L. Liggieri, G. Loglio, E. Santini, A. Zanobini, Colloids SurfacesA 323, 99 (2008)26. P.F. Noble, O.J. Cayre, R.G. Alargova, O.D. Velev, V. Paunov, J. Am. Chem. Soc. 126,8092 (2004)27. B. Madivala, J. Fransaer, J. Vermant, Langmuir 25, 2718 (2009)28. M.G. Basavaraj, G.G. Fuller, J. Fransaer, J. Vermant, Langmuir 22, 6605 (2006)29. N.K. Humblet-Hua, E. van der Linden, L.M.C. Sagis, Soft Matter 9, 2154 (2013)30. J.M. Jung, R. Mezzenga, Langmuir 26, 504 (2009)31. J. Jung, D.Z. Gunes, R. Mezzenga, Langmuir 26, 15366 (2010)Characterization of Complex Fluid-Fluid Interfaces 532. L. Isa, J. Jung, R. Mezzenga, Soft Matter 7, 8127 (2011)33. O.G. Jones, R. Mezzenga, Soft Matter 8, 876 (2012)34. S.G. Bolder, H. Hendrickx, L.M.C. Sagis, E. van der Linden, Appl. Rheol. 16, 258 (2006)35. A. Javadi, N. Mucic, M. Karbaschi, J. Won, M. Lotfi, A. Dan, V. Ulaganathan,G. Gochev, A. Makievski, V. Kovalchuk, et al., Eur. Phys. J. Special Topics 222, 7(2013)36. L.M.C. Sagis, Eur. Phys. J. Special Topics 222, 31 (2013)37. L.M.C. Sagis, Eur. Phys. J. Special Topics 222, 39 (2013)38. P.A. Ru¨hs, N. Scheuble, E.J. Windhab, P. Fischer, Eur. Phys. J. Special Topics 222, 47(2013)39. L.M.C. Sagis, et al., Eur. Phys. J. Special Topics 222, 61 (2013)40. P. Fischer, Eur. Phys. J. Special Topics 222, 73 (2013)41. T. Verwijlen, P. Moldenaers, J. Vermant, Eur. Phys. J. Special Topics 222, 83 (2013)42. S. Vandebril, A. Franck, G.G. Fuller, P. Moldenaers, J. Vermant, Rheologica Acta 49,131 (2010)43. L.M.C. Sagis, H.C. O¨ttinger (submitted) (2013)44. L.M.C. Sagis (submitted) (2013)45. L.M.C. Sagis, Eur. Phys. J. Special Topics 222, 99 (2013)46. L.M.C. Sagis, Eur. Phys. J. Special Topics 222, 105 (2013)47. R.G. Larson, The Structure and Rheology of Complex Fluids (Oxford University Press,Oxford, 1999)48. H.C. O¨ttinger, Beyond Equilibrium Thermodynamics (Wiley-Intersience, Hoboken,2005)49. L.M.C. Sagis, M. Ramaekers, E. van der Linden, Phys. Rev. E 63, 051504 (2001)50. A.D. Rey, Rheol. Acta 39, 13 (2000)51. A.D. Rey, Macromol. Theory Simul. 9, 156 (2000)52. A.D. Rey, Eur. Phys. J. 2, 169 (2000)53. E.S. Oh, D.C. Lagoudas, J.C. Slattery, Phil. Mag. 85, 2249 (2005)54. L.M.C. Sagis, Soft Matter 17, 7727 (2011)55. I. Santamaria-Holek, Z.J. Grzywna, J.M. Rubi, Eur. Phys. J. Special Topics 222, 129(2013)56. A. Lervik, S. Kjelstrup, Eur. Phys. J. Special Topics 222, 143 (2013)57. K. Glavatskiy, D. Bedeaux, Eur. Phys. J. Special Topics 222, 161 (2013)58. T. Kru¨ger, S. Frijters, F. Gu¨nther, B. Kaoui, J. Harting, Eur. Phys. J. Special Topics222, 177 (2013)59. J.M. Park, M.A. Hulsen, P.D. Anderson, Eur. Phys. J. Special Topics 222, 199 (2013)60. S. Gross, A. Reusken, Eur. Phys. J. Special Topics 222, 211 (2013)

Dynamics of complex fluid-fluid interfaces: Experiments, theory, and simulation

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Dynamics of complex fluid-fluid interfaces: Experiments, theory, and simulation

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