Dynamics, structure, and function of interfacial regions

Mann, J. Adin

doi:10.1021/la00061a002

Cited by 34 publications

(9 citation statements)

References 3 publications

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“…Each fluid can be characterized by a set of visco-elastic parameters, in direct analogy with the three-dimensional case (Goodrich 1981;Gaines Jr 1966;Mann Jr 1985;Mann Jr, Crouser & Meyer 2001). The net attraction between film molecules, in the neighbourhood of the interface, leads to a line tension, or energy per unit length, λ, associated with the boundary between domains.…”

Section: Langmuir Films and Line Tensionmentioning

confidence: 99%

Domain relaxation in Langmuir films

et al. 2007

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We report on theoretical studies of molecularly thin Langmuir films on the surface of a quiescent subfluid and qualitatively compare the results to both new and previous experiments. The film covers the entire fluid surface, but domains of different phases are observed. In the absence of external forcing, the compact domains tend to relax to circles, driven by a line tension at the phase boundaries. When stretched (by a transient applied stagnation-point flow or by stirring), a compact domain elongates, creating a bola consisting of two roughly circular reservoirs connected by a thin tether. This shape will then relax slowly to the minimum-energy configuration of a circular domain. The tether is never observed to rupture, even when it is more than a hundred times as long as it is wide. We model these experiments by taking previous descriptions of the full hydrodynamics, identifying the dominant effects via dimensional analysis, and reducing the system to a more tractable form. The result is a free boundary problem for an inviscid Langmuir film whose motion is driven by the line tension of the domain and damped by the viscosity of the subfluid. Using this model we derive relaxation rates for perturbations of a uniform strip and a circular patch. We also derive a boundary integral formulation which allows an efficient numerical solution of the problem. Numerically this model replicates the formation of a bola and the subsequent relaxation observed in the experiments. Finally, we suggest physical properties of the system (such as line tension) that can be deduced by comparison of the theory and numerical simulations to the experiment. Two movies are available with the online version of the paper. IntroductionIn this paper we develop a manageable model of the experimentally observed relaxation dynamics of a molecularly thin film with two fluid phases at an air/water interface. Our model refines previous work and is motivated by experimental observations. It is both analytically tractable and allows an efficient, accurate and stable numerical solution via a boundary integral technique. The model explains some observed experimental phenomena and in particular offers a more general method for measuring the line tension of the film. We neglect long-range electrostatic effects, which could be added in a straightforward manner at a later time, as well as viscosity and compressibility within the film. These approximations are reasonable for a wide but not universal range of experimental conditions, as discussed below.

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Section: Langmuir Films and Line Tensionmentioning

confidence: 99%

Domain relaxation in Langmuir films

et al. 2007

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“…2.2 SURFACE PROPERTIES. -By analogy with the three-dimensional case, e corresponds, for isotropic strain, to the modulus of hydrostatic compression in the plane of the film (K), whereas for uniaxial strain it also involves [30] the corresponding shear modulus (S ) :…”

Section: Capillary Waves -Capillary Modes Arementioning

confidence: 99%

Viscoelastic relaxation of insoluble monomolecular films

1988

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Glycerol mono-oleate monolayers at the air-water interface have been investigated by quasielastic light scattering from thermally excited capillary waves over a wide range of wave numbers. Using a relatively novel data analysis procedure four surface viscoelastic properties were deduced ab initio from the light scattering data : surface elastic moduli and viscosities governing shear normal to the monolayer (≡ tension) and dilation in the film plane. The tension and dilational modulus were compared with classical, equilibrium values in the first rigorous comparison of its kind. Various effects suggested that the two moduli were affected by rather different relaxation processes : discrepancies between the light scattering and equilibrium values of the two elastic moduli occurred in different states of the monolayer, and the two surface viscosities (both zero for the clean subphase) behaved very differently on monolayer compression. These effects were observed to be frequency dependent. In the fully compressed monolayer state the transverse shear modulus was characterised by an exponential relaxation, of time scale ∼ 9 μs. This relaxation time fell exponentially on monolayer expansion, reaching 100 ns for molecular areas ∼ 60 Å 2. Slower processes than these were rigorously excluded. The dilational modulus was generally less well determined than that affecting transverse shear. However in the expanded monolayer state, the data sufficed to demonstrate much slower relaxation, τ ∼ 290 μs. Possible molecular mechanisms are briefly discussed

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“…The amphiphilic nature and rich two-dimensional phase properties of phospholipids allow convenient assembly of well-ordered monomolecular films at interfaces. There is currently much interest in understanding the molecular interaction in organized, oriented membrane model systems . In particular, the formation of domain structures within phospholipid monolayers has been an area of intense study,1b because domain formation implies lateral phase separation and partitioning of membrane function within microdomains of a defined structure.…”

Section: Introductionmentioning

confidence: 99%

Scanning Electrochemical Microscopy Studies of Electron Transfer through Monolayers Containing Conjugated Species at the Liquid−Liquid Interface

1998

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The rates of electron transfer (ET) between two redox species through a monolayer of saturated dipalmytoyl phosphocholine and polyconjugated 2(3-(diphenylhexatrienyl)propanoyl)-1-hexadecanoyl-sn-glycero-3phosphocholine phospholipids adsorbed at the interface of two immiscible electrolyte solutions (ITIES) were measured by scanning electrochemical microscopy. Comparison of the ET rates shows that addition of phospholipids with conjugated hydrocarbon chains increases the ET rate by at least a factor of 2 compared to films with only saturated hydrocarbon chains. This difference was sufficiently high to obtain information about distribution of lipid molecules in monolayers formed by mixing two lipids. Lateral scanning of an ultramicroelectrode tip across the lipid monolayer comprised of two different phospholipids showed that each lipid forms microsize domains. The rate of ET across a monolayer of lipid adsorbed at the ITIES was also probed as a function of temperature. A sharp decrease in ET rate with temperature suggests a phase transition of the hydrocarbon chains of the lipid molecules. The phase transition increases the ET distance between the two redox centers with a resultant decrease in ET rate.

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Dynamics, structure, and function of interfacial regions

Cited by 34 publications

References 3 publications

Domain relaxation in Langmuir films

Domain relaxation in Langmuir films

Viscoelastic relaxation of insoluble monomolecular films

Scanning Electrochemical Microscopy Studies of Electron Transfer through Monolayers Containing Conjugated Species at the Liquid−Liquid Interface

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