Analysis of the magnetic rod interfacial stress rheometer

Reynaert, Sven; Brooks, Carlton F.; Moldenaers, Paula; Vermant, Jan; Fuller, Gerald G.

doi:10.1122/1.2798238

Cited by 149 publications

(189 citation statements)

References 29 publications

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“…Careful inspection of the data from the lowest thickness (d<50 m) however shows a small deviation which can be ascribed to the drag due to the water subphase, which becomes comparable to that of the film when this becomes too thin. This effect has already been found and discussed in the literature [16]. If we suppose, in a simple approximation, a linear superposition of these effects, a rough estimate of the subphase drag is obtained: |G| sub =10 N/m, a value fully consistent with the accuracy previously obtained from the analysis of G'.…”

Section: Rheometer Calibrationsupporting

confidence: 86%

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Equilibrium and out-of-equilibrium dynamics in a molecular layer of azopolymer floating on water studied by Interfacial Shear Rheology

Orsi

Cristofolini

Fontana

2011

Journal of Non-Crystalline Solids

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Abstract:We report the details of the construction and calibration of an ultra sensitive surface rheometer, inspired by the setup described in [C.F. Brooks et al Langmuir 15, 2450], which makes use of high resolution video tracking of the motion of a floating magnetized needle and is capable of measuring the viscoelastic response of a Langmuir monolayer with an accuracy of 10 -5 N/m. This instrument is then employed for the rheological characterization of a Langmuir monolayer of a photosensitive azobenzene polymer, which can be brought out of equilibrium by a suitable photoperturbation. The complex dynamic shear modulus G= G' + i G" is measured as a function of temperature and illumination power and wavelength. The reversible rheological ch anges induced in the film by photo-perturbation are monitored during time, observing a transition from a predominantly elastic (G' > G'') to a viscoelastic (G' ≈ G'') regime. These results are confirmed by comparison with independent measurements performed by us using other rheological techniques. Finally a discussion is made, taking into account the results of a recent x-ray photon correlation spectroscopy experiment on the same polymer in equilibrium and out of equilibrium.

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Section: Rheometer Calibrationsupporting

confidence: 86%

“…The results could be modelled as the response of a forced-damped oscillator of mass m, spring constant k and damping constant d, in analogy with [16]. …”

Section: Design Of the Instrumentmentioning

confidence: 99%

Equilibrium and out-of-equilibrium dynamics in a molecular layer of azopolymer floating on water studied by Interfacial Shear Rheology

Orsi

Cristofolini

Fontana

2011

Journal of Non-Crystalline Solids

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“…5). This viscometer is one of the most sensitive instruments for measuring interfacial shear rheological parameters (21) and is capable of measuring surface shear moduli in a wide range of values (22). The prime feature of this rheometer is its long magnetic needle floating at the interface, which is moved by an external magnetic field (15,22,23).…”

Section: Shear Measuring Techniquesmentioning

confidence: 99%

Interfacial rheology: An overview of measuring techniques and its role in dispersions and electrospinning

Pelipenko¹,

Kristl²,

Rošic³

et al. 2012

Acta Pharmaceutica

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Colloidal disperse systems represent the increasing number of modern delivery systems whose primary characteristic, a large interfacial area, causes thermodynamic instability. Therefore, the foremost challenge in dispersion design is the reduction of interface instability and an understanding of the behaviour of interfaces. Interfacial rheology is one of the most powerful tools for observing occurrences at the interphase. As previously mentioned, the stability of such systems is provided by the formation of a stable interfacial layer of surfactants around each dispersible particle. The stability of these systems can be improved by using more than one surfactant, but it must be kept in mind that different surfactants can have varying mechanisms of stabilisation, some of which can be mutually incompatible. Surfactant selection is therefore crucial and must be based on physicochemical properties, stability of the interfacial film, mobility of the molecules in the interfacial film, HLB, film formation kinetics, compatibility and interactions between molecules on the surface, CMC, etc. Interfacial rheological properties have yet to be thoroughly explored. Only recently, methods have been introduced that provide sufficient sensitivity to reliably determine viscoelastic interfacial properties. In general, interfacial rheology describes the relationship between the deformation of an interface and the stresses exerted on it.Due to the variety in deformations of the interfacial layer (shear and expansions or compressions), the field of interfacial rheology is divided into the subcategories of shear and dilatational rheology. While shear rheology is primarily linked to the long-term stability of dispersions, dilatational rheology provides information regarding short-term stability. Interfacial rheological characteristics become relevant in systems with large interfacial areas, such as emulsions and foams, and in processes that lead to a large increase in the interfacial area, such as electrospinning of nanofibers.

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“…A comprehensive theoretical analysis of this type of devices and a detailed experimental study of its range of applicability have been reported in [51].…”

Section: Methods Of Shear Rheologymentioning

confidence: 99%

Methods of measuring rheological properties of interfacial layers (Experimental methods of 2D rheology)

2009

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-Current methods of studying the rheological properties of interfacial layers at the interfaces of fluids are reviewed. This area of research includes two-dimensional 2D rheology. Regardless of the similarities between the parameters of rheological properties of two-dimensional and bulk (three-dimensional) systems, when measuring surface properties, it is necessary to reformulate the main experimental methods to allow for the different dimensions of surface and bulk characteristics of material. Parameters of shear and dilational (measured upon expansion-compression) properties of interfacial layers are distinguished, and the latter are considered to be independent parameters of a system. The most attention was given to the rotational methods of measuring shear viscosity and the components of the complex 2D elastic modulus, as well as to measuring surface tension upon harmonic changes of the bubble (droplet) surface area, which allows characteristics of the dilational behavior of thin liquid films to be determined. Both groups of methods are widely used in laboratory practice and realized in the form of a number of original and commercial instruments. Dilational measurements of interfacial layers can also be performed with oscillations of a movable barrier on a Langmuir trough. In addition, methods based on the propagation of capillary waves across the surface of a liquid, as well as rarer methods of capillary flow in thin channels forced by either a surface tension gradient or the motion of the interface, are considered.

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Analysis of the magnetic rod interfacial stress rheometer

Cited by 149 publications

References 29 publications

Equilibrium and out-of-equilibrium dynamics in a molecular layer of azopolymer floating on water studied by Interfacial Shear Rheology

Equilibrium and out-of-equilibrium dynamics in a molecular layer of azopolymer floating on water studied by Interfacial Shear Rheology

Interfacial rheology: An overview of measuring techniques and its role in dispersions and electrospinning

Methods of measuring rheological properties of interfacial layers (Experimental methods of 2D rheology)

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