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We investigate the flow of viscous interfaces carrying an insoluble surface active material, using numerical methods to shed light on the complex interplay between Marangoni stresses, compressibility, and surface shear and dilatational viscosities. We find quantitative relations between the drag on a particle and interfacial properties as they are required in microrheology, i.e., going beyond the asymptotic limits. To this end, we move a spherical particle probe at constant tangential velocity, symmetrically immersed at either the incompressible or compressible interface, in the presence and absence of surfactants, for a wide range of system parameters. A full three-dimensional finite element calculation is used to reveal the intimate coupling between the bulk and interfacial flows and the subtle effects of the different physical effects on the mixed-type velocity field that affects the drag coefficient, both in the bulk and at the interface. For an inviscid interface, the directed motion of the particle leads to a gradient in the concentration of the surface active species, which in turn drives a Marangoni flow in the opposite direction, giving rise to a force exerted on the particle. We show that the drag coefficient at incompressible interfaces is independent of the origin of the incompressibility (dilatational viscosity, Marangoni effects or a combination of both) and that its higher value can not only be related to the Marangoni effects, as suggested earlier. In confined flows, we show how the interface shear viscosity suppresses the vortex at the interface, generates a uniform flow, and consequently increases the interface compressibility and the Marangoni force on the particle. We mention available experimental data and provide analytical approximations for the drag coefficient that can be used to extract surface viscosities. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including suspension mechanics, foams and pastes' mixtures, and nonlinear viscoelasticity.

An antibubble is a liquid droplet wrapped by a thin layer of gas, inside a bulk liquid usually of the same composition. The lifetime of an antibubble is governed by the drainage of the gas between the two liquid-gas interfaces populated by surfactants. Depending on the relative magnitude of surface viscosity and elastic moduli, which directly depend on or are determined by the nature of surfactants, the lifetime of an antibubble may vary a lot, from few seconds to few minutes. While such a difference can be predicted with models that include the role of interfacial properties, they were not observed experimentally in previous studies, due to important sources of dispersion. In this review, the main sources of dispersion are identified, such as (i) the initial amount of gas embedded in the antibubble, (ii) the level of saturation of gas in the bulk liquid, (iii) the presence of dust particles (<0.5 μm) in the gas, and (iv) three-dimensional flow effects. By accounting for these various effects, we obtain a coherent view on the lifetime of an antibubble, as a function of its radius and the surface rheology, with excellent consistency between experiments and modeling. Results thus demonstrate that controlling the size and lifetime of antibubbles is achievable. Unlabelled Image • Surface elasticity plays a dominant role in antibubble lifetime for small surfactant molecules; • Above a threshold, the lifetime is almost independent on the bulk concentration of surfactants; • Accounting precisely for gas dissolution in the liquid is crucial to obtain qualitative agreement with modeling. • The antibubble lifetime increases with the radius; • In controlled conditions, the antibubble collapse is shown to be a deterministic process; [ABSTRACT FROM AUTHOR]

The article focuses on the study by P. J. Yunker and colleagues, which proposes particle-shape effects for building particle network between air and water interface to prevent coffee-ring effect. It says that the proposed method raises interfacial viscosity; thus, hinders suspended particles to reach the drop edge. The study also shows the significance of shape and surface tensions and the addition of little ellipsoids in suspension of spheres to prevent ellipsoidal particles and ring formation.

Capacitance measurements provide unique insights into the thickness, compressibility, and composition of large-area membrane bilayers and are used here in addition to demonstrate the successful incorporation of model ion channels. The simultaneous ability to control the bilayer size, manipulate tension, and optically monitor and electrically stimulate freestanding membranes enables precise determination of their specific capacitance and thickness across a wide range of areas. We confirm that membranes formed by this recently developed technique have capacitive properties similar to those formed by existing protocols, including solvent-free approaches, and discuss the effect using either hexadecane or squalene as the oil solvent. The results obtained here are relevant for other methods where lipid membranes are reconstituted from a bulk oil solvent. Because biological membranes have a diverse phospholipid profile, we show that the technique can successfully reconstitute membranes with binary composition mixtures. As an outlook, we show the capability of model membrane proteins, specifically α-hemolysin and alamethicin, to be incorporated into the formed bilayers and measure ion transport. [ABSTRACT FROM AUTHOR]

Drop-shape analysis using pendant or sessile drops is a well-established experimental technique for measuring the interfacial or surface tension, and changes thereof. The method relies on deforming a drop by either gravity or buoyancy and fitting the Young–Laplace equation to the drop shape. Alternatively one can prescribe the shape and measure the pressure inside the drop or bubble using pressure tensiometry. However, when an interface with a complex microstructure is present, extra and anisotropic interfacial stresses may develop due to lateral interactions between the surface-active moieties, leading to deviations of the drop shape or even a wrinkling of the interface. To extract surface-material properties of these complex interfaces using drop-shape analysis or pressure tensiometry, the Young–Laplace law needs to be generalized in order to account for the extra and anisotropic stresses at the interface. In the present work, we review the different approaches that have been proposed to date to extract the surface tension as the thermodynamic state variable, as well as other rheological material properties such as the compression and the shear modulus. To evaluate the intrinsic performance of the methods, computer generated drops are subjected to step-area changes and then subjected to analysis using the different methods. Shape-fitting methods, now combined with an adequate constitutive method, do however perform rather poorly in determining the elastic stresses, especially at small area strains. An additional measurement o f the pressure or capillary-pressure tensiometry is required to improve the sensitivity. However, pressure-based methods still require the knowledge of the undeformed reference state, which may be difficult to achieve in practice. Moreover, it is not straightforward to judge from what point onwards one needs to go beyond the Young–Laplace equation. To overcome these limitations, a method based on stress fitting, which uses a local force balance method, is introduced here. One aspect of this new method is the use of the Chebyshev transform to numerically describe the contour shape of the drop interface. For all methods we present a detailed error analysis to evaluate if, and with what precision, surface material parameters can be extracted. Depending on the desired information, different ideal experimental conditions and most suitable methods are discussed, in addition to having a criterion to investigate if extra and anisotropic stresses matter. [ABSTRACT FROM AUTHOR]

Interfacial rheological properties play a key role in the stability of a wide range of high-interface materials and thin films. For many systems, it is desirable to understand the response of the interface to a change of composition in the surrounding bulk phases. Stimuli, such as changes in pH or electrolyte concentration, can have a major effect on the structure and properties of the interfacial layer, or induce adsorption and desorption phenomena. Shear rheology is a particularly sensitive measure of such changes, as it only probes the extra stresses in the interface, regardless of possible variations in interfacial tension. In the present work, a widely used geometry for interfacial rheometry, the double-wall ring, is modified to enable subphase exchanges. The trade-off between the speed of exchange and the stress exerted by the flow in the subphase onto the interface is carefully considered. The optimal geometrical design is found by employing Computational Fluid Dynamics (CFD). A geometry with inlets positioned at the bottom and outlets near the interface minimizes the mixing time. Experiments on interfaces with colloidal particles and proteins, subjected to changes in electrolyte concentration and pH, respectively, are used to evaluate the performance of the setup. [ABSTRACT FROM AUTHOR]

The destabilization, fragmentation, and atomization of thin fluid sheets governs processes such as the aerosolization of sneeze ejecta, agrochemical spraying, and fuel injection in liquid rocket engines. Although the evolution, stability, and breakup of fluid sheets composed of a Newtonian liquid has been extensively studied, the morphology and dynamics of viscoelastic fluid sheets remains poorly understood. This manuscript provides a theoretical and numerical framework that integrates the effects of fluid elasticity, surface tension, inertia, and viscosity to predict the morphology, velocity, and stress within stable fluid sheets composed of viscoelastic fluids as a function of the dimensionless Weber, Reynolds, and Weissenberg numbers. We find a non-monotonic behavior in the sheet's size, velocity, and stress distribution as a function of the ratio between the Weissenberg and the Weber numbers. In particular, a minimum in the sheet's size and a maximum in the stress occur when such a ratio is of the order of unity. We interpret these results as the consequence of the competing effects of the growth-favoring inertia and the restoring elastic forces acting within the sheet. • We study the dynamics of viscoelastic liquid sheets formed by two impinging jets. • Three dimensionless groups: Weber (W e), Reynolds (R e), and Weissenberg (W i) numbers. • Viscosity, elasticity, inertia, and capillarity are quantified by W e , R e , and W i. • A set of governing equations is developed and solved in terms of W e , R e , and W i. • A non-monotonicity in sheet size and stress is revealed for W i / W e ∼ 1. • The non-monotonicity represents a departure from Newtonian behavior. • At W i / W e ∼ 1, sheets also encounter a maximum in the extensional stress. • W i / W e is the ratio between the fluid relaxation time and the process timescale. • Large W e and low R e induce larger non-monotonicities. [ABSTRACT FROM AUTHOR]

The hydrodynamics of thin films is an important factor when it comes to the stability and rheology of multiphasic materials, such as foams, emulsions, and polymer blends. However, there have so far been only limited experimental studies addressing the dynamics of individual free-standing thin films at conditions similar to those encountered on macroscopic scales. In this article, we study a well-characterized system of a water-in-oil emulsion stabilized by a non-ionic surfactant (SPAN80) close to its CMC. We employ a dynamic thin film balance, to study the dynamics of freestanding films under both constant and time-varied pressure drops. We compare with the recently published results of Narayan et al. (2020) on colliding droplets of the same system with a hydrodynamic microfluidic trap, and show for the first time that agreement between the two lengthscales is possible, which indicates that the coalescence is indeed dominated by the dynamics in the film. We then address the scatter in the coalescence times and show that it can be affected by extrinsic factors, as well as by variations in the collision angle. Finally, we discuss the difficulties of extracting insight on the coalescence mechanism from coalescence time distributions when different effects such as impurities, small pressure variations, collision angle variations, and possible Marangoni-related instabilities are at play. [ABSTRACT FROM AUTHOR]

An analysis of the interfacial behaviour of two alternative protein derivatives with high solubility has been carried out at two different pH values (2 and 8). The protein derivatives (protein content higher than 50 wt.%) have a globular protein fraction mainly consisting of sarcoplasmic proteins (CFS); and a protein hydrolysate, (CFH), both obtained from crayfish surpluses. The physicochemical characterisation included protein solubility (higher than 80%) and surface charge as well as chemical analysis (elementary, sulfhydryl and disulphide groups). This was complemented with an interfacial characterization included measuring the surface pressure and surface dilatational measurements with a drop tensiometer, and interfacial shear rheology measurements performed using a double-wall-ring geometry. Whereas both types of protein derivative have significant interfacial activity (surface pressure between 20 and 40 mN/m), the difference in their behaviour is small In contrast, a strong influence of pH on the interfacial behaviour has been found for both soluble protein fractions. At pH 2, globular sarcoplasmic protein fraction yields lower surface pressures but highly viscoelastic interfaces, with 2D gel-like behaviour. At pH 8, on the other hand, CF proteins form quite rigid and more brittle interfaces, being resistant to dilatational deformations and showing high sensitivity to shear. [ABSTRACT FROM AUTHOR]

Understanding the interfacial structure–property relationship of complex fluid–fluid interfaces is increasingly important for guiding the formulation of systems with targeted interfacial properties, such as those found in multiphase complex fluids, biological systems, biopharmaceuticals formulations, and many consumer products. Mixed interfacial flow fields, typical of classical Langmuir trough experiments, introduce a complex interfacial flow history that complicates the study of interfacial properties of complex fluid interfaces. In this article, we describe the design, implementation, and validation of a new instrument capable of independent application of controlled interfacial dilation and shear kinematics on fluid interfaces. Combining the Quadrotrough with both in situ Brewster angle microscopy and neutron reflectometry provides detailed structural measurements of the interface at the mesoscale and nanoscale in relationship to interfacial material properties under controlled interfacial deformation histories. [ABSTRACT FROM AUTHOR]

Thin liquid films arise in many technological applications and biological phenomena. They also present a fascinating object of study, because of a rich interplay between capillarity, hydrodynamics, interfacial transport phenomena and interfacial rheology, as well as the effects of interaction forces when films thin down to molecular thicknesses. Recent advances in experimental techniques have given further insights in the variety of physical phenomena, which can occur. These techniques are briefly reviewed. How these techniques can be utilised is illustrated by recent studies addressing the effect of interfacial rheological stresses on drainage, the interplay between capillarity and hydrodynamics during film retraction, and the solutocapillary stabilisation of films. Finally, we briefly discuss the challenges of conducting drainage measurements at high and varied capillary numbers and how these could be overcome by the combined use of experiments and simulations. [ABSTRACT FROM AUTHOR]

Fluid–fluid interfaces, laden with polymers, particles or other surface-active moieties, often show a rheologically complex response to deformations, in particular when strong lateral interactions are present between these moieties. The response of the interface can then no longer be described by an isotropic surface tension alone. These "structured" soft-matter interfaces are found in many industrial applications, ranging from foods, cosmetics and pharmaceuticals, to oil recovery. Also many biomedical applications involve such interfaces, including those involving lung surfactants and biofilms. In order to understand, design and optimize processes in which structured interfaces are present, flow predictions of how such multiphase systems deform are of the utmost importance, which is the goal of "computational interfacial rheology", the main topic of this review. We start by rigorously establishing the stress boundary condition used in the computation of multi-phase flows, and show how this changes when the interface is rheologically complex. Then, constitutive models for the extra stress in interfaces, ranging from 2D generalized Newtonian to hyperelastic and viscoelastic, are reviewed extensively, including common pitfalls when applying these models. This is followed by an overview of different approaches to measure interfacial rheological properties, and a discussion of advanced numerical implementations for deforming interfaces. We conclude with an outlook for this relatively young and exciting field. • Review of the advances in computational interfacial rheology. • Derivation of the stress boundary condition in the presence of structured interfaces. • Extensive treatment of constitutive models for structured interfaces. • Overview of numerical methods used in interfacial rheometry. • Overview of advanced numerical implementations for deforming structured interfaces. [ABSTRACT FROM AUTHOR]

High-frequency rheology is a form of mechanical spectroscopy which provides access to fast dynamics in soft materials and hence can give valuable information about the local scale microstructure. It is particularly useful for systems where time-temperature superposition cannot be used, when there is a need to extend the frequency range beyond what is possible with conventional rotational devices. This review gives an overview of different approaches to high-frequency bulk rheometry, i.e. mechanical rheometers that can operate at acoustic (20 Hz–20 kHz) or ultrasound (> 20 kHz) frequencies. As with all rheometers, precise control and know-how of the kinematic conditions are of prime importance. The inherent effects of shear wave propagation that occur in oscillatory measurements will hence be addressed first, identifying the gap and surface loading limits. Different high-frequency techniques are then classified based on their mode of operation. They are reviewed critically, contrasting ease of operation with the dynamic frequency range obtained. A comparative overview of the different types of techniques in terms of their operating window aims to provide a practical guide for selecting the right approach for a given problem. The review ends with a more forward looking discussion of selected material classes for which the use of high-frequency rheometry has proven particularly valuable or holds promise for bringing physical insights. [ABSTRACT FROM AUTHOR]

Multiphase fluids and highly non-Newtonian fluids often show wall slip. The typical approach to reduce wall slip in experiments is to use roughened geometries, which are thin porous layers. However, the presence of the roughness introduces in itself an apparent wall slip due to the flow within the porous layer. To account for wall slip typically, measurements must be run at several gaps in a plate-plate device. With Newtonian fluids, the apparent wall slip can be conveniently accounted for in the measurements at a single gap since it can be accurately predicted using models describing the flow of Newtonian fluids through and over porous media. Here, we extend this approach to viscoelastic fluids by using Minale's model [Phys. Fluids 28, 023102 and 023103 (2016)] for the flow of second order fluids (SOFs) through and over a porous medium. In this work, we first validate the theoretical predictions and then propose an experimental protocol to measure a SOF with rough geometries by executing the experiments at a single chosen gap. Two Boger fluids are used as model SOFs, and three different rough geometries are considered: Two commercial crosshatched plates and a homemade pillared one. The apparent wall slip is shown to be reduced for the viscoelastic fluids, with respect to the Newtonian case, and agreement with the theoretical predictions is excellent. [ABSTRACT FROM AUTHOR]

The steady state flow of a concentrated dispersion of starlike micelles above the colloidal glass transition concentration is interrogated by superimposing a small amplitude straining motion orthogonal to the main flow direction. Strain amplitude sweeps reveal that the linear response region of the orthogonal perturbation increases with increasing flow rate, consistent with a fluidization of the materials. Orthogonal dynamic frequency sweeps (ODFSs) are obtained for a wide range of shear rates probing the full flow curve. The shear-induced fluidization of the initially glassy suspension is more clearly evidenced by the appearance of a crossover frequency ω c in ODFS, which steadily increases, reflecting a faster structural relaxation under shear. The dependence of ω c on the shear rate is sublinear and follows a power law with an exponent of 0.8. We show that the shape of the orthogonal viscoelastic spectrum changes at a critical shear rate γ ˙ cr , indicative of a structural relaxation modulus that changes from exponential at lower shear rates to multistep with alternating exponential and power law response at higher shear rates. We finally provide a theoretical framework which explains the observed sublinear power law dependence of the crossover frequency and relates it with the shear rate dependence of the viscosity measured by the flow curve. [ABSTRACT FROM AUTHOR]

Nonlinear rheometry of interfaces is very challenging because of the limits of current day instrumentation and the intricate coupling of flows at interfaces and in the bulk. The use of time periodic flows may constitute a first step in addressing this issue. Fourier transform rheology (FTR) measurements with quasi-monolayers at the air-water interface are used in order to assess the suitability of the different devices to investigate nonlinear interfacial shear viscoelasticity. The probe material was a poly (methyl methacrylate) forming a soft glassy interface, whereas complementary measurements were performed with a polystyrene latex suspension forming a predominantly viscous interface at intermediate surface coverages. The obtained data with the magnetic rod rheometer (ISR) were compared against those obtained with the bicone and the double wall ring geometries attached to standard rotational rheometers. In particular, an unexpected appearance of even in addition to odd harmonics is discussed in terms of flow field asymmetry.Graphical abstract [ABSTRACT FROM AUTHOR]

In food-grade emulsions, particles with an appropriate surface modification can be used to replace surfactants and potentially enhance the stability of emulsions. During the life cycle of products based on such emulsions, they can be exposed to a broad range of pH conditions and hence it is crucial to understand how pH changes affect stability of emulsions stabilized by particles. Here, we report on a comprehensive study of the stability, microstructure, and macroscopic behavior of pH-controlled oil-in-water emulsions containing silica nanoparticles modified with chitosan, a food-grade polycation. We found that the modified colloidal particles used as stabilizers behave differently depending on the pH, resulting in unique emulsion structures at multiple length scales. Our findings are rationalized in terms of the different emulsion stabilization mechanisms involved, which are determined by the pH-dependent charges and interactions between the colloidal building blocks of the system. At pH 4, the silica particles are partially hydrophobized through chitosan modification, favoring their adsorption at the oil-water interface and the formation of Pickering emulsions. At pH 5.5, the particles become attractive and the emulsion is stabilized by a network of agglomerated particles formed between the droplets. Finally, chitosan aggregates form at pH 9 and these act as the emulsion stabilizers under alkaline conditions. These insights have important implications for the processing and use of particle-stabilized emulsions. On one hand, changes in pH can lead to undesired macroscopic phase separation or coalescence of oil droplets. On the other hand, the pH effect on emulsion behavior can be harnessed in industrial processing, either to tune their flow response by altering the pH between processing stages or to produce pH-responsive emulsions that enhance the functionality of the emulsified end products. [ABSTRACT FROM AUTHOR]

A strategy to halt dissolution of particle-coated air bubbles in water based on interfacial rheology design is presented. Whereas previously a dense monolayer was believed to be required for such an "armored bubble" to resist dissolution, in fact engineering a 2D yield stress interface suffices to achieve such performance at submonolayer particle coverages.We use a suite of interfacial rheology techniques to characterize spherical and ellipsoidal particles at an air-water interface as a function of surface coverage. Bubbles with varying particle coverages are made and their resistance to dissolution evaluated using a microfluidic technique. Whereas a bare bubble only has a single pressure at which a given radius is stable, we find a range of pressures over which bubble dissolution is arrested for armored bubbles. The link between interfacial rheology and macroscopic dissolution of ~100 μm bubbles coated with ~1 μm particles is presented and discussed. The generic design rationale is confirmed by using nonspherical particles, which develop significant yield stress at even lower surface coverages. Hence, it can be applied to successfully inhibit Ostwald ripening in a multitude of foam and emulsion applications. [ABSTRACT FROM AUTHOR]

The stabilisation of foam bubbles is of both scientific interest and technological importance. In this respect, the study of polyglycerol ester-based nonionic surfactants is highly relevant as they lead to remarkable foam stability. The present work investigates the thermodynamic and rheological properties leading to this stability with a particular focus on out-of-equilibrium conditions of the surface. These may occur after bubble coalescence events, which lead to a compression of the interface. To separate the effects of such a compression on surface tension and the extra stresses which arise due to deformation of the interface, a double wall ring geometry mounted in a ribbon trough was used. Surface tension and the linear viscoelastic properties are shown to be affected differently by compression of the surface. The surface tension relaxes to an equilibrium value while the surface moduli will continue to rise which each compression step. The presence of multilayered structures, which have been reported for polyglycerol esters, explains how these differences arise. The polyglycerol ester-based nonionic surfactants are an example of materials where a true surface rheological response, related to the extra and deviatoric stresses, can be used to limit coalescence. [ABSTRACT FROM AUTHOR]

Clean technology in dehydration of acetic acid using pervaporative separations inspired by plant dewatering systems is studied in this work. The novel polyphenylsulfone-based membranes, modified with silica nanoparticles, were used to dehydrate a binary mixture of acetic acid and water. The Stöber process was applied for the synthesis of monodispersed silica colloids by hydrolysis of alkyl silicates and condensation of silicic acid in alcoholic solution. The surface free energy of the synthesized silica particles was altered through a silanization treatment with hexamethyldisilazane to convert the surface hydroxyl groups to trimethylsilyl[–Si(CH 3 ) 3 ] groups. The synthesized particles and the modified polyphenylsulfone based membranes were characterized using dynamic light scattering, scanning electron microscopy, atomic force microscopy, Fourier-transform infrared and macroscopic contact angle measurements. Pervaporation was used for the dehydration of 70 wt% acetic acid at 70 °C using nine different membrane variations. Inspired by the natural dewatering in plants containing silica, the performance of the synthetic silica nanoparticles filled-membranes was investigated. Similar to plants, the incorporation of silica nanoparticles in these membranes significantly affected the dewatering process. It was found that at higher concentrations of silica, an improvement of membrane properties was observed, particularly in terms of selectivity. Besides that, the hydrophilicity and surface roughness increases when sufficient amounts of silanols groups were present on the membrane surface. It was concluded that more hydrophilic silica should be first produced and incorporated into the membranes for efficient removal of water from acetic acid. This can be achieved by controlling the composition ratio of ammonium hydroxide, water and ethanol for the nanoparticle fabrication. The effect of different nanoparticle types on membrane morphology and pervaporation performance is also discussed in detail in this work. [ABSTRACT FROM AUTHOR]

A semi-rigid, semi-flexible SU-8 polymer microdevice was designed to measure changes in interfacial tension at an air–water interface. The suspended microtensiometer enclosed a clean air–water interface, with an insoluble surfactant on the exterior. The difference in surface tension between the inside and the outside of the device, called the surface pressure, caused the 850 μm by 3 mm device to deflect. Finite element simulations were performed to predict device behavior prior to fabrication. Finished devices were tested in a Langmuir trough during multiple compression and expansion cycles using large area changes and slow compression speeds. Shorter experiments subjecting the interface to rapid local monolayer concentration variations were also performed. A platinum Wilhelmy plate was used as an independent surface pressure measurement. The microtensiometer had a theoretical resolution of 0.02 mN m −1 . [ABSTRACT FROM AUTHOR]

Abstract: The interfacial properties of crayfish protein isolate (CFPI) and chitosan solutions (CH) at the air–water interface have been studied. An analysis of the surface pressure and interfacial shear rheology has been carried out as a function of CFPI and/or CH contents, at a fixed pH 2. The results indicate that a combination of CFPI and CH may produce a good strategy to stabilize systems. Both CFPI and CH are surface active, and synergistic effects may be obtained providing control over surface pressure. These effects are highly dependent on CFPI or CH contents. The former reduces surface tension whereas the latter enhances interfacial viscoelasticity. Previously, a transition from fluid-like behaviour to a gel-like behaviour was observed by increasing the CFPI content. However, interfaces composed of CH display a more pronounced viscoelastic nature, the effect however saturating at higher bulk concentrations. Furthermore, usage of highly sensitive interfacial shear techniques, such as the magnetic rod interfacial stress rheometer or the double wall ring, both of them providing consistent results, has proven to be highly useful to study the macroscopic viscoelastic properties of CFPI/CH interfacial films at levels that cannot be detected by other methods. [Copyright &y& Elsevier]

Oscillatory measurements are often used to explore the nonlinear response of materials, with recently a strong focus on using large amplitude oscillatory experiments. However, the superposition of an oscillatory motion onto a steady-state shear flow is a method where the kinematic history experienced by the sample is simpler. Such a superposed oscillation can be applied either orthogonal or parallel to the main flow direction. Both superposed deformation modes can now be achieved on rotational rheometers equipped with a force-rebalanced transducer, the orthogonal mode requiring a minor modification to the control loop of the normal force. In the present work, the nonlinear properties of a wormlike micellar (WLM) solution are studied. The results are compared with the predictions of the Giesekus model, which is chosen both for its capability to describe the WLM response and for being one of the simplest continuum models that incorporate an anisotropic microstructure. From the fluid response in the homogeneous flow regime, a rate-dependent relaxation time and a rate-dependent plateau modulus can be derived. The latter provides insight into the structural anisotropy during flow at short length scales, which in this case is isotropic. Further analysis of the superposition moduli can be used to separate and quantify the effects of flow on the reptation and breaking of the chains. In the shear-banding regime, the orthogonal moduli show a weaker dependence on shear rate compared to the predictions of the Giesekus model, yet they remain sensitive to changes in the shear-banded state. [ABSTRACT FROM AUTHOR]

Abstract: The interfacial behaviour of a crayfish protein isolate (CFPI) produced as by-product from the food industry has been studied at the air–water surface at two pH values (2 and 8). An analysis of the surface pressure and interfacial shear behaviour has been carried out as a function of CFPI content for the two mentioned pH values. The results indicate that CFPI shows higher surface pressure, smaller aggregates and higher interfacial viscoelasticity at pH 8 than at pH 2, being highly dependent on CFPI content. In fact, a transition from fluid-like behaviour to a gel-like behaviour have been obtained by increasing the protein content. These results are in agreement with the higher solubility and z-potential values and the longer emulsion stability found under alkaline conditions. Furthermore, usage of highly sensitive interfacial shear techniques, such as the magnetic rod interfacial stress rheometer or the double wall ring, both of them providing rather coincident results, has proven to be highly useful to study the viscoelastic properties of CFPI interfacial films at levels that cannot be detected by other methods. [Copyright &y& Elsevier]

Abstract: The performance of four different lipid-based (Tween 80–Captex 200P, Tween 80–Capmul MCM, Tween 80–Caprol 3GO and Tween 80–soybean oil) and one commercially available micronized formulation (Lipanthyl Micronized®) of the lipophilic compound fenofibrate was compared in vitro in various biorelevant media and in vivo in rats. In simulated gastric fluid without pepsin (SGFsp) and fasted state simulated intestinal fluid (FaSSIF), only Tween 80–Captex 200P system resulted in a stable fenofibrate concentration, but no supersaturation was obtained. The other three lipid based systems created fenofibrate supersaturation; however they did not maintain it. In fed state simulated intestinal fluid (FeSSIF), all lipid-based formulations resulted in complete dissolution of fenofibrate during the experiment, which represented a supersaturated state for Tween 80–Capmul MCM and Tween 80–Caprol 3GO systems. In both FaSSIF and FeSSIF, all lipid-based formulations yielded a higher fenofibrate concentration than the micronized formulation. Contrary to the in vitro results, no significant difference in the in vivo performance was observed among the four tested lipid-based formulations both in the fasted and the fed states. The in vivo performance of all lipid-based formulations was better than that of Lipanthyl Micronized®, in the fasted as well as in the fed state. The fact that for the lipid based systems the in vitro differences in pharmaceutical performance were not translated into in vivo differences can be attributed to the continuous excretion of bile in the gastrointestinal tract of rats, causing enhanced solubilizing capacity for lipophilic drugs. This study clearly points to the conflicting situation that might arise during the preclinical phase of the development of lipid based formulations of lipophilic drugs as the performance of such systems is very often evaluated by both in vitro release studies in human biorelevant media as well as in vivo studies in rats. Care must be taken to select a relevant animal model. [Copyright &y& Elsevier]

Abstract: In order to gain a better understanding of the reasons of successful self-microemulsifying drug delivery systems (SMEDDS) formulation, ten poorly water-soluble drugs, exhibiting different physicochemical properties, were selected. The solubility of the compounds was determined in various oils (long and medium chain) and surfactants (HLB>12 and HLB<10). The best performing excipients were selected for SMEDDS formulation. The droplet size and zeta potential of SMEDDS were measured in the absence and the presence of drug. Media, time and the presence of drug showed little or no influence on droplet size of most systems. Some systems displayed a different zeta potential in the presence of drugs. In vitro pharmaceutical performance of the SMEDDS formulations was investigated using the dialysis bag method in reverse mode next to conventional in vitro release methodology. The results suggested that the measured concentration of the compounds inside the dialysis bag corresponded to solubility of the compound in the release medium, which suggested that the formation of micelles inside the dialysis bag was delayed or disturbed. Conventional in vitro release methodology with pH change from acidic to neutral appeared as a simple method which gives valuable information about the dispersion and the solubilization ability of the SMEDDS formulation at different pHs. In general, formulate-ability in SMEDDS was found to depend on the solubility of the drugs in the excipients and log P of the compounds (the optimal log P was found between 2 and 4). [Copyright &y& Elsevier]

Encapsulating poorly soluble drugs in mesoporous silicates is an emerging strategy to improve drug dissolution. This study evaluates the applicability of the ordered mesoporous silicate SBA-15 as an excipient to enhance dissolution, for a test series of 10 poorly soluble compounds with a high degree of physicochemical diversity (carbamazepine, cinnarizine, danazol, diazepam, fenofibrate, griseofulvin, indomethacin, ketoconazole, nifedipine, and phenylbutazone). A generic solvent impregnation method was used to load all model compounds. The target drug content was 20%. The physical nature of the formulations was investigated using differential scanning calorimetry (DSC) and the pharmaceutical performance evaluated by means of in vitro dissolution. Aliquots of each formulation were stored at 25°C/52% RH for 6 months, and again subjected to DSC and in vitro dissolution. The target drug content of 20% was attained in all cases. DSC data evidenced the noncrystalline state of the confined drugs. All SBA-15 formulations exhibited an enhanced dissolution as compared to their corresponding crystalline materials, and the high pharmaceutical performance of all formulations was retained during the 6 months storage period. The results of this study suggest that encapsulation in SBA-15 can be applied as a dissolution-enhancing formulation approach for a very wide variety of poorly soluble drugs. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2648–2658, 2009 [ABSTRACT FROM AUTHOR]

Swarming is the fastest known bacterial mode of surface translocation and enables the rapid colonization of a nutrient-rich environment and host tissues. This complex multicellular behavior requires the integration of chemical and physical signals, which leads to the physiological and morphological differentiation of the bacteria into swarmer cells. Here, we provide a review of recent advances in the study of the regulatory pathways that lead to swarming behavior of different model bacteria. It has now become clear that many of these pathways also affect the formation of biofilms, surface-attached bacterial colonies. Decision-making between rapidly colonizing a surface and biofilm formation is central to bacterial survival among competitors. In the second part of this article, we review recent developments in the understanding of the transition between motile and sessile lifestyles of bacteria. [Copyright &y& Elsevier]