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International audience; We propose an original microbubble encapsulation process, using electrostatics as a driving force to guide either particles or polymerizable precursors to the bubble surface. Taking advantage of attractive interactions between surfactant-laden charged bubbles and oppositely charged self-assembling species, our method produces capsules with diverse protective shells that remain stable for years. Considering heterogeneous electrostatic double-layer interactions, we quantitatively predict critical particle surface potentials required for complete encapsulation. The particle-based shells can be disintegrated with a pH adjustment, allowing for a controlled release of encapsulated payloads, while the glassy continuous silicate capsules are chemically resistant to pH changes. Our process, which can be equally applied to liquid droplets, easily scales up for industrial developments.

Letter; International audience; No abstract available

International audience

International audience

Increased muscle tone and exaggerated tendon reflexes characterize most of the individuals after a spinal cord injury (SCI). We estimated seven parameters from the pendulum test and used them to compare with the Ashworth modified scale of spasticity grades in three populations (retrospective study) to assess their spasticity. Three ASIA B SCI patients who exercised on a stationary FES bicycle formed group F, six ASIA B SCI patients who received only conventional therapy were in the group C, and six healthy individuals constituted the group H. The parameters from the pendulum test were used to form a single measure, termed the PT score, for each subject. The pendulum test parameters show differences between the F and C groups, but not between the F and H groups, however, statistical significance was limited due to the small study size. Results show a small deviation from the mean for all parameters in the F group and substantial deviations from the mean for the parameters in the C group. PT scores show significant differences between the F and C groups and the C and H groups and no differences between the F and C groups. The correlation between the PT score and Ashworth score was 0.88. © 2017 IEEE. This is the peer-reviewed version of the article: Popovic-Maneski, L., Aleksic, A., Metani, A., Bergeron, V., Cobeljic, R., Popovic, D.B., 2018. Assessment of Spasticity by a Pendulum Test in SCI Patients Who Exercise FES Cycling or Receive only Conventional Therapy. IEEE Transactions on Neural Systems and Rehabilitation Engineering 26, 181–187. [https://doi.org/10.1109/TNSRE.2017.2771466]

Whether it is from the patient’s or the physical therapist’s point of view, FES cycling can be considered either as a recreational activity, or an engaging rehabilitation tool. In both cases, it keeps patients with lower-limb paralysis motivated to sustain a regular physical activity. Thus, it is not surprising that it was selected as one of the six disciplines of the first Cybathlon competition held on October 8, 2016. However, many unresolved issues prevent FES cycling from being an activity practiced outdoors on a daily basis; such as, low power production, rapid muscle fatigue, precise electrode positioning, lack of systematic procedures to determine stimulation patterns, and the difficulty of transferring disabled riders from their wheelchair to the tricycle. This article documents the challenges we faced during preparation for the Cybathlon 2016 FES cycling race, and provides results obtained during different phases of the process. A particular specificity of our team was that, unlike most other teams where pilots were mainly paraplegic, both the primary and backup pilots for team ENS de Lyon are C6/C7 tetraplegics, with neither voluntary control of their abdominal muscles nor hand grip, and only partial use of their arms.

Introduction/Background Individuals with cervical spinal cord injury experience tetraplegia with dramatic impairment of upper limb (UL) including hand function and decreased autonomy. In absence of very recent evidence and meta-analysis, we addressed UL rehabilitation effectiveness after tetraplegia. Material and method Two independent reviewers performed the systematic review and meta-analysis addressing Pubmed, Pedro, Central and Scopus®. We considered studies with a randomized controlled trial design, published in English language, which included individuals with tetraplegia and measured UL rehabilitation effect on strength, somesthesia, hand function and autonomy. Results From 573 records identified, 24 studies were included totaling 517 participants with C2 to C7 tetraplegia (ASIA A to D). Interventions lasted from 66 to 3780 minutes. Three different strategies were used i) bottom-up (namely massed practice, Functional Electrical Stimulation – FES, resistance or robotic training), ii) neuromodulation (i.e. electrical nerve, trans-cranial or magnetic stimulations), or iii) top-down (brain computer interfaces with FES or virtual reality). The 17 studies analyzed displayed heterogeneity for all outcomes except for strength. Overall, strength significantly increased with positive but non-significant effect on hand function and autonomy. Sub-analysis revealed a significant effect on strength only for bottom-up strategy. All other sub-analyzes albeit non-significant revealed at least a medium effect size for all outcomes with exception to the very small effect size displayed for somesthesia. Conclusion These results support the effectiveness of UL rehabilitation on strength using. There is a potential interest of using bottom-up and neuromodulation strategies to improve hand function and autonomy but with heterogeneity between interventions and participants. Conversely, there is no evidence for top-down strategy and interventions targeting somesthesia appear ineffective. Further effort on funding may promote high-quality multi-centric studies with increased standardization in intervention and participants to completely address UL rehabilitation effectiveness after tetraplegia while separating recovery and compensation effects.

Introduction Le sport sur ordonnance propose de facon schematique, aux patients ayant une affectation de longue duree (ALD), de pratiquer une activite physique adaptee (APA) prescrite par un medecin dans le cadre d’un parcours de soin. Cette pratique n’est pas remboursee par la securite sociale, mais correspondant a la volonte de promouvoir des therapeutiques non medicamenteuses. Materiels et methodes Il s’agit d’analyser le decret no 2016-1990 [1] et les documents associes, tels que l’instruction interministerielle no dgs/ea3/dgesip/ds/sg/2017/81 [2] portant guide sur les conditions de dispensation de l’APA prescrite par le medecin traitant a des patients atteints d’une ALD ou le rapport du Groupe de Travail « Activite physique et prise en charge des personnes atteintes de maladies chroniques. Quelles competences pour quels patients ? Quelles formations ? » [3] , pour mesurer les enjeux et les consequences concretes de son application. Ceci en se centrant particulierement sur les acteurs socio-economiques et le monde sportif. C’est une analyse de droit economique, et plus particulierement la methode substantielle, qui sera utilisee pour etudier ces differents textes. Cette methode permet de produire de nouvelles qualifications par un mouvement de retroaction des faits sur le droit. Resultats L’analyse juridique des textes laisse apparaitre, d’une part, des incertitudes quant a la competence des differents acteurs et souleve, d’autre part, des interrogations, notamment quant a la place des mutuelles et aux reponses des federations sportives face a ces nouveaux publics. L’etude vise a mesurer, en pratique, les consequences de ces incertitudes juridiques. Conclusion Le decret risque de modifier en profondeur l’organisation et la pratique des APA pour les patients beneficiant d’une ALD.

International audience; Foams produced from non-aqueous media are less common than water-based foams but they play an important role in many industries and engineering processes. The low surface tension of hydrocarbon fluids limits the adsorption of common surface activity substances and different compounds and methods must be considered to generate and stabilize oil-based foam. Likewise, the destruction of unwanted non-aqueous based foam requires specific considerations not found with aqueous systems. Of particular interest are petroleum-based foams, which are highly complex due to the wide variety of compounds and gases that can be found. We provide an overview of the major mechanisms known to be important for non-aqueous foam stability with a spotlight on crude-oil foams.

We study the effects of vertical sinusoidal vibrations on a liquid droplet with a low surface tension (ethanol) deposited on a solid substrate. In a precise range of amplitudes and frequencies, the drop exhibits a dramatic worm-like shape instability with a strong symmetry breaking, comparable to the one observed by Pucci et al. (Phys. Rev. Lett., 106 (2011) 024503) on a vibrated floating lens. However, the geometry of our system is much simpler since it does not involve the oscillation and deformation of a liquid-liquid-air contact line. We show that the Faraday waves appearing on the surface of the droplet control its shape and we draw a systematic phase diagram of the instability. A simple theoretical model allows us to derive a relation between the elongation of the droplet and the amplitude of the Faraday wave, in good agreement with measurements of both quantities., 7 pages, 4 figures

Background: Evidence has recently emerged indicating that in addition to large airborne droplets, fine aerosol particles can be an important mode of influenza transmission that may have been hitherto underestimated. Furthermore, recent performance studies evaluating airborne infection isolation (AII) rooms designed to house infectious patients have revealed major discrepancies between what is prescribed and what is actually measured. Methods: We conducted an experimental study to investigate the use of high-throughput in-room air decontamination units for supplemental protection against airborne contamination in areas that host infectious patients. The study included both intrinsic performance tests of the air-decontamination unit against biological aerosols of particular epidemiologic interest and field tests in a hospital AII room under different ventilation scenarios. Results: The unit tested efficiently eradicated airborne H5N2 influenza and Mycobacterium bovis (a 4- to 5-log single-pass reduction) and, when implemented with a room extractor, reduced the peak contamination levels by a factor of 5, with decontamination rates at least 33% faster than those achieved with the extractor alone. Conclusion: High-throughput in-room air treatment units can provide supplemental control of airborne pathogen levels in patient isolation rooms.

To better understand the diffusion of Pneumocystis in the environment, airborne shedding of Pneumocystis carinii in the surrounding air of experimentally infected rats was quantified by means of a real-time polymerase chain reaction assay, in parallel with the kinetics of P. carinii loads in their lungs. P. carinii DNA was detected in the air 1 week after infection and increased until 4-5 weeks after infection before stabilizing. A significant correlation was shown between lung burdens and the corresponding airborne levels, suggesting the possibility of estimating the fungal lung involvement through quantification of Pneumocystis in the exhaled air.

Objective.To evaluate the performance of a new mobile air-treatment unit that uses nonthermal-plasma reactors for lowering the airborne bioburden in critical hospital environments and reducing the risk of nosocomial infection due to opportunistic airborne pathogens, such asAspergillus fumigatus.Methods.Tests were conducted in 2 different high-risk hospital areas: an operating room under simulated conditions and rooms hosting patients in a pediatric hematology ward. Operating room testing provided performance evaluations of removal rates for airborne contamination (ie, particles larger than 0.5μm) and overall lowering of the airborne bioburden (ie, colony-forming units of total mesophilic flora and fungal flora per cubic meter of air). In the hematology service, opportunistic and nonpathogenic airborne fungal levels in a patient's room equipped with an air-treatment unit were compared to those in a control room.Results.In an operating room with a volume of 118 m3, the time required to lower the concentration of airborne particles larger than 0.5μm by 90% was decreased from 12 minutes with the existing high-efficiency particulate air filtration system to less than 2 minutes with the units tested, with a 2-log decrease in the steady-state levels of such particles (PPPConclusion.Our data indicate that the mobile, nonthermal-plasma air treatment unit tested in this study can rapidly reduce the levels of airborne particles and significantly lower the airborne bioburden in high-risk hospital environments.

We investigate the shear surface rheology of a thermosensitive polymer, PNIPAM (poly(N-isopropylacrylamide)), adsorbed at the air−water interface using an interfacial stress rheometer. This polymer is characterized by a lower critical solution temperature, LCST, of 32 °C; i.e., PNIPAM chains undergo a coil to globule transition as the temperature is increased above the LCST. We measure a spectacular increase in the surface shear elasticity and viscosity of PNIPAM layers as a function of the temperature around the LCST due to an increase in the amount of adsorbed species as the solvent quality decreases for PNIPAM chains. Moreover, the layers undergo a transition from a Newtonian liquidlike state to an elastic state due to an increase in intermolecular entanglements. We also show that the heating protocols have a strong influence on the rheological properties of the layers. In particular, we show that when the solutions are continuously heated from ambient temperature to well above the LCST, PNIPAM chains ...

We have studied the drainage of foams made from Newtonian and non-Newtonian solutions of different viscosities. Forced-drainage experiments first show that the behavior of Newtonian solutions and of shear-thinning ones (foaming solutions containing either Carbopol or Xanthan) are identical, provided one considers the actual viscosity corresponding to the shear rate found inside the foam. Second, for these fluids, a drainage regime transition occurs as the bulk viscosity is increased, illustrating a coupling between surface and bulk flow in the channels between bubbles. The properties of this transition appear different from the ones observed in previous works in which the interfacial viscoelasticity was varied. Finally, we show that foams made of solutions containing long flexible PolyEthylene Oxide (PEO) molecules counter-intuitively drain faster than foams made with Newtonian solutions of the same viscosity. Complementary experiments made with fluids having all the same viscosity but different responses to elongational stresses (PEO-based Boger fluids) suggest an important role of the elastic properties of the PEO solutions on the faster drainage.

A novel in-situ streaming-potential optical reflectometry apparatus (SPOR) was constructed and utilized to probe the molecular architecture of aqueous adsorbates on a negatively charged silica surface. By combining optical reflectometry and electrokinetic streaming potentials, we measure simultaneously the adsorption density, gamma, and zeta potential, zeta, in a rectangular flow cell constructed with one transparent wall. Both dynamic and equilibrium measurements are possible, allowing the study of sorption kinetics and reversibility. Using SPOR, we investigate the adsorption of a classic nonionic surfactant (pentaethylene glycol monododecyl ether, C12E5), a simple cationic surfactant (hexadecyl trimethylammonium bromide, CTAB) of opposite charge to that of the substrate surface, and two cationic polyelectrolytes (poly(2-(dimethylamino)ethyl methacrylate), PDAEMA; (poly(propyl methacrylate) trimethylammonium chloride, MAPTAC). For the polyethylene oxide nonionic surfactant, bilayer adsorption is established above the critical micelle concentration (cmc) both from the adsorption amounts and from the interpretation of the observed zeta potentials. Near adsorption saturation, CTAB also forms bilayer structures on silica. Here, however, we observe a strong charge reversal of the surface. The SPOR data, along with Gouy-Chapman theory, permit assessment of the net ionization fraction of the CTAB bilayer at 10% so that most of the adsorbed CTAB molecules are counterion complexed. The adsorption of both C12E5 and CTAB is reversible. The adsorption of the cationic polymers, however, is completely irreversible to a solvent wash. As with CTAB, both PDAEMA and MAPTAC demonstrate strong charge reversal. For the polyelectrolyte molecules, however, the adsorbed layer is thin and flat. Here also, a Gouy-Chapman analysis shows that less than 20% of the adsorbed layer is ionized. Furthermore, the amount of charge reversal is inversely proportional to the Debye length in agreement with available theory. SPOR provides a new tool for elucidating aqueous adsorbate molecular structure at solid surfaces.

Using the oscillating drop method as well as the interfacial stress rheometer (ISR), we measure the surface dilational and shear properties of adsorbed layers of oppositely charged polymer−surfactant complexes at the air−water interface. These data are compared to foam volume data measured for the corresponding solutions. We show that the shear surface moduli G‘ and G‘ ‘ exhibit a maximum at a molar ratio of polymer monomers and surfactant in solution equal to 1. This maximum is strongly correlated to surface ellipticity measurements that indicate a strong adsorption of polymer−surfactant complexes at the air−water interface. These hydrophobic interfacial complexes generate a viscoelastic layer due to the polymer chain entanglements and hydrophobic interactions between bound surfactant. The viscous behavior of the surface layers is further characterized via creep, frequency sweep measurements, and surface aging experiments. Over a 10 h period we find that G‘ and G‘ ‘ increase logarithmically with time, re...

The adsorption and complexation of polystyrene sulfonate (a highly charged anionic polyelectrolyte) and dodecyltrimethylammonium bromide (a cationic surfactant) at the air-water interface can lead to interfacial gels that strongly influence foam-film drainage and stability. The formation and characteristics of these gels have been studied by combining surface tension, ellipsometry, and foam-film drainage experiments. Simultaneously, the solution electromotive force is measured and used to track the polymer-surfactant interactions in the bulk solution. We find that surface gelation occurs above the critical aggregation concentration in solution but before bulk precipitation of the polymer-surfactant complexes. Furthermore, we reveal that strong readsorption of polymer-surfactant complexes occurs during the resolubilization of the precipitated complexes at high surfactant concentrations (i.e., >>critical micelle concentration). Seemingly overlooked in the past, this readsorption significantly influences the surface rheological properties and foam-film drainage of these systems.

Recent advances in our understanding of ‘complex fluids’ have lead to the development of new chemical additives in the agricultural industry, which provide more efficient products and a higher level of public and environmental protection. Here we present one example that deals with the improved application of herbicides and pesticides during the spray treatment of plants. Using judiciously chosen dilute polymer solutions, one can simultaneously improve the spray characteristics, droplet deposition, and product retention onto the targeted plant surface. Achieving these combined benefits, requires a delicate balance between fluid hydrodynamics and the molecular interactions that control the phase behaviour of the sprayed solutions. To cite this article: V. Bergeron, C. R. Physique 4 (2003).

The interactions between two macroscopic surfaces approaching one another underlies many of the phenomena observed in Colloid and Interface science. In Russia this gave rise to the branch of colloid science now referred to as Surface Forces. Important discoveries, such as the molecular organization of solvent molecules at an interface, have been unveiled by surface force measurements. More recently, forces and structures at macromolecular length scales have been uncovered. In particular, oscillatory force profiles have been detected from aqueous solutions containing polyelectrolytes. The force-structure relationship can reflect organization in the bulk solution or the internal structure of the adsorbed layer. Using a range of surface force techniques, combined with X-ray and neutron scattering results, we review the main features of these fascinating systems and provide an overview of how they relate to other systems such as micellar solutions, polymer-surfactant complexes and simple solvents.

Several combinations of polyelectrolyte−surfactant mixtures are studied to probe the various structure−property relationships these systems produce in thin liquid foam films. We show that either bulk solution properties or surface specific adsorption of the polymer−surfactant complexes formed can dominate the thin-film behavior. Above the polymer overlap concentration, Cp*, oscillatory force profiles are observed. In agreement with previous studies, we find that the oscillation period, Δh, scales as the negative square root of the polymer concentration, Δh ∼ Cp-1/2. In addition, by comparing directly the bulk polymer correlation length, ξ, to the oscillation period, we establish for the first time that Δh = ξ for these systems. These findings are compared to oscillatory force behavior seen with micellar solutions which display a scaling relation with micelle concentration, Cm, which follows Δh ∼ Cm-1/3. The different scaling exponents are explained by the local cylindrical and spherical symmetry of the mo...

Whether standing in the shower, spilling the morning coffee or going to work in the rain, each day typically begins with water droplets splashing off a solid surface. In fact these phenomena are so common that they often go unnoticed. However, the basic physics that governs the dynamics of water droplets is extremely rich, and understanding these events in detail has important scientific and technological consequences.

Centrifugation can be used to remove the continuous aqueous phase of an oil-in-water emulsion. The cream that remains after most of the water has been removed has the structure of a biliquid foam; it can be redispersed in water. Examination of this cream through electron microscopy shows polyhedral oil cells separated by thin films. The thickness of these films has been measured through small-angle neutron scattering. The results yield a disjoining pressure isotherm, where the film thickness is solely determined by the pressure applied to extract water during centrifugation. For hexadecane-in-water biliquid foams, stabilized with sodium dodecyl sulfate (SDS), this isotherm has two states, the common black film (CBF; water thickness beyond 25 A) and the Newton black film (NBF; (water thickness of 13 A). At low pressures (1−50 atm), the films are in the CBF state, where the measured disjoining pressure matches the entropic pressure of the counterions, calculated from the Poisson−Boltzmann equation. At high ...

The forces and structures that develop at and between fluid interfaces are responsible for the stability of foam, emulsion and wetting films. Although these forces are less studied than the interactions occurring between solid surfaces, recent quantitative studies of films created between fluid interfaces are providing new information that both complements previous findings obtained with solid surfaces, and reveals unique and important differences for films confined between fluid interfaces. Noteworthy is that fluid interfaces can be much more mobile, thus fluctuations and interfacial boundary conditions can produce a rich variety of phenomena at these interfaces.

This review is a topical survey of the forces and structures in thin liquid soap films. Included is a description of both the more classical forces, such as electrostatic double-layer and dispersion forces, together with new and emerging areas of research that cover so-called `supramolecular' forces. This latter category covers self-assembly of macromolecular structures confined in a thin-film region together with surface-induced adsorption of macromolecular complexes. In addition, recent extensions of the relation between thin-film forces and film stability are reviewed.

The alkytrimethylammonium bromide surfactant series, CnTAB, n = 10, 12, 14, 16, is used to perform a systematic study of the forces and stability of foam films produced from soluble cationic surfactants. Both surface tension and disjoining pressure isotherms are measured for each surfactant. This information is then combined with neutron reflectivity and dynamic surface tension results found in the literature to provide an understanding of how the surfactant chain length can effect the forces and stability in thin-liquid films. For stable films, we find good quantitative agreement between the interaction forces measured in foam films and those reported from surface force studies on similar systems. We also find that the surfactant's hydrocarbon chain length and packing can strongly influence film stability. For highly purified surfactants an abrupt increase in film stability is seen when extending the chain length from C12TAB to C14TAB. When an uncharged cosurfactant is present, this stability transition ...

The most widely used industrial antifoams are based on polydimethylsiloxane (PDMS) oils, yet very little fundamental information exists for these products. In most formulations hydrophobically modified particles are dispersed in the oil to increase antifoam efficiency but the primary mechanism responsible for this effect has remained unclear. To address these needs, we provide a systematic study on PDMS-based antifoams for a wide range of common surfactant solutions. By measuring surface and interfacial tensions, contact angles, oil spreading rates, particle size distributions and individual film stability characteristics, in parallel with foam stability measurements, we are able to quantitatively evaluate the parameters believed important for PDMS-based antifoam action. We find that a significant loss of antifoam performance (based on a 60 s foam-life criterion) correlates with an antifoam globule size reduction to less than 6 μm. Furthermore, we provide direct evidence that hydrophobically modified particles, situated at the oil/water interface, puncture the aqueous interface as antifoam globules approach, thereby accelerating oil entry and antifoam efficiency.

The forces acting between colloidal particles and between surfaces are of utmost importance for determining the behaviour of dispersed systems and adhesion phenomena. Several techniques are now available for direct measurement of these surface forces. In this review we focus on some of these methods. Two techniques for measuring forces between macroscopic solid surfaces; the interferometric surface force apparatus, known as the SFA, and a novel instrument which is based on a bimorph force sensor, the so-called MASIF, are described in some detail. Forces between a macroscopic surface and a particle can be measured with the atomic force microscope (AFM) using a colloidal probe, or by employing total internal reflection microscipy (TIRM) to monitor the position of a colloidal particle trapped by a laser beam. We also describe two different techniques that can be used for measuring forces between “soft” interfaces, the thin film balance (TFB) for single foam, emulsion and solid/fluid/fluid films, and osmotic stress methods, commonly used for studying interactions in liquid crystalline surfactant phases or in concentrated dispersions. The advantages and limitations of each of these techniques are discussed and typical results are presented.

Subsurface bilayers are found to exist at the air-water interface of spontaneously forming vesicular solutions of sodium bis(2-ethylhexyl)sulfosuccinate, (AOT). The bilayers produce long-range repulsive forces that increase the stability of foam and emulsion films formed from these solutions. In addition, during film formation and adhesion of two interfaces possessing subsurface bilayers, tubular networks of wrinkled bilayers become trapped within the film. This phenomenon is analogous to pocket formation in lipid membrane multilayers seen during a binding transition, and the resulting networks slowly evolve through processes that mimic two-dimensional foam coarsening.

Foam-film disjoining pressure and surface tension isotherms are measured for solutions containing mixtures of charged surfactants and an anionic random-block copolymer, acrylamide−acrylamidesulfonate. When combined with an anionic surfactant, dioctyl sulfosuccinate (AOT), the polyelectrolyte shows no indication of direct surface interactions and the surfactant behaves as a simple electrolyte. However, when copolymer is added to cationic dodecyltrimethylammonium bromide (C12TAB) solutions, strong polymer−surfactant interactions create an enhanced adsorption of both components to the air−water interface. The resulting polymer−surfactant surface layers subsequently produce long-range thin-film interactions that have not been seen before. For the C12TAB−polymer solutions, film stratification is observed 3 orders of magnitude below the critical micelle concentration and nearly two orders of magnitude below the critical aggregation concentration (cac). This new type of film stratification is consistent with rec...

Disjoining pressure isotherms for foam films made from a nonionic surfactant, octyl β-glucoside, are measured at different surfactant concentrations, ionic strengths, and solution pH values. Below the cmc an electrostatic double-layer repulsion is present and dominates the long-range interaction. The decay length of the forces agrees with the expected Debye length and the measured long-range interactions are consistent with solutions to the nonlinear Poisson−Boltzmann equation using constant charge conditions. The deduced surface charge densities increase with pH and ionic strength but decrease with increasing surfactant concentration. At, or just above, the cmc, surfactant covers the interface and suppresses the charge sufficiently to induce a transition from a common black film to a Newton black film. Ultimately, the film stability is determined by both surface forces and elasticity. Combining both, via an overall film tension, leads to a general expression for the film elasticity.

The foaming behavior of nonionic alkyl glucosides, in terms of foamability and foam stability, has been investigated using various methods. Three different foam tests, two dynamic methods (the Bikerman cylinder and the Watkins funnel) and one static method, have been employed for measuring the foamability and foam stability of nonionic surfactant solutions made from either a linear octyl β-glucoside, a linear octyl α-glucoside, or a branched octyl α-glucoside, 2-ethylhexyl α-glucoside. At low surfactant concentration there is only a small difference in foamability between the surfactants, which remains when the salt concentration increases. At all surfactant concentrations tested octyl β-glucoside is observed to be the best foaming agent. The stability of the individual foam lamellae has also been studied with the thin-film-balance (TFB) technique. The stabilizing forces in these nonionic foam films are, in most cases, electrostatic double-layer forces. The thickness dependence of the repulsive forces is ...

Spreading at the air−solution interface, of poly(dimethylsiloxane) (PDMS), a widely used ingredient in commercial antifoaming agents, depends strongly on the type of surfactant dissolved in solution. To isolate which polymer−surfactant interactions control the process, we measure surface pressure isotherms for PDMS on a wide variety of surfactant solutions. Moreover, we directly probe the influence of electrostatic forces by addition of a 1:1 electrolyte to the solutions. Although surfactant type, anionic, cationic, or nonionic, and level of charge play only a minor role, the length of the surfactant tail can control the PDMS spreading behavior. For the homologous series of alkyltrimethylammonium bromides, a critical carbon chain length of 14 is found, above which PDMS displays “complete” wetting behavior. However, shorter chain lengths can induce a metastable condition of “pseudopartial” wetting. We utilize both two dimensional polymer scaling concepts and generalized spreading coefficients to rationaliz...

We directly measure, for the first time, disjoining pressure isotherms for asymmetric oil/aqueous surfactant/gas (i.e., pseudoemulsion) films using a modified version of the porous-plate technique first developed by Mysels in conjunction with thin-film interferometry. Dynamic film-thinning experiments are also performed on individual foam and pseudoemulsion films. At SDS surfactant concentrations above the critical micelle concentration (CMC) (0.1 M SDS), the pesudoemulsion films exhibit the same step-wise layer thinning observed in foam films under similar conditions. Further, we conduct dynamic thinning experiments on solid/liquid/gas systems and show that aqueous 0.2 M CTAB films sandwiched between glass and air also display discrete thinning transitions. All of these stratification transitions arise from oscillations in the disjoining pressure isotherm, generated by amphiphilic structuring within the film. For 0.1 M SDS dedecane/air pesudoemuslion films, the slope and peak height of the disjoining-pressure oscillations increase with each subsequent amphiphilic layer as film thickness decreases. Magnitudes of the structural forces are low (

From the frontiers of research on ice dynamics in its broadest sense, this review surveys the structures of ice, the patterns or morphologies it may assume, and the physical and chemical processes in which it is involved. Open questions in the various fields of ice research in nature are highlighted, ranging from terrestrial and oceanic ice on Earth, to ice in the atmosphere, to ice on other Solar System bodies and in interstellar space. © 2012 American Physical Society., European Science Foundation workshop Euroice 2008 held in Granada, Spain from 1–4 October 2008; Spanish national project, Hielocris, financed by the Consejo Superior de Investigaciones Científicas; funding from FWF, Austria (No. P23027); MINCINN, Spain (No. FIS2010-16455, No. PR2010-0012, and No. FIS2010-22322-528C02-02); and SNSF, Switzerland (No. 200021121857)

Foam flowing in porous media can exhibit large flow resistances that make it an attractive fluid for improving underground oil recovery. To be an effective displacement fluid, however, the lamellae, which discretize the gas into foam bubbles, must remain stable. This work studies how the stability of single foam films, as gauged by the magnitude of their disjoining pressures, influences the flow resistance of foam in porous media. Steady state pressure gradients of flowing foam in 2.3 μm2 permeability glass beadpacks and disjoining pressure isotherms of single foam films are measured for 10−3 M and 0.017 M sodium dodecyl sulfate (SDS) solutions with and without NaCl. The constant-rate flow experiments show that the addition of salt to 10−3 M SDS increases the pressure gradient in the beadpacks from 0.1 to 4 MPa m−1 at 0.50 M NaCl. Surfactant solutions of 0.017 M SDS content exhibit pressure gradients of 22 MPa m−1, quite independent of salt concentration. Likewise addition of salt to the 10−3 M SDS solutions dramatically influences the disjoining pressure isotherms by raising the rupture pressure from 0.5 to above 15 kPa at 0.50 M NaCl. The 0.017 M SDS solutions display rupture pressures above 30 kPa, independent of salt concentration. We conclude that high repulsive disjoining pressures in single foam films lead to strong foam in porous media with large flow resistance. Further, we find that the limiting capillary pressure for rapid foam coalescence in porous media is close to the rupture pressure of foam lamellae as obtained from measured disjoining pressure isotherms.

The unique mobility-control properties of foam in porous media make it an attractive choice as an injection fluid for enhanced oil recovery. Unfortunately, in many cases oil has a major destabilizing effect on foam. Therefore, it is important to understand how oil destabilizes foam and what surfactant properties lead to increased stability against oil. To explain the stability of foam in porous media in the presence of oil, we generalize the ideas of spreading and entering behavior using Frumkin-Deryaguin wetting theory. This formulation overcomes the inherent deficiencies in the classical spreading and entering coefficients used to explain foam stability against oil. We find that oil-tolerant foam can be produced by making the oil surface ``water wet``. To test our theoretical ideas, we measure foam-flow resistance through 45--70 {mu}m glass beadpacks, surface and interfacial tensions, and disjoining pressure isotherms for foam and pseudoemulsion films for a variety of surfactant/oil systems. Most notably, we measure pseudoemulsion-film disjoining pressure isotherms for the first time and directly establish that pseudoemulsion film stability controls the stability of the foam in the systems we tested. Moreover, we demonstrate the correspondence between stable pseudoemulsion films, negative entering behavior, and oil-tolerant foams.

Disjoining pressure isotherms are measured for single, isolated foam films stabilized with sodium dodecyl sulfate above the critical micelle concentration (cmc). The measured isotherms exhibit an equilibrium oscillatory component that extends out to film thicknesses as large as 50 nm. The oscillations originate from surfactant structuring within the film and are responsible for the multiple black films extensively studied by Perrin in 1918. We find that as film thickness decreases, the slopes and peak heights of the oscillations increase for each subsequent black film encountered. The discrete changes in film thickness observed at each black film transition range from 6 to 10 nm and are a function of the ionic strength and surfactant concentration. Pressures required to rupture the multiple black films are several orders of magnitude lower than the final film-rupture pressure. Finally, the oscillatory form of the disjoining pressure permits quantitative interpretation of stepwise thinning behavior observed in films containing surfactant above the cmc. 50 refs., 13 figs.

Foam, emulsion, and pseudoemulsion films stabilized by surfactants above the critical micelle concentration exhibit pronounced stepwise thinning or stratification. Dynamic removal of a layer is initiated by the formation and subsequent sheeting of a hole (or holes) at each step of the stratified thinning. We outline a nonlinear hydrodynamic stability analysis which successfully models the dynamics of hole formation and sheeting by accounting for an equilibrium oscillatory structural component in the disjoining pressure isotherm. Initiation of a hole is attributed to the nonlinear growth of a hydrodynamic instability during film thinning under the action of a constant capillary pressure and an oscillatory disjoining pressure. Subsequent growth or sheeting of the hole is explained by outward fluid flow within the inhomogeneous thin film as radial pressure gradients develop from curvature variations and viscous resistance to flow. Qualitative comparison is made between the proposed hydrodynamic theory and experimental observations of thinning events and rates. 32 refs., 6 figs.

Thin liquid foam films stabilized with the addition of a temperature-sensitive neutral polymer, poly(N-isopropylacrylamide) (PNIPAM), in the presence of varying amounts of an anionic surfactant, SDS, were investigated using the thin-film balance. Data were analyzed in light of new and previously reported neutron reflectivity data describing the adsorption behavior of PNIPAM/SDS mixtures at the single air-water interface. In the case of thin films prepared from pure polymer solutions, unexpectedly thick and stable films were observed, and increases in solution temperature or polymer molecular weight induce corresponding increases in the thin-film thickness. This behavior is attributed to a stabilization of the films by repulsive entropic forces between long dangling polymer tails adsorbed at the interfaces. The addition of SDS causes a striking decrease in the thin-film thickness that is very well correlated with the desorption of polymer chains from the interface resulting from polymer-surfactant interactions in the bulk. Upon SDS introduction, repulsive forces stabilizing the films vary from purely entropic forces for small amounts of surfactant to supramolecular oscillatory forces at high SDS concentrations, whereas a combination of electrostatic and entropic forces is expected in intermediate concentration regions. Properties of thin films made from PNIPAM and SDS are thus highly sensitive to parameters such as the polymer-surfactant ratio, temperature, and molecular weight, offering precise control of the thin-film thickness that could be used to tailor foam characteristics.

Background: Invasive aspergillosis is one of the most lethal airborne dangers for immune-suppressed subjects. Providing patient protection from such airborne threats requires costly and high-maintenance facilities. We herein evaluate a new self-contained mobile unit as an alternative for creating a patient protective environment. Methods: Airborne contamination levels were monitored for different simulated scenarios and under actual clinical conditions. Functional tests were used to challenge the unit under adverse conditions, and a preliminary clinical study with patients and staff present was performed at 2 different French hospitals. Results: Functional tests demonstrated that the unit can rapidly decontaminate air in the protected zone created by the unit and in the surrounding room. In addition, the protected zone is not sensitive to large disturbances that occur in the room. The clinical study included 4 patients with 150 accumulated days of testing. The protected zone created by the unit systematically provided an environment with undetectable airborne fungal levels (ie, ,1 CFU/m 3 ) regardless of the levels in the room or corridor (P , .01). Conclusions: These tests show that the unit can be used to create a mobile protective environment for immune-suppressed patients in a standard hospital setting. (Am J Infect Control 2007;35:460-6.) Invasive aspergillosis, notably Aspergillus fumigatus, is one of the most lethal airborne dangers for immunesuppressed subjects. Although the reported attributable mortality from invasive pulmonary aspergillosis differs depending on the patient population studied, the Centers for Disease Control and Prevention (CDC) reports rates as high as 95% in recipients of allogeneic bone marrow transplants and patients who have aplastic anemia, compared with rates of 13%-80% in leukemic patients. 1 The most important nosocomial infection caused by Aspergillus sp is pneumonia, and the primary route of acquiring Aspergillus sp infection is via inhalation of the fungal spores. In severely immunesuppressed patients, primary Aspergillus sp pneumonia results from invasion of local lung tissue

Spike-shaped structures are produced by light-driven ablation in very different contexts. Penitentes 1-4 m high are common on Andean glaciers, where their formation changes glacier dynamics and hydrology. Laser ablation can produce cones 10-100 microns high with a variety of proposed applications in materials science. We report the first laboratory generation of centimeter-scale snow and ice penitentes. Systematically varying conditions allows identification of the essential parameters controlling the formation of ablation structures. We demonstrate that penitente initiation and coarsening requires cold temperatures, so that ablation leads to sublimation rather than melting. Once penitentes have formed, further growth of height can occur by melting. The penitentes intially appear as small structures (3 mm high) and grow by coarsening to 1-5 cm high. Our results are an important step towards understanding and controlling ablation morphologies., Accepted for publication in Physical Review Letters