Propriétés physico-chimiques des mousses : études approfondies sur des mousses modèles et études exploratoires sur de nouvelles mousses.

This experimental thesis on the physics of liquid foams highlights the coupling between the different organization length scales in foams. In the first part of this work we report some results about the physical chemistry of aqueous foams by testing new formulations. We show how a surfactant foam doped with laponite presents an unusual behaviour, and interfacial studies about a thermo sensitive polymer, poly(N-isopropylacrylamide), and a photosensitive surfactant (AzoTAB). In a second part, we talk about a new experimental protocol in oscillatory rheology applied to aqueous foams and discuss about acoustical properties of this material.Dans cette thèse expérimentale sur la physique des mousses liquides, plusieurs thématiques sont abordées ayant pour point commun la mise en évidence du couplage entre les différentes échelles d'organisation de la mousse. La première partie traite plus spécifiquement de physico chimie par la modification de la formulation des solutions utilisées. Nous avons ainsi réalisé des mousses dopées à la laponite, présentant des propriétés inhabituelles. Nous exposons par ailleurs les résultats d'études interfaciales d'un polymère thermosensible, le poly(N-isopropylacrylamide) et d'un tensioactif photosensible (AzoTAB). Dans la seconde partie de cette thèse, nous discutons d'un nouveau protocole de rhéologie appliqué aux mousses ainsi que de propriétés acoustiques de ce matériau

Propriétés physico-chimiques des mousses (études approfondies sur des mousses modèles et études exploratoires sur de nouvelles mousses)

Dans cette thèse expérimentale sur la physique des mousses liquides, plusieurs thématiques sont abordées ayant pour point commun la mise en évidence du couplage entre les différentes échelles d'organisation de la mousse. La première partie traite plus spécifiquement de physico chimie par la modification de la formulation des solutions utilisées. Nous avons ainsi réalisé des mousses dopées à la laponite, pre sentant des propriétés inhabituelles. Nous exposons par ailleurs les résultats d'études interfaciales d'un polymère thermosensible, le poly(N-isopropylacrylamide) et d'un tensioactif photosensible (AzoTAB). Des expériences réalisées en micropesanteur sont finalement présentées. Dans la seconde partie de cette thèse, nous discutons d'un nouveau protocole de rhéologie appliqué aux mousses ainsi que de propriétés acoustiques de ce matériau.This experimental thesis on the physics of liquid foams highlights the coupling between the different organization length scales in foams. In the first part of this work we report some results about the physical chemistry of aqueous foams by testing new formulations. We show how a surfactant foam doped with laponite presents an unusual behaviour, and interfacial studies about a thermo sensitive polymer, poly(N-isopropylacrylamide), and a photosensitive surfactant (AzoTAB). Some experiments realised in microgravity are presented. In a second part, we talk about a new experimental protocol in oscillatory rheology applied to aqueous foams and discuss about acoustical properties of this material.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

From the Thermal Responsivity of a Model Polymer to Responsive Interfaces,Foams and Gels

Liquid dispersions like foams or emulsions, as well as gels, are potentially good templates for conceiving stimuli-responsive materials ; in particular, this is due to the hierarchical organization at different lengthscales and to the fact that tiny effects at mesoscopic scales can have strong macroscopic impact. So, doping soft materials with responsive molecules is a possible route to create macroscopic responsive materials. However, one has to understand how the responsivity at the scale of the molecule can be efficiently transposed to supramolecular and macroscopic structures. In that respect, we have investigated - starting from a model thermo-responsive polymer - if and how responsive liquid interfaces, foams and gels can be made. By responsive, we mean drastic and reversible changes induced by changing temperature only over a small range of degrees. Here we report results based on the use of poly N-isopropylacrylamide - PNIPAM - a thermo-sensitive polymer, which is known to have various reversible configurations in bulk depending on the temperature. We first present interfacial results showing how dynamical properties (both the dilational and shear interfacial rheology) can be widely and reversibly tuned by small changes of temperature, and how the mixing with surfactants modify these results. Based on these results, we present our attempts to make thermo-sensitive 3D foams, containing PNIPAM associated or not with surfactants : we then discuss if and how the foam properties can be strongly and reversibly tuned by the external temperature. Lastly, we present results on pnipam-based gels ; together with responsive properties, we will show that macroscopic deformations (bending, twisting) can be induced if the thermal stimuli is not spatially homogeneous. All together, these studies have allowed us to better understand how complex the route from a stimuli-responsive molecule to a stimuli-responsive materials can be

Dynamics of poly-nipam chains in competition with surfactants at liquid interfaces : from thermoresponsive interfacial rheology to foams.

International audienceWe report results on the interfacial viscoelasticity and foaming of solutions of a thermoresponsive polymer (poly-n-isopropylacrylamide) with and without added surfactants, and as a function of temperature. With pure polymer solution, a clear transition is evidenced: both interfacial shear and dilational rheology shift from a fluid-like to a solid-like behavior at a well-defined temperature. The high temperature regime shows that the layer shares many features with soft glassy systems. At all temperatures, the foaming is low and the foam produced is unstable. Adding a surfactant not only helps to foam and to stabilize the foam, but also removes the thermal responsivity of the interfacial viscoelasticity. Under the conditions used here, we observe that the surfactant concentration threshold for altering the high temperature interfacial viscoelasticity is low, and is of the order of 1% of the surfactant critical micelle concentration. It turns out to be very different from critical values for the polymer-surfactant association found previously by structural studies (in bulk and at interface), and also below the threshold value required to stabilize the foam

Towards new type of foams and responsive materials

Aqueous foams are usually made with solutions of low molecular weight surfactants. The properties of such surfactant foams are well characterized, and foams are now widely used in industry as well as everyday life. Today, in order to create new applications, it is important to develop new types of foams or emulsions having original behavior, especially in their aging. It is then also tempting to use foam as templates for creating responsive materials. Here we present our first attempts of making new type of foams by adding original chemical components in the foam formulation. We first present results on foams containing laponite particles. Solutions of laponite are an example of colloidal glasses. By adjusting the laponite concentration, we can tune the timescale of the laponite glass transition. In that respect, within the liquid network of the foam, this glass transition can be obtained at any desired time during the foam aging. We then show how this effect has an impact on the drainage, coarsening and rheological properties of the foam. We also report results with foams containing thermosensitive polymers, and show how the foam behavior can be tuned by the external temperature. Lastly, we present some results with foam stabilized by different types of surfactant di-mer (gemini-like molecules) and tri-mer. For all our experiments, we have monitored the foaming and the 3D foam stability by electrical, optical and acoustic methods. Different types of foams are made for all the systems : at various bubble size and liquid fraction, in order to determine for which conditions the effects are optimized

Oscillatory rheometry of aqueous foams : surfactant, liquid fraction, aging and protocol effects

International audienceWe report a new set of rheological data on well controlled aqueous foams. We investigate and analyze how the linear viscoelastic regime, the foam yielding and the non-linear regimes above yielding actually depends on the interfacial properties, bubble size, liquid fraction and foam age. Results are compared to previous works on foams and emulsions, and to models. The viscoelastic linear properties and yield stress are strongly dependent on the liquid fraction, and for a low molecular weight surfactant, providing "fluid-like" interfaces, a universal behavior is recovered. However, discrepancies are observed for protein foams, and are discussed in relation to the interface and thin film properties. We also discuss the features of the non linear regimes above the yield stress, which cannot be fully explained by recent models. As the foam ages, the evolution of the viscoelastic properties can be interpreted in terms of foam drainage and coarsening; nevertheless, some of the aging effects remain unexplained. We also present the results of a new mode of oscillatory experiments, at constant shear rate the macroscopic results obtained with this new protocol turn out to be strikingly well correlated to microscopic measurements at the bubble scale. We then show that a same solid-liquid transition is obtained either by applying a deformation, or by the foam coarsening; we propose that the transition is controlled by a Deborah number De, which can be seen either as a frequency ratio or a deformation ratio. For De 1)

Thermo-Responsive Interfaces, Films and Foams

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