Contribution à la Compréhension de l'Evolution des Propriétés Multiéchelles des Emulsions

The optimization of the stability of emulsions, which are thermodynamically unstable, is one of the major challenge of the cosmetic industry. For more than 20 years, many non-invasive methods and techniques have been developed to measure as objectively as possible the physicochemical properties of these emulsions. These methods aim at evaluating their stability (temporal evolution), their efficiency and their safety (non-toxicity), and become more and more sophisticated as the elaboration processes of these products become complex and innovative. The thesis seeks to define an innovative strategy to optimize the stability of emulsions by a multi-scale, multi-physics approach. It studies more particularly simple cosmetic emulsions, stabilized by an emulsifier. Classically, characterization techniques at macroscopic and microscopic scales are used. Nevertheless, these techniques alone do not allow to anticipate the demixing process. It is indeed necessary to use in complement new non-destructive techniques allowing to follow the structural evolution at the mesoscopic scale. The study carried out highlights new viscoelastic and dielectric quantities characteristic of their structure at this scale. They are based on a better theoretical and experimental consideration of multiple relaxation times, related to destabilization phenomena. From a 6 months study of more than a dozen emulsions of different composition and formulation, controlled and repeatable, the follow-up of their evolution tends to show the relevance of these techniques. They allow not only to trace the variations of interfacial properties, but also to have a simultaneous follow-up of structural modifications. Ultrasonic microrheology and radiofrequency impedancemetry by induction, for example, allow to trace the critical micellar concentration of surfactants and the phase inversion temperature of emulsions. With the aim of using these techniques in industry, the analysis of formulations in tanks was compared to stability tests in tubes. Thanks to the multi-scale and multimodal approach developed, trends in emulsion evolution can be deduced in a predictive manner.L’optimisation de la stabilité des émulsions, thermodynamiquement instables, est un des enjeux majeurs de l’industrie cosmétique. Depuis plus de 20 ans, de nombreuses méthodes et techniques non invasives ont été développées en vue de mesurer le plus objectivement possible, les propriétés physico-chimiques de ces émulsions. Ces méthodes visent à évaluer leur stabilité (évolution temporelle), leur efficacité et leur innocuité (non toxicité), et deviennent d’autant plus perfectionnées que les processus d’élaboration de ces produits deviennent complexes et innovants. La thèse cherche à définir une stratégie innovante d’optimisation de la stabilité des émulsions par une approche multi-échelle, multi-physique. Elle étudie plus particulièrement les émulsions cosmétiques simples, stabilisées par un émulsifiant. Classiquement, des techniques de caractérisation aux échelles macroscopiques et microscopiques sont utilisées. Néanmoins, à elles seules, ces techniques ne permettent pas d’anticiper le processus de démixtion. Il est en effet nécessaire d’utiliser en complément de nouvelles techniques non destructives permettant de suivre l’évolution structurelle à l’échelle mésoscopique. L’étude réalisée met en exergue de nouvelles grandeurs viscoélastiques et diélectriques caractéristiques de leur structure à cette échelle. Elles sont basées sur une meilleure prise en compte théorique et expérimentale des temps de relaxations multiples, liés aux phénomènes de déstabilisation. A partir d’une étude sur 6 mois de plus d’une douzaine d’émulsions de composition et de formulation différentes, maitrisées et répétables, le suivi de leur évolution tend à montrer la pertinence de ces techniques. Elles permettent non seulement de remonter aux variations des propriétés interfaciales, mais également d’avoir un suivi simultané des modifications structurales. La microrhéologie ultrasonore et l’impédancemétrie radiofréquence par induction, permettent, par exemple, de remonter à la concentration micellaire critique des tensioactifs et la température d’inversion de phase des émulsions. Dans un objectif d’utilisation de ces techniques dans l’industrie, l’analyse des formulations en cuve a été comparée aux essais de stabilité en tube. Grâce à l’approche multi-échelle et multimodale développée, on peut déduire de manière préventive les tendances de l’évolution des émulsions

Contribution to the knowledge of the multi-scale properties evolution of emulsions

L'optimisation de la stabilité des émulsions, thermodynamiquement instables, est un des enjeux majeurs de l'industrie cosmétique. Depuis plus de 20 ans, de nombreuses méthodes et techniques non invasives ont été développées en vue de mesurer le plus objectivement possible, les propriétés physico-chimiques de ces émulsions. Ces méthodes visent à évaluer leur stabilité (évolution temporelle), leur efficacité et leur innocuité (non toxicité), et deviennent d'autant plus perfectionnées que les processus d'élaboration de ces produits deviennent complexes et innovants.La thèse cherche à définir une stratégie innovante d'optimisation de la stabilité des émulsions par une approche multi-échelle, multi-physique. Elle étudie plus particulièrement les émulsions cosmétiques simples, stabilisées par un émulsifiant. Classiquement, des techniques de caractérisation aux échelles macroscopiques et microscopiques sont utilisées. Néanmoins, à elles seules, ces techniques ne permettent pas d'anticiper le processus de démixtion. Il est en effet nécessaire d'utiliser en complément de nouvelles techniques non destructives permettant de suivre l'évolution structurelle à l'échelle mésoscopique.L'étude réalisée met en exergue de nouvelles grandeurs viscoélastiques et diélectriques caractéristiques de leur structure à cette échelle. Elles sont basées sur une meilleure prise en compte théorique et expérimentale des temps de relaxations multiples, liés aux phénomènes de déstabilisation. A partir d'une étude sur 6 mois de plus d'une douzaine d'émulsions de composition et de formulation différentes, maitrisées et répétables, le suivi de leur évolution tend à montrer la pertinence de ces techniques. Elles permettent non seulement de remonter aux variations des propriétés interfaciales, mais également d'avoir un suivi simultané des modifications structurales. La microrhéologie ultrasonore et l'impédancemétrie radiofréquence par induction, permettent, par exemple, de remonter à la concentration micellaire critique des tensioactifs et la température d'inversion de phase des émulsions.Dans un objectif d'utilisation de ces techniques dans l'industrie, l'analyse des formulations en cuve a été comparée aux essais de stabilité en tube. Grâce à l'approche multi-échelle et multimodale développée, on peut déduire de manière préventive les tendances de l'évolution des émulsions.The optimization of the stability of emulsions, which are thermodynamically unstable, is one of the major challenges of the cosmetic industry. For more than 20 years, many non-invasive methods and techniques have been developed to measure as objectively as possible the physicochemical properties of emulsions. These methods aim to evaluate their stability (temporal evolution), their efficiency and their safety (non toxicity), and become more and more sophisticated as the elaboration processes of these products become complex and innovative.The thesis seeks to define an innovative strategy to optimize the stability of emulsions by a multi-scale, multi-physics approach. It studies more particularly simple cosmetic emulsions, stabilized by an emulsifier. Classically, characterization techniques at macroscopic and microscopic scales are used. Nevertheless, these techniques do not allow to anticipate the demixing process. It is necessary to use new non-destructive techniques in complement, to follow the structural evolution at the mesoscopic scale.The study carried out highlights new viscoelastic and dielectric quantities characteristic of their structure at this scale. They are based on a better theoretical and experimental consideration of multiple relaxation times, related to destabilization phenomena. From a 6 months study of more than a dozen controlled and repeatable emulsions of different composition and formulation, the follow-up of their evolution tends to show the relevance of these techniques. They allow not only to trace the variations of interfacial properties, but also to have a simultaneous follow-up of structural modifications. Ultrasonic microrheology and radio frequency impedancemetry by induction allow, for example, to trace the critical micellar concentration of surfactants and the phase inversion temperature of emulsions.With the aim of using these techniques in industry, the analysis of formulations in tanks has been compared to stability tests in tubes. Thanks to the developed multi-scale and multimodal approach, trends in emulsion evolution can be deduced in a predictive manner

Etude Multi-Echelle et Multi-Physique de l’Ordre d’Introduction des Phases d’une Emulsion

International audiencePour optimiser la stabilité d'une émulsion, une investigation multi-échelle est nécessaire. Les moyens préventifs classiques d'étude se font par l'analyse de l'inversion de phase (H/E ou E/H) ou par le changement de paramètres, tels que la composition, le procédé d'émulsification et les conditions environnementales. Ce travail consiste en une étude préliminaire multiphysique et multi échelle, par un changement d'ordre d'introduction des phases. Les caractéristiques mécaniques et électriques sont étudiées à deux échelles d'investigation par deux nouvelles techniques : rhéologie ultrasonore et impédancemétrie radiofréquence. La comparaison des caractéristiques, macroscopiques et mésoscopiques, cherche à identifier les grandeurs d'influence précurseurs d'une (in)stabilité

Multimodal O/W emulsion structuration characterization using water and emulsion thickening ranges

International audienceTo ensure the stability of emulsions, a thickening agent is often used to induce a higher viscosity of the continuous aqueous phase and reduce the possibility of gravitational separation(1). In some cases, these agents require a base to increase the thickening of emulsions and this process can be observed by following the viscosity as a function of the pH(2). Our work attempts to show the link between gelation process and emulsion stability investigated through the use of two innovative measurement techniques at the mesoscopic scale: micro-rheology by ultrasounds and electrical complex dielectric characterization by contactless radiofrequency spectroscopy. The first one allows to better understand the emulsion structuration through the measurement of the visco-elastic properties(3). The second one is used to get information about polarizability of the mixing and conductivity of the continuous phase(4). A comparison is done between the aqueous phase (water + Carbopol® CETD 2050: gel phase) and the equivalent emulsion (aqueous phase + oil: Isopropyl Palmitate + surfactants: Eumulgin® SMO 20/Cutina® GMS V), for different pH by changing the amount of base (Triethanolamine). Both are made on the same pH range (3.5 – 6) to emphasize steric behavior rather than the electrical one. The mesoscopic characterizations highlight the impact of oil on the gelation state. They also show the limits of pH adjustments on increasing viscosity and electronic repulsion between oil droplets, which are stability-promoting factors. The results are completed by complementary classical characterizations such as conductivity, rheological and optical microscopy measurements, to correlate them with documented macroscopic knowledge(5). (1) Piorkowski D.T., et al, 2014(2) Abdolmaleki K., et al, 2016(3) Gauthier V., et al, 2017(4) Dinh T.H.N., et al, 2016(5) Gutowski I., et al, 200

Phase Inversion Temperature Monitoring with Contactless RF Impedancemetry for O/W Emulsion Optimization

International audienceThe phase inversion temperature (PIT) designates the temperature for which a heated emulsion changes from an Oil-in-Water (O/W) state to a Water-in-Oil (W/O) state during a rise in temperature[1]. This important parameter is used to optimize the emulsion stability by finding an optimal storage condition or on the contrary to determine the optimal formulation for oil recovery[2]. The PIT can be affected by three main variables: formulation, composition and protocol[3], and several technics can be used to identify this singular temperature. It is mostly determined by conductometry at a macroscopic scale and it can also be followed by viscosity measurements or endothermic transition determination[4]. In order to optimize the formulation, it is interesting to evaluate the PIT accurately at a mesoscopic scale. Our work aims to identify the PIT and the inner changes taking place in O/W emulsions by monitoring the complex dielectric properties at radiofrequency (RF) range (140 MHz). A contactless RF impedance measuring device developed by the SATIE Laboratory is used[5]. This non-destructive and non-invasive technique allows to measure simultaneously conductivity (σ) and permittivity (ε) evolutions of complex fluids. The first one is directly related to the charge mobility while the second one is related to the polarizability. The ratio between the dissipated and stored energies provides information on the internal structure of the studied environment.The measurement results obtained with our RF impedancemeter are compared with those obtained by low frequency conductivity. The measurements are carried out in parallel between 10 to 90°C for eleven different chosen compositions. This comparison shows phenomena measured respectively at two scales of investigation: mesoscopic and macroscopic. This comparison helps to link the electrical evolutions inside the emulsions. These measurements also enable to monitor the stability of these emulsions over time and to correlate them with the overall structuration of the emulsions. These results were supplemented by additional observations by optical microscopy and ultrasonic rheology.[1]K. Shinoda and H. Arai, “The Effect of Phase Volume on the Phase Inversion Temperature of Emulsions Stabilized with Nonionic Surfactants,” J. Colloid Interface Sci., vol. 25, no. 3, pp. 429–431, 1967, doi: https://doi.org/10.1016/0021-9797(67)90051-3.[2]G. Lemahieu, J. F. Ontiveros, V. Molinier, and J.-M. Aubry, “Using the dynamic Phase Inversion Temperature (PIT) as a fast and effective method to track optimum formulation for Enhanced Oil Recovery,” J. Colloid Interface Sci., vol. 557, pp. 746–756, 2019, doi: https://doi.org/10.1016/j.jcis.2019.09.050.[3]J. L. Salager, “Emulsion Phase Inversion Phenomena,” in Emulsions and Emulsion Stability, 2006, pp. 185–226.[4]V. B. Souza, L. S. Spinelli, G. Gonzalez, and C. R. E. Mansur, “Determination of the phase inversion temperature of orange oil/water emulsions by rheology and microcalorimetry,” Anal. Lett., vol. 42, no. 17, pp. 2864–2878, 2009, doi: 10.1080/00032710903137392.[5]X. Zhou, “Nouveau systeme de controle radiofréquence de micro-algues pour la santé et le bien-être,” Université de Cergy Pontoise, 2016

Multimodal O/W emulsion structuration characterization using water and emulsion thickening ranges

International audienceTo ensure the stability of emulsions, a thickening agent is often used to induce a higher viscosity of the continuous aqueous phase and reduce the possibility of gravitational separation(1). In some cases, these agents require a base to increase the thickening of emulsions and this process can be observed by following the viscosity as a function of the pH(2). Our work attempts to show the link between gelation process and emulsion stability investigated through the use of two innovative measurement techniques at the mesoscopic scale: micro-rheology by ultrasounds and electrical complex dielectric characterization by contactless radiofrequency spectroscopy. The first one allows to better understand the emulsion structuration through the measurement of the visco-elastic properties(3). The second one is used to get information about polarizability of the mixing and conductivity of the continuous phase(4). A comparison is done between the aqueous phase (water + Carbopol® CETD 2050: gel phase) and the equivalent emulsion (aqueous phase + oil: Isopropyl Palmitate + surfactants: Eumulgin® SMO 20/Cutina® GMS V), for different pH by changing the amount of base (Triethanolamine). Both are made on the same pH range (3.5 – 6) to emphasize steric behavior rather than the electrical one. The mesoscopic characterizations highlight the impact of oil on the gelation state. They also show the limits of pH adjustments on increasing viscosity and electronic repulsion between oil droplets, which are stability-promoting factors. The results are completed by complementary classical characterizations such as conductivity, rheological and optical microscopy measurements, to correlate them with documented macroscopic knowledge(5). (1) Piorkowski D.T., et al, 2014(2) Abdolmaleki K., et al, 2016(3) Gauthier V., et al, 2017(4) Dinh T.H.N., et al, 2016(5) Gutowski I., et al, 200

Particle filters for partially observed Markov chains

Paper WA2―5International audienceWe consider particle filters in a model where the hidden states and the observations form jointly a Markov chain, which means that the hidden states alone do not necessarily form a Markov chain. This model includes as a special case non-linear state-space models with correlated Gaussian noise. Our contribution is to study propagation of errors, stability properties of the filter, and uniform error estimates, using the framework of Le Gland and Oudjane

Another Multiparametric Way In Planning Of Experiments For O/W Emulsion Design

International audienceDefining an effective way to design stable emulsions with limited resources is a challenge that every laboratory is facing at least once. Two ways of experiments have been trending as a cost-and-time-efficient method to explore factor impact (environmental ones such as temperature, or inherent like composition), and finally optimize formulations: i. multidimensional methods based on a dichotomic approach which require to change parameters one by one. These methods are commonly known to be quite ineffective to accurately correlate parameters; ii. in Design of Experiments (DOE), only a restricted number of experiments are required to understand, develop and predict new paths to formulation or new theories, though it usually requires specific and expensive software and specific mathematic skills. Our work aims to show a resource-effective way to plan experiments based on a random equidistribution of raw material ratios (Oil/Surfactants/Water: O/S/W) in order to identify O/W emulsion stability condition boundary

Another Multiparametric Way In Planning Of Experiments For O/W Emulsion Design

International audienceDefining an effective way to design stable emulsions with limited resources is a challenge that every laboratory is facing at least once. Two ways of experiments have been trending as a cost-and-time-efficient method to explore factor impact (environmental ones such as temperature, or inherent like composition), and finally optimize formulations: i. multidimensional methods based on a dichotomic approach which require to change parameters one by one. These methods are commonly known to be quite ineffective to accurately correlate parameters; ii. in Design of Experiments (DOE), only a restricted number of experiments are required to understand, develop and predict new paths to formulation or new theories, though it usually requires specific and expensive software and specific mathematic skills. Our work aims to show a resource-effective way to plan experiments based on a random equidistribution of raw material ratios (Oil/Surfactants/Water: O/S/W) in order to identify O/W emulsion stability condition boundary

Remuneration systems used in the fishing sector and their consequences on crew wages and labor rent creation

In most fisheries worldwide, crew are paid through different shared remuneration systems rather than a fixed wage. In shared remuneration systems, wages can significantly increase when the economic performance of vessels improve, and consequently provide incentives to workers. However, in recent years, mainly due to high overexploitation levels that lead to reduced productivity and consequently lower salaries shared remuneration systems have lost their attractiveness. Different remuneration systems applied in fisheries world-wide are described and analyzed comparatively. Results explain how crew wages and rent distribution outcomes vary between the different remuneration systems depending on the state of exploitation of the resource