Developing microcapsule membranes for the encapsulation of active ingredients of varying molecular weights

Over the last 5 years our research group has developed a range of microcapsule and particle designs adapted to the characteristics of the ingredient to be encapsulated. In this presentation, I will give examples of core-shell particles for use in electrophoretic display applications and semi-permeable and impermeable microcapsule shells for the encapsulation of large and small molecular weight species. I will first focus on our ability to use environment-responsive polymers to manage the permeability of the polymer shells built around emulsion droplets precursors and the potential to use membrane emulsification techniques to enable the manufacture of such emulsions on multi-litre scales. Subsequently, I will introduce a recently developed method for the preparation of metal-coated emulsion droplets for the long-term retention of small, volatile encapsulated species. I will indicate the key aspects of the synthesis method for such metal shells and demonstrate our ability to control the thickness of the shell deposited on the surface of the droplets and exemplify the release properties of these microcapsule

Toward a soft image watermarking

This paper introduces a new approach of watermarking for copyright protection. The goal of the method is to hide signatures composed of w segments of r bits in digital images. The framework itself is founded upon a wavelet transformed domain, and an additive embedding rule using products of orthogonal basis functions. We will show how the choice of different kinds of orthogonal functions allows to improve the robustness of the watermarking scheme to signal processing or geometric attacks.Cet article introduit une nouvelle méthode de tatouage pour la protection d'images fixes. La méthode permet de cacher une signature dans une image, sous la forme de w paquets de r bits. Le schéma de tatouage est additif, et la marque elle-même est calculée par addition de produits de couples de fonctions orthogonales. Nous montrerons comment le choix des fonctions orthogonales peut être fait, de façon à rendre le tatouage robuste face à différents types d'attaques. Puis, nous donnerons quelques résultats permettant d'apprécier la robustesse du tatouage, et discuterons des améliorations possibles pouvant être apportées à une telle méthode

Watermarking security: theory and practice

This article proposes a theory of watermarking security based on a cryptanalysis point of view. The main idea is that information about the secret key leaks from the observations, for instance watermarked pieces of content, available to the opponent. Tools from information theory (Shannon's mutual information and Fisher's information matrix) can measure this leakage of information. The security level is then defined as the number of observations the attacker needs to successfully estimate the secret key. This theory is applied to two common watermarking methods: the substitutive scheme and the spread spectrum based techniques. Their security levels are calculated against three kinds of attack. The experimental work illustrates how Blind Source Separation (especially Independent Component Analysis) algorithms help the opponent exploiting this information leakage to disclose the secret carriers in the spread spectrum case. Simulations assess the security levels derived in the theoretical part of the article

Watermarking security part II: practice

This second part focuses on estimation of secret parameters of some practical watermarking techniques. The first part reveals some theoretical bounds of information leakage about secret keys from observations. However, as usual in information theory, nothing has been said about practical algorithms which pirates use in real life application. Whereas Part One deals with the necessary number of observations to disclose secret keys (see definitions of security levels), this part focuses on the complexity or the computing power of practical estimators. Again, we are inspired here by the work of Shannon as in his famous article [15], he has already made a clear cut between the unicity distance and the work of opponents' algorithm. Our experimental work also illustrates how Blind Source Separation (especially Independent Component Analysis) algorithms help the opponent exploiting this information leakage to disclose the secret carriers in the spread spectrum case. Simulations assess the security levels theoretically derived in Part One

Watermarking security part I: theory

This article proposes a theory of watermarking security based on a cryptanalysis point of view. The main idea is that information about the secret key leaks from the observations, for instance watermarked pieces of content, available to the opponent. Tools from information theory (Shannon's mutual information and Fisher's information matrix) can measure this leakage of information. The security level is then defined as the number of observations the attacker needs to successfully estimate the secret key. This theory is applied to common watermarking methods: the substitutive scheme and spread spectrum based techniques. Their security levels are calculated against three kinds of attack

Facile two-step encapsulation of small species in a metallic shell

Microencapsulation of small volatile chemicals remains an unsolved challenge for both industry and academia as most capsule walls tend to be permeable to such species. Metal coated capsules are of particular interest as they offer much reduced diffusion coefficient for this same species. A continuous metal shell can provide reduced permeability compared to a standard a polymer shell and can prevent the escape of volatile encapsulated compounds. The permeability of continuous metal films is much lower than that of polymer shells due to their crystalline structure. Additionally, there is potential opportunity to exploit electrical, mechanical, optical and magnetic properties of the metallic shell for additional capsule functionality. Metal encapsulated compounds can have improved shelf life, potentially including those with high sensitivity to water and oxygen. Metallic encapsulation of small species has successfully been demonstrated within our research group1; however the process developed so far has used a solvent evaporation method to form a polymeric capsule on which the metallic film is deposited. This technique tends to start with an oil phase mixture where the oil to be encapsulated is only present up to ~15% and is only suitable for a number of oils and stabilisers due to limiting wetting characteristics. Additionally harmful solvents which require adequate ventilation such as dichloromethane are often used. Other methods exist to produce polymer shells encapsulating an emulsion core, however these also often suffer from initial loss of a small, volatile core via diffusion through the polymer shell during processing. In the method proposed here the metallic film is deposited directly onto a Pickering emulsion droplet stabilised with the catalytic nanoparticles, hence allowing 100% of the active material to be encapsulated. It removes the need for a polymer shell all together. In the method we developed, polymer stabilised platinum nanoparticles act as both the emulsifier by adsorbing to the oil-water interface and the catalyst for the growth of a secondary metallic gold film via electroless deposition. In this presentation we will show the effect of gold salt concentration on the resulting metal film thickness and oil release rates. Please click Additional Files below to see the full abstract

Étude du crabe rouge profond Geryon quinquedens en Côte d'Ivoire. 2 - Éléments de biologie et d'écologie avec références aux résultats obtenus au Congo

Geryon quinquedens is present along the West African continental slope at depths from 300 to 1000 m, on silt-clay sediments. Geryon is a cold and rather poorly oxygenated water loving species. It is easily caught by traps as it is a scavenger and predatory crustacea. In a given area its distribution does not appear to be homogeneous: for example, densities of red crabs are higher in the eastern and western region of Côte d'Ivoire than in the central zone. Similar observations can be made off Congo, Angola and United States. It can be assumed that there is a relation between the abundance of Geryon and the productivity level of the area. Geographical variations of sex ratio are suspected to be correlated with the density distribution. Males and females have not the same bathymetric distribution: females are only common in the shallower waters (300-500 m) whereas males are present in the whole biotope. Seasonal migrations occur down and up the slope in both the sexes and are certainly related to the reproductive biology. Knowledge of the reproductive biology is also necessary to understand fishing-trap catch rate: egg maturation extends over several months and ovigerous females are exceptionally caught by traps; males also are less available during the same period (March to August) when migrations are less important; in this period, mean size increases and probably this happens at the end of a moult. From September to February the catch-rates increase. Growth is slow compared with other littoral Guinean Crustacea (Peneides). Females become sexually mature at a size of 80 mm (carapace width): modification in the allometric relations of abdomen and carapace are then conspicuous

Conference Program

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Controlled adsorption of metallic nanoparticles on polymeric microcapsules with a view to growing secondary continuous metal films

Small, volatile actives cannot be micro-encapsulated efficiently over the lifetime of a product using current encapsulation techniques. This is due to the inherent porosity of the polymeric membranes which are used as the capsule shell material. We have developed a method for preventing undesired loss of encapsulated actives which prevents loss of the core into ethanol over 90 days +. Oil core microcapsules are produced using oil-in-water emulsification followed by co-solvent extraction to precipitate a polymeric shell around the oil core. Metallic catalytic nanoparticles are then physically adsorbed onto the microcapsules and used to catalyse the growth of a continuous secondary metallic film via electroless deposition. It is important to have good control over the primary nanoparticle adsorption density which requires a good control over and understanding of the original nanoparticle (NP) synthesis. In this work we use Quartz crystal microbalance (QCM) and transmission electron microscopy (TEM) to demonstrate the ability to control NP adsorption densities by varying several parameters such as concentration of polymeric stabiliser used in the original NP dispersion synthesis and NP dispersion concentration. We show that NP films form in seconds and demonstrate good adsorption energies. We also discuss/explain the semi regular hexagonal packing of the NP cores we observe under TEM. Please click Additional Files below to see the full abstract