Catanionic surfactants in polar cohesive solvents. Impact of solvent physical parameters on their aggregation behavior

On trouve peu d'études, dans la littérature, sur les tensioactifs (TA) catanioniques - formés d'une paire d'ions entre un TA anionique et un TA cationique - en milieu nonaqueux. Nous avons voulu rationaliser, dans ce travail, le comportement d'agr´egation de ce type de tensioactifs en les étudiant comparativement dans l'eau, dans le formamide, dans le glycérol et dans des mélanges de ces solvants polaires et cohésifs. Nous avons pour ce faire synthétis´e trois différents types de TA catanioniques (alcanoate d'alkylammonium, tétradécanoate de norbornène méthylène ammonium, alcanoate de N-alkylammonium-1-d´eoxy-D-glucitol). Les TA catanioniques ont la propriété de s'agréger en vésicules dans l'eau. Dans le cas des autres solvants ou mélanges des solvants, nous avons constat que le type d'agrégat que forment les TA catanioniques dépend de deux principaux facteurs : la constante diélectrique du solvant et le degré d'interaction entre les deux TA. En effet, le formamide ayant une constante diélectrique plus élevée que l'eau, il exerce une force dissociative sur la paire d'ions qui peut ainsi être séparée pour conduire `a un mélange de TA ioniques monocaténaires formant alors des micelles. D'autre part, une augmentation de l'effet hydrophobe, obtenu en utilisant des chaînes hydrophobes plus longues, renforce la paire d'ions et conduit `a la formation de vésicules dans le formamide pur. Par ailleurs, l'étude du système tétradécanoate de norbornène méthylène ammonium a également montré l'importance des interactions hydrophobes entre les têtes polaires, un autre facteur pouvant favoriser la formation de vésicules dans le formamide pur.In the literature, little work has been done on catanionic surfactants in non-aqueous solution. Catanionic surfactants are ion pairs composed of an anionic and a cationic surfactant. In the frame of this work, we wanted to rationalize the aggregation behavior of this surfactant type by studying them in water, in formamide, in glycerol and in some mixtures of these polar and cohesive solvents. For this issue, we synthesized three different types of catanionic surfactants (alkylammonium alkanoate, norbornene methyleneammonium tetradecanoate, N-alkylammonium-1-deoxy-D-glucitol alkanoate). Catanionic surfactants usually form vesicles in water. In the case of non-aqueous solvents and mixtures of solvents, we could observe that the type of aggregates formed with catanionic surfactants depends on two major factors: the dielectric constant of the solvent and the degree of interaction between the two surfactants. Effectively, formamide having a higher dielectric constant than water exerts a dissociative force on the ion pair. The ion pair can be separated leading to a mixture of monocatenar ionic surfactants, which then forms micelles. On the other hand, hydrophobic effects can be increased using longer hydrophobic chains, which reinforce the ion pair and lead to the formation of vesicles in pure formamide. Moreover, the study on the norbornene methyleneammonium tetradecanoate showed the importance of hydrophobic headgroup-headgroup interactions, an additional parameter which can favor vesicle formation in pure formamide

Passive microrheology as a useful tool for milk gel analyses

Passive microrheology based on Diffusing Wave Spectroscopy (DWS) [1,2] is presented as a straightforward tool for the analysis of milk gel preparation. Diffusing Wave Spectroscopy consists of analysing the interferential images of light, which is backscattered by the sample. This so called speckles images, which are detected by a CCD camera, change in time due to the Brownian motion of the particles that scatter the light. The variation of the images as a function of time can be directly correlated to the viscoelastic properties of the sample. As it is an optical method, it is perfectly adapted to study the weak gels of milk products. Nowadays, milk gels such as yogurts or chees have attracted lots of interest due to its growing market. The milk properties, such as pH, calcium content and protein content are very important and change significantly the cheese properties. This work shows how passive microrheology can be used to follow up the milk gel formation with exact gel time determination. Gel time was determined by a new rescaling method, namely Time-Cure Superposition (TCS) [3,4]. This data processing determines the gel point according to the Winter-Chambon criterion [5]. Moreover, the viscoelastic properties of the preparation can be compared according to parameters, such as the protein enrichment, calcium ion addition or others. Results were compared to other instruments (texturometers, rheometer, Optigraph®, etc.). References: [1] D. A. Weitz et al., in Dynamic Light Scattering, W. Brown (Ed.) (Oxford Univ. Press, New York (1993), Chap. 16. [2] D. J. Pine et al., Phys. Rev. Lett. 1988, 60, 1434. [3] T. H. Larsen, E. M. Furst, Phys. Rev. Letters, 2008, 100, 14600 [4] K. M. Schultz, E. M. Furst, Soft Matter, 2012, 8, 6198 [5] H. H. Winter, F. Chambon, J. Rheology 1986, 30, 364-38

Prediction of collapse time of polymer stabilized O/W emulsions

Polymers are widely used in the industry as an ingredient to increase the stability of formulations. Depending on their concentration, they can act as depletion agents or gel agent. The stability of these systems is driven by the polymers and the structure of the network of droplets and can lead to collapse of the emulsions. In this work, Multiple Light Scattering device is used to monitor the behaviour of w/o emulsions stabilized with polymers. The heart of the optical scanning analyser is a detection head, which moves up and down along a flat-bottomed cylindrical glass cell (see figure). The detection head is composed of a pulsed near infrared light source (wavelength = 880 nm) and two synchronous detectors. The transmission detector (at 180°) receives the light, which goes through the sample, while the backscattering detector (at 45°) receives the light scattered backward by the sample. The detection head scans the entire height of the sample, acquiring transmission and backscattering data every 40 µm. Please click Additional Files below to see the full abstract

Catanionic surfactants in polar cohesive solvents (impact of solvent physical parameters on their aggregation behavior)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Impact of Solvent Physical Parameters on the Aggregation Process of Catanionic Amphiphiles

International audienc

Solvent-free model for self-assembling amphiphilic cyclodextrins. An off-lattice Monte Carlo approach in two dimensions

By performing off-lattice Monte Carlo simulations in a two-dimensional space, we investigate the aggregation behavior of model Bouquet-shaped amphiphilic cyclodextrins. These molecules are able to self-assemble into a variety of supramolecular structures, such as micelles, vesicles, and long double-layered filaments. At high packing fractions, inverted micellar phases and lamellar liquid crystals have also been observed. Despite the number of approximations and restrictions imposed in our model, where the solution degrees of freedom are kept implicit and only the main physicochemical details are considered, we are able to reproduce the self-assembling behavior of amphiphilic cyclodextrins in its essential and most characteristic picture. The calculations of the cluster size distribution, density profiles, and radial distribution functions permit the characterization of the aggregates formed in the self-assembly process.A.P. acknowledges a Beatriu de Pinós postdoctoral grant from Generalitat de Catalunya (2009BP-B00058)This work has also been supported by grant 2009-SGR-961 from Generalitat de Catalunya.Peer reviewe

Reference materials for measuring the size of nanoparticles

This article discusses the requirements for reference materials (RMs) for measuring the size of nanoparticles (NPs). Such RMs can be used for instrument calibration, statistical quality control or interlaboratory comparisons. They can come in the form of suspensions, powders or matrix-embedded materials [i.e. NPs integrated in a natural matrix (e.g., food, soil, or sludge)]. At present, uncertainty about the most suitable form of material, the most relevant measurands and the most useful metrological-traceability statement inhibits the production of NP RMs. In addition, the lack of validated methods and qualified laboratories to produce NP RMs present formidable challenges. Metal, inorganic and organic NPs are available, but most of them are intended to be laboratory chemicals. With the exception of latex materials, certified RMs are not available, although some metrology institutes have started to develop such materials for colloidal gold and silica particles.The financial support by the European Commission through the 7th Framework Program, Contract No. 245162, Nanoparticles in Food: Analytical methods for detection and characterization (NanoLyse) is gratefully acknowledged.Peer reviewe

Physico-chemical characterization of hexosomesand vesicles from nature-like branched-chain glycolipids

Trabajo presentado al 3rd International NanoFormulation 2012, celebrado en Barcelona entre el 28 de mayo y el 1 de junio de 2012