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Ref Arxiv: 1811.06903
DOI: 10.1039/c7sm00596b
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Vegetable oil based hybrid films were developed thanks to a novel solvent- and heating- free method at the air-water interface using silylated castor oil cross-linked via a sol-gel reaction. To understand the mechanism of the hybrid film formation, the reaction kinetics was studied in detail by using complementary techniques: rheology, thermogravimetric analysis, and infrared spectroscopy. The mechanical properties of the final films were investigated by nano-indentation, whereas their structure was studied using a combination of wide-angle X-ray scattering, electron diffraction, and atomic force microscopy. We found that solid and transparent films form in 24 hours and, by changing the silica precursor to castor oil ratio, their mechanical properties are tunable in the MPa-range by about a factor of twenty. In addition to that, a possible optimization of the cross-linking reaction with different catalysts was explored and finally, cytotoxicity tests were performed on fibroblasts proving the absence of film toxicity. The results of this work pave the way to a straightforward synthesis of castor-oil films with tunable mechanical properties: hybrid films cross-linked at the air-water interface combine an easy and cheap spreading protocol with the features of their thermal history optimized for possible future micro/nano drug loading, thus representing excellent candidates for the replacement of non-environment friendly petroleum-based materials.

Ref HAL: hal-01588917_v1
DOI: 10.1039/c7py00531h
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Block copolymer assemblies are fascinating objects that have been studied for years. In this work, the PS-PNaSS-PS ABA triblock copolymer was synthesized by RAFT polymerization and self-assembled in a selective medium (THF/water). Various morphologies of aggregates were identified (spheres, cylinders, and vesicles) but we focused on large compound vesicles which gave birth to porous materials after solvent evaporation. The change in solvent composition upon drying was modeled and correlated to the change in morphology observed using microscopy techniques such as AFM, TEM and cryo-TEM. The large compound vesicles were found to partially fuse to form a bulk material before the vesicular compartments were opened to yield pores of about 30 nm.

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DOI: 10.1039/c6cp06475b
WoS: WOS:000394940400044
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Gene therapy is based on nucleic acid delivery to pathogenic cells in order to modulate their gene expression. The most used non viral vectors are lipid-based nanoaggregates, which are safer than viral carriers and have been shown to assemble easily with both DNA and RNA. However, the transfection efficiency of non viral carriers still needs to be improved before intensive practise in clinical trials can be implemented. For this purpose the in depth characterization of the complexes formed by nucleic acids and their transporters is of great relevance. In particular, information on the structure and assembly mechanism can be useful to improve our general knowledge of the se artificial transfection agents. In this paper the complexation mechanism of short interfering RNA and DNA molecules (siRNA and siDNA, respectively) with cationic micelles are investigated by combining Small Angle X-Ray Scattering experiments and Molecular Dynamics simulations. Micelles were obtained by Gemini surfactants with different spacer length (12-3-12, 12-6-12). The siRNA and siDNA used were double strand molecules characterized by the same length and homologous sequence, in order to perform close comparison. We showed that complexes appear in solution immediately after mixing and, therefore, the investigation of complex formation requires fast experimental techniques, such as stopped-flow synchrotron SAXS. The obtained systems had internal arrangement constituted by layers of squeezed micelles alternating the nucleic acids. Both SAXS and MD analysis allowed to evaluate the mean size of complexes in the range of few nanometers, with looser and less ordered stacking for the DNA containing aggregates.

Résumé:

In a first part I will focus on the destabilization of dilute oil-in-water emulsion-based liquid sheets expanding in air. A sheet results from the collision of a single tear on a small solid target ; it disintegrates through the nucleation and growth of holes that perforate the sheet. We have developed an optical technique that allows the determination of the time and space-resolved thickness of the sheet to gain a, understanding of the physical mechanisms f the perforation events This bursting based-liquid sheet destabilization is at the origin of emulsion-based anti-drift formulations are developed for agricultural spray. In a second part, I will investigate freely expanding sheets formed by ultra soft spherical gel beads of elastic but also liquid droplets with various surface tensions, and simple viscoelastic fluids (Maxwell fluids), produced by impacting them on a silicon wafer covered with a thin layer of liquid nitrogen that suppresses viscous dissipation by an inverse Leidenfrost effect. The experiments reveal a universal behaviour of the impact dynamics with impact velocity, for both solids and liquids, and even viscoelastic fluids, that we have rationalized .

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DOI: 10.1021/acs.langmuir.7b00170
WoS: 000399263600013
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6 Citations
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A single-drop experiment based on the collision of one drop of liquid on a small solid target is used to produce liquid sheets that are visualized with a fast camera. Upon impact, the drop flattens into a sheet that is bounded by a thicker rim and radially expanding in air. Emulsion-based liquid sheets are destabilized through the nucleation of holes that perforate the sheet during its expansion. The holes grow until they merge together and form a web of ligaments, which are then destabilized into drops. We propose the perforation mechanism as a sequence of two necessary steps. The emulsion oil droplets first enter the air/water interface, and then spread at the interface. We show that the formulation of the emulsion is a critical parameter to control the perforation as the addition of salt or amphiphilic copolymers can trigger or completely inhibit the perforation mechanism. We demonstrate that the entering of the droplets at the air/water interface is the limiting step of the mechanism. Thin-film forces such as electrostatic or steric repulsion forces stabilize the thin film formed between the interface and the approaching oil droplets, thus preventing the entering of droplets at the interface and in turn inhibiting the perforation process. We theoretically rationalize the successive steps in the approach and entering of an oil droplet at the film interface and the role of salt and amphiphilic polymer in the different steps.