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The aim of this paper is to determine how microgels adsorb at a model oil-water interface and how they adapt their conformation to compression, which gives rise to surface elasticity depending on the microgel packing. The structure of the film is determined by the Langmuir films approach (forced compression) and compared to spontaneous adsorption using the pendant drop method. The behaviour of microgels differs significantly from that of non-deformable particles but resembles that of linear polymers or proteins. We also correlate the properties of microgels spontaneously adsorbed at model interfaces to their forced adsorption during emulsification. Finally we propose a route to easily control a posteriori the microgel packing at the surface of droplets and the flow properties of emulsions stabilised by the microgels.

Monodispersed poly(N-isopropylacrylamide) submicrometric microgels modified with a phenylboronic acid (PBA) derivative have been synthesized by precipitation polymerization. Particles with a well-controlled size and adjustable composition were obtained. These particles were found to be glucose responsive at a pH close to the pKa of the PBA derivative, with a swelling degree proportional to the concentration of glucose. In addition, the response to glucose was found to strongly depend on the initial state of the microgel, which depended itself on the initial temperature and the functionalization degree of the particle. This result explained the fundamental difference in the behavior of PBA-poor particles and rich ones in the presence of electrolyte. Interestingly, the latter exhibited a high swelling ratio in the presence of glucose at physiological electrolyte concentration. These particles may serve as building blocks for the design of colorimetric sensors based on the light diffraction of colloidal crystals.

Poly(N-isopropylacrylamide) (pNIPAM) microgels are soft and deformable particles, which can adsorb at liquid interfaces. In the present paper, we study the two-dimensional organization of charged and quasi-neutral microgels with different cross-linking densities, under compression at the air-water interface and the transfer of the microgel monolayer onto a solid substrate at different surface pressures. At low cross-linking densities, the microgels form highly ordered hexagonal lattices on the solid substrate over large areas, with a unique lattice parameter that decreases continuously as the surface pressure increases. We thus prove that the microgel conformation evolves at the air-water interface. The microgels undergo a continuous transition from a highly flattened state at low surface coverage, where the maximal polymer segments are adsorbed at the interface, to entangled flattened microgels, and finally the thickening of the layer up to a dense hydrogel layer of compacted microgels. Moreover, two batches of microgels, with and without charges, are compared. The contribution of electrostatic interactions is assessed via changing the charge density of the microgels or modulating the Debye length. In both cases, electrostatics does not change the lattice parameter, meaning that, despite the microgel different swelling ratio, charges do not affect neither interactions between particles at the interface nor microgels adsorption. Conversely, the cross-linking density has a strong impact on microgel packing at the interface: increasing the cross-linking density strongly decreases the extent of microgel flattening and promotes the occurrence of coexisting hexagonally ordered domains with different lattice parameters.

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Short carbon nanotubes have been modified selectively on one end with metal using a bulk technique based on bipolar electrochemistry. A stabilized suspension of nanotubes is introduced in a capillary containing an aqueous metal salt solution, and a high electric field is applied to orientate and polarize the individual tubes. During their transport through the capillary under sufficient polarization (30 kV), each nanotube is the site of water oxidation on one end and the site of metal ion reduction on the other end with the size of the formed metal cluster being proportional to the potential drop along the nanotube.

We used soft microgels made of poly(N-isopropylacrylamide) (pNIPAM) of variable cross-linking degrees and the same colloidal size to stabilize oil-in-water Pickering emulsions. The extent of droplet flocculation increased and the resistance of the emulsions to mechanical stresses decreased as the cross-linking density was augmented. Large flat films were separating the droplets, and we could measure the adhesion angle at the junction with the free interfaces through several microscopy methods. The size of the flat films and the values of the angles were reflecting strong adhesive interactions between the interfaces as a result of microgel bridging. In parallel, cryo-SEM imaging of the thin films allowed a precise determination of their structure. The evolution of the adhesion angle and of the film structure as a function of microgels cross-linking density provided interesting insights into the impact of particle softness on film adhesiveness and emulsion stability. We exploited our main findings to propose a novel route for controlling the emulsions end-use properties (flocculation and stability). Owing to particle softness and thermal sensitivity, the interfacial coverage was a path function (it depended on the sample "history"). As a consequence, by adapting the emulsification conditions, the interfacial monolayer could be trapped in a very dense and rigid configuration, providing improved resistance to bridging flocculation and to flow-induced coalescence.