This work reports an experimental study of the kinetics and mechanisms of gelation of carbon nanotubes (CNTs)−hyaluronic acid (HA) mixtures. These materials are of great interest as functional biogels for future medical applications and tissue engineering. We show that CNTs can induce the gelation of noncovalently modified HA in water. This gelation is associated with a dynamical arrest of a liquid crystal phase separation, as shown by small-angle light scattering and polarized optical microscopy. This phenomenon is reminiscent of arrested phase separations in other colloidal systems in the presence of attractive interactions. The gelation time is found to strongly vary with the concentrations of both HA and CNTs. Near-infrared photoluminescence reveals that the CNTs remain individualized both in fluid and in gel states. It is concluded that the attractive forces interplay are likely weak depletion interactions and not strong van der Waals interactions which could promote CNT rebundling, as observed in other biopolymer−CNT mixtures. The present results clarify the remarkable efficiency of CNT at inducing the gelation of HA, by considering that CNTs easily phase separate as liquid crystals because of their giant aspect ratio.

We report theoretical predictions and measurements of the capillary force acting on a spherical colloid smaller than the capillary length that is placed on a curved uid interface of arbitrary shape. By coupling direct imaging and interferometry, we are able to measure the in situ colloid contact angle and to correlate its position with respect to the interface curvature. Extremely tiny capillary forces down to femto-Newton can be measured with this method. Measurements agree well with a theory relating the capillary force to the gradient of Gaussian curvature and to the mean curvature of the interface prior to colloidal deposition. Numerical calculations corroborate these results.

Besides nanostructured materials, individual particles are key elements for nanosciences. The structuring properties of liquid crystals (LCs) are appealing to assemble them, to organize them on substrates or to design functional composites.We present here an overview on particles/LC systems, the size of the dispersed particles being larger than the typical LC length.We first summarize the large number of advances made these last 10 years concerning microparticles assemblies. We then discuss the evolution of the relevant interactions between nanoparticles (NPs) dispersed in LCs when their size decreases from micrometers to nanometers. This allows us to discuss the various assemblies which can be obtained, either in LC bulk, at interfaces or within LC distorted areas or topological defects. Finally, we consider the recent possibilities to use NPs as building elements of complex fluids. We discuss accordingly the LC phases, which can be obtained with pure inorganic NPs in concentrated solution, as well as the self-assemblies which can be obtained when NPs are covered by organic mesogenic ligands.

A seminal paper [D. R. Nelson, Nano Lett., 2002, 2, 1125.] has proposed that a nematic coating could be used to create a valency for spherical colloidal particles through the functionalization of nematic topological defects. Experimental realizations however question the complex behaviour of solid particles and defects embedded in such a nematic spherical shell. In order to address the related topological and geometrical issues, we have studied micrometer-sized silica beads trapped in nematic shells. We underline the mechanisms that strongly modify the texture of the simple (particle-free) shells when colloidal particles are embedded. Finally, we show how the coupling between capillarity and nematic elasticity offers new ways to control the valence and directionality of shells.

The self-assembly of a bis-urea phenylene-bridged silsesquioxane precursor during sol-gel synthesis has been investigated by in situ infrared spectroscopy, optical microscopy and light scattering. In particular, the evolution of the system as a function of processing time was correlated with covalent interactions associated with increasing polycondensation and non-covalent interactions such as hydrogen bonding. A comprehensive mechanism based on the hydrolysis of the phenylene-bridged organosilane precursor prior to the crystallization of the corresponding bridged silsesquioxane via H bonding and subsequent irreversible polycondensation is proposed.

Liquid crystal ordering is an opportunity to develop novel materials and applications with spontaneously aligned nanotubes or graphene particles.Nevertheless, achieving high orientational order parameter and large monodomains remains a challenge. In addition, our restricted knowledge of the structure of the currently available materials is a limitation for fundamental studies and future applications. This paper presents recent methodologies that have been developed to achieve large monodomains of nematic liquid crystals. These allow quantification and increase of their order parameters. Nematic ordering provides an efficient way to prepare conductive films that exhibit anisotropic properties. In particular, it is shown how the electrical conductivity anisotropy increases with the order parameter of the nematic liquid crystal. The order parameter can be tuned by controlling the length and entanglement of the nanotubes. In the second part of the paper, recent results on graphene liquid crystals are reported. The possibility to obtain water-based liquid crystals stabilized by surfactant molecules is demonstrated. Structural and thermodynamic characterizations provide indirect but statistical information on the dimensions of the graphene flakes. From a general point of view, this work presents experimental approaches to optimize the use of nanocarbons as liquid crystals and provides new methodologies for the still challenging characterization of such materials.

A post-synthesis alignment of individual single-walled carbon nanotubes (SWCNTs) is desirable for translating their unique anisotropic properties to a macroscopic scale. Here, we demonstrate excellent dispersion, orientation and concomitant-polarised photoluminescence of SWCNTs in a nematic chromonic liquid crystal. The methods to obtain stable suspension are described, and order parameters of the liquid crystal matrix and of the nanotubes are measured independently.