We study the alignment of single-wall carbon nanotubes in polyvinylalcohol composites using polarized Raman and photoluminescence spectroscopies. Nanotubes are well dispersed down to the individual scale in the composites as revealed by the strong photoluminescence signal. Alignment can be continuously adjusted by hot stretching the composites. We propose a simple relation to measure the order parameter based on the assumption that only one single component of the Raman polarizability tensor is nonzero. The similar profiles of spectra measured in different polarization configurations validate this assumption. The orientation of the nanotubes under uniaxial stretching is well modelized by a simple affine model assuming deformation at constant volume.

1. INTRODUCTION A first order phase transition from an undercooled isotropic phase to an ordered phase usually yields complex morphologies, resulting from the competition between growth and diffusion. Fundamental issues, such as the non-linear dendritic growth of crystals, are however well understood and several numerical methods now satisfactorily reproduce the main experimental features of the growth patterns of crystals. On the contrary, the growth forms of soft condensed phases and their dynamics are often very qualitatively described. The main reason is that the softness of the nuclei introduces couplings -difficultly handled- between the growth mechanisms, the elasticity field and the appearing of macroscopic defects. I will illustrate some underlying mechanisms and their role on the formation of the two typical out-of-equilibrium patterns of smectic liquid crystal phases: the “batonnets” and the cylindrical filaments. 2. INTERFACE ANISOTROPY, ELASTICITY AND DENDRITIC GROWTH Volumic faceting [1] was introduced to describe how a lamellar phase responds to an anisotropy in its interface energy by deforming when the interface orientation is imposed. This mechanism controls the change of texture of a slab of lamellar phase growing from a flat substrate with hybrid anchorings [2, 3]. A recent work [4] has shown that a similar mechanism could explain the change of texture during the growth of lamellar phase nuclei and the formation of onions. We have closely examined the dynamics of a sponge-to-lamellar phase transition which tend to form complex “ batonnets” rather than onions. We show that the observed intermittent dynamics and the unusual growth patterns can be explained by a temporal succession of volumic faceting mechanisms and a standard dendritic growth [5]. 3. FORMATION OF FILAMENTS: THE ROLE OF THE INTERFACE AREA Apart from the “batonnets”, layered systems often form filaments (called myelins in lyotropic systems) when the anchoring at the interface is preferably homeotropic. The formation of filaments has been observed in various situations such as the isotropic-to SmA phase transitions or during the hydration of surfactants. We have recently shown that filaments could be formed in nematic [6] and smectic emulsions in water, without any volume change by using surfactants that spontaneously spread on the liquid crystal/water interface. The dynamics of formations and the main properties of the filaments will be described. REFERENCES 1. Fournier, J.-B., “Focal conic faceting in SmA liquid crystals” J. Phys. II., 1, 845, (1991). 2. Blanc, C. and Kleman, M., “Tiling the plane with Focal Conic Domains”, Phys. Rev. E, 62, 6739, (2000). 3. Blanc, C. and Kleman, M., “The confinement of smectics with a strong anchoring”, Eur. Phys. J. E, 4, 241, (2001). 4. Iwashita, Y. and Tanaka, H., “Spontaneous onion-structure formation from planar lamellar nuclei”, Phys. Rev. E, 98, 145703, (2007). 5. Blanc, C., to be published. 6. Toquer, G.; Phou, T.; Monge, S.; Grimaldi, A.; Nobili, M.; Blanc, C. ; “Colloidal Shape Controlled by Molecular Adsorption at Liquid Crystal Interfaces”, J. Phys. Chem. B., (Letter), in press (2008).

Lyotropic nematic aqueous suspensions of single-wall carbon nanotubes can be uniformly aligned in thin cells by shearing. Homogeneous anisotropic thin films of nanotubes can be prepared by drying the nematic. Optical transmission between parallel or crossed polarizers is measured and described in order to estimate the dichroic ratio. The order parameter is measured using polarized Raman spectroscopy and found to be quite weak due to entanglement of the nanotubes and/or to an intrinsic viscoelastic behavior of the nanotube suspensions.

The synthesis of novel ionic liquid crystals (ILCs) based on bis- and trisimidazolium salts (I-, BF4-, and [N(SO2CF3)2]-) bearing hydrophobic hexadecyl chains and a bridging mesitylene moiety is reported. The study of their mesomorphic properties is presented, including the characterization of the Smectic A phase by differential scanning calorimetry and polarized optical microscopy. A detailed powder X-ray diffraction (p-XRD) study as a function of temperature confirmed that cooling gives rise to a glass transition from the liquid-crystalline smectic A phase to a metastable lamellar phase. In addition, in the case of bisimidazolium iodide, the ability of these molecules to form self-aggregates in solution has been demonstrated by diffusion nuclear magnetic resonance (NMR) experiments. --------------------------------------------------------------------------------

The ability to control finely the structure of materials remains a central issue in colloidal science. Due to their elastic properties, liquid crystals (LC) are increasingly used to organize matter at the micrometer scale in soft composites. Textures and shapes of LC droplets are currently controlled by the competition between elasticity and anchoring, hydrodynamic flows, or external fields. Molecules adsorbed specifically at LC interfaces are known to orient LC molecules (anchoring effect), but other induced effects have been poorly explored. Using specifically designed amphitropic surfactants, we demonstrate that large-shape transformations can be achieved in direct LC/water emulsions. In particular, we focus on unusual nematic filaments formed from spherical droplets. These results suggest new approaches to design new soft LC composite materials through the adsorption of molecules at liquid crystal interfaces.

A long-range ordered organic/inorganic material is synthesized from a bissilane, (EtO)3Si–(CH2)3–NHCONH–C6H4–NHCONH–(CH2)3–Si(OEt)3. This crosslinked sol–gel solid exhibits a supramolecular organization via intermolecular hydrogen bonding interactions between urea groups (–NHCONH–) and covalent siloxane bonding, Si–O–Si . Time-resolved in situ X-ray measurements (coupling small- and wide-angle X-ray scattering techniques) are performed to follow the different steps involved in the synthetic process. A new mechanism based on the crystallization of the hydrolyzed species followed by their polycondensation in solid state is proposed.