Jean-François Blach

BaTiO3 ferroelectric nanoparticles dispersed in 5CB nematic liquid crystal: Synthesis and electro-optical characterization

We report in this paper studies on a mixture of nematic liquid crystal (5CB) and BaTiO3 ferroelectric nanoparticles (NPs). Apart a drastic change in the electro-optical (EO) properties of this mixture, which is reported as a conclusion, we focused our attention onto the characteristics of those NPs. The initial powder obtained by solid way is first analyzed: this material is crystallized in the ferroelectric phase as shown by x-ray diffraction and Raman spectroscopy. A high speed second milling was performed to obtain NPs: they have been characterized by high resolution transmission electron microscopy (size and structural characterizations) and by dynamic light scattering. Then these NPs were blended with a nematic liquid crystal (5CB). Raman spectroscopy measurements were used to measure and compare the scalar order parameter of both samples. The EO properties were measured in planar liquid crystal cell configuration by using classical EO setup. We amazingly found a significant decrease in the Freederic...

Experimental study of the nonlocality of spatial optical solitons excited in nematic liquid crystal

In this paper we report on experiments performed to estimate the nonlocality of the reorientational nonlinearity in thick nematic liquid crystal samples. The aim of this work is to characterize the index distribution induced by a soliton-like optical beam. For this purpose, we have studied the attraction of two spatial optical solitons counter propagating parallel to each other and at different small distances. By pulsing one of them, we strongly reduce its influence on the medium and we analyse its trajectory to recover the index variation associated with its steady-state counterpart.

Bioinspired Titanium Drug Eluting Platforms Based on a Poly-β-cyclodextrin–Chitosan Layer-by-Layer Self-Assembly Targeting Infections

In the field of implantable titanium-based biomaterials, infections and inflammations are the most common forms of postoperative complications. The controlled local delivery of therapeutics from implants through polyelectrolyte multilayers (PEMs) has recently emerged as a versatile technique that has shown great promise in the transformation of a classical medical implant into a drug delivery system. Herein, we report the design and the elaboration of new biodegradable multidrug-eluting titanium platforms based on a polyelectrolyte multilayer bioactive coating that target infections. These systems were built up in mild conditions according to the layer-by-layer (L-b-L) assembly and incorporate two biocompatible polysaccharides held together through electrostatic interactions. A synthetic, negatively charged β-cyclodextrin-based polymer (PCD), well-known for forming stable and reversible complexes with hydrophobic therapeutic agents, was exploited as a multidrug reservoir, and chitosan (CHT), a naturally occurring, positively charged polyelectrolyte, was used as a barrier for controlling the drug delivery rate. These polyelectrolyte multilayer films were strongly attached to the titanium surface through a bioinspired polydopamine (PDA) film acting as an adhesive first layer and promoting the robust anchorage of PEMs onto the biomaterials. Prior to the multilayer film deposition, the interactions between both oppositely charged polyelectrolytes, as well the multilayer growth, were monitored by employing surface plasmon resonance (SPR). Several PEMs integrating 5, 10, and 15 bilayers were engineered using the dip coating strategy, and the polyelectrolyte surface densities were estimated by colorimetric titrations and gravimetric analyses. The morphologies of these multilayer systems, as well as their naturally occurring degradation in a physiological medium, were investigated by scanning electron microscopy (SEM), and their thicknesses were measured by means of profilometry and ellipsometry studies. Finally, the ability of the coated titanium multilayer devices to act as a drug-eluting system and to treat infections was validated with gentamicin, a relevant water-soluble antibiotic commonly used in medicine due to its broad bactericidal spectrum.

Elastic constants, viscosity and response time in nematic liquid crystals doped with ferroelectric nanoparticles

We report on the role of ferroelectricity on the physical and electro-optic parameters in suspensions of nanoparticles in cyclohexane based, fluorinated nematic liquid crystals. The dielectric and elastic constants, response time, and viscosity of the suspensions were analyzed experimentally and compared with the undoped samples. Our study shows a decrease in the splay elastic constant and an increase in the dielectric constants, together with an increase in the average rotational viscosity.

Noncovalent functionalization of multiwall carbon nanotubes by methylated-β-cyclodextrins modified by a triazole group

Multiwall carbon nanotubes have been efficiently suspended into water thanks to methylated β-cyclodextrins (CDs) containing a triazole group, itself substituted in the 4-position by hydrophilic moieties.

The investigation of an electrically stabilized optical spatial soliton induced in a nematic liquid crystal

A spatial soliton is induced between two optical fibres in a liquid crystal medium and the associated optical power transmitted is measured. The signal/noise (S/N) ratio of the device is estimated and then improved by applying an extra voltage along the propagation axis. Besides this applicative result, which is the first step towards realistic optical switches, we show that the response curve of such a coupler gives information on the soliton propagation regime in a highly nonlocal medium, namely the longitudinal structure of the soliton envelope. In addition, it is shown that the extra voltage allows control of the nonlocality, approaching a Kerr-like medium for strong voltage.

Electrically charged dispersions of ferroelectric nanoparticles

It is found that ferroelectric nanoparticles synthesized by the sol-gel technique and milling can become charged during the fabrication. The balance between the concentrations of positively and negatively charged particles depends on the material, the treatment of particles, and concentration of the surfactant agent. It is suggested that the nanoparticles become charged due to their collisions during the milling and sonication.

Enhancement in nanoscale electrical properties of lead zirconic titanate island fabricated by focused ion beam

Lead zirconic titanate (PZT) microscale island (1 μm–100 nm) was fabricated by focused ion beam before its crystallization, followed by the annealing treatment at the crystallization temperature. Local electrical properties were evaluated by piezoresponse force microscopy technique. Compared to the PZT island fabricated after crystallization, the result shows that there is noticeable enhancement in nanoscale electrical properties of PZT island fabricated before crystallization, especially when the island size decreases. Raman spectra and Kelvin force microscopy result both show that there are little degradations on the PZT surface after this amorphous etching process. The mechanism will be discussed in this paper. These results are very beneficial to the development of the ferroelectric film applications in the dynamic random access memory, ferroelectric random access memory, and micro-electro-mechanical system field.

Measuring and Monitoring Optically Induced Thermal or Orientational Non–Locality in Nematic Liquid Crystal

Nonlinear propagation in nematic liquid crystals and spatial optical quasi-soliton can be generated via either thermal or orientational nonlinear process. These particular propagation modes can potentially be used in photonic and telecom devices, on the condition that they are well controlled, thus first to be properly measured. We first briefly review the measurements techniques, focussing on the newest one, based on a Raman scattering measurement. Then, it is demonstrated that there are two main ways to control the non-locality in spatial optical soliton either by using a time dependent source, or by playing with boundary conditions. Examples are given for each case.

A direct novel synthesis of highly uniform dispersed ruthenium nanoparticles over P6mm ordered mesoporous carbon by host–guest complexes

We report a novel concept to prepare a highly ordered mesoporous carbon with a uniform dispersion of ruthenium nanoparticles of 1–2 nm size range using a nano-templating method, based on the combined utilization of a β-cyclodextrin host–guest complex and ruthenium trichloride as respective sources of carbon and metal. The composite material synthesized (Ru@MCA-2) through the polymerization and carbonization of these metallo-supramolecular assemblies possesses high surface area and high pore volume after the removal of the silica template and exhibits high catalytic activity in the hydrogenation of unsaturated fatty acid methyl esters. The reusability of this nanoreplicated catalyst is also demonstrated.