F. Ciuchi

Amine-functionalized SBA-15 in poly(styrene-b-butadiene-b-styrene) (SBS) yields permeable and selective nanostructured membranes for gas separation

New nanostructured hybrid membranes for gas separation have been prepared and characterized for the first time in the literature by using a block copolymer, poly(styrene-b-butadiene-b-styrene) (SBS), and aminated SBA-15. Short mesopore channels, platelet SBA-15 particles with a high surface density of 3-aminopropyl grafts (3.8 nm−2) and modest surface area reduction (45%) were prepared, characterized and used as a filler. The gas transport characterization of the hybrid membranes indicates that with a 10 wt% content of aminated filler, outstanding performances in terms of selectivity and permeability for the CH4/N2 and the CO2/N2 gas pairs can be obtained. In particular, the CH4/N2 ideal selectivity of 7.3 is higher than the values of the existing block co-polymers used for this separation and of mixed matrix membranes described to date in the literature. Membranes with such a high separation factor may enable the exploitation of natural gas with high N2 content and increase the amount of methane that can be economically recovered. The combination of the CO2/N2 ideal selectivity of 53 with a CO2 permeability of 173 Barrer demonstrates that the new hybrid membranes prepared in this study deserve further attention as a practical commercial solution also for the post-combustion capture of carbon dioxide. Finally, the small and flat particles dispersed in the polymer lend themselves to the fabrication of thin industrial membranes with enhanced productivity.

Langmuir−Blodgett Film of Hydrophobin Protein from Pleurotus ostreatus at the Air−Water Interface

We present results concerning the formation of Langmuir-Blodgett (LB) films of a class I hydrophobin from Pleurotus ostreatus at the air-water interface, and their structure as Langmuir-Blodgett (LB) films when deposited on silicon substrates. LB films of the hydrophobin were investigated by atomic force microscopy (AFM). We observed that the compressed film at the air-water interface exhibits a molecular depletion even at low surface pressure. In order to estimate the surface molecular concentration, we fit the experimental isotherm with Volmers equation describing the equation of state for molecular monolayers. We found that about (1)/ 10 of the molecules contribute to the surface film formation. When transferred on silicon substrates, compact and uniform monomolecular layers about 2.5 nm thick, comparable to a typical molecular size, were observed. The monolayers coexist with protein aggregates, under the typical rodlet form with a uniform thickness of about 5.0 nm. The observed rodlets appear to be a hydrophilic bilayer and can then be responsible for the surface molecular depletion.

Permanent polarization gratings in elastomer azo-dye systems: comparison of layered and mixed samples

An investigation was carried out of permanent polarization gratings recorded in films of polymer (elastomer) and azo dye written by two orthogonally circularly polarized Ar-ion laser beams. The films prepared were of two kinds, namely, a mixture of dye and polymer and a layered structure, i.e., a thin polymer film covered with dye. In both samples gratings with long-time stability were observed. The layered sample had higher diffraction efficiency than the mixed sample for low writing intensities when no reliefs were present and pure polarization holograms were recorded. For higher recording intensities, reliefs were observed in both cases: The mixed sample’s efficiency was much higher than that of the layered sample, suggesting that layered systems inhibit formation of reliefs. The stability of the recorded structures can be attributed to molecular interactions between polymer and dye.

Lasing in an intermediate twisted phase between cholesteric and smectic A phase

This work describes the observation of lasing in an intermediate chiral phase of a dye-doped cholesteric liquid crystal mixture. This intermediate phase exists between cholesteric and smectic A phase and it presents anomalous selective reflection properties. The lasing was observed at the long-wavelength edge of the photonic band gap.

Dynamical homeotropic and planar alignments of chromonic liquid crystals

We report on our latest studies on alignment of chromonic liquid crystals, a special class of molecules which recently attracted the attention of researchers. In particular, we show a detailed study of planar anchoring of disodium cromoglycate (DSCG) and, for the first time in the literature, a stable homeotropic alignment, achieved using a surface property of the alignment layer, i.e. the hydrophobicity. Excellent candidates from this point of view are pure polybutadiene (PB) and polydimethylsiloxane (PDMS). In fact, for the former the homeotropic anchoring stabilizes after one day, while for the latter stabilization occurs soon after cooling from the isotropic phase. After a long time both types of alignments (planar and homeotropic) evolve into thermodynamically stable configurations, i.e. ribbon structures. An explanation of the behaviour is given.

All-optical control of localized plasmonic resonance realized by photoalignment of liquid crystals

Large shifts in the plasmonic resonances of a thin film of gold nanorods (GNRs) are induced through the modulation of the local refractive index of the neighboring dielectric medium. This change is enabled through light-induced surface reorientation of a nematic liquid crystal in contact with a nanometer-thin photoalignment layer coating the GNR film. The presence of isolated and well distributed GNRs, both before and after the photoalignment layer deposition, is shown through atomic force and scanning electron microscopy. Exposure of the photoalignment layer to polarized light is shown to reorient aligned nematic liquid crystal molecules to an orthogonal direction, thereby changing the local refractive index of the medium in close proximity to the GNR film. This large change in the local dielectric strength is shown to cause a broad red shift of the localized plasmonic longitudinal resonance and almost no shift in the local transverse resonance. The ability to remotely and quickly change the plasmonic properties of this GNR system marks a breakthrough towards the realization of all-optical plasmonic and photonic devices such as plasmonic colour filters.

Optical and electrical characterization of a gold nanoparticle dispersion in a chiral liquid crystal matrix

We report on the effect of gold nanoparticle (Au NP) dispersion in a chiral nematic liquid crystal (LC). Polarized optical microscopy and X-ray diffraction measurements evidence the insurgence of an order change in the LC host. Moreover, a comparative analysis based on dielectric and voltammetric spectroscopies performed on pure LC and on Au NP-doped LC shows that Au NP’s presence besides affecting LC order influences its electric properties: ion conductivity results importantly reduced, and beyond a threshold value of the applied field electrophoresis phenomena are induced.

ac and dc electro-optical response of planar aligned liquid crystal cells

Interaction of static electric fields with a nematic is complicated because of the presence of charges, which originates from aligning layers or from molecular breakdown, affecting the electro-optic response of a liquid crystal cell. We analyze the aligning layers effect on the electro-optical response and develop a model based on a description of the ion balance on the conducting plates taking into account both drift current and saturation effects due to the ion migration inside the cell, neglecting diffusion current. The model well agrees with data for low voltages, while for higher ones, diffusion current should be taken into account.

Control of transient biaxial order in calamitic nematics

The biaxial order reconstruction in nematics (BORN) is a dynamical effect which can change the topology of nematic textures. The BORN can be induced in a nematic material submitted to strong external constraints, as in the case of bulk textural distortions due to an electric field in a π cell. In this work, we show how suitable dopants for a thermotropic calamitic nematic can influence its transient biaxial order and, hence, the electric BORN threshold.

Effects of Gold Nanoparticle Dispersion in a Chiral Liquid Crystal Matrix

In this article, we report experimental studies on the effect of gold nanoparticle dispersion in a cholesteric liquid crystal matrix. Besides deeply affecting liquid crystal structural order upon inducing phase transition toward unexpected smectic-like phases, the presence of nanoparticles causes important changes in the liquid crystal electric properties, increasing liquid crystal conductivity and influencing ions diffusion.