Fiore Pasquale Nicoletta

Light Responsive Polymer Membranes: A Review

In recent years, stimuli responsive materials have gained significant attention in membrane separation processes due to their ability to change specific properties in response to small external stimuli, such as light, pH, temperature, ionic strength, pressure, magnetic field, antigen, chemical composition, and so on. In this review, we briefly report recent progresses in light-driven materials and membranes. Photo-switching mechanisms, valved-membrane fabrication and light-driven properties are examined. Advances and perspectives of light responsive polymer membranes in biotechnology, chemistry and biology areas are discussed.

Doxorubicin loaded magneto-niosomes for targeted drug delivery

In chemotherapy the magnetic drug targeting to a specific organ or tissue is proposed on the assumption that magnetic fields are harmless to biological systems. In this light we have vehiculated doxorubicin as model drug by novel magneto-niosomes in order to evaluate the physico-chemical properties of the obtained formulations and the in vitro release profile. Tween 60 and Pluronic L64 have been used as surfactants and the formulation cytotoxicity has been performed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolum bromide and trypan blue dye esclusion tests. Results show that niosome dimensions and doxorubicin entrapment efficiencies are influenced by bilayer composition. In addition, formulations are able to control the deliver and release of the drug active form in a retarded manner. No additional toxicity, due to the encapsulation of ferrofluid into niosomes core, has been detected.

Fine adjustment of conductivity in polymer-dispersed liquid crystals

The electrical properties of polymer-dispersed liquid crystals (PDLCs) are an important characteristic in their electro-optical performance. Conductivity effects can set up depolarization fields in the films reducing the effective field across the liquid crystal droplets. Both theoretical and experimental investigations have confirmed that the electric field across nematic droplets depends on the liquid crystal and polymer conductivities. In this letter, we have found that the doping of a PDLC with low percentages of a conductive polymer allows a fine adjustment of polymer matrix conductivity. In addition, we have found a large reduction in the re-orientation fields and relaxation times as a function of conductive polymer loading. Results are in rather good agreement with a simple phenomenological model.

A method to produce reverse-mode polymer-dispersed liquid-crystal shutters

Reverse-mode operation shutters have been achieved by combining the techniques of the traditional means of making polymer-dispersed liquid crystals and nematic curvilinear aligned phases. Nematic microemulsions, obtained by a thermally induced phase separation, have been photopolymerized in an external force field. After the polymerization, films show 85% transmittance in the OFF state, while it decreases to less than 1% when an electric field of about 2 V μm−1 at 1 kHz is applied. The rise-time values, about 2 ms, are in the same range as those obtained with normal-mode polymer-dispersed liquid-crystal films. On the contrary, decay time shows longer values.

Angular Transmission of Polymer Dispersed Liquid Crystals Films

Abstract The angular transmission of Polymer Dispersed Liquid Crystals (PDLC) films has been experimentally investigated as a function of droplets dimension, refractive indices and thickness of sample. The experimental data have been interpreted in terms of the Anomalous Diffraction Approximation slightly modified in order to take into account extra-scattering phenomena generated by some of the peculiar PDLC characters. The dimension of the droplets and refractive index difference between polymer and liquid crystal are found to be the most important factors affecting the light transmission as well as extra scattering factors.

Morphology and electro-optical properties of reverse mode polymer dispersed liquid crystals

We have investigated the morphology and electro-optical properties of reverse mode polymer dispersed liquid crystals as a function of liquid crystal loading. Reverse mode shutters have been obtained by a polymerization-induced phase separation of mixtures, consisting of a liquid crystalline monomer and a non-reactive nematic liquid crystal, placed between rough conductive surfaces. Such surfaces are able to keep the photopolymerizable mixtures homeotropically aligned without the use of any aligning polymer substrate. OFF state transmittances are always larger than 80% and the switching fields decrease if the non-reactive liquid crystal percentage is increased. Both rise and decay times are always lower than 10 ms. The electro-optical properties have been related to the sample morphology and a simple mode is proposed.

Monomer-liquid crystal emulsions for switchable films

We have followed the phase separation process in mixtures of an organic monomer and nematic liquid crystals at different cooling rates. Systems form liquid crystal droplets in a liquid crystal-saturated monomer matrix and in some cases emulsions are stable over several months. Homogeneous droplet size distributions are obtained for faster cooling rates. We report the droplet size distribution, the behavior of the critical solution temperature as a function of liquid crystal content, and some electro-optical properties of different emulsions. The long stability and the electro-optical response show that such systems could be used as promising, low voltage, switchable films.

Enhancement of electro-optical performance in nematic emulsion films

We have found new monomers which are able to give stable nematic and isotropic emulsions with micron-sized droplets. A poor contrast ratio in optical transmittance is obtained when thin electro-optical films of nematic emulsions are prepared with only one monomer. Matching between a monomer matrix refractive index and that of a liquid crystal, and a consequent improvement of the electro-optical performance of emulsion films have been obtained by mixing such monomers. The films thus prepared show opacities less than 1% in the absence of an applied field and a transmittances increase up to 85% by applying a 0.2 V μm−1 electric field at 1 kHz. The long time stability, the high contrast ratio, and the low driving fields suggest that nematic emulsion films are promising systems for electro-optical applications.

Microparticles based on chitosan/carboxymethylcellulose polyelectrolyte complexes for colon delivery of vancomycin.

The aim of this work was to prepare polyelectrolyte complexes based on chitosan (CH) and carboxymethylcellulose (CMC) for colon delivery of vancomycin (VM). Various batches of polyelectrolyte complexes, using three different CH/CMC weight ratios (3:1, 1:1 and 1:3), were prepared and collected as microparticles by spray-drying process. Microparticles were characterized in terms of yield, encapsulation efficiency, drug loading, morphology and mucoadhesion properties. Microparticles water-uptake and VM release as well as its protection against gastric pepsin degradation were also investigated. Finally, the antibacterial activity against Staphylococcus aureus, a Gram-positive model strain, was evaluated. The best formulation CH/CMC 1:3 was selected based on the encapsulation efficiency, water-uptake and drug release rate. Moreover, microparticles were able to prevent VM degradation and showed a good antibacterial activity against S. aureus. Finally, to improve the release of VM in the colon the selected formulation was coated with lauric acid.

Rough surfaces for orientation control in reverse mode polymer dispersed liquid crystal films

Reverse mode operation shutters have been achieved with polymer dispersed liquid crystals by means of polymerization-induced phase separation of nematic mixtures consisting of a low molecular mass liquid crystal and a liquid crystalline monomer. Fluid mixtures were homeotropically aligned by rough surfaces and transparent films were obtained after polymerization. Transmittance in the OFF state can be larger than 80% and decreases to less than 1% when an electric field of about 2 V μm-1 at 1 kHz is applied (ON state). Both rise and decay times can be lower than 10 ms and the drop in the OFF state normal transmittance is drastically reduced with respect to conventional polymer dispersed liquid crystals since samples exhibit a reverse morphology. The role played by surface roughness is also discussed.