The conformational evolution of elongated polymer solutions tailors the polarization of light-emission from organic nanofibers

Polymer fibers are currently exploited in tremendously important technologies. Their innovative properties are mainly determined by the behavior of the polymer macromolecules under the elongation induced by external mechanical or electrostatic forces, characterizing the fiber drawing process. Although enhanced physical properties were observed in polymer fibers produced under strong stretching conditions, studies of the process-induced nanoscale organization of the polymer molecules are not available, and most of fiber properties are still obtained on an empirical basis. Here we reveal the orientational properties of semiflexible polymers in electrospun nanofibers, which allow the polarization properties of active fibers to be finely controlled. Modeling and simulations of the conformational evolution of the polymer chains during electrostatic elongation of semidilute solutions demonstrate that the molecules stretch almost fully within less than 1 mm from jet start, increasing polymer axial orientation at the jet center. The nanoscale mapping of the local dichroism of individual fibers by polarized near-field optical microscopy unveils for the first time the presence of an internal spatial variation of the molecular order, namely the presence of a core with axially aligned molecules and a sheath with almost radially oriented molecules. These results allow important and specific fiber properties to be manipulated and tailored, as here demonstrated for the polarization of emitted light.Comment: 45 pages, 10 figures, Macromolecules (2014

Models of polymer solutions in electrified jets and solution blowing

Fluid flows hosting electrical phenomena make the subject of a fascinating and highly interdisciplinary scientific field. In recent years, the extraordinary success of electrospinning and solution blowing technologies for the generation of polymer nanofibers has motivated vibrant research aiming at rationalizing the behavior of viscoelastic jets under applied electric fields or other stretching fields including gas streams. Theoretical models unveiled many original aspects in the underpinning physics of polymer solutions in jets, and provided useful information to improve experimental platforms. This article reviews advances in the theoretical description and numerical simulation of polymer solution jets in electrospinning and solution blowing. Instability phenomena of electrical and hydrodynamic origin are highlighted, which play a crucial role in the relevant flow physics. Specifications leading to accurate and computationally viable models are formulated. Electrohydrodynamic modeling, theories for the jet bending instability, recent advances in Lagrangian approaches to describe the jet flow, including strategies for dynamic refinement of simulations, and effects of strong elongational flow on polymer networks are reviewed. Finally, the current challenges and future perspectives of the field are outlined and discussed, including the task of correlating the physics of the jet flows with the properties of realized materials, as well as the development of multiscale techniques for modelling viscoelastic jets.Comment: 135 pages, 42 figure

Amphotericin B-loaded nanoparticles for local treatment of cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) is an infectious, parasitic disease caused by the protozoan Leishmania. Amphotericin B (AMB) is a macrolide polyene antibiotic presenting potent antifungal and antileishmanial activity, but due to poor water solubility at physiological pH, side effects, and toxicity, its therapeutic efficiency is limited. In the present study, poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) loaded with AMB were generated to reduce drug toxicity and facilitate localized delivery over a prolonged time. AMB NPs were characterized for particle size, zeta potential, polydispersity index, and degree of aggregation. In vitro assessments demonstrated its sustained activity against Leishmania major promastigotes and parasite-infected macrophages. A single intralesional administration to infected BALB/c mice revealed that AMB NPs were more effective than AMB deoxycholate in terms of reducing lesion area. Taken together, these findings suggest thatAMB NPs improve AMB delivery and can be used for local treatment of CL.This research was funded by the GIP program of the Deutsche Forschungsgemeinschaft (DFG) German Research Foundation. EZ wish to acknowledge the financial support of the RBNI-The Russell Berrie Nanotechnology Institute at the Technion. CLJ holds the Michael and Penny Feiwel Chair of Dermatology

Electrospun Conjugated Polymer/Fullerene Hybrid Fibers: Photoactive Blends, Conductivity through Tunnelling-AFM, Light-Scattering, and Perspective for Their Use in Bulk-Heterojunction Organic Solar Cells

Hybrid conjugated polymer/fullerene filaments based on MEH-PPV/PVP/PCBM are prepared by electrospinning, and their properties assessed by scanning electron, atomic and lateral force, tunnelling, and confocal microscopy, as well as by attenuated total reflection Fourier transform-infrared spectroscopy, photoluminescence quantum yield and spatially-resolved fluorescence. Highlighted features include ribbon-shape of the realized fibers, and the persistence of a network serving as a template for heterogeneous active layers in solar cell devices. A set of favorable characteristics is evidenced in this way in terms of homogeneous charge transport behavior and formation of effective interfaces for diffusion and dissociation of photogenerated excitons. The interaction of the organic filaments with light, exhibiting specific light-scattering properties of the nanofibrous mat, might also contribute to spreading incident radiation across the active layers, thus potentially enhancing photovoltaic performance. This method might be applied to other electron donor-electron acceptor material systems for the fabrication of solar cell devices enhanced by nanofibrillar morphologies embedding conjugated polymers and fullerene compounds.Comment: 35 pages, 9 figure

Thermally Driven Selective Nanocomposite PS-PHB/MGC Nanofibrous Conductive Sensor for Air Pollutant Detection

The potentials to use the working temperature to tune both the sensitivity and the selectivity of a chemical sensor based on a nanostructured and nanocomposite polymer layer have been investigated and described. Thus, in a single step, a peculiar chemical layer was grown up onto IDE (Interdigitated Electrode) microtransducers by electrospinning deposition and using a single-needle strategy. The 3-component nanofibers, obtained from a mixture of polystyrene and polyhydroxibutyrate (insulating thermoplastics) and a known concentration of mesoporous graphitized carbon nanopowder, appeared highly rough on the surface and decorated with jagged islands but homogeneous in shape and diameter, with the nanofillers aggregated into clusters more or less densely packed through the fibers. The resulting sensor was conductive at room temperature and could work between 40 and 80°C without any apparent degradation. As the fibrous sensing layer was heated, the current increased and the sensitivity to some classes of VOCs such as an oxidizing gas drastically changed depending on the working temperature. More in detail, the sensor resulted highly sensitive and selective to acetic acid at 40°C but the sensitivity fell down, decreasing by 96%, when the sensor operated at 80°C. On the other hand, although an increase in temperature caused a general decrease in sensitivity to the tested VOCs (with a maximum of 14, 81, and 78% for amine, acetone and toluene, respectively) and water vapors (with a maximum of 55%), higher temperature affected only slightly the amine permeation, thus modifying the partial selectivity of the sensor to these chemicals. Conversely, when the operating temperature increased, the sensitivity to the detected gas, NO2, increased too, reporting a ~2 ppb limit of detection (LOD), thus confirming that the temperature was able to drive the selectivity of nanocomposite polymeric sensors

Characterization of solvent-spun polyester nanofibers

The aim of this study was to examine the properties of polyester nanofibers produced by the electro-spinning method. Solvent-spun nanofibers with different concentrations of poly(ethylene terephthalate) (13,16, and 20 wt %) were produced. The morphology and surface energy of the fibers were analyzed by scanning electron microscopy and contact angle measurements. Tensile testing, dynamic mechanical analysis, and differential scanning calorimetry were carried out to characterize the thermal and mechanical properties. X-ray diffraction and attenuated total reflection Fourier transform infrared spectroscopy tests were performed to analyze the microstructural properties. The results show that a nanoweb of the 16 wt % solution had better mechanical and thermal behaviors because of the increased molecular orientation in the amorphous structure and the narrower fiber diameter distribution in the web

From Chaos to Order: Evaporative Assembly and Collective Behavior in Drying Liquid Crystal Droplets

The emergence of dynamic assembly and collective motion in living systems are marvels of nature that suggest universal principles for governing self-organization. By drying a drop of surfactant-stabilized liquid crystal emulsions, we present a simple form of evaporative assembly and collective motion in colloidal droplets. Driven by local evaporation flux distribution and capillary force, the dynamic mode in these swimming liquid crystal droplets highly depends on their intrinsic configurations, exhibiting a macroscopic transition from chaotic to well-organized. The combination of collective behavior, speed distribution, interparticle interaction, formation of topological defects and dislocations in a swarm of hexagonal ordered liquid crystal droplets produced a myriad of dynamical states, which suggest a means of mimicking the nonequilibrium state of living matter with controlled properties