Charge Transfer in Self-Assembled Fullerene-Tetraphenylporphyrin Non-Covalent Multilayer

Self-assembly of organic molecules is a promising method for generating multilayer systems for fabrication of functional devices. In particular, fullerene (C60) and porphyrin molecules offer a variety of binding modes, including π-π interactions, dipole electrostatic attraction, and hydrogen bonding, to tailor the charge separation and charge recombination limiting device performance. Here, we investigate multilayer systems obtained by the sequential physical vapor deposition of C60 and tetraphenylporphyrin (H2TPP) layers, focusing on the effect of the interfaces on the charge transfer processes. Absorbance spectra indicate noncovalent-like π-stacking, with the increment of fullerene interfaces shifting the porphyrin Soret band toward the blue. Similarly, surface photovoltage measurements in the multilayer systems show that as the number of interfaces increases, so does the photogeneration of charge. Charge separation follows carrier generation given that the recombination time, associated to trap states, decreases. This behavior indicates that the Donor-Acceptor nature of the fullerene-porphyrin bilayer system is conserved, and even enhanced, in the multilayer film, and that the number of interfaces aid to the formation of selective paths for charge carrier collection, demonstrating its potential in optoelectronic devices.

BEHAVIOUR ASSESSMENT OF TRIDIMENSIONAL MULTILAYER FIBROUS STRUCTURES AS RESPIRATORY PROTECTION SUBSTRATES

Despite the growing appearance of new solutions for social masks, there are still few aimed for the use by professionals in frequent contact with the public, since depending on the of the functions they perform, still have special needs regarding thermophysiological comfort, high protection level and reusability, such as firefighters and police officers. Aiming at the development of a multilayer filtration system combining threedimensional and planar fibrous structures, the present study intends to verify the feasibility of applying warpknit spacers as diffuser filters for nano and micro particles. Therefore, three different spacer structures performance was studied, and then combined with planar knit structures to enhance the comfort characteristics and its bacterial filtration efficiency (BFE). The diffusion filtration performance of the samples, due to the particle size, it was found a direct relation between the outer layer density and porosity with its filtration capacity of microparticles. Moreover, the increase in the spacer thickness revealed more problems diffusing water vapor molecules. To achieve the standard requirements, the samples Techno_1 and 2 were developed and tested. The addition of a new fibrous structure increased substantially the filtration efficiency without damaging the comfort characteristics of the Spacers. Considering the BFE standard tests for facemask certification, despite it was possible to achieve filtration rates above 70% for the samples Techno_1 and 2. In addition, its washability and performance durability were tested and stated as viable to be applied as a social facemask with level III of protection for at least 25 washing cycles, despite having noticed a decrease in the filtration efficiency, in both samples, in the order of 10%, due to the unbalance of mechanical properties of the fibrous structures in the multilayer systems.

Investigation of Integrated Reactive Multilayer Systems for Bonding in Microsystem Technology

For the integration of a reactive multilayer system (iRMS) with a high exothermic reaction enthalpy as a heat source on silicon wafers for low-temperature bonding in the 3D integration and packaging of microsystems, two main conflicting issues should be overcome: heat accumulation arising from the layer interface pre-intermixing, which causes spontaneous self-ignition during the deposition of the system layers, and conductive heat loss through the substrate, which leads to reaction propagation quenching. In this work, using electron beam evaporation, we investigated the growth of a high exothermic metallic Pd/Al reactive multilayer system (RMS) on different Si-wafer substrates with different thermal conduction, specifically a bare Si-wafer, a RuOx or PdOx layer buffering Si-wafer, and a SiO2-coated Si-wafer. With the exception of the bare silicon wafer, the RMS grown on all other coated wafers underwent systematic spontaneous self-ignition surging during the deposition process once it reached a thickness of around 1 m. This issue was surmounted by investigating a solution based on tuning the output energy by stacking alternating sections of metallic reactive multilayer Pd/Al and Ni/Al systems that have a high and medium enthalpy of exothermic reactions, respectively. This heterostructure with a bilayer thickness of 100 nm was successfully grown on a SiO2-coated Si-wafer to a total thickness of 3 m without any spontaneous upsurge of self-ignition; it could be electrically ignited at room temperature, enabling a self-sustained propagating exothermic reaction along the reactive patterned track without undergoing quenching. The results of this study will promote the growth of reactive multilayer systems by electron beam evaporation processing and their potential integration as local heat sources on Si-wafer substrates for bonding applications in microelectronics and microsystems technology.

Phase Transformation and Characterization of 3D Reactive Microstructures in Nanoscale Al/Ni Multilayers

Reactive multilayer systems represent an innovative approach for potential usage in chip joining applications. As there are several factors governing the energy release rate and the stored chemical energy, the impact of the morphology and the microstructure on the reaction behavior is of great interest. In the current work, 3D reactive microstructures with nanoscale Al/Ni multilayers were produced by alternating deposition of pure Ni and Al films onto nanostructured Si substrates by magnetron sputtering. In order to elucidate the influence of this 3D morphology on the phase transformation process, the microstructure and the morphology of this system were characterized and compared with a flat reactive multilayer system on a flat Si wafer. The characterization of both systems was carried out before and after a rapid thermal annealing treatment by using scanning and transmission electron microscopy of the cross sections, selected area diffraction analysis, and differential scanning calorimetry. The bent shape of multilayers caused by the complex topography of silicon needles of the nanostructured substrate was found to favor the atomic diffusion at the early stage of phase transformation and the formation of two intermetallic phases Al0.42Ni0.58 and AlNi3, unlike the flat multilayers that formed a single phase AlNi after reaction.

Multilayer Films Based on Chitosan/Pectin Polyelectrolyte Complexes as Novel Platforms for Buccal Administration of Clotrimazole

Buccal films are recognized as easily applicable, microbiologically stable drug dosage forms with good retentivity at the mucosa intended for the therapy of oromucosal conditions, especially infectious diseases. Multilayer films composed of layers of oppositely charged polymers separated by ionically interacting polymeric chains creating polyelectrolyte complexes represent very interesting and relatively poorly explored area. We aimed to develop the antifungal multilayer systems composed of cationic chitosan and anionic pectin as potential platforms for controlled delivery of clotrimazole. The systems were pharmaceutically characterized with regard to inter alia their release kinetics under different pH conditions, physicomechanical, or mucoadhesion properties with using an animal model of the buccal mucosa. The antifungal activity against selected Candida sp. and potential cytotoxicity with regard to human gingival fibroblasts were also evaluated. Interactions between polyions were characterized with Fourier transform infrared spectroscopy. Different clotrimazole distribution in the films layers highly affected their in vitro dissolution profile. The designed films were recognized as intelligent pH-responsive systems with strong antifungal effect and satisfactory safety profile. As addition of chitosan resulted in the improved antifungal behavior of the drug, the potential utilization of the films in resistant cases of oral candidiasis might be worth of further exploration.

Effect of Surfactant on the Formation of Chitosan/ε-Polycaprolactone Blend Films for Food Packaging Applications

The objective of this study was to develop and characterize chitosan-ε-polycaprolactone (CHI/PCL) polymer blends with Tween 80 as a compatibilizer for application in packaging. The blends were produced by casting, with up to 10% (w/w) PCL in the CHI matrix. These blends were characterized in terms of their microstructure, chemical interactions, mechanical and thermal properties, solubility and water vapor permeability (WVP). The micrographs showed microsphere-like structures from the PCL in the continuous phase of CHI. Fourier transform infrared spectroscopy (FTIR) indicated a high interaction between CHI amino groups and PCL carbonyls, resulting in blends with greater ductility than the pure CHI film, thus providing greater flexibility. In the crystallinity analyses, the presence of PCL favored an increase in crystalline regions, limiting the passage of light. Given the results, blends are an alternative for application in multilayer systems and can be considered for use as a biodegradable fraction in food packaging.