We performed an extensive characterization of an electrospinning process to evaluate how the process parameters and precursor solution characteristics affect the fibers morphology. The work was conducted using precursor solutions with different concentrations of polyacrylonitrile (PAN) diluted in a fixed amount of N,N/dimethylformamide (DMF). Fibers obtained with this process can find important applications in the field of nanosensors. The characteristics of the electrospun fibers were analyzed as a function of the solution viscosity, applied voltage and distance between the needle tip (positive electrode) and the collector plate (grounded electrode). The electrical current was monitored during the deposition process and its behavior was correlated with the characteristics of the fibers obtained. Our results demonstrate that the diameter of the fibers increases with increasing viscosity and applied voltage. The number of deposited fibers also increases with the applied voltage. Also, viscosity and applied voltage strongly affect the shape, length and morphology of the fibers. Of particular interest, we demonstrated that by monitoring the electrical current it is possible to control the fibers morphology and bead concentration. The distance between tip and collector plate determines the way the fibers arrive on the collector plate. A main contribution of this study was the definition of conditions to controllably obtain fibers that are smooth and that present diameters in the range between 140 and 300 nm.

Neste trabalho é descrita a construção de um microssistema em silício para retenção de íons cobre(II). Processo fotolitográfico convencional foi empregado para transferir o padrão de microcanais para o substrato de silício. Utilizando corrosão por íons reativos (RIE) com plasma de SF6, foram produzidos canais de 50 µm de largura e 10 µm de profundidade. Os canais foram selados com vidro de borossilicato utilizando-se a técnica de soldagem anódica. Para promover a retenção dos íons cobre(II), a superfície dos canais foi modificada através de reação de silanização com N-(beta-aminoetil)-gama-aminopropiltrimetóxisilano. Os íons cobre(II) foram detectados amperometricamente na saída do canal utilizando-se um eletrodo de ouro. Os íons cobre(II) foram eluídos com HCl 50 mmol L-1 em um sistema micro-FIA com fluxo de 100 µL min-1. A reprodutibilidade em termos de área e altura do pico foram de 4,6 % e 10 %, respectivamente, para três injeções consecutivas de 600 µL de solução de cobre(II) 10 µmol L-1.

This work describes the construction of a silicon microchip for retention of copper(II) metal ions. Conventional photolithographic process was applied to transfer the generated pattern to silicon wafers. Using Reactive Ion Etching (RIE), SF6 based, channels 50 µm wide and 10 µm deep were produced. The channels were sealed with borosilicate glass using anodic bonding process. The surface of the channels were modified with N-(beta-aminoethyl)-gamma-aminopropyltrimetoxysilane through a silanization reaction to promote the adsorption of copper(II) ions. An amperometric detector was placed at the microchip outlet and copper(II) ions were detected by a gold electrode at 0 V (against Ag/AgCl(KCl sat.) reference electrode). Copper(II) ions were retained and eluted with HCl 50 µmol L-1 in a micro-flow system at a flow rate about 100 µL min-1. Reproducibility in the peak area and height were about 4.6 % and 10 %, respectively, for three consecutive injections of 600 µL of 10 µmol L-1 copper(II) sample.

This work addresses the formation of nanofibers (with hundred of nanometers) by using electrospinning (electrostatic deposition) aiming at applications as sensors. Different quantities of a colloidal dispersion of graphite particles were blended with polyacrylonitrile (PAN) and N,N dimethylformamide (DMF), resulting in a series of solutions with carbon concentrations ranging from 0 to 25%. Precipitation was observed depending on the concentration of carbon added to the precursor blend. As a consequence, the relative viscosity decreases, due to PAN molecules removal from the solution by carbon particles adsorption, forming precipitates. The resulting fibers show an irregular shape, as observed by SEM and the diameters decrease with the increase of the carbon concentration in the precursor blend. The incorporation of carbon particles in the fibers was confirmed by FTIRS and Raman spectroscopy.