Browsing by Author "Moura, L."
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- Detection of explosive vapors using organic thin-film transistorsPublication . Bentes, E.; Gomes, Henrique L.; Stallinga, Peter; Moura, L.Field effect transistors (FETs) based on organic materials were investigated as sensors for detecting 2,4,6-trinitrotoluene (TNT) vapors. Several FET devices were fabricated using two types of semiconducting organic materials, solution processed polymers deposited by spin coating and, oligomers (or small molecules) deposited by vacuum sublimation. When vapors of nitroaromatic compounds bind to thin films of organic materials which form the transistor channel, the conductivity of the thin film increases and changes the transistor electrical characteristic. The use of the amplifying properties of the transistor represents a major advantage over conventional techniques based on simple changes of resistance in polymers frequently used in electronic noses.
- Implementation of a spiking neural networkPublication . Pacheco, E.; Moura, L.; Ruano, AntonioReconfigurable systems allow the implementation of hardware using a Hardware Description Language (HDL). This allows a simple implementation and on-line reconfiguration, which are big advantages when compared to traditional electronic circuits, while maintain its main advantages: parallelism and speed. When an analogue system is considered, in this case a Field Programmable Analogue Array (FPAA), another advantage his added, the precision of the results. The neural networks allow fast outputs with low errors for complex systems.
- Preparation and characterization of low dispersity anionic multiresponsive core-shell polymer nanoparticlesPublication . Pinheiro, J. P.; Moura, L.; Fokkink, R.; Farinha, J. P. S.We prepared anionic multistimuli responsive core–shell polymer nanoparticles with very low size dispersity. By using either acrylic acid (AA) or methacrylic acid (MA) as a comonomer in the poly(N-isopropyl acrylamide) (PNIPAM) shell, we are able to change the distribution of negative charges in the nanoparticle shell. The particle size, volume phase transition temperature, and aggregation state can be modulated using temperature, pH, or ionic strength, providing a very versatile platform for applications in sensors, medical diagnostics, environmental remediation, etc. The nanoparticles have a glassy poly(methyl methacrylate) (PMMA) core of ca. 40 nm radius and a cross-linked PNIPAM anionic shell with either AA or MA comonomers. The particles, p(N-AA) and p(MA-N), respectively, have the same total charge but different charge distributions. While the p(MA-N) particles have the negative charges preferentially distributed toward the inner shell, in the case of the p(N-AA) particles the charge extends more to the particle outer shell. The volume phase transition temperature (TVPT) of the particles is affected by the charge distribution and can be fine-tuned by controlling the electrostatic repulsion on the particle shell (using pH and ionic strength). By suppressing the particle charge we can also induce temperature-driven particle aggregation.