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Evaluation and diagnosis of blood alterations is a common request for clinical laboratories, requiring a complex technological approach and dedication of health resources. In this paper, we present a microfluidic device that owing to a novel combination of hydrodynamic and dielectrophoretic techniques can separate plasma from fresh blood in a microfluidic channel and for the first time allows optical real-time monitoring of the components of plasma without pre- or post-processing. The microchannel is based on a set of dead-end branches at each side and is initially filled using capillary forces with a 2-μL droplet of fresh blood. During this process, stagnation zones are generated at the dead-end branches and some red blood cells (RBCs) are trapped there. An electric field is then applied and dielectrophoretic trapping of RBCs is used to prevent more RBCs entering into the channel, which works like a sieve. Besides, an electroosmotic flow is generated to sweep the rest of the RBCs from the central part of the channel. Consequently, an RBC-free zone of plasma is formed in the middle of the channel, allowing real-time monitoring of the platelet behavior. To study the generation of stagnation zones and to ensure RBC trapping in the initial constrictions, two numerical models were solved. The proposed experimental design separates up to 0.1 μL blood plasma from a 2-μL fresh human blood droplet. In this study, a plasma purity of 99 % was achieved after 7 min, according to the measurements taken by image analysis. Graphical Abstract Schematics of a real-time plasma monitoring system based on a Hydrodynamic and direct-current insulator-based dielectrophoresis microfluidic channel.

With thermally stimulated depolarization currents, we researched the relaxations of crosslinked polyethylene as it is used in medium-voltage cable insulation. Through conventional polarization two heteropolar peaks stand up in the spectra, at 80 and 105°C. As the sample is annealed, a homopolar peak is developed at about 99°C. With window polarization, our results indicated that the 80°C peak is a structured peak related to polar crosslinking subproducts and impurities. The 105 and 99°C peaks are fitted to the general kinetic-order model because the 105°C peak is related to free-charge detrapping at the crystalline phase, in the bulk and maybe at the amorphous-crystal interphases, and the peak that is observed at 99°C is due to injected charge. Annealing at high temperatures promotes the creation of traps in the material. Charge trapping at T Ͻ 70°C seems to be related to the increased insulator resistivity with annealing time.

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The glass transition in amorphous poly(ethylene terephthalate) is studied by thermally stimulated depolarization currents (TSDC) and differential scanning calorimetry (DSC). The ability of TSDC to decompose a distributed relaxation, as the glass transition, into its elementary components is demonstrated. Two polarization techniques, windows polarization (WP) and non-isothermal windows polarization (NIW), are employed to assess the influence of thermal history in the results. The Tool-Narayanaswami-Moynihan (TNM) model has been used to fit the TSDC spectra. The most important contributions to the relaxation comes from modes with non-linearity (x) around 0.7. Activation energies yield by this model are located around 1 eV for polarization temperature (T p ) below 50 • C and they raise up to values higher than 8 eV as T p increases (up to 80 • C). There are few differences between results obtained with WP and NIW but, nonetheless, these are discussed. The obtained kinetic parameters are tested against DSC results in several conditions. Calculated DSC curves at several cooling and heating rates can reproduce qualitatively experimental DSC results. These results also demonstrate that modelization of the non-equilibrium kinetics involved in TSDC spectroscopy is a useful experimental tool for glass transition studies in polar polymers.

Aquesta és una còpia de la versió author's final draft d'un article publicat a la revista Analytical and bioanalytical chemistry.La publicació final està disponible a Springer a través de http://dx.doi.org/10.1007/s00216-016-9629-2 This is a copy of the author 's final draft version of an article published in the journal Analytical and bioanalytical chemistry. AbstractDirect-current insulator-based dielectrophoresis (DC-iDEP) is a well-known technique that benefits from the electric field gradients generated by an array of insulating posts to separate or trap biological particles. In this work, we propose a novel figure of merit to find an efficient design of the post-array distribution in a microfluidic channel. To characterization can be used to reduce the required electric field to achieve effective particle trapping and, therefore, avoid the negative effects of Joule heating in cells or viable particles.

Dynamic electrical analysis shows that at high temperatures (above the glass transition temperature), the electrical properties of polyetherimide are strongly influenced by space charge. In this article we have studied the relaxation of space charge in two commercial varieties of polyetherimide: Ultem 1000 and Ultem 5000. Their conductive properties were determined by dynamic electrical analysis, using the electric modulus formalism. The complex part of the electric modulus was fitted to Coelho’s model which considers ohmic conductivity and diffusion as the prevailing charge transport mechanisms. The complex part of the electric modulus exhibits a peak in the low frequency range that can be associated with space charge. A good agreement between experimental and calculated data is observed after the fitting process to Coelho’s model. Differences in the electrode behavior were required: blocking electrode conditions in the case of Ultem 5000 and partially blocking electrode for Ultem 1000. In both cases the conductivity determined is thermally activated and it increases with the temperature due to an increasing mobility, as their carrier densities do not vary significantly in the temperature range studied.

We studied the space charge behavior in crosslinked polyethylene cable insulation with thermally stimulated depolarization current (TSDC). The role of the semiconducting layers of the cable in space charge formation was determined with several experiments carried out with two different cables. TSDC spectra were obtained through the exchange of the semiconducting layers of each cable with aluminum or silver coatings. Heteropolar current peaks at 80 and 105 °C were observed in the TSDC spectrum. As a sample was annealed at high temperatures, the creation of traps in the material was promoted, and a homopolar contribution at 98 °C developed. This homopolar mechanism was linked to the diffusion, with annealing, of ionic components from the semiconducting layers into the insulation bulk. The penetration depth of these components was studied with Fourier transform infrared in sections obtained at several depths starting at the outer surface of the cable insulation. These diffused components remained on the crystal surfaces, and they became trapping centers for free charge. Charge injection from the semiconducting electrodes and homopolar trapping of injected charges on these components took place afterwards during polarization. This process tended to saturation. Besides this mechanism, the continuous dissociation of molecules took place in the material with thermal annealing. This ionic charge generation resulted in an increase in the heteropolar contribution of the TSDC spectrum. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4164–4174, 2004