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Shiroma L.Y.,University of Campinas | Santhiago M.,University of Campinas | Gobbi A.L.,Brazilian Synchrotron Light Laboratory (LNLS) | Kubota L.T.,University of Campinas
Analytica Chimica Acta | Year: 2012

The present work describes the construction and application of a simple, low cost and sensitive microfluidic paper-based device with electrochemical detection for the detection of paracetamol and 4-aminophenol. The separation channels of a width of 2.0mm were created on paper using a wax printing process to define the regions of the device. A baseline separation level of the analytes can be obtained in 0.1molL -1 acetate buffer solution at pH 4.5 and by injecting 500nL of the standard solutions at 12mm from the working electrode. The electrochemical detection system was created at the end of the channels through a process known as sputtering. The previously separated analytes were detected at the end of the hydrophilic separation channel by applying a potential of 400mV vs. pseudo Au on the working electrode. Experimental variables such as type of paper (cation exchanger and n1), pH, sample volume, applied potential and distance of sample injection were evaluated and, under the conditions of higher response, it was possible to obtain detection limits of 25.0 and 10.0μmolL -1 for paracetamol and 4-aminophenol, respectively. © 2012 Elsevier B.V..

Lagos M.J.,University of Campinas | Lagos M.J.,Brazilian Synchrotron Light Laboratory (LNLS) | Sato F.,Federal University of Juiz de fora | Galvao D.S.,University of Campinas | Ugarte D.,University of Campinas
Physical Review Letters | Year: 2011

Face centered cubic metals deform mainly by propagating partial dislocations generating planar fault ribbons. How do metals deform if the size is smaller than the fault ribbons? We studied the elongation of Au and Pt nanorods by in situ electron microscopy and ab initio calculations. Planar fault activation barriers are so low that, for each temperature, a minimal rod size is required to become active for releasing elastic energy. Surface effects dominate deformation energetics; system size and shape determine the preferred fault gliding directions which induce different tensile and compressive behavior. © 2011 American Physical Society.

Chiaramonte T.,University of Campinas | Tizei L.H.G.,University of Campinas | Tizei L.H.G.,Brazilian Synchrotron Light Laboratory (LNLS) | Ugarte D.,University of Campinas | Cotta M.A.,University of Campinas
Nano Letters | Year: 2011

InP nanowire polytypic growth was thoroughly studied using electron microscopy techniques as a function of the In precursor flow. The dominant InP crystal structure is wurtzite, and growth parameters determine the density of stacking faults (SF) and zinc blende segments along the nanowires (NWs). Our results show that SF formation in InP NWs cannot be univocally attributed to the droplet supersaturation, if we assume this variable to be proportional to the ex situ In atomic concentration at the catalyst particle. An imbalance between this concentration and the axial growth rate was detected for growth conditions associated with larger SF densities along the NWs, suggesting a different route of precursor incorporation at the triple phase line in that case. The formation of SFs can be further enhanced by varying the In supply during growth and is suppressed for small diameter NWs grown under the same conditions. We attribute the observed behaviors to kinetically driven roughening of the semiconductor/metal interface. The consequent deformation of the triple phase line increases the probability of a phase change at the growth interface in an effort to reach local minima of system interface and surface energy. © 2011 American Chemical Society.

Pontes R.B.,University of Sao Paulo | Rocha A.R.,Federal University of ABC | Sanvito S.,Trinity College Dublin | Fazzio A.,University of Sao Paulo | And 2 more authors.
ACS Nano | Year: 2011

By performing ab initio density functional theory (DFT) calculations and electronic transport simulations based on the DFT nonequilibrium Green's functions method we investigate how the conformational changes of a benzene-1,4-dithiol molecule bonded to gold affect the molecular transport as the electrodes are separated from each other. In particular we consider the full evolution of the stretching process until the junction breaking point and compare results obtained with a standard semilocal exchange and correlation functional to those computed with a self-interaction corrected method. We conclude that the inclusion of self-interaction corrections is fundamental for describing both the molecule conductance and its stability against conformational fluctuations. © 2011 American Chemical Society.

Tischer P.C.S.F.,Federal University of Parana | Sierakowski M.R.,Federal University of Parana | Westfahl H.,Brazilian Synchrotron Light Laboratory (LNLS) | Tischer C.A.,Federal University of Parana
Biomacromolecules | Year: 2010

In this work, bacterial cellulose was subjected to a high-power ultrasonic treatment for different time intervals. The morphological analysis, scanning electron microscopy, and atomic force microscopy revealed that this treatment changed the width and height of the microfibrillar ribbons and roughness of their surface, originating films with new nanostructures. Differential thermal analysis showed a higher thermal stability for ultrasonicated samples with a pyrolysis onset temperature of 208 °C for native bacterial cellulose and 250 and 268 °C for the modified samples. The small-angle X-ray scattering experiments demonstrated that the treatment with ultrasound increased the thickness of the ribbons, while wide-angle X-ray scattering experiments demonstrated that the average crystallite dimension and the degree of crystallinity also increased. A model is proposed where the thicker ribbons and crystallites result from the fusion of neighboring ribbons due to cavitation effects. © 2010 American Chemical Society.

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