Mauro M. Costa

Bio: Mauro M. Costa is an academic researcher from University of São Paulo. The author has contributed to research in topics: Isothermal process & Polystyrene. The author has an hindex of 5, co-authored 6 publications receiving 174 citations.

Corona charging of polymers: recent advances on constant current charging

Abstract: This paper contains a brief overview on the recent developments of corona charging of polymers, with emphasis on the current corona triode. This latter method, which has been successfully applied to several types of polymer, is a legacy from Prof. Bernhard Gross' work in Sao Carlos, Brazil. Following a short introduction to corona charging, the experimental setups are described, especially with regard to the advantages in the constant current method. A few examples are given of the use of the constant current corona triode in the investigation of electrical properties of nonpolar and ferroeleectric polymers. The application of corona charging to pole nonlinear optic (NLO) polymers is discussed, including the perspectives for the constant current charging method for the NLO field.

On optical phase conjugation in polystyrene films containing the azobenzene dye Disperse Red 1

Abstract: Optical phase conjugation in polystyrene films containing the commercially available azobenzene dye Disperse Red 1 was measured using CW laser radiation generated by a frequency-doubled YAG laser of total power 50 mW The degenerate four-wave mixing (DFWM) experiment allowed for measurement of the build-up time of the phase-conjugate signal and phase-conjugate reflectivity as a function of dye concentration and input beam intensities The phase-conjugate reflectivities reached 01% in polystyrene films containing 25 wt% of the dye, with the phase-conjugate signal build-up time constants amounting to about 100 ms The appearance of a phase-conjugate signal is linked with a build-up of absorption-induced gratings of a mixed (phase and amplitude) nature Interesting thermally induced effects such as lensing effects and nonlinear chaotic behaviour of the phase-conjugate signal were observed

Electric‐field‐induced phase changes in polyvinylidene fluoride: Effects from corona polarity and moisture

Abstract: The constant‐current corona triode has been used to charge and monitor the surface potential buildup of polyvinylidene fluoride samples in α form. Under dry air and positive polarity it is possible to pole the samples to sufficiently high electric fields so as to cause a phase change from the nonpolar to the polar δ form. This phase transition is confirmed by x‐ray diffractograms. Surface potential measurements on δ samples display a ferroelectric behavior in which a plateau appears in the surface potential buildup curve due to the dipole reorientation. The values of the remanent polarization and the coercive field were estimated to be ∼50 mC/m2 and ∼65 MV/m, respectively.

Nonlinear refractive indices of polystyrene films doped with azobenzene dye Disperse Red 1

Abstract: Nonlinear refractive indices of polystyrene films containing azobenzene dye Disperse Red 1 (DR1) have been measured as a function of wavelength using the single beam Z-scan technique with a Fourier analysis of the transmittance time evolution. Although the C.W. excitation is carried out far from the absorption resonance region, the large nonlinear optical response has its origin in a thermal effect. We were able to find the thermal diffusivity coefficient of the sample.

Formation and relaxation of poled order in dye doped polystyrene probed by isothermal and nonisothermal current measurements

Abstract: Experimental results are presented on isothermal and nonisothermal electric current measurements obtained with a polystyrene and disperse red 1 guest–host system containing different percentages of the dye. The superposition principle holds for isothermal measurements and polarization currents seem to be almost independent of temperature in the range from 30 to 70 °C, below the glass transition temperature Tg. Thermally stimulated depolarization (TSD) current measurements show that the polarization induced in the samples depends strongly on poling conditions. Samples poled at temperatures above Tg have a lower polarization than those poled just below Tg. If the poling temperature Tp is far below Tg, the TSD current peak appears at much higher temperatures than Tp. The TSD curves differ somewhat from corresponding curves obtained during linear heating under applied voltage.

Laser-matter interaction in the bulk of a transparent solid: confined microexplosion and void formation

Abstract: We present here the experimental and theoretical studies of a single femtosecond laser pulse interaction inside a bulk of transparent media (sapphire, glass, polymer). This interaction leads to the drastic transformations in a solid resulting in a void formation inside a dielectric. The laser pulse energy is absorbed within a volume of approximately $0.15\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}{\mathrm{m}}^{3}$ creating a pressure and temperature comparable to that in the core of a strong multi-kilo-tons explosion. The material within this volume is rapidly atomized, ionized, and converted into a tiny super-hot dense cloud of expanding plasma that generates strong shock and rarefaction waves which result in the formation of a void, whose diameter is $\ensuremath{\sim}200\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ (for a $100\phantom{\rule{0.3em}{0ex}}\mathrm{nJ}$ pulse in sapphire). The way this structure forms can be understood from high-temperature plasma hydrodynamics. We demonstrate that unique states of matter characterized by temperatures $\ensuremath{\sim}{10}^{5}\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, heating rates up to the ${10}^{18}\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{s}$, and pressures more than 100 times the strength of any material were created using a standard table-top laser in well-controlled laboratory conditions. We discuss the properties of the laser-affected solid and possible routes of laser-affected material transformation to the final state long after the pulse end. These studies will find application for the design of new materials and three-dimensional optical memory devices, and for formation of photonic band-gap crystals.

A paper-based nanogenerator as a power source and active sensor

Abstract: Paper-based functional electronic devices endow a new era of applications in radio-frequency identification (RFID), sensors, transistors and microelectromechanical systems (MEMS). As an important component for building an all paper-based system that can work independently and sustainably, a paper-based power source is indispensable. In this study, we demonstrated a paper-based nanogenerator (pNG) that can convert tiny-scale mechanical energy into electricity. The pNG relies on an electrostatic effect, and the electrostatic charges on the paper were generated by the corona method. The instantaneous output power density of a single-layered pNG reached ∼90.6 μW cm−2 at a voltage of 110 V, and this instantaneously illuminated 70 LEDs. In addition, by sticking the pNG to a movable object, such as the page of a book, the power harvested from the mechanical action of turning the page can drive an LED, which presents its outstanding potential in building paper-based, self-powered systems and as active sensors.

Patterned piezo-, pyro-, and ferroelectricity of poled polymer electrets

Abstract: Polymers with strong piezo-, pyro-, and ferroelectricity are attractive for a wide range of applications. In particular, semicrystalline ferroelectric polymers are suitable for a large variety of piezo- and pyroelectric transducers or sensors, while amorphous polymers containing chromophore molecules are particularly interesting for photonic devices. Recently, a new class of polymer materials has been added to this family: internally charged cellular space-charge polymer electrets (so-called “ferroelectrets”), whose piezoelectricity can be orders of magnitude higher than that of conventional ferroelectric polymers. Suitable patterning of these materials leads to improved or unusual macroscopic piezo-, pyro-, and ferroelectric or nonlinear optical properties that may be particularly useful for advanced transducer or waveguide applications. In the present paper, the piezo-, pyro-, and ferroelectricity of poled polymers is briefly introduced, an overview on the preparation of polymer electrets with patterned...

Cantilever-based electret energy harvesters

Abstract: Integration of structures and functions has permitted the electricity consumption of sensors, actuators and electronic devices to be reduced. Therefore, it is now possible to imagine low-consumption devices able to harvest energy from their surrounding environment. One way to proceed is to develop converters able to turn mechanical energy, such as vibrations, into electricity: this paper focuses on electrostatic converters using electrets. We develop an accurate analytical model of a simple but efficient cantilever-based electret energy harvester. We prove that with vibrations of 0.1g (~1 m s−2), it is theoretically possible to harvest up to 30 µW per gram of mobile mass. This power corresponds to the maximum output power of a resonant energy harvester according to the model of William and Yates. Simulation results are validated by experimental measurements, raising at the same time the large impact of parasitic capacitances on the output power. Therefore, we 'only' managed to harvest 10 µW per gram of mobile mass, but according to our factor of merit, this is among the best results so far achieved.

Piezoelectric polymer electrets

Abstract: In this review the physical properties, mechanisms and models are reviewed which explain the high piezoelectricity of the ferroelectric polymers of the polyvinylidene fluoride (PVDF) family, the odd nylons, the vinylidene cyanide (VDCN) copolymers and polyurea. Because PVDF and its copolymers with trifluoroethylene (TrFE) and tetrafluoroethylene (TFE) have been studied extensively in the last 25 years the main part of the review deals with these polymers. Additionally a short summary of the different piezoelectric applications of PVDF is presented. The odd nylons, the VDCN copolymers and the polyurea are compared with PVDF to show the different stabilization mechanisms of the remanent polarization and the different temperature behavior of the piezoelectricity. This review not only concentrates on the work done in the last few years but in order to describe the behavior of these polymers in detail, it is necessary to go back to the roots. Therefore many articles from the late seventies and early eighties are included.