Renato Amaral Minamisawa

Digital Image Analysis to Standardize a Photometric Method in Colorimetric Quantification

Abstract Techniques applying digital images increasingly have been used in biology, medicine, physics, and other research areas. The image coordinates can represent light intensities values to be detected by a CCD. Based on this concept, a photometric system composed of a LED source and a digital camera as a detector was used for optical density measurements. Standards for permanganate, glucose, and protein solutions were determined by colorimetric methods using our device. Samples of protein of Pasteurella mutocida bacteria membrane and, also, fractions of rabbit kidney membrane, rich in Na, K‐ATPase, with unknown concentrations were dosed through the Hartree method using our photometric system.

DIFFERENTIAL 3ω METHOD FOR THERMAL MEASUREMENTS

The 3ω technique has been applied to measure thermal properties of thin films and suspended wires. In this article, we report the implementation and technical design of a 3ω system to measure the thermal conductivity in small dimension structures. Alternating current is applied to a line heater that dissipates power and varies its resistance. The 3ω voltage drop across the heater provides information that determines the thermal properties of the heater or of the adjacent material. A differential bridge is used to subtract the first harmonic voltage and systematic noise. We introduce the use of a synchronous detector associated with the differential bridge to obtain the in-phase and out-of-phase components of the third harmonic signal. The combination improves the bridge method for a broad range of frequency analysis that permits either thermal conductivity and/or heat capacity measurements.

Glassy Polymeric Carbon Resistivity as a Function of Carbon Nanotubes

Glassy Polymeric Carbon (GPC) is a material widely used because of its high temperature properties, inertness and biocompatibility [1]. GPC samples were prepared from a phenolic resin, cured in a careful process at 100 oC and pyrolyzed to 1000 oC. In this work, we have introduced 3wt%, 10wt%, and 20 wt% of Carbon Nano Tubes (CNT) in the precursor resin to study the evolution of the electrical conductivities of the nanocomposite as a function of the CNT concentration.

Chemical, Mechanical and Electrical Properties of Glassy Polymeric Carbon

Glassy Polymeric Carbon (GPC) is obtained by a molding technique, in various shapes, from a phenolic resin precursor. The heat treatment of the precursor is achieved in three stages up to 1000 °C. Similar GPC materials produced in our laboratory displayed large strain to failure ratio, small thermal expansion coefficient and low density. Like all carbon forms, is attacked by oxygen, especially atomic oxygen. Nevertheless the kinetics for reaction with atmospheric oxygen is very slow. We investigated the composition and structural changes of the phenolic precursor as a function of temperature and evaluated materials stability when exposed to high temperatures in presence of hydrogen or oxygen.

Electret Pattern Fornation in Teflon by Pyroeletric and Photogalvanic Electron Emission From LiNbO 3

High field emission of electrons in the c direction of pyroelectric LiNbO3 has recently been reported [Ref.1]. With modest temperature variations, electron energies are shown to be sufficient to produce the characteristic X-rays from niobium in the crystal and from an adjacent copper foil. We report using these energetic electrons to create the patterned electret state in ETFE (Ethylenetetrafluoroethylene) and in FEP (Tetrafluoroethylene-hexa-fluoropropylene). Temperature sufficient to cause electron emission was established in a LiNbO3 crystal near or in contact with the polymer films. The persistent negative charge near the surface of the films could then be measured nondestructively with a capacitive probe, which we have developed for other electret applications. Photogalvanic electron emission produced by light illumination of the doped photosensitive LiNbO3 crystal was also tested for the electret pattern formation. The charge density injected into the polymer inferred from our measurements is limited by the maximum energy of the pyroelectrically and photogalvanically emitted electrons since the electret field opposes the pyroelectric and photogalvanic field. The density and spatial distribution of charges injected by the pyroelectricity of LiNbO3 into TEFLON electrets are consistent with a selffocusing effect observed in a vacuum by the authors of reference