R.A.M. Carvalho

Hydrophobic plasma polymerized hexamethyldisilazane thin films: characterization and uses

Hexametildisilazane (HMDS) plasma polymerized thin films obtained using low frequency power supplies can be used to make adsorbent films and turn surfaces hydrophobic. The aim of this work was to verify the hydrophobicity and adsorption properties of HMDS thin films (with and without the addition of oxygen, resulting in double or single layer films) obtained using an inductive reactor powered with a 13.56 MHz power supply. Single and double layer thin films were deposited on silicon for film characterization, polypropylene (PP) for ultraviolet (UVA/UVC) resistance tests, piezoelectric quartz crystal for adsorption tests. The double layer (intermixing) of HMDS plasma polymerized films and HMDS plasma oxidized surfaces showed a non-continuous layer. The films showed good adhesion to all substrates. Infrared analysis showed the presence of CHn, SiCH3, SiNSi and SiCH2Si within the films. Contact angle measurements with water showed hydrophobic surfaces. UVA/UVC exposure of the films resulted in the presence of cross-linking on carbonic radicals and SiCH2Si formation, which resulted in a possible protection of PP against UVA/UVC for a duration of up to two weeks. Adsorption tests showed that all organic reactants were adsorbed but not water. Plasma etching (PE) using O2 showed that even after 15 minutes of exposure the films do not change their hydrophobic characteristic but were oxidized. The results point out that HMDS films can be used: for ultraviolet protection of flexible organic substrates, such as PP, for sensor and/or preconcentrator development, due to their adsorption properties, and in spatial applications due to resistance for O2 attack in hostile conditions, such as plasma etching.

USE OF THIN FILMS OBTAINED BY PLASMA POLYMERIZATION FOR GRAIN PROTECTION AND GERMINATION ENHANCEMENT

In this work, preliminary results of the use of hydrophobic thin films obtained by plasma deposition to protect grains and seeds are presented: grains coated by the films did not present biological degradation when stored in a saturated water vapor environment, but had their germination accelerated in the presence of water. A model that explains the difference of behavior of the films when exposed to water in vapor form or in liquid form, based on the formation of microchannels within the film that lead to water uptake in seeds, is presented. The model was successfully tested using quartz crystal measurements, which showed that the microchannels within the films can favor the adsorption and permeation of water when the films are immersed in water.

TEOS PLASMA POLYMERIZED THIN FILMS AS A STATIONARY PHASE IN MICRO PRECOLUMNS USED FOR RETENTION OF ORGANIC AND INORGANIC COMPOUNDS

The aim was the manufacturing of miniaturized precolumns for retention and/or separation of compounds, in gas or liquid phase. Polysiloxane thin films obtained by plasma polymerization of Tetraethoxysilane (TEOS) were deposited in microcolumns, made of acrylic or aluminum, and ana-lyzed by Quartz Crystal Microbalance using organic com-pounds in a large range of polarity, carried by nitrogen, and ionic compounds, carried by water. As deposited, TEOS film allows the retention of volatile organic compounds and water, i.e. it is useful for sample pretreatment. After water exposure, TEOS films can be used not only for electrochromatography but also for gas and liquid chromatography. Thus, this micro precolumn has innumerable applications not only in retention or separation for chemical analysis (microTAS) but also for educational purposes, such as teaching new materials and analytical techniques.

Cerebral revascularization ina case of ischemic cerebrovascular disease

Dr. Eberval Gadelha Figueiredo – Rua Oscar Freire 1456 / 34 05409-010 São Paulo SP Brasil. E-mail: ebgadelha@yahoo.com It is well established that patients with transient ischemic attacks (TIA) or minor strokes that are found to have occlusive lesions of major brain-supplying vessels are prone to develop subsequent significant stroke. The underlying pathophysiology of cerebral ischemia within this large and heterogeneous group of patients remains matter of debate. Considerable controversy exists on the relative importance of thrombembolic versus hemodynamic mechanisms. Following the introduction of extracranialintracranial (EC-IC) bypass, the procedure was rapidly accepted as a way to increase cerebral perfusion in patients with ischemic cerebrovascular disease. However, the disappointing results of the Cooperative Study on EC-IC Bypass in 1985, led to the virtual abandonment of this procedure for the management of occlusive cerebrovascular disease. With the advent of contemporary imaging methods and functional blood flow studies, it has been demonstrated that a subset of patients with occlusive cerebrovascular disease is characterized by a severely impaired hemodynamic status. In such cases, the EC-IC bypass may represent an attractive and effective procedure to prevent cerebral hemodynamic failure. Retrospectively and particularly in view of new evidence on the pathophysiology of cerebral ischemia, the decision of the ECIC trial of suggesting abandoning EC-IC bypass completely seems premature. We present a clinical case of an EC-IC bypass performed in a patient with proved cerebral hemodynamic impairment. Additionally, the current indications, surgical options and clinical outcome are discussed. These cases are rarely reported in the Brazilian literature and many patients who probably could benefit from this procedure are often overlooked.