Softcover reprint of the hardcover 1 st edition 1980All righ ts reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any focm or by any means, electronic, mechanical, photocopying, microftlming, recording, or otherwise, without written permission from the Publisher We wish to express our deep appreciation to Professor Mario Teruggi of the University of La Plata, Argentina, for his advice on English style and to Professor Rutherford Aris of the University of Minnesota, for his encouragement. PrefaceThe world we live in exhibits, on different scales, many phenomena related to the diffusion of gases. Among them are the movement of gases in earth strata, the aeration of soils, the drying of certain materials, some catalytic reactions, purification by adsorption, isotope separation, column chromatography, cooling of nuclear reactors, and the permeability of various packing materials.The evolution of the understanding of this subject has not always been straightforward and progressive-there has been much confusion and many doubts and misunderstandings, some of which remain to this day. The main reason for the difficulties in the development of this subject is, we now know, the lack of an understanding of the effects of walls on diffusing systems.Textbooks usually treat diffusion on two levels: at the physicochemical or molecular level, making use of the kinetic theory of gases (which while a very rigorous and well-founded theory nevertheless is valid only for systems without walls), or at the level of a transport phenomenon, a level geared toward applications. The influence of walls is usually disregarded or is treated very briefly (for example, by taking account of the Knudsen regime or by introducing a transition regime of limited validity) in a way unconnected with previous studies. As a consequence, the extensive, generalized, and well-founded knowledge of systems without walls has often been applied without sound basis to real situations, i.e., to systems with walls.Only recently has a unifying theory, the dusty gas model, been developed that correctly takes account of the influence of walls and which thus clarifies many of the problems and much of the confusion that has beset this subject. The dusty gas model shows why, for example, the fluxes of the species in a binary system are not always equal and opposite (and its predictions in this regard have been experimentally verified), it shows clearly that there is a difference between systems "without walls" and vii viii Preface systems "without wall effects," and it clarifies the nature of the total diffusive flux of a system and the nature of the coupling between the diffusive and viscous fluxes.In this book we present the subject of diffusion from the point of view of the dusty gas model, pointing out where the confusion and errors have arisen-and where they can and still unfortunately do arise if care is not taken. We will be more concerned with the foundations and preliminary questions than with the applications.In t...

(7600) Mar del Plata, Argentina SynopsisThe curing reaction of a commercial bisphenol A diglycidyl ether (BADGE) with ethylenediamine (EDA) was studied by differential scanning calorimetry. Different kinetic expressions were found with isothermal (low temperature rafige) and dynamic (high temperature range) runs. Two competitive mechanisms are shown to be present: an autocatalytic one (activation energy E = 14 kcal/mol) and a noncatalytic path characterized by a second-order reaction with E = 24.5 kcal/mol. At low temperatures both mechanisms took place simultaneously, showing a significant decrease in the reaction rate after the gel point. At high temperatures only the noncatalytic reaction was present, without showing a noticeable rate decrease in the rubber region. Also, a third-order dependence of the glass transition temperature on reaction extent is shown.

Superparamagnetic nanocomposites were obtained by dispersion of oleic acid (OA)-coated magnetite NPs in an epoxy system based on diglycidylether of bisphenol A (DGEBA) modified with OA. Dispersion of conventional oleic acidstabilized magnetite NPs in a typical epoxy matrix is not possible due to the dissimilar chemical structures of the organic coating and the reactive solvent. However, by modification of a DGEBA-based epoxy with 20 wt % OA, we obtained a suitable reactive solvent to disperse up to at least 8 wt % of OA-stabilized magnetite NPs. A tertiary amine was used to catalyze the epoxy−acid reaction and initiate the homopolymerization of the epoxy excess. Both reactions occurred practically in series, first the epoxy−acid and then the epoxy homopolymerization. It was necessary to complete the first reaction to attain a very good dispersion of magnetite NPs in the reactive solvent previous to the occurrence of the final reaction. Magnetization curves and TEM images revealed a uniform dispersion of individual nanoparticles in the cross-linked epoxy. A sample containing 8 wt % OA-coated magnetite NPs exhibited a temperature increase of 25 °C at its surface when exposed to an alternating magnetic field. The temperature increase was enough to induce the shape memory effect of the nanocomposite.