CONICET | Buscador de Institutos y Recursos Humanos

The prediction of transport phenomena involving molecular diffusion usually requires an accurate knowledge about the diffusion coefficient. In many problems the diffusion coefficient, which often is non constant, is unavailable. The ambiguity associated with available diffusion coefficients is often high since coefficients are usually measured under conditions which are different from those of the particular interest. In this study, an special in situ approach was adopted in order to determine the diffusion coefficient of low atomic weight molecules in hydrogels by Synchrotron Radiation Micro X-ray Fluorescence (SR-MXRF). The methodology allows determining the dependence of the diffusion coefficient as a function of time and concentration. It is based on quick-freeze and slicing methods which were employed with success in the past. Using an analytical solution of Fick law, the diffusion coefficient is estimated based on the calculated spatial concentration profiles, fitted to the measured concentrations in the sample slices. These measurements can be done in situ with high spatial resolution and excellent detection sensitivity by SR-MXRF. We think that these properties of SR-MXRF were not enough applied until now and should be of increasing interest to do all kind of in situ studies of kinetic effects. The present work is very useful to study the release of plant nutrients by special hydrogels like chitosan, polyurethanes etc. These hydrogels laden with nutrients can produce a long term and uniform supply of plants, which guarantee a very rapid, luxurious and a continued growth for an extended period. The knowledge required to control this technology is very useful for our country because it could optimise the agriculture production.

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