FRACTAL ANALYSIS OF THE DISTRIBUTION OF HIGH-VISCOSITY FLUIDS IN POROUS SUPPORTS

The distribution of a highly viscous fluid in porous media has been investigated by the example of polymer-coated supports for liquid chromatography. A system of practical interest in protein separation, namely polybutadiene on porous silica LiChroshper Si 300, has been explored. The values of the surface fractal dimensions for the parental support and the samples with varying polymer loading have been obtained from low-temperature nitrogen adsorption isotherms using the thermodynamic method. The increase of polymer content does not have a significant impact on the surface properties. The fractal dimensions for polymer-coated samples do not differ essentially from the value of 2.22, inherent for the parental support, over the scale range of about 10-150 angstrom. The effect of defractalization, which is characteristic for wetting films, has not been observed. On the basis of the fractal analysis, we concluded that the polymer is predominantly sited in inclusions or ganglia and the pore volume is filled at random with bulk polymer. The proposed ganglia model for the polymer distribution in porous supports describes sufficiently the observed changes in the pore structure caused by the polymer loading. It is consistent within dependent solid-state NMR measurements and can be used for the interpretation of chromatographic data. The thermodynamic method of the fractal analysis based on adsorption and/or capillary experimental data is recommended for the investigation of high-viscosity liquids or other host phase distributions in different porous systems.