RESUMO
Inverse gas chromatography is currently used for the determination of the surface properties of divided solids by probing the surface with alkanes or polar molecules of known properties. This paper suggests the use of a new topological index for the description of the probe's (alkanes) geometry and hence of their accessibility to the solid's surface. The proposed index (chiT) derives from the well known Wiener index. The application of chiT for the determination of the dispersive component of the surface energy of pyrogenic silica, but also for the evaluation of the geometric heterogeneity of lamellar silica, is described. Further, goethite and zirconia samples were submitted to similar analysis. Copyright 1997 Academic Press. Copyright 1997Academic Press
RESUMO
The application of the new morphological index chiT, which is an extension of Wiener's index for the evaluation of the retention data of apolar and polar solutes used in inverse gas chromatography, is described. Indeed, chiT performs satisfactorily, surpassing the other molecular descriptors employed so far. Examples of applications on silica and graphite samples are presented. It appears that the new index allows a unique evaluation of the Lewis acid-base surface characteristics of solid surfaces. Copyright 1997 Academic Press. Copyright 1997Academic Press
RESUMO
The interaction between metallic iron pigments (MPs) and the actual constituents of magnetic ink is examined by first determining the adsorption isotherms and analyzing by FTIR the type of bonding that is established between the constituents and MP. Then, following the approach described in a previous paper using model compounds, the formation of electrical charges on MPs is examined through acoustophorometric (Electrokinetic amplitude or ESA) measurements. It is shown that the variation in ESA is related to charge transfer processes and reflects the MP-constituent interactions. Finally, adsorption competitions are shown and the importance of the method of preparation (order of mixing of the ingredients of the ink) is illustrated. Copyright 1997 Academic Press. Copyright 1997Academic Press
RESUMO
The adsorption of stearic acid and bis(2-ethylhexyl) phosphate, from toluene and THF solutions, on magnetic iron pigments (MP) was examined. Adsorption isotherms as well as the concomitant variations of surface electrical (zeta) potential were determined. The formation of electrical surface charges is explained by charge transfer processes between the solvents, the adsorbates, and MP. An adsorption competition is evidenced when contacting MP with the adsorbates using 14C-labeled stearic acid.
RESUMO
Inverse gas chromatography (IGC) at infinite dilution was used to characterize the fumed silica surface. The silica was modified by chemical treatment with either dimethyldichlorosilane or trimethylchlorosilane. To observe the silica and poly(dimethylsiloxane) (PDMS) interactions, we used apolar (alkanes) and polar probes (chloroform, benzene, tetrahydrofuran, etc.), but also model molecules of PDMS such as linear and cyclic oligomers of PDMS with two to five monomer units. It is shown that PDMS oligomers are very appropriate to discriminate the silylated silicas.
