posted on 2016-12-12, 00:00authored byPhilip Kensbock, Dan Eugen Demco, Smriti Singh, Khosrow Rahimi, Radu Fechete, Andreas Walther, Annette Monika Schmidt, Martin Möller
In the presence of additives such
as etidronic acid (1-hydroxyethane-1,1-diphosphonic
acid, HEDP), a process of peptizing of Laponite clay gels takes place.
The peptizing process at the molecular level was directly revealed
by 31P and 1H high-resolution magic-angle sample
spinning (HRMAS) NMR spectroscopy. Two NMR spectral components were
detected and assigned to free etidronic acid and bound to the Laponite
disk edges. Furthermore, with increase of temperature the ratio of
bound-to-free etidronic acid increases. This thermal activation process
could be explained by the increase in electrical polarization of the
hydroxyl group at the edges and by the exfoliation of the tactoids
that leads to more access to the additive molecules to the electrical
charges of platelet edges. 31P HRNMR spectroscopy on sodium
fluorohectorite with an aspect ratio of ∼750 shows a reduction
of the bound etidronic acid molecules. Transmission electron microscopy
(TEM), field-emission scanning microscopy (FESEM), UV–vis spectrophotometry,
dynamic light scattering (DLS), and zeta potential results support
the proposed peptizing mechanisms.