| 總結: | <p>We studied the use of Laponite EP, an organically surface coated laponite, as an alternative of
xanthan in product formulation. Its combination with bentonite in agrochemical formulation
showed similar rheological behaviour as the commonly used xanthan - bentonite combination.
Laponite EP and bentonite display some synergism: analogous rheological properties could not
be achieved using each clay alone or using a non-coated laponite RD - bentonite blend. The
microstructure suggested two networks cooperating. The results highlighted the effect of the
coating on the rheology of the clay and the product. Although the surface coating did not impact
the surface charge of the clay, it may have prevented the adsorption of other components on its
surface. The rheological behaviour of the gel Laponite EP - bentonite under diverse conditions
was modelled using a mixture design approach. We varied the amount of salt (MgCl2) and
surfactant (Tween 20) in the solution as well as the pH (from 4 to 9). We focused on modelling
the storage modulus G′, the loss modulus G′′ and the critical stress σ<sub>c</sub>. The models obtained
underlined some complex interactions with antagonistic effects between the components.</p>
<p>The ageing of attapulgite, bentonite gels and their mixture was examined using rheology (oscillatory
and creep tests) and microscopy (HPF Cryo-SEM and X-Ray tomography). The rheological
results showed that the gels became stronger and more viscous with time. For bentonite, this
could be explained by the rearrangement of the platelets over time and an increase in their
connections. Regarding attapulgite, the strengthening of the gel was delayed compared to the
other gels due to a change in the long range structure of the network getting more large pores.
The rheological trend followed by the clay blend is similar to the one found for bentonite which
determines its rheology. However, the evolution of the microstructure formed by the platelets
in the mixture differs. The pore size distribution of the blend was analogous to the one found
for attapulgite. Microscopic images suggested the formation of two networks interacting. Akin
to bentonite, the long range structure of the gel did not show any drastic change with time.
Therefore, the time effect on the rheology of the composite may have been due to stronger
interactions between the needles and the platelets at a short range.</p>
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