A series of organically modified clays (OMCs) with a surfactant loading range from 0.625 to 2.5 times
the cation exchange capacity (CEC) were melt-mixed with maleated polypropylene (PPMA). Wide-angle
X-ray diffraction and transmission electron microscopy results of these nanocomposites show that dispersion
of clays becomes unfavorable in the PPMA matrix during melt intercalation as the surfactant loading
increases in the process of modifying clays, though larger interlayer distances are obtained in their
corresponding OMCs. It is even important that clays uniformly disperse at the nanoscale level in the PPMA
matrix when the surfactant loadings are below the CEC, which implies that incomplete exchange of inorganic
cations in the process of modifying clay benefits the dispersion of clays in the PPMA matrix.
Excess intercalation of cationic surfactants into Na+-montmorillonites (MMTs) was investigated in
organically modified silicates (OMSs), synthesized with MMTs and octadecylammonium chloride (OAC)
by systematically varying the surfactant loading level from 0.625 to 1, 1.25, 1.56, 2, and 2.5 with respect
to the cation exchange capacity (CEC) of MMTs. Wide-angle X-ray diffraction and thermogravimetric
analysis results indicated that the continuous increase of interlayer distances came from the entering of
surfactants into the interlayer of MMTs. Excess surfactants were extracted with a Soxhlet apparatus,
which showed two kinds of intercalation states of surfactants in the interlayer when the surfactant loading
level was beyond the CEC. Fourier transform infrared spectroscopy and differential scanning calorimetry
were used to explore the microstructures of OMSs. It was found that the surfactants arranged more orderly
as the loading level increased and the excess surfactants piled up in the interlayer together with counterions,
forming a sandwiched surfactant layer. On the basis of the results, the layer structures of OMSs and the
mechanism by which the surfactants entered the interlayer were expounded: surfactant cations entered
the interlayer through cation exchange reactions and were tightly attracted to the silicate platelet surfaces
when the surfactant loading level was below the CEC; however, excess cationic surfactants entered the
interlayer together with counterions through hydrophobic bonding and formed a sandwiched layer in the
interlayers, leading to a continuous increase of the interlayer distance, when the surfactant loading level
was beyond the CEC.
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