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No abstract

The melt rheological properties of layered silicate nanocomposites with maleic anhydride (MA) functionalized polypropylene are contrasted to those based on ammonium-terminated polypropylene. While the MA functionalized PP based nanocomposites exhibit solid-like linear viscoelastic behavior, consistent with the formation of a long-lived percolated nanoparticle network, the single-end ammonium functionalized PP based nanocomposites demonstrated liquid-like behavior at comparable montmorillonite concentrations. The differences in the linear viscoelasticity are attributed to the presence of bridging interactions in MA functionalized nanocomposites. Further, the transient shear stress of the MA functionalized nanocomposites in start-up of steady shear is a function of the shear strain alone, and the steady shear response is consistent with that of non-Brownian systems. The weak dependence of the steady first normal stress difference on the steady shear stress suggests that the polymer chain mediated silicate network contributes to such unique flow behavior.

β-Cyclodextrin derivatives, MRCD and p-MRCD, which have a 4-(dimethylamino)azobenzene moiety with a carbonyl substituent at 2′ and 4′ positions, respectively, have been prepared as color change indicators for detecting organic compounds. In a 10% ethylene glycol solution, MRCD and p-MRCD form intramolecular self-complexes in which the pendant dye moiety is included in the cyclodextrin cavity with an orientation parallel and perpendicular to the cyclodextrin axisis, respectively. When guest molecules are added to the acidic solutions of MRCD (pH 1.60) and p-MRCD (pH 2.40), they exhibit color changes from yellow to red for MRCD and from orange to red for p-MRCD. These color changes, which arise from the structural change of the dye moieties from the azo form to the azonium one, are caused when MRCD and p-MRCD undergo a conformational change in which the dye moieties inserted in the cyclodextrin cavities are excluded to outside of the cavities upon guest accommodation. The extent of the guest-induced color changes of MRCD and p-MRCD depend on the shape, size, number, and position of the functional group of guest molecules. Selectivities between MRCD and p-MRCD in guest detection are roughly parallel and reflected in the host-guest binding constants. Among guest molecules examined, ursodeoxycholic acid and chenodeoxycholic acid were detected by MRCD and p-MRCD with high sensitivities. 1-Adamanetanecarboxylic acid and (-)borneol were also detected with high sensitivities. In neutral conditions, however, the selectivity in guest detection of p-MRCD is different from that in acidic conditions as shown by the fact that, for example, 1-adamantanol and 2-adamantanol were detected by p-MRCD with larger sensitivities than 1-adamanetanecarboxylic acid. The result indicates that the ionic nature of the guest molecules is an important factor for detection of the guest molecules. All these results demonstrate that MRCD and p-MRCD can be used as color change indicators for detecting various organic compounds in aqueous solution.