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The addition of six different clays (laponite, montmorillonite, halloysite, and their organomodified counterparts) to poly(methyl methacrylate), polystyrene, and their blends was studied. The morphologies of the obtained composites were studied using transmission electron microscopy and scanning electron microscopy. Small angle oscillatory shear experiments, as well as shear induced coalescence tests, were carried out to evaluate the role of the clay as a coalescence inhibitor. Using the six different clays enabled the evaluation of the effect of the clay location and the clay platelet size for a given location (matrix, dispersed phase, interphase) on the coalescence phenomenon. A decrease of the dispersed phase of the blend was generally observed upon the addition of the clay. Clays located exclusively in the matrix (laponite, montmorillonite, halloysite, and modified halloysite) were shown to migrate to the interface during coalescence tests, inducing a decrease of coalescence at a certain extent of migration. Modified montmorillonite, located at the interface, was the most efficient clay at inhibiting coalescence, due to relaxation of Marangoni stresses with an important barrier effect. Overall, it was shown that having a certain size of a nanoparticle is essential for it to locate at the interface and inhibit coalescence. Nanoparticles with a larger size than the droplets are not able to locate at the interface and, therefore, do not have an effect on coalescence. Conversely, nanoparticles whose size is 10% or less of the droplet were found to be well dispersed in the whole blend. These particles did not have a preferred location nor had an effect on coalescence. [ABSTRACT FROM AUTHOR]

The compatibilization mechanism of poly(methylmethacrylate) (PMMA)/polystyrene (PS) blends induced by PMMA-b-PS block copolymers of different molar masses (30 and 104 kg/mol) was studied. The blend morphologies with and without copolymers were observed by scanning electron microscopy. The rheological behavior was studied performing small amplitude oscillatory shear experiments. The experimental results were compared to Palierne's model predictions. Shear induced coalescence tests were also conducted. Contrary to what was expected, adding block copolymers did not result in a refinement of the droplet size. However, it induced Marangoni stresses, a decrease in interfacial tension and an inhibition of coalescence of the dispersed phase. During coalescence tests, a decrease in the relaxation time due to Marangoni stresses with time was revealed. This interesting behavior contradicts previous works on the subject, and is believed to be due to a migration of block copolymers to the interface during the tests rather than droplets' coalescence. As such, the morphology was explained by the fact that block copolymers are not entirely at the interface initially. Also, the block copolymer with a higher molecular mass was shown more efficient at inhibiting coalescence, indicating that the compatibilization mechanism is a combination of Marangoni stresses and steric hindrance. [ABSTRACT FROM AUTHOR]

In this work, the effect of adding organoclay (Cloisite 20A) to a poly(methyl metacrylate) (PMMA)/polystyrene (PS) blend was evaluated in order to understand the compatibilization mechanism taking place. The blend morphology was quantified using micrographs obtained by scanning electron microscopy and observed by transmission electron microscopy. The state of dispersion of the clay was studied using small angle X-ray scattering and wide angle X-ray scattering and by applying the Carreau-Yasuda with a yield stress model to small amplitude oscillatory shear (SAOS) data. Morphological analyses revealed that the clay was intercalated, that its addition resulted in a decrease in the size of the dispersed phase and that it was preferentially located at the interface, except in the case of saturated interfaces, in which case the remaining clay was dispersed in PMMA. By applying the simplified Palierne model to SAOS experiments, the interfacial tension between the polymers forming the blend was inferred and shown to decrease upon addition of clay. The relaxation spectra inferred from the SAOS data, using the Honerkamp and Weese method, revealed four relaxation times: Relaxation of PMMA and PS chains, relaxation of the droplet shape, as well as an additional relaxation phenomenon attributed to the Marangoni stress. Although Marangoni stresses have already been studied in the case of blends compatibilized by block copolymers, this is the first time that it has been evidenced in the case of a clay as compatibilizer. [ABSTRACT FROM AUTHOR]