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Unusual Polystyrene Nanocomposite Structure Using Emulsifier-Modified Layered Double Hydroxide as Nanofiller

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journal contribution
posted on 12.08.2008, 00:00 by Abdallah Illaik, Christine Taviot-Guého, Jérôme Lavis, Sophie Commereuc, Vincent Verney, Fabrice Leroux
A new hybrid organic inorganic assembly between an emulsifier, 4[12-(methacryloylamino)dodecanoylamino] benzenesulfonate acid (MADABS) and layered double hydroxide (LDH) of cation composition Zn2Al is described, as well as its subsequent dispersion into styrene. The characterization of the new hybrid LDH assembly by 1D electron density pictures the interleaved emulsifier well ensconced between LDH sheets, while showing the impossibility for the molecules to polymerize themselves. Indeed, the strong interdigitation abates the in situ polymerization. LDH/emulsifier:polystyrene nanocomposites, Zn2Al/MADABS:PS, are prepared by bulk polymerization, and “apparent immiscible” and intercalated PS nanocomposite structures are alternatively observed as a function of the thermal pretreatment of the filler. The rheological data are indicative of microstructural changes between the samples. For the precalcined filler, the PS nanocomposite presents a shear thinning exponent of −0.55 in the low frequency domain, associated to a hump shape for the damping coefficient δ, both curvatures consistent with the increase of glass transition temperature Tg, whereas the other sample exhibits a shear thinning exponent of 0 and a general behavior closely related to PS in spite of an increase in the elastic modulus G′ and the loss modulus G′′ of small amplitude. Such differences in the nanocomposite structure are further confirmed by TEM direct observations, with the presence of a tactoid network or of particle agglomerates when the filler is precalcined or not, respectively. Contrary to the general idea that pervades that intercalated polymer structure means an increase in the interaction between polymer chain and filler and consequently an enhancement of the mechanical properties, it is here demonstrated that such a behavior may be in conjunction with agglomerates while an opposite tendency is observed for the non-intercalated structure with the observation of an unusual solid-like structure for PS nanocomposite arising from friction welding effects between LDH tethered MADABS molecules and PS polymer chains.