No abstract

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 T g, 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.

International audienceA hybrid organic inorganic layered double hydroxide incorporating 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) is characterized by means of XRD, FTIR, and XPS. The in situ polymerization is scrutinized by 13C CPMAS as well as by a set of XRD experiments with varying temperature. It is found that the in situ polymerization is complete at 200 °C, and the hybrid framework sustains temperatures as high as 350 °C. Direct incorporation of poly(AMPS) is reported and the resulting hybrid LDH phases studied. Subsequently, all generated hybrid platelets are used as organo-modified 2D-type filler dispersed into polystyrene (PS). An immiscible PS composite structure with salient gel-like viscoelastic properties is obtained after bulk polymerization. In the low-frequency region, the typical Newtonian flow behaviour of PS is found to change progressively against filler loading into a shear-thinning behaviour evidenced by a pseudo-plateau in the elastic and loss modulus curves and associated with a shift of the glass transition temperature of PS to higher temperature. It is interpreted by hybrid LDH platelet domains presenting a large interface with the polymer, thus having the effect of restricting the plastic deformation by obstructing polymer chain motion. Such dispersed hybrid LDH tactoids forming a three-dimensional percolated network are indirectly evidenced by the enhancement of the dielectric properties illustrated by an increase in bulk dc conductivity of about one order at room temperature and in the dissipation factor. The study shows that hybrid LDH assembly is of relevance in topical applications regarding mechanical reinforcement as well as electrostatic energy dissipation. © 2010 The Royal Society of Chemistry