Interfacial tension in binary polymer blends in the presence of block copolymers. 2. Effects of additive architecture and composition

The effect of the macromolecular architecture and composition of block copolymer additives on the reduction of the interfacial tension between two immiscible homopolymers is investigated. A series of (polyisoprene)2(polystyrene), I2S, graft copolymers with constant molecular weight and varying composition are utilized as additives in polystyrene/polyisoprene blends. The interfacial tension decreases with the addition of small amounts of copolymer and reaches a plateau at higher copolymer concentration. The interfacial tension at interfacial saturation depends on copolymer composition exhibiting a minimum, which is lower than that using a symmetric diblock with the same molecular weight. Moreover, the interfacial tension at saturation depends on the side of the interface the copolymer is introduced; adding it to the polyisoprene phase is much more efficient than adding it to polystyrene. This is due to the asymmetric architecture of the copolymer and points to the fact that a local equilibrium can only be attained in such systems: the copolymer reaching the interface from one homopolymer phase probably does not diffuse to the other phase. The fact that this behavior is not a kinetic effect is verified using (polystyrene)2(polysoprene), S2I, grafts, which show the mirror image behavior. The effectiveness of the interfacial modifiers is, thus, controlled by the unfavorable interactions, which drive the additive toward the interface, and the possibility of micelle formation, which hinders its activity

Effect of nanoclay on natural rubber microstructure

The inclusion of highly anisotropic clay nanoparticles (nanoclays) in cross-linked natural rubber (NR) provides a more homogeneous distributed network structure and induces an early onset as well as enhancement of crystallization under uniaxial deformation. The molecular structure of the polymer network and its morphological changes during deformation were characterized by using broadband dielectric spectroscopy and in situ synchrotron wide-angle X-ray diffraction, respectively. It was found that the presence of nanoclay introduces a dual crystallization mechanism due to the alignment of nanoparticles during stretching. The improved properties in NR-nanoclay nanocomposites can be attributed to both microstructural and morphological changes induced by nanoclay as well as to the nanoclay mobility in the NR matrix during crystallization. The interplay of these factors during deformation contributes to the formation of a supernetwork structure containing cross-linked chemical chains, nanofiller, and crystallizable networks with similar length scales. © 2008 American Chemical Society.The authors gratefully acknowledge the financial support of the Spanish Ministry of Science and Innovation (MICINN) through project MAT 2004-00825. This work made use of the Cornell Center for Materials Research Experimental Facilities. Additionally, J. Carretero-Gonza´lez acknowledges support from MICINN in the form of a FPI grant, R. Verdejo a Juan de la Cierva contract from MICINN, and B. S. Hsiao is supported by the National Science Foundation (DMR-0405432Peer Reviewe