Morphological evolution of block copolymer nanocomposites submitted to extensional flows

Abstract

In this work, the effect of extensional flow on the morphology of polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) triblock copolymers and their clay-containing nanocomposites was evaluated. Four types of SEBS copolymers with different block compositions and cylindrical morphology were chosen to understand the effects of cylinder orientation and state of clay dispersion on the evolution of morphology during extensional flow. The effect of clay concentration (ranging from 2.5 to 7.5 wt. %) was also studied. The samples were subjected to extensional flow using a Sentmanat extensional rheometer attached to a rotational rheometer at Hencky strain rates varying from 0.01 to 20 s À1 . Small angle X-ray scattering analysis was subsequently performed to evaluate the morphological changes caused by extensional flow. When preoriented block copolymers [SEBS-30% PS (polystyrene)] and their nanocomposites undergo elongation, the styrene cylinders and clay nanoparticles align themselves in the flow direction and their rheological behavior and morphological evolution are influenced by the stretching direction (longitudinal and transverse), strain rate magnitude, clay concentration, and dispersion state of the clay nanoparticles. When isotropic block copolymers (SEBS-13% PS) undergo elongation, it was observed that the PS cylinders only exhibit structural alignment in the stretching direction in the presence of clay. Block copolymer molecules can exhibit different relaxation times depending upon the volume fraction of PS domains (13% or 30%). The addition of clay, however, hinders complete relaxation, helping to promote a permanent domain alignment after flow cessation, especially in hard-to-align copolymers. V C 2016 The Society of Rheology.

Compatibilization mechanism induced by organoclay in PMMA/PS blends

“…This could be due to the fact that at higher clay content, the formation of aggregates could occur more easily because of the interactions between particles. A similar behavior was observed by Amurin et al [34]. Figure 4 shows the complex viscosities measured for pure PMMA and PS which clay was added.…”

Effect of elongational flow on immiscible polymer blend/nanoparticle composites: a molecular dynamics study

“…32 Triblock block copolymers self-assembly with clay nanoparticle additives have also been studied under elongational flow, and formed hexagonal cylindrical morphologies. 33 In polystyrene-talc composites, foaming behaviour was studied under extensional stresses and nucleation was found to improve for higher stress and larger talc particles. 34 However, it is difficult for these experiments to gain fundamental insights into the driving forces behind the particle placement due to their short time scales.…”

Tuning the mechanical and dielectric properties of clay‐containing thermoplastic elastomer nanocomposites

“…More details regarding the processing parameters corresponding to each technique and the procedure to obtain nanocomposite films are available in Refs. .…”

“…The obtained morphologies of the studied materials depend mainly on the external forces applied during the selected fabrication technique and also on the fraction of the PS block. An exhaustive characterization of these morphologies by small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM) was reported in previous publications . The nomenclature of the nanocomposites and short descriptions of their morphologies are provided in Table .…”

“…However, another fraction of PS cylinders remained probably isotropic. This imperfect alignment of PS cylinders in SEBS‐13 was attributed to the low fraction of PS block . SEBS‐20‐based materials prepared by film blowing extrusion featured also complex morphologies depending on the air inflation ratio .…”