Shear-Induced Orientation in Well-Exfoliated Polystyrene/Clay Nanocomposites

Journal Article · Mon Mar 26 04:00:00 EDT 2012 · Macromolecules

DOI:https://doi.org/10.1021/ma2012738· OSTI ID:1035383

Dykes, Laura M.C.; Torkelson, John M; Burghardt, Wesley R ^[1]

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1. NWU

We report measurements of shear-induced particle orientation in highly exfoliated polystyrene/clay nanocomposites. Samples were prepared using an in situ polymerization technique, in which native clay is organically modified with a cationic surfactant that incorporates a polymerizable vinylbenzyl moiety. Controlled radical polymerization was used during the synthesis to limit the molecular weight and polydispersity of the nanocomposite polymer matrix. Flow-induced orientation was measured in the flow-gradient plane of shear flow using synchrotron-based small-angle X-ray scattering. Despite the small rotational diffusivity expected for the clay particles, significant particle orientation was only observed at relatively high rates in steady shear or at high frequencies in large-amplitude oscillatory shear. Measurements of orientation upon flow cessation provided direct evidence of a structural relaxation process that was orders of magnitude faster than estimates of rotational Brownian motion. It is suggested that this fast relaxation arises from either relaxation of shear-induced distortion of partially flexible exfoliated clay sheets in a highly entangled nanoparticle network or coupling of particle and polymer dynamics.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: NSF
• OSTI ID: 1035383
• Journal Information: Macromolecules, Journal Name: Macromolecules Journal Issue: (3) ; 02, 2012 Vol. 45
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

36 MATERIALS SCIENCE
CLAYS
MOLECULAR WEIGHT
ORIENTATION
POLYMERIZATION
POLYMERS
RADICALS
RELAXATION
SCATTERING
SHEAR
SURFACTANTS
SYNTHESIS