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Ziadeh, Mazen ; Weiß, Stephan ; Fischer, Bianca ; Förster, Stephan ; Altstädt, Volker ; Müller, Axel H. E. ; Breu, Josef:
Towards completely miscible PMMA nanocomposites reinforced by shear-stiff, nano-mica.
In: Journal of Colloid and Interface Science.
Bd. 425
(2014)
.
- S. 143-151.
ISSN 1095-7103
DOI: https://doi.org/10.1016/j.jcis.2014.03.040
Abstract
Optimizing the reinforcement of polymers with nanoplatelets requires optimization of the aspect ratio and the moduli of the filler while providing a complete stress transfer. Employing a novel shear-stiff, nano-mica with large aspect ratio, we focus on maximizing the interfacial interaction between filler and matrix. External surfaces of the nano-mica were selectively modified by a polycationic macro-initiator and two PMMA-polymer brushes of length below and above critical entanglement length, respectively, and the mechanical properties of the three PMMA nanocomposites were measured. The multiple electrostatic anchoring groups of the macro-initiator not only provide reliable adhesion but at the same time allow the variation of the degree of protonation providing a local match between the charge densities of the clay surface and the adsorbed macro-initiator. PMMA coating of the nano-mica via surface initiated polymerization yielded long-term stable suspensions in THF that showed birefringence of a nematic phase.
Solution blending of the PMMA coated nano-mica allows for dispersing single clay tactoids in the translucent PMMA nanocomposites at 5 wt% clay loading as determined by transmission electron microscopy (TEM). Although significantly improved mechanical properties could be achieved as compared to nanocomposites made with conventional clay fillers, the full potential – as expressed by Halpin–Tsai equations – of the PMMA coated nano-mica can still not be completely utilized. This is attributed to the non-wetting character of the densely packed PMMA brushes attached to planar nanoplatelets.