Morphological Investigations of Organic/Inorganic Nanocomposites Fabricated to Achieve Controlled Dispersion at High Loa
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Morphological Investigations of Organic/Inorganic Nanocomposites Fabricated to Achieve Controlled Dispersion at High Loadings Andrew J. Duncan, Andrew B. Schoch, Christopher S. Gold, Joseph L. Lenhart, Frederick L. Beyer U.S. Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5069, U.S.A.
ABSTRACT Realization of property enhancements inherent to the presence of nanoparticles continues to be a challenge for the production of bulk nanocomposite materials with commercially available techniques. This study combines twin-screw compounding with surface modification of SiO2 nanoparticles to enable targeted dispersion in a SEBS block copolymer. Production of these composites with high levels of well-dispersed particulates aims to leverage aggregation for production of hierarchical structure. The aggregation state of the particles as well as the level of order in the block copolymer morphology was determined through USAXS and TEM. Particles coated with ligands miscible with the end-blocks of the BCP (minority component) increased dispersion at all loading levels observed up to 10 vol%. Ligands employed to increase miscibility of the nanoparticle with the mid-block (majority component) resulted in large aggregates for all loadings without disturbance of the BCP morphology. INTRODUCTION Most research efforts to realize the multifunctional benefits of polymeric nancomposites have focused primarily on low volume percent loadings and precise control of functional nanoparticle placement in polymer hosts.[1-4] Our goal is to maximize loading of the functional particulate in the polymer template with minimal or controlled variation of the morphological structure. Coincident dispersion of the nanoparticle and stability of the polymer morphology provide hierarchically structured functional materials. Local aggregation extends the hierarchical structure and influences the composite’s properties similar to microscopic fillers.[5] Bulk processing techniques were employed to create scalable functional materials that retain the benefits of nanofillers within the polymer nanostructure. Controlled incorporation of multi-functional particulates into polymer matrices requires a complex balance of thermodynamic and entropic contributions to the free energy of the composite system. Prior efforts to create well-dispersed systems that realize the multi-functional benefits of incorporating high surface area to volume ratio species are quite extensive and have often employed the microphase separated morphologies associated with block copolymers.[6-7] With respect to the thermodynamic contribution, minimization of the Flory-Huggins parameter (χ) between species tethered to the surface of the nanoparticle and the matrix polymers has demonstrated success in organization of variously sized particles in block copolymers.[8]
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The approach detailed here tailors non-specific interactions between the particulate and polymeric host. Aliphatic or aromatic ligands were grafted onto the surface of nano-SiO2 to tailor the miscibility of the nanopa
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