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Bimodal Surface Ligand Engineering: The Key to Tunable Nanocomposites
journal contribution
posted on 2013-01-29, 00:00 authored by Ying Li, Peng Tao, Anand Viswanath, Brian C. Benicewicz, Linda S. SchadlerTuning the dispersion of inorganic nanoparticles within
organic
matrices is critical to optimizing polymer nanocomposite properties
and is intrinsically difficult due to their strong enthalpic incompatibility.
Conventional attempts to use polymer brushes to control nanoparticle
dispersion are challenged by the need for high graft density to reduce
particle core–core attractions and the need for low graft density
to reduce the entropic penalty for matrix penetration into the brush.
We validated a parametric phase diagram previously reported by Pryamtisyn
et al. (Pryamtisyn, V.; Ganesan, V.; Panagiotopoulos, A. Z.; Liu,
H.; Kumar, S. K. Modeling the Anisotropic Self-Assembly of Spherical
Polymer-Grafted Nanoparticles. J. Chem. Phys. 2009, 131, 221102) for predicting dispersion
of monomodal-polymer-brush-modified nanoparticles in polymer matrices.
The theoretical calculation successfully predicted the experimental
observation that the monomodal-poly(dimethyl siloxane) (PDMS)-brush-grafted
TiO2 nanoparticles can only be well dispersed within a
small molecular weight silicone matrix. We further extended the parametric
phase diagram to analyze the dispersion behavior of bimodal-PDMS-brush-grafted
particles, which is also in good agreement with experimental results.
Utilizing a bimodal grafted polymer brush design, with densely grafted
short brushes to shield particle surfaces and sparsely grafted long
brushes that favor the entanglement with matrix chains, we dispersed
TiO2 nanoparticles in high molecular weight commercial
silicone matrices and successfully prepared thick (about 5 mm) transparent
high-refractive-index TiO2/silicone nanocomposites.