Grafted Low Molecular Weight Polymers as Steric Stabilizers of Commercial Titania Nanoparticles in Polydimethylsiloxane Fluids

Abstract

A commercial titania nanopowder was surface modified by grafting with polydimethylsiloxane (PDMS) polymers with a molecular weight of 5000, and characterized for particle dispersion and rheology in a silicone oil fluid medium. Methods employed include TEM, TGA, dynamic light scattering, and steady shear and dynamic rheology. Estimates of the adsorbed amount of grafted chains suggest the steric layer is at the interface of the mushroom and brush conformation regions. The interaction energy between the particles is modeled using van der Waals expressions and steric repulsion derived from self-consistent field theory calculations. Calculations show that the steric layer is a “wet” brush under good (athermal) solvent conditions, and is of low grafting density. These results are related to flow properties and fluid structure up to absolute volume fractions of 37%, corresponding to effective volume fractions of 63.9 vol%. Based on the effective volume fraction, a fluid to solid transition is found at 60.5 vol%. This system shows that nanoparticle dispersion can be effective even with low density brush layers and good solvent conditions.

Keywords:

• Grafted polymer
• nanoparticle
• rheology
• titania

Acknowledgments

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy National Nuclear Security Administration under contract DE-AX04-934AL85000. Funding for this work was provided by Sandia National Laboratories LDRD program. Thanks go to Tom Headley for TEM images.