Fluids with thermally conductive nanoparticles can provide improved heat transfer. Practical nanofluids will be likely based on lubricating oils for the continuous phase and systems that have extended service temperature ranges. A model system based on poly(a-olefin) synthetic base oil modified with poly(dimethylsiloxane) to lower the mixture's pour point with graphite as a conductive additive was studied. Phase separation of the oligomer mixture occurred at temperatures less than -15 degrees C. Graphite particles were etched using citric acid pretreatment to create hydroxyl and carboxyl groups on their surfaces. A coupling reaction between the hydroxyl groups on graphite and chloro groups on silanes gave rise to poly(a-olefin)-philic graphite particles. Similarly, a coupling reaction between the carboxyl groups on graphite surface and amine groups on silanes gave rise to poly(dimethylsiloxane)-philic graphite particles. SEM, FT-IR, and TG-MS measurements were used to verify the presence of coupling agents on the surface and to estimate the thickness of the coatings. Upon separation of the mixture, each functionalized graphite type migrated exclusively to its preferred phase. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012