A novel method for the organic modification of a ceramic thermal conductive filler (a-alumina) with cold plasma was developed for the preparation of elastomer thermal interface materials with high thermal conductivities and low moduli. The a-alumina fillers were first coated with low-molecular-weight polydimethylsiloxane (PDMS) by solution dispersion and then treated in argon plasma for different time. The modified a-alumina fillers were characterized with high-resolution transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results revealed that a thin PDMS film with several nanometers thick was tightly coated on the surface of the alumina filler after plasma treatment, and this thin film could not be removed by 48 h of Soxhlet extraction with n-hexane at 120 degrees C. Plasma modification of the alumina could dramatically weaken the strength of the fillerfiller networks and, thus, remarkably reduce the modulus of the alumina-filled silicone rubber composites but did not affect the thermal conductivity of the composites. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012