A simple, scalable procedure that does not require covalent modification of the filler or specialized high shear mixers is described for preparing well-dispersed carbon nanotube composites. Excellent particle dispersions of multiple-walled carbon nanotubes (NTs) and carbon black (CB) in polystyrene (PS) are obtained by coating the particles with a < 2-nm layer of PS adsorbed from dilute solution, prior to incorporation in the composite. Improved mechanical properties of composites containing coated particles, especially NT, are demonstrated by dynamic mechanical analysis at low frequency and low amplitude. Formation of a partially immobilized region of polymer surrounding the particles is quantified using flow microcalorimetry with ethyl acetate or methyl ethyl ketone vapor to measure the increase in solvation enthalpy in this region. This calorimetlic method is applied to both composites and compacted powder mixtures of NT or CB with PS. The response of integral heat of vapor sorption as a function of particle loading in powder mixtures is similar to percolation curves reported for mechanical and electrical properties of composites. (c) 2006 Wiley Periodicals, Inc.