The purpose of this study was to determine the effects of fillers on the adhesion at polystyrene (PS) and polymethyl methacrylate (PMMA) interfaces and to improve this adhesion. One filler, carbon black, is used in the automotive industry as a strengthening agent in tires, because it improves the mechanical and thermodynamic properties of the material. It is known that tires sometimes fall apart due to tread separation, a result of poor adhesion between the rubber interfaces involved. The effect of carbon black on bulk properties in polymers has been the subject of previous research; my experiments investigated the impact of carbon black on the strength of adhesion in polymers. First, PS and PMMA slabs were molded in a hot press at 150°C. Solutions were created containing varying concentrations of carbon black in toluene, along with PS or PMMA. The solutions were then spun-cast onto the polymer slabs at 2500 rpm for 20 seconds, leaving a thin film of polymer containing carbon black. Ellipsometry was used to confirm a constant film thickness of 1000Å. Each coated slab was then joined with another slab of the same type in the hot press, so adhesive bonds could form. The resulting "sandwich" sample could then be tested via the Asymmetric Double Cantilever Beam (ADCB) test. This method allows the adhesion to be measured by propagating a crack at the interface, and measuring the length of the crack. Crack measurement allows for the calculation of the fracture toughness, or Gc, a value that quantifies adhesion. Three different types of N299 carbon black, obtained from Cabot Corp., were tested: untreated (standard), heat-treated at 1100°C, and heat-treated at 2400°C. The treated particles had been heated for 90 minutes. The results showed that increasing concentrations of carbon black increasingly diminished the fracture toughness of the PS/PS interface. However, the heat-treated grades of carbon black did not exhibit quite as drastic an effect, particularly the type treated at 2400°C. This finding is significant, because it shows that carbon black, while beneficial to various bulk properties of polymers, can lower the adhesion at polymer interfaces. In tires, poor adhesion between the polymers can lead to tread separation, since the tread must adhere to the rest of the tire. Future work will utilize Atomic Force Microscopy (AFM) to examine interfaces that have undergone adhesive failure and characterize the adhesion. Secondary Ion Mass Spectroscopy (SIMS) will be used to measure the impact of the carbon black fillers on diffusion, a quantity that is directly related to adhesive strength. Further experimentation will also be done with other fillers, colloidal silica and clay, to determine an effect on fracture toughness. This project was funded by NSF 011974-1011151 and Simons Grant 265210.