The Effect of Carbon Black and Colloidal Silica Fillers on the Fracture Toughness at Polymethylmethacrylate Interfaces
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DD9.12.1
The Effect of Carbon Black and Colloidal Silica Fillers on the Fracture Toughness at Polymethylmethacrylate Interfaces
Mordechai J. Bronnerю, Anshul A. Shah† Hyun-Joong Kim*,‡, Dennis G. Peiffer& Miriam Rafailovich§, and Jonathan Sokolov§
юRambam Mesivta High School, 15 Frost Lane, Lawrence NY, 11559; †Ward Melville High School, 380 Old Town Rd., East Setauket, NY 11733;
*,‡
School of Biological
Resources and Materials Engineering, Seoul National University, Suwon 441-744, Korea;& Exxon Mobil Research and Engineering, Annandale, NJ §Department of Materials Science & Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794-2275
Abstract We have measured the fracture toughness of PMMA slabs with carbon black and colloidal silica fillers placed at the interface. The results show that the fracture toughness decreases linearly with carbon black concentration. The fracture toughness scales as annealing time, t1/2 indicating that it is diffusion limited. Addition of Colloidal Silica drastically reduces the fracture toughness regardless of concentration and annealing time. These results indicate that carbon black introduces physical cross links which decrease dynamics whereas colloidal silica produces permanent chemical cross links which prevent diffusion across the interface.
DD9.12.2
Introduction Fillers are of great importance to industry since they can be used to control various properties of materials such as hardness, heat resistance, and electrical conductivity simply by varying their concentration1 . Fillers are also commonly used to reinforce polymers by increasing their modulus and impact resistance. Recently Zhang et al 2 have shown that when strong interactions exist between the filler particles and the polymer matrix, the dynamics can be drastically slowed down. The reported that the interfacial width between layers of partially miscible polyolefin rubbers, decreased from 100nm to 2 nm with the addition of only 5% carbon black. This was interpreted as being the three dimensional analogue of the phenomenon previously observed by Zheng et al3 for thin polymer films near an attractive substrate. Here interactions pin the chains in the layer adjacent to the interface and trap chains in subsequent layers for up to several hundred nanometers from the interface. The long range of the interactions implied that the dynamics can be reduced even for very low concentrations, where only a few polymer chains are in direct contact with the filler surfaces. This model was further confirmed by Zhang et al2 by who demonstrated that the addition of colloidal Silica, where the interactions with the Si surface were screened, had only minimal effects on the interfacial width. Since this is not an equilibrium phenomenon, it would not affect the bulk properties of the materials. On the other hand, it is expected to have large effects on adhesion and interfacial fracture toughness which require chain mobility across interfaces to provide strength. In this paper we will report on measurement of
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