Manipulating Solid-Surface Properties with Polymeric Agents
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MANIPULATING SOLID-SURFACE PROPERTIES WITH POLYMERIC AGENTS
H. WATANABE*, S.S. PATEL"*, J.F. ARGILLIER***, E.E. PARSONAGE+, J. MAYS++, N. DAN-BRANDON .. AND M. TIRRELL Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455 * Department of Macromolecular Science, Faculty of Science, Osaka University,
"*
Toyonaka, Osaka 560, Japan. AT&T Bell Laboratories, 600 Mountain Ave, Murray Hill, NJ 07974-2070.
*** ATOCHEM, Centre d'Application de Levallois, 95, rue Danton, 92300 LevalloisPerret, France. + 3M, 3M Center, Bldg 201-2N-19, St. Paul, MN 55144-1000. ++ Department of Chemistry, University of Alabama, Birmingham AL 35294. +++ Department of Polymer Reaserch, Weizmann Institute, Rehovot, Israel.
ABSTRACT Colloidal processing offers a way to minimize undesired heterogeneities in the fabrication of advanced ceramics. Stable dispersions can be created by manipulation of interparticle potential. Adsorption of diblock copolymer amphiphiles provides a way to obtain long range repulsive interactions between particles, at comparatively low polymer coverage, thereby enabling suspension stabilization. In this study we investigate the relationship between copolymer structure and adsorbed layer characteristics, and specifically, the nature and range of interactions. We find that the surface density and interaction range are governed by a characteristic measure of the copolymer asymmetry. In the case of copolymers where one of the blocks is ionic, and therefore water soluble, we find a hysteresis in the interaction forces, indicating a meta-stable state of the polymer layer.
Mat. Res. Soc. Symp. Proc. Vol. 249. ©1992 Materials Research Society
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INTRODUCTION Fabrication of advanced ceramics involves synthesis and processing of submicron ceramic particles of a wide variety of shapes, compositions and sizes. To prevent brittleness due to crack appearance and propagation, homogeneous structures are desired. One way of minimizing undesired heterogeneities is by colloidal processing: Monodisperse particle size can be obtained in suspension, so that subsequent consolidation (by slip casting, pressure filtration, tape casting or injection molding) produces uniform microstructures. The interactions between colloidal particles can be manipulated via surface modifying agents. These are required to prevent spontaneous coagulation of particles, while not hindering compression into ordered, dense structure. The modified interparticle potential can be also used to adjust suspension rheological and mechanical properties during processing. The amount of surface modifier needs to be comparatively small, so as to simplify removal and reduce the possibility of contamination to the ceramic material.
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L Figure 1 Adsorbed diblock copolymers layers. The anchor block adsorbs on the surface, forming a dense film, while the buoy block forms a swollen layer. If the number of chains per area, a is smaller than the overlap value, the buoy chains do not interact. L is the thickness of
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