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Polymer colloids.

Many commercially important polymers are made and used as latexes, colloidal dispersions of polymer particles (typically 100nm diameter) in water. Although traditional polymer properties such as molecular weight and branching are important, often it is the colloidal properties which govern the success of many latex applications. Rheology, shelf life, an other key properties are determined by particle/particle interactions.

We have two projects at McMaster investigating particle-particle interactions in latex systems. In one the objective is to determine, for the first time, the minimum combinations of chain length and density of steric (surface stabilizing) polymer for colloidal stability. Our system is poly(methyl methacrylate) latex dispersed in heptane and colloidally stabilized by a surface layer of polydimethylsiloxane (silicone). The approach is to chemically degrade the silicone to the point at which the latex aggregates while monitoring the properties of the silicone on the particle surfaces This new information will be used to evaluate statistical mechanical models of colloidal stabilization.

ln a second project related to particle/particle interactions, we are investigating the preparation and characterization of novel latexes stabilized by a surface layer of poly(Nisopropyl acrylamide). The use of this polymer as a stabilizer offers the possibility of having latexes whose colloidal stability can be turned on, or off, by changing temperature.

New projects have started as part of the Mechanical and Chemimechanical Wood-Pulps network which is part of the Federal Network of Centres of Excellence. Work at McMaster in this area includes the synthesis of novel watersoluble polymeric flocculants for the paper-making process, the use of water soluble polymers to prevent colloidal pitch deposition, and the role of polymeric foam control agents in determining the properties of dispersed air in pulp suspension.

All our projects have in common the interaction of colloid and polymer science. To this end, we have established at McMaster many state-of-the-art facilities for characterizing colloidal dispersions including particle size, particle charge, electrophoretic mobility and rheological properties. These functions support both research and contract work at McMaster.
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Author:Pelton, Robert H.
Publication:Canadian Chemical News
Date:Apr 1, 1991
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