title: Steric Stabilization of Colloids by Poly(dimethylsiloxane) in Carbon Dioxide: Effect of Cosolvents.
abstract: Steric stabilization and flocculation of colloids with surface-grafted poly(dimethylsiloxane) (PDMS) chains are examined in liquid and supercritical carbon dioxide with and without hexane as a cosolvent. Neither poly(methyl methacrylate) (PMMA) nor silica particles with grafted 10,000 g/mol PDMS could be stabilized in pure CO(2) at pressures up to 345 bar at 25 degrees C and 517 bar at 65 degrees C without stirring. The addition of 15 wt% hexane to CO(2) led to stable dispersions with sedimentation velocities of 0.2 mm/min for 1-2 µm PMMA particles. The critical flocculation pressure of the colloids in the hexane/CO(2) mixture, determined from turbidity versus time measurements, was found to be the same for silica and PMMA particles and was well above the upper critical solution pressure for the PDMS-CO(2) system. The addition of a nonreactive cosolvent, hexane, eliminates flocculation of PMMA particles synthesized through dispersion polymerization in CO(2) with PDMS-based surfactants. Copyright 2000 Academic Press.
authors.affiliation: Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas, 78712
authors.initials: MZ
authors.lastname: Yates
authors.initials: PS
authors.lastname: Shah
authors.initials: KP
authors.lastname: Johnston
authors.initials: KT
authors.lastname: Lim
authors.initials: S
authors.lastname: Webber