|Research||Carnegie Mellon University|
Department of Chemical Engineering
Department of Biomedical Engineering
Center for Complex Fluids Engineering
Center for Environmental Implications of Nanotechnology
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A new class of surface active material, nanoparticulate polymer brushes have proven to be highly efficient stabilizers of solid-stabilized “Pickering” emulsions. Whereas conventional colloids normally require concentrations on the order of 0.1 to 1 wt% to stabilize a Pickering emulsion, nanoparticulate polymer brushes can do so at concentrations as low as 0.008 wt%. This emulsifying efficiency correlates with the strong tendency of such nanoparticles to produce large surface pressures and significant interfacial dilatational moduli at low bulk and surface concentrations. In addition to high emulsifying efficiency, when nanoparticulate brushes are prepared with polymers that display a lower critical solution temperature, it is possible to produce emulsions that exhibit thermally responsive de-emulsification or emulsions with rheological properties that are irreversibly tuned by temperature cycling processes. See Saigal et al. “Pickering emulsions stabilized by nanoparticles with thermally responsive grafted polymer brushes,” Langmuir 26, 15200-15209 (2010).
We have studied the adsorption behaviors of nanoparticulate brushes not only at oil/water interfaces that are relevant for emulsification, but also at solid/liquid interfaces that are relevant to applications as dispersants, conditioners or lubricants. For example, adsorption isotherms for multi-arm poly(ethylene oxide) star polymers were compared to linear PEO at the silica/water interface. The dense packing of PEO in the compact star polymers leads to adsorbed layers that contain approximately three times as much PEO per unit area compared to adsorbed layers of linear PEO chains that have the same overall degree of polymerization as the star polymers. These dense layers are expected to be effective surface conditioners. Nevertheless, despite having lower extents of adsorption, the linear chains adsorb preferentially and can displace star polymers from the surface, consistent with prior theoretical predictions. See Saigal et al. “Poly(ethylene oxide) star polymer adsorption at the silica/aqueous interface and displacement by linear poly(ethylene oxide),” Langmuir 29, 3999-4007, 2013.
N. Saleh, T. Sarbu, K. Sirk, G.V. Lowry, K. Matyjaszewski, R.D. Tilton, “Oil-in-water emulsions stabilized by highly charged polyelectrolyte-grafted silica nanoparticles,” Langmuir 21, 9873-9878 (2005). DOI: 10.1021/la050654r
T. Saigal, H. Dong, K. Matyjaszewski, R.D. Tilton, “Pickering emulsions stabilized by nanoparticles with thermally responsive grafted polymer brushes,” Langmuir 26, 15200-15209 (2010). DOI: 10.1021/la1027898
N.J. Alvarez, S.L. Anna, T. Saigal, R.D. Tilton, L.M. Walker, “Dynamics and rheology of polymer-grafted nanoparticles at air-water and xylene-water interfaces,” Langmuir 28, 8052-8063 (2012). DOI: 10.1021/la300737p
W. Li, Y. Yu, M. Lamson, M.S. Silverstein, R.D. Tilton, K. Matyjaszewski “PEO-based star copolymers as stabilizers for water-in-oil or oil-in-water emulsions,” Macromolecules 45, 9419-9426 (2012). DOI 10.1021/ma3016773
T. Saigal, A. Yoshikawa, D. Kloss, M. Kato, P.L. Golas, K. Matyjaszewski, R.D. Tilton “Stable emulsions with thermally responsive microstructure and rheology using poly(ethylene oxide) star polymers as emulsifiers,” Journal of Colloid and Interface Science 394, 284-292 (2013). DOI 10.1016/j.jcis.2012.11.033
G. Dunér, E. Thormann, A. Dedinaite, P.M. Claesson, K. Matyjaszewski, R.D. Tilton, “Nanomechanical mapping of a high curvature polymer brush grafted from a rigid nanoparticle,” Soft Matter 8, 8312-8320 (2012). DOI:10.1039/C2SM26086GT. Saigal, J.K. Riley, P.L. Golas, R. Bodvik, P.M. Claesson, K. Matyjaszewski, R.D. Tilton, “Poly(ethylene oxide) star polymer adsorption at the silica/aqueous interface and displacement by linear poly(ethylene oxide),” Langmuir 29, 3999-4007, 2013. DOI 10.1021/la305085a.