Thursday, September 9, 2010, 10:00 am — CFN Building 735 - Room B
NOTE: Seminar will be held in CFN Building 735 - Room B.
Recently, there has been increased interest in the controlled formation of dense, micron-sized nanoparticle clusters for a variety of applications, including digital printing, cellular imaging, and targeted therapies. Creating such assemblies via controlled aggregation of primary particles that are nanoscale, rather than direct synthesis of micron-sized particles structures, is desirable because a high degree of functionality can be incorporated onto the surface of each primary nanoparticle.
The classic experimental and theoretical work on microstructure and aggregation kinetics of attractive colloids focuses on systems with short-range attractions that form fractal aggregates and gels. However, the physics of formation of dense clusters appears to be quite different, with dense microclusters occurring in systems with intermediate-range attractive forces. In this talk, I will discuss how the large-scale structure and rheology of attractive dispersions can be tuned via the strength and range of interparticle attractions. Two experimental systems will be described in detail: (i) spherical polystyrene particles with hydrophobically-modified polyacrylic acid chains attached to the surface, and (ii) a disk-shaped synthetic clay, LaponiteÂ®, with poly(ethylene oxide) chains that weakly adsorb to the surface. Small-angle and ultra small-angle neutron scattering (SANS and USANS) results suggest that the surface roughness of clusters increases with increasing strength of attraction. Moreover, the rheology of system (ii) displays interesting re-entrant behavior, whereby gels of LaponiteÂ® particles melt and decrease in viscosity as interparticle attractions increase. This phenomena, which may be related to particle clustering, enables processing of dispersions with high particle loadings.
Hosted by: Alex Harris
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