|
|
||
|
Soft Materials and Rheology Group Research Interfacially-active particles This research is supported by the National Science Foundation. Particles whose surfaces are partially wetted by two fluids
can adsorb at the interface between the two fluids.
Often the energy required to desorb the particles
from the interface is extremely large and hence the particles adsorb almost
irreversibly. In the recent past, we have examined two remarkable
consequences of such irreversible adsorption, viz. film climbing (Fig. 1),
and interfacial jamming (Fig. 2). Finally, a remarkable effect in
particle-containing emulsions is bridging wherein in which a single particle
can simultaneously adsorb on the surface of two drops at once (Fig. 3). Not
surprisingly, these phenomena tremendously affect the structure and flow
properties of liquid/liquid systems. We are now examining the structure and rheology of ternary
systems of particles and two liquids. In our research, the two liquids are
molten polymers. This is partly because of our interest in controlling the
structure and properties of polymer blends. But it is also convenient
experimentally since we are able to quench the structure by cooling and
therefore characterize the structure on the scale of the two-phase
morphology, and also on the scale of single particles. Finally, in collaboration with Prof. Sanford Asher, we are
applying the film-climbing method to develop 2D photonic crystal sensors.
Fig. 1: An unstable Pickering emulsion with particles adsorbed
at the interface allows a film to climb up the walls of the vial. Download full
details in Cheng & Velankar, Colloids and Surfaces A, 315, 275-284, 2008.
Fig. 2: Left: A non-spherical drop of glycol in oil with
particles adsorbed at the interface. Due to the particle jamming, the drop
cannot recover its nonspherical shape. Right: A
controlled jamming experiment in a spinning drop tensiometer.
Download
full details in Cheng and Velankar,
Langmuir, 25, 4412-4420, 2009
Fig. 3: Left:Two
drops bridged by a single particle. Right: A cluster of drops, with numerous
particle bridges. Download full details in Thareja & Velankar,
Rheol. Acta, 46, 405-412,
2007. Questions, Suggestions,
Comments? Send e-mail to velankar@pitt.edu
|
Current projects Interfacially-active
particles Natural and
synthetic papillae
|
|
