NayaniDr. Karthik Nayani

Using surface tension-driven instabilities for breaking up oil films

This research theme is motivated by a simple table-top experiment wherein a large drop of oil is placed atop a petri-dish filled with water. We explore several means of creating surface tension-driven instabilities to break down the large oil drop into tiny droplets. This system will be used to model the cleaning up of oil spills. In particular, the role of orientational elasticity in influencing jet-breakup will be explored.   In addition, the more general topic of droplet breakup in ordered fluids will be examined. Specific efforts are directed towards droplet breakup studies of lyotropic chromonic liquid crystals wherein open questions regarding the rheological behavior of these fluids (wormlike micellar solutions or rigid rods) remain to be answered.

Biomimicry of structural color using CNCs

Natural photonic crystals present extraordinary optical properties and provide valuable design principles for applications from light harvesting devices to anticounterfeit films. Photonic crystals are abundant in several biological species including beetles, butterflies and even certain classes of berries. The remarkable ability of cellulose nanocrystals (CNC) suspensions to form helical structures that persist in solvent-free films highlights their potential for use in photonic applications. Additionally, the tunability of the physical characteristics of CNC suspensions, including their chiral pitch length via changes in ionic strength, counter-ions and temperature, make them well-suited for replication of structural color found in nature.  Potential applications of research on CNCs include reflective windows and anticounterfeit materials. Specifically, we explore the fundamentals involved in the transfer of chiral structures of CNCs to organosilica substrates.  Two such substrates, when sandwiched with a nematic retarder, can create energy-efficient windows capable of total reflection. We are also interested in transferring chiral structures formed by CNCs onto non-planar geometries of organosilica substrates such as hemi-spheres and toroids which have promise for omnidirectional lasing.