Soft Matter 'Odes': from the life and death of viscoelastic jets to the structural color of jeweled beetles

12:15 in the M-Building, room 3201 A, for details see www.softmatter.gatech.edu/baglunch.html


Most industrial and biological materials exist, or are processed, in the form of multicomponent, microstructured fluids, and their ultimate function and use is dependent on the understanding of the optics,...

12:15 in the M-Building, room 3201 A, for details see www.softmatter.gatech.edu/baglunch.html


Most industrial and biological materials exist, or are processed, in the form of multicomponent, microstructured fluids, and their ultimate function and use is dependent on the understanding of the optics, dynamics, elasticity & extensibility and self-assembly (ODES) of the constituent soft or squishy materials. With the guiding idea of designing beautiful and useful patterns, possibly by mimicking nature, I will present two examples of "odes" in soft matter:


   Surface tension driven break-up of cylindrical fluid elements into droplets plays a crucial role in the use or processing of paints, inks, insecticides and pesticides, cosmetics, food, etc, as well as in drop formation during sneezing. The industrial fluids are typically formulated using dilute polymer solutions, and are exposed to a wide range of shear (1 - 106 s-1) and extension rates (in excess of 103 s-1). Since the polymer solutions and the resulting dispersions have low viscosity (~10 mPas) and short relaxation times (<1 ms), their non-Newtonian behavior is not apparent in the conventional rheometric measurements. However, the presence of even a dilute concentration of polymer alters the character of instability growth and capillary break-up during jetting. I experimentally study the influence of both elasticity and extensibility on the growth of instability and pinch-off dynamics of harmonically perturbed jets of weakly viscoelastic fluids. In this talk, I will describe how and when capillary thinning analysis can be applied to the capillary break-up during jetting to measure the rheological response of weakly viscoelastic fluids. I will also discuss how the dynamics of the capillary break-up and satellite formation during jetting is influenced by the amplitude and frequency of the imposed disturbances.


In the second part of my talk, I will proceed to a discussion of the cellular pattern that decorates the exoskeleton of Chrysina Gloriosa. The metallic green beetle that displays circularly polarized iridescence has hexagonal cells (~10 mm each) that coexist with pentagons and hexagons, and we find that the fraction of hexagons decreases with curvature. Each cell consists of nearly concentric, nested arcs that lie on the surface of a shallow cone. We inferred that patterns are structurally and optically analogous to the focal conics domains formed on the free surface of a cholesteric liquid crystal. Perhaps the study of capillary break-up and structural color will allow us to design better light harvesting devices in future, or potentially result in sprayable hair color or paints that display iridescence.

Event Details

Date/Time:

  • Date: 
    Friday, January 21, 2011 - 7:15am

Location:
MSE 3201 A