Samruddhi Kamble's Talk

Mar 21, 2013 - 17:00

Mar 21, 2013 - 18:00

Room 118 (Creativity Hall) Ground Floor Chemical Engineering Department

Seminars

Samruddhi Kamble PhD Student IIT Bombay and NCL Pune

Colloidal dispersion play a substantial role in a wide range of natural and technologically important products used frequently in our daily life. These range from personal care products like shampoos tooth paste etc.; health care products like ointments syrups etc.; Food products like milk chocolates ice-creams mayonnaise etc.; and also paints.  Most of these materials are viscoelastic and are known as soft solids/soft matter. These materials are sheared during various processing applications where they are required to flow or change from being predominantly elastic to predominantly plastic (liquid like). This solid to liquid transition is called as yielding. Yielding in these non-Newtonian fluids is a complex phenomenon and it pertains to their complex microstructure various physical/chemical interactions between their components and the multiconstituent nature of these systems. The flow induces changes in the microstructure which in turn affects the mechanical properties of the final product. It is important to investigate the structure of soft matter over a hierarchy of length and time scales and to see how the structure leads to properties of the material .To understand the microstructure and flow behavior of these complex materials usually simple colloidal suspensions are studied as model systems. We investigate dense suspensions of deformable PolyN-isopropylacrylamide (PNIPAM) microgels as model system to study soft pasty materials. PNIPAM is a thermoresponsive polymer and undergoes a large volume phase transition (VPTT) at ~320C. Thus the volume fraction in this system can be tuned by merely changing the temperature without changing the number density. The sensitivity to change size on changing temperature allows the microgels to be packed in volume fractions greater than 1 and thus serves as a good model for soft colloidal glasses.We use Diffusive Wave Spectroscopy (DWS) a state of the art technique in light scattering to investigate the micro-structure and dynamics in this system under quiescent conditions. The yielding studies involve use of mechanical rheology specifically under large amplitude oscillatory shear where we study the non-linear response of these materials. From our results we show that highly concentrated suspensions of deform-able materials show complex dynamics under quiescent as well as under nonlinear deformations. We also ascertain universal attributes of yielding in a variety of soft materials when sheared under large amplitude oscillatory shear.