Interfacial Rheology by Oscillating Drop method

Rheology is the study of flow of matter. It is well known that surfactants, polymers when added to a fluid tend to go to an interface, thus altering the interfacial properties. This may lead to formation of robust layers that exhibit socalled ‘viscoelastic’ properties: both liquidlike and solidlike behaviors are present. The knowledge of the mechanical properties of interfacial layers is important in many areas including food, cosmetics biomedical and pharmaceutical industries.

The shape of a pendant drop is a result of balance between surface tension and gravity forces. Any change in the drop area leads to a change in the surface energy. Now some of that energy can be stored in the surface owing to its elastic nature and some of it can be dissipated owing to the viscous nature of the interface.

We intend to study the behavior of colloidal particles at an interface. For this we use a thermo-sensitive polymer Poly N-Isopropyl Acrylamide （PNIPAM）. This polymer has a unique property that it changes its size with temperature. We will be studying the viscoelastic properties of the interfacial layers of these polymer particles using the Oscillating pendant drop method. What we do is create a stable pendant drop and form a layer of colloidal particles at the interface. We then change the shape of the drop by a small amount by constantly dispensing and withdrawing a very tiny volume of liquid. The viscous and elastic components of the interfacial modulus can thus be found out. We will inspect how do these interfacial properties change with temperature, the concentration of particles etc.