The ring-like stains are formed due to the accumulation of coffee particles at the edge of the drop as the water evaporates. This is because the water molecules at the edge of the drop evaporate faster than those in the centre, creating a flow of liquid towards the edge. The coffee particles are then carried along with this flow and accumulate at the edge of the drop.
In the case of liquid crystals, which are materials that exhibit both liquid and crystalline properties, the coffee-ring effect is even more pronounced. This is because liquid crystals have a tendency to align themselves in a particular direction, which can create even more pronounced flow patterns.
The IISc physicists, led by Professor Saptarshi Basu, studied the coffee-ring effect in liquid crystals using a variety of techniques, including optical microscopy and interferometry. They found that the size and shape of the coffee rings depended on the concentration of liquid crystals in the drop, as well as the temperature and humidity of the surrounding environment.
The researchers also found that the coffee rings could be used to create patterns on surfaces. By carefully controlling the evaporation conditions, they were able to create coffee rings with different sizes and shapes. This could have potential applications in the fields of optics and materials science.
The study, published in the journal Physical Review Letters, provides new insights into the physics of drying droplets and could have potential applications in the fields of optics and materials science.
