A TALE OF GLASS TADPOLES

 PRINCE RUPERT'S DROPS - IN A NUTSHELL 

                                                         KOUSTAV BHATTACHARJEE                                                                           

 DATE :- 03.03.2022

Prince Rupert's drops first gained widespread fame in 1660, when Prince Rupert of the Rhine (of Germany) brought a few of the curiosities to King Charles II of England. (The teardrops, which are made by pouring molten glass into cold water, had likely been known to glassblowers centuries earlier.) Charles then handed them over to the Royal Society, which published its first scholarly investigation of their properties in 1661.

        Strong head

In the new study, Chandrasekar relied on a slightly different technique called integrated photoelectricity , to reveal the mysteries of the glass tadpoles' heads. The technique calls for placing the object in a pool of water and then passing polarized light waves, or light that is oriented in a single plane, through the material. Internal stresses inside the material change the polarization of the light. Looking at the polarization of the outgoing light waves through special filters reveals the internal stresses inside the object — in this case, the head of the drop and the tail. 

These stresses formed because the type of glass used in these teardrops — which expands dramatically with heat — also shrinks dramatically when exposed to cold water. During the process to make these drops, the molten glass is dipped in cold water. When the glass hits the water, the outside cools faster than the inside. The outside layer of the glass then forms a kind of "jacket" that squishes the inside. Because the inside is still cooling, and because the total forces acting in the object have to equal zero, the head forms tensile stresses on its interior, the researchers reported in their paper, which was published online in Applied Physics Letters. 

The reason the compressive stress on the outside of the drops prevents fracturing is somewhat intuitive; the compression is squishing the atoms of the glass closer together – so they have no place to go. Fractures also don't move as easily through materials under compression. By contrast, most materials tend to break more easily when they are being pulled apart in tension.

However, even these shatter-resistant confections will eventually crack under pressure; for instance, if the heads of the drops are put inside a vise with enough pressure, they too will eventually turn to powder, though not quite as spectacularly as in the tail-snapping process, Chandrasekar said.

( SOURCE:- live science)