Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Taylor cone

thumb|right|300 px|Electrospray diagram depicting the Taylor cone, jet and plume A Taylor cone refers to the cone observed in electrospinning, electrospray and hydrodynamic spray processes from which a jet of charged particles emanates above a threshold voltage. Aside from electrospray ionization in mass spectrometry the Taylor cone is important in colloid thrusters used in fine control and high efficiency (low power) thrust of spacecraft. History This cone was described by Sir Geoffrey Ingram Taylor in 1964 before electrospray was "discovered". Sir Geoffrey Taylor 1964 Disintegration of Water Droplets in an Electric Field Proc. Roy. Soc. London. Ser. A 280 383 http://links.jstor.org/sici?sici=0080-4630%2819640728%29280%3A1382%3C383%3ADOWDIA%3E2.0.CO%3B2-Q&size=LARGE 1382 10.1098/rspa.1964.0151 This work followed on the work of ZelenyZeleny, J. The Electrical Discharge from Liquid Points, and a Hydrostatic Method of Measuring the Electric Intensity at Their Surfaces. Physical Review 1914 3 69 10.1103/PhysRev.3.69 where in 1917 he photographed a cone-jet of glycerine under high electric field and the work of several others, Wilson & Taylor (1925), The bursting of soap bubbles in a uniform electric field Proc. Cambridge Philos. Soc. 1925 C. T. Wilson G. I Taylor 22 728 Nolan (1926) Proc. R. Ir. Acad. Sect. A 1926 J. J. Nolan 37 28 and Macky (1931). Some Investigations on the Deformation and Breaking of Water Drops in Strong Electric Fields Proceedings of the Royal Society of London. Series A October 01, 1931 W. A. Macky 133 822 565–587 10.1098/rspa.1931.0168|url=http://www.journals.royalsoc.ac.uk/content/c6188343042555vw/fulltext.pdf|format=PDF|accessdate=2007-10-25 Taylor was primarily interested in the behavior of water droplets in strong electric fields, such as in thunderstorms. Taylor cone formation When a small volume of electrically conductive liquid is exposed to an electric field ,the shape of liquid starts to deform from the shape caused by surface tension alone. As the voltage is increased the effect of the electric field becomes more prominent and as it approaches exerting a similar amount of force on the droplet as the surface tension does a cone shape begins to form with convex sides and a rounded tip. This approaches the shape of a straight generatrix (cone) with a whole angle (width) of 98.6°. When a certain threshold voltage has been reached the slightly rounded tip inverts and emits a jet of liquid. This is called a cone-jet and is the beginning of the electrospray process in which ions may be transferred to the gas phase. It is generally found that in order to achieve a stable cone-jet a slightly higher than threshold voltage must be used. As the voltage is increased even more other modes of droplet disintegration are found. The term Taylor cone can specifically refer to the theoretical limit of a perfect cone of exactly the predicted angle or generally refer to the approximately conical portion of a cone-jet after the electrospray process has begun. Theory Sir Geoffrey Ingram Taylor in 1964 described this phenomenon, theoretically derived based on general assumptions that the requirements to form a perfect cone under such conditions required a semi-vertical angle of 49.3° (a whole angle of 98.6°) and demonstrated that the shape of such a cone approached the theoretical shape just before jet formation. This angle is known as the Taylor angle. This angle is more precisely where is the first zero of (the Legendre polynomial of order 1/2). Taylor's derivation is based on two assumptions: (1) that the surface of the cone is an equipotential surface and (2) that the cone exists in a steady state equilibrium. To meet both of these criteria the electric field must have azimuthal symmetry and have dependence to counter the surface tension to produce the cone. The solution to this problem is: where (equipotential surface) exists at a value of (regardless of R) producing an equipotential cone. The magic angle necessary for for all R is a zero of between 0 and which there is only one at 130.7099°. The complement of this angle is the Taylor angle. References