In needle electrospinning, the polymer solution at the nozzle tip receives four main forces: surface tension force, electric force, viscoelastic force, and gravity, as shown in Fig. 6.1. Surface tension tends to reduce the liquid surface area. Induced by a high electric voltage, charge accumulation occurs on the liquid surface, giving rise to the electric force. At a low applied voltage, under the influence of electric force, the droplet is deformed to balance the forces received. With an increase in the applied voltage, the solution droplet evolves from a hemi-sphere to a cone shape (Taylor cone) and a high electric force is thus concentrated at the apex of the Taylor cone. When the electric field is above a critical value, the droplet at the cone tip overcomes its surface tension. Jet is formed and ejected into the electric field formed between the nozzle tip and collector.