Electroosmotic flow has been the main liquid pumping method because it does not require moving parts. The EOF in a network of channels has been modeled by the electric current flowing in a network of resistors using Kirchoff’s rules. On the basis of this study, a better control of liquid flow can be achieved by designing channels of different solution resistances and by applying different voltages.324 Surface modification of the microchannel is sometimes necessary to manipulate the direction and magnitude of EOF (see Section 3.2.1).