Electroosmotic flow (EOF) exists widely at the solid-liquid interface in the
presence of external electric field. However, the EOF driven by an alternating
current (AC) electric field in diverse chemical environments was far from being
well understood due to limited experimental investigations. In this
investigation, through the high-resolution laser-induced fluorescent
photobleaching anemometer (LIFPA), the transient velocity according to the AC
EOF on the electric double layer (EDL) far from the electrodes has been
experimentally characterized, by means of time series and power spectra. With
analyzing the transient velocity, the transition of AC EOF from linear to
nonlinear behavior is observed in a broad parameter space, e.g. mean flow
velocity, the frequency and intensity of the AC electric field, and the pH
value of the bulk fluid. To take all these parameters into account, an
electro-inertial velocity has been applied as the characteristic velocity,
instead of the commonly applied Helmholtz-Smouluchowski velocity. Then, the
transitional electric field intensity EA,Cβ and the corresponding
dimensionless parameter Znlcβ are systematically studied. A power-law
relationship between the linear term coefficient Zlβ and Znlcβ has been
established, with the scaling exponents determined by the pH value of the
electrolyte solution. We hope the current investigation can provide a deeper
understanding of the transition of AC EOF and the instantaneous response of
EOFs in other forms. It also provides a simple model to understand the coupling
between electric field and fluid flow, in both linear and nonlinear status