Micro liquid bridge in periodic electric pulses: The impact of frequency

A floating liquid bridge can be generated when voltage is applied across two beakers in DC or high-frequency AC conditions. However, this leaves a wide range of scanning frequencies unknown for the stability of the floating liquid bridge. In this work, we investigated the stability of a micro-floating liquid bridge under periodic voltage pulses, characterized by a high-speed camera and current recording systems. We found that the electrical current perfectly revealed the stability and dynamics of liquid bridges and, thus, can be used as a new approach to study the liquid bridge in the absence of an imaging system. We found six different states of liquid bridges based on their stability, as well as their current characteristics. The phase diagram indicated that, besides the electrocapillary number, the frequency of voltage pulses is another crucial factor for the liquid bridge stability. We unveiled the strong electrical impacts on the liquid bridge formation and breakup dynamics, and we found that the critical time of liquid bridge formation and breakup is an order of magnitude longer than that predicted value, without considering the charging and discharging process. We corrected the formation and breakup time of the floating liquid bridge, considering the Maxwell stress-reduced capillary force in the charging and discharging process, which well explained our experimental observation. Our study provides new insights into the dynamics and stability of liquid bridges, which may be useful for printing in the future.