Transient Filling of Sacrificially Etched Nanochannels by Capillarity

In this paper we present results of an experimental investigation that explores the transient filling of nanochannels due to capillarity. The nanochannels explored here were fabricated using sacrificial metal cores and were designed to mimic the parallel-plate channel geometry. Channels of heights ranging from 41 to 91 nm were utilized in the experimental program and both aluminum and chromium were utilized as the sacrificial metal from which the channels were formed. The filling dynamics of channels that were closed on one end were also explored. The data reveal that the channels fabricated with aluminum as the sacrificial core yield marked departure from expected behavior, with the apparent frictional constant significantly elevated above classical values. Potential reasons for the departure are discussed. Channels fabricated with chromium cores result in behavior that yields much less deviation from anticipated Stokes flow behavior. However, for these channels the meniscus speed is observed to vary markedly across the channels transverse width. Channels that are closed on one end yield behavior that is significantly different from the open-ended channel results. Here the meniscus becomes destabilized as it approaches the capped channel end and the trapped air becomes entrained by the liquid and dispersed without evidence of bubble existence.