Mechanism of one-step voltage pulse detachment of porous anodic alumina membranes

The mechanism for one-step detachment of porous anodic alumina (PAA) membranes by using an electrochemical voltage pulse technique is systematically studied. Electrochemical oxidation of pretreated aluminum foil results in a thin oxide layer called barrier layer alumina (BLA) between the formed PAA and the Al substrate. Achievement of through-hole PAA membranes requires electrolytes of highly concentrated perchloric acid containing biacetyl and a short detaching pulse voltage of 5–10 V higher than the film forming potential. The influence of the PAA forming potential, voltage pulse height (0–10 V), and the nature of electrolytes on the efficiency of detachment have been systematically investigated. The successful detachment of the PAA could only be achieved with systems giving appropriate transient current upon application of an optimal voltage pulse. Based on the experimental results and the electropolishing mechanism of aluminum, a two-step detachment process of PAA freestanding films is proposed. In this mechanism, the detachment of PAA film from the aluminum substrate upon application of a short voltage pulse is followed by a pores-opening process. The present mechanism is promising for preparation of freestanding PAA films with various pores sizes, which are important for nanomaterial synthesis.