Conditions for depositions of multiple LB films for different divalent cations were determined experimentally at the pK(A) of the system. The pK(A) of the fatty acid-subphase salt system is the pH at which half of the fatty acid heads are dissociated. Stable Y-type depositions take place in full immersion/removal cycles. Under certain conditions, full depositions occur only during the downstroke (X-type) or during the upstroke (Z-type). Experiments show a clear trend between pK(A) of the system and loss of stability of Y-depositions toward full depositions taking place during immersion only, i.e., YX transitions. Stable Y-type depositions can be achieved for most divalent cations at lame dipping speeds. Dipping speed necessary to maintain stable Y-depositions depend on the pK(A) of the system; the lower the pK(A) the larger the dipping speed. The accumulated time spent by the solid substrate under the water subphase is not a good indicator of YX transition because the number of dipping cycles is also a relevant variable. For a given number of cycles, the lower regions of the solid substrate are most affected by transition because they spent a larger time under the water subphase. (c) 2004 Elsevier Inc. All rights reserved.