Flow pattern split streamline

A remarkable analysis of the role of hydrodynamics in LB depositions was done by de Gennes (1986). This analysis concerns only deposition during removal of the solid substrate, de Gennes recognizes that the only flow pattern that would allow Y-deposition is a split-ejection streamline in the liquid phase. However, he uses as a reference the work of Huh and Scriven (1971), but their hydrodynamic theory predicts a rolling motion in the liquid phase. 

Petrov and Petrov (1998) developed a molecular hydrodynamic theory of film deposition during removal. Their theory correctly assumes a flow pattern - which we identified as a split streamline - between the solid substrate and the monolayer in Figure 10.5 (c). This pattern is indeed the necessary pattern for successful deposition during removal, but it is not the only flow pattern for solid removal at all dynamic contact angles. Petrov and Petrov (1998) address the kinetics of water removal between the solid and the monolayer and the formation of wet or dry monolayers depending on the amount of water entrained. 

Figure 10.4 Schematic representation of flow patterns near a moving contact line during immersion of a solid substrate into a pool of liquid, (a) Split-injection streamline in phase B and rolling pattern in phase A. (b) Transition flow pattern with motionless interface and rolling motion in phases A and B. (c) Rolling motion in phase B and split-ejection streamline in phase A...

When a wetting solid is removed from the liquid phase, the flow pattern in the liquid phase is the split-ejection streamline pattern shown in Figure 10.5 (c). The interface liquid-air moves toward the contact line and a Z-type LB deposition is possible. During removal, transfer ratios of the monolayer show a strong dependence with the relative... 

Region IV is the window of operation for successful deposition of Y-type films. The flow pattern in this region is typical during removal of solids with dynamic contact angles 0 < < 90°. The split-ejection streamline is in the liquid phase and the interface... 

For very small dynamic contact angles, the liquid is not completely removed by the split streamline and it is entrained between the film and the solid surface, creating what is known as a wet LB film. Water trapped between the solid surface and the LB monolayer prevents adhesion and is a leading cause of monolayer instability. Petrov etal. (1980) sketched the flow pattern near the moving contact line. The flow pattern is the one described here for region IV. The authors, however, reference Huh and Scriven (1971)... 

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