The Origin of Nanoscopic Grooving on
Vesicle Walls in Submarine Basaltic Glass:
Implications for Nanotechnology
Figure 5
Modelling the propagation of viscous fingering trees across the central portion of the vesicle wall from Figure 1(b). In this computer-aided interpretive drawing of dynamic viscous fingering, the colours show the time-dependent development of the branching viscous fingers according to a realistic growth model. Specifically, colours were assigned by assuming that finger velocities are constant as they increase in length but decelerate by half as they spread out into terminal bulbs and then stop. This assumption is consistent with experimental results for macroscopic viscous fingering, which show that tip velocity is constant at constant flow rate, even during tip-splitting events and shielding of other fingers that slow to a stop [24]. In this growth model, it is also assumed that all neighbouring viscous fingers originating from the same tension gash started growing at the same time (see an explanation of this process in Section 3.2). Based on morphology, viscous fingers C and D are interpreted to have arrived at the same location at the same time (indicated on the figure with a star symbol) and consequently undergone a competition to outgrow one another in that region. This indicates that viscous fingers originating from both tension gashes were growing at the same time, constraining a delay of 0.5m of growth time from one tension gash to the other as shown in the figure (i.e., competing finger D is 0.5m longer than C when measuring back from the star). Examining the colours of neighbouring fingers where shielding events occur is one measure of the reliability of the resulting growth model. For instance, the colour of the very end of finger E shows that according to this model, it was properly shielded by finger D because it arrived approximately 1m of growth time after finger D had passed in front of it. Similarly, finger F was shielded by finger G in the right sequence. Some fingers seem to have been shielded prematurely however (denoted by “p”), in that their tips slowed and stopped growing before the shielding finger had already arrived. Three 1.5m wide Cu-bearing Fe-sulfide spherules are also shown (grey), which acted as obstacles that shielded viscous fingers. Note that this drawing was made using higher resolution SEI images of the area highlighted in Figure 1(b), which are not shown.
