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NANO-SCALE VISUALIZATION OF LIQUID INTERFACES DURING COALESCENCE AND RAPTURE
 

Summary: NANO-SCALE VISUALIZATION OF LIQUID INTERFACES
DURING COALESCENCE AND RAPTURE
Experiments by Jacob Israelachvili and Gary Leal are focusing on the way two liquid-vapor and
liquid-liquid interfaces coalesce and detach. This is being studied using a Surface Forces
Apparatus to bring two surfaces together with control at the ångstrom level, and Multiple Beam
Interferometry to monitor the shapes of and distance between the interacting surfaces. The
results reveal many subtle effects, including local surface deformations just before coalescence,
for example, bulging in or bulging out, depending on the liquids (their viscosity and interfacial
tension) and experimental conditions (shear rate or approach velocity), and nano-scale ripples
that are analogous to the (macroscopic) ripples seen on the water surface of a still lake when it
is disturbed by a stone or by wind. Separation, too, can be accompanied by interesting effects
such as fingering and cavitation, both occurring at the nano- or submicron-scales. The two
figures below ­ the first on coalescence, the second on separation ­ illustrate schematically
what can be directly visualized and quantitatively measured in the these experiments.
Figure 1. Surface deformations during the approach of two curved surfaces (R=1 cm) of liquid
poly-butadiene (PBD) in liquid poly-dimethyl-siloxane (PDMS) as visualized in SFA
experiments using both multiple beam interference fringes and standard optical microscopy.
Top row: side view of section (plane) passing through the center of the contact region at slow
approach. Bottom row: side view at fast approach. At low approach rates, hydrodynamic
deformations are small and the interfaces bulge towards each other before coalescing at the

  

Source: Akhmedov, Azer - Department of Mathematics, University of California at Santa Barbara

 

Collections: Mathematics