TY  - EJOU
AU  - Planchette, Carole  
AU  - Lorenceau, Elise  
AU  - Brenn, Günter  

TI  - Binary Collisions of Immiscible Liquid Drops for Liquid Encapsulation
T2  - Fluid Dynamics \& Materials Processing

PY  - 2011
VL  - 7
IS  - 3
SN  - 1555-2578

AB  - This work is dedicated to a general description of collisions between two drops of immiscible liquids. Our approach is mainly experimental and allows us to describe the outcomes of such collisions according to a set of relevant parameters. Varying the relative velocity U as well as the impact parameter X we can build for each pair of investigated liquids a nomogram X,U showing three possible regimes: coalescence, head-on separation and off-center separation. In this paper, we also study the influence of the liquid properties, i.e. viscosity, density, surface and interfacial tensions using a set of aqueous glycerol solutions together with a set of silicon and perfluorinated oils. We show that the coalescence regime always leads to full spreading of the oil on the aqueous drop (encapsulation) in contrast to the separation regimes where part of the oil is expelled from the encapsulated drop. For head-on separation, three different mechanisms were identified: reflexive separation, single-reflex separation, and crossing separation. Concerning the stability limits of such collisions, the aqueous phase seems to be of little influence in the range of studied liquids. For off-center collisions, the efficiency of the encapsulation is measured via the amount of oil forming the encapsulating shell. We show that the thickness of this coating can be tuned independently from the liquid properties and drop relative velocity by varying the impact parameter. Finally, we briefly address the case of unequal sized drops and the regimes observed for head-on separation.
KW  - Binary drop collisions
KW  -  immiscible liquids
KW  -  crossing separation
KW  -  instability onset
KW  -  encapsulation efficiency

DO  - 10.3970/fdmp.2011.007.279