Experimental Studies of the Two Phase Flow and Monodispersed Pickering Emulsions Stabilized by LaponiteRD in a Microfluidic T- Junction
Monodispersed droplets were produced in a microfluidic T-junction by controlling flow rates of dispersed and continuous phases. The space between each droplet was controlled and it was similar between different droplets. The main observation of the experiments is that the droplet size is directly proportional to the flow rate of dispersed phase and inversely proportional to the flow rate of the continuous phase. The effect of viscosity on drop size is not straightforward but the influence of viscosities on droplet formation can be deduced from the capillary number. In the squeezing regime droplets are sheared off right at T-junction and the breakup is dominated by the interfacial tension force. As the velocity of the driving flow increases so called the dripping and jetting regimes happen, and the interfacial velocity is not high enough for clean snap-off, and fluids proceed in laminar flow for some distance before the snap-off occurs. Adding clay in dispersed phase slightly increases the droplet size and capillary value. Even in the same regime for different viscosities in continuous phase, capillary number varied a lot but not as much for the clay. We expect either higher concentration of clay or sufficient time needs to affect the clay on droplet size effectively.
The most stable water-in-oil emulsions was formed in the experiment by using Laponite RD as emulsifier under conditions where the particles are flocculated via salt at higher concentrations of clay and high viscous polar oil (castor oil) used as continuous phase. Emulsions have been generated in a T-junction in two situations. First, emulsions at constant salt concentration for different clay concentrations. Second, emulsions at constant concentration of Laponite RD with decreasing concentration of salt. The changes in the drop size distributions with time are rationalized in terms of either coalescence or Ostwald ripening which is prompt initially but eventually stable. Emulsions were made with both non-polar oil (silicone oil) and polar oil (castor oil). It was found that the stability of emulsions dependent on the type of oil. Nonpolar oils like silicon oil was not suitable for preparing stable W/O emulsions, whereas polar oil like castor oil made stable W/O emulsions possible.
Place, publisher, year, edition, pages
Institutt for fysikk , 2014. , 75 p.
IdentifiersURN: urn:nbn:no:ntnu:diva-25743Local ID: ntnudaim:12165OAI: oai:DiVA.org:ntnu-25743DiVA: diva2:740204
Fossum, Jon Otto, Professor