Ablation of water drops suspended in asphaltene/heptol solutions due to spontaneous emulsification

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Science Advances  25 Oct 2019:
Vol. 5, no. 10, eaax8227
DOI: 10.1126/sciadv.aax8227
  • Fig. 1 Interfacial properties at the oil/water interface.

    Aqueous phase consists of deionized water. Oil phase consists of asphaltene (1 mg/ml) molecules dissolved in two solutions: pure toluene and 40/60 heptane/toluene mixture in volume. (A) Results for interfacial moduli as a function of strain are shown. The storage modulus, Gs, is represented by closed symbols, whereas the loss modulus, Gs, is represented by open symbols. Experiments performed with toluene only as a solvent are identified by gray circles; black squares identify the experiments performed with a 40/60 heptol mixture. (B) Interfacial tension as a function of time. For both cases, the surface tension initially decreases rapidly followed by a very slow decreasing process.

  • Fig. 2 Microfluidic device used for experiments.

    (A) Schematic drawing of the co-flow microfluidic device used. Pictures of the drop are taken at time intervals. Because of spontaneous emulsification, the initially formed water drop (B) reduces in size (C and D) as a function of time, while micron-sized droplets appear in the drop’s vicinity. The white circles in (B) to (D) represent the initial size of the drop. The oil phase consists of asphaltenes (1 mg/ml) in toluene.

  • Fig. 3 Normalized water drop’s volume as a function of time for different initial drop sizes.

    The oil phase are (A) toluene only, (B) 40/60 heptane/toluene mixture by volume, (C) asphaltenes (1 mg/ml) dissolved in toluene, and (D) asphaltenes (1 mg/ml) dissolved in a 40/60 heptol mixture by volume.

  • Fig. 4 Drop size effect on spontaneous emulsification behavior.

    (A) Radius as a function of time for drops at different initial sizes immersed in asphaltenes (1 mg/ml) in toluene. The rate at which the drops shrink, α, depends on the initial drop size rather than its current size. In addition, the rate increases as the initial drop size decreases. (B) Internal pressure of drops as a function of time. ΔP is the pressure difference between the inside and the outside of the drop due to its curvature. The internal pressure remains relatively constant although the drop is slowly shrinking due to spontaneous emulsification. (C) The slope α increases exponentially with the inverse of the drop’s initial area (1/R02). (D) Internal pressure of drops also increases exponentially with the inverse of the drop’s initial area (1/R02).

Supplementary Materials

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Linear behavior of radius as a function of time.
    • Fig. S2. Experimental setup for internal pressure measurements.
    • Fig. S3. Interfacial stress, τ, at the oil/water interface.

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