Research ArticleAPPLIED SCIENCES AND ENGINEERING

Normal stress difference–driven particle focusing in nanoparticle colloidal dispersion

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Science Advances  07 Jun 2019:
Vol. 5, no. 6, eaav4819
DOI: 10.1126/sciadv.aav4819
  • Fig. 1 Particle focusing in a model nanoparticle dispersion.

    (A) Schematic diagram for the noncolloidal particle PS bead (6 μm diameter; 0.01 volume %) focusing experiments in a nanoparticle dispersion (nominal volume fraction, 22 volume %; 16.2 nm diameter; LUDOX HS-40) in a circular tube (inner diameter, 25 μm). (B) SAXS analysis of the nanoparticle dispersion (LUDOX HS-40). (C) Top: Development of particle focusing of the PS beads in a capillary tube at a flow rate of 20 μl hour−1 (Pec = 0.002). The probability distribution functions (PDFs) were obtained on the basis of the centers of particles, and the labels denote the distance from the inlet. Bottom: Distribution of particles according to flow rates (50 to 200 μl hour−1 denoted as labels; 0.005 ≤ Pec ≤ 0.02) at a location 8 cm downstream from the inlet. The images were acquired by the z projection of 2000 images using the min intensity mode in ImageJ software (see Materials and Methods for the details of imaging). a.u., arbitrary units.

  • Fig. 2 Secondary flow generation in a square channel in the nanoparticle dispersion.

    (A) Schematic diagram for the secondary flow–assisted single-line focusing in a square channel and an overlay of the postulated streamlines for the secondary flow generated by the second normal stress difference (N2). (B) Distributions of PS beads in a square straight PDMS channel (w × h, 25 μm × 25 μm; length, 5 cm) for the flow rates ranging from 20 to 100 μl hour−1 at a location 4.8 cm downstream from the inlet. The images were acquired by the z projection of 2000 images using the min intensity mode in ImageJ software (see Materials and Methods for the details of imaging). (C and D) Visualization experiments to investigate the mixing occurrence in Newtonian fluid (C) (65 wt % glycerin aqueous solution; viscosity, 15.2 mPa·s) and nanoparticle dispersion (D) (viscosity, 14.5 mPa·s; LUDOX HS-40) in a square channel. The same three fluid streams flowed into a square straight PDMS channel (w × h, 25 μm × 25 μm; length, 4 cm) except for the presence of the fluorescent dye; the fluorescent dye was added to the two side streams and not to the central stream (total flow rate in the straight region: 50 μl hour−1). The fluorescence intensity profiles were measured along the cross-stream direction at locations 0.2, 2, and 3.8 cm downstream from the junction point of the three streams.

  • Fig. 3 Screening effect of the electrostatic repulsive interaction on the elastic property of the model nanoparticle dispersion by electrolyte addition.

    (A) SAXS analyses of DI water and PBS-added nanoparticle dispersions (final PBS concentration ≈ 1× PBS; φp = 0.21). (B) Shear viscosity data in DI water and PBS-added nanoparticle dispersions. (C) Particle distributions in DI water and PBS-added nanoparticle dispersions in a square PDMS channel (w × h, 25 μm × 25 μm; length, 5 cm) at a location 4.8 cm downstream from the inlet at flow rates of 50 and 100 μl hour−1. The images were acquired by the z projection of 2000 images using the standard deviation mode in ImageJ software (see Materials and Methods for the details of imaging). (D) PDFs in DI water (DIW) and PBS-added nanoparticle dispersions.

  • Fig. 4 Particle focusing in blood plasma–constituting protein solutions.

    (A) Schematic diagram for the PDMS microchannel used for the lateral particle migration experiments in protein solutions. The data and error bars denote average values and standard deviations, respectively (n = 5). (B) PDFs in 4% (w/w) BSA solution in DI water, Newtonian fluid [15% (w/w) glycerin solution in DI water], and 4% (w/w) BSA solution in 1× PBS solution at a flow rate of 10 μl hour−1. (C) PDFs in 1.5% (w/w) γ-globulin (γ-G) solutions and in a mixture of 1.5% (w/w) γ-globulin and 4% (w/w) BSA in 1× PBS at a flow rate of 10 μl hour−1. The data and error bars denote average values and standard deviations, respectively (n = 3).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/6/eaav4819/DC1

    Supplementary Text S1. Particle pressure–driven lateral migration.

    Supplementary Text S2. Measurement of relaxation time using particle migration.

    Supplementary Text S3. Inertial particle migration.

    Fig. S1. Distributions of PS beads according to flow rates, particle sizes, and colloidal particle volume fractions.

    Fig. S2. Measurement of the relaxation time of nanoparticle dispersion (LUDOX HS-40).

    References (4152)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text S1. Particle pressure–driven lateral migration.
    • Supplementary Text S2. Measurement of relaxation time using particle migration.
    • Supplementary Text S3. Inertial particle migration.
    • Fig. S1. Distributions of PS beads according to flow rates, particle sizes, and colloidal particle volume fractions.
    • Fig. S2. Measurement of the relaxation time of nanoparticle dispersion (LUDOX HS-40).
    • References (4152)

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