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Olga Kuksenok

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Modeling chemical reactions in immiscible fluids in microchannels Presentation (windows Only) & PDF file
Local control of periodic pattern formation in driven binary immiscible fluid Presentation (windows Only) & PDF file

Binary Fluid within the Microchannels: Morphological instabilities and periodic droplet formation.

What happens if we drive two parallel fluid streams, A (in blue) and B (in yellow) through the patterned microchannel?

  • Case 1:

    Patches on the top and on the bottom substrates are in registry and form a “checkerboard”. In the first set of patches, A-like (B-like) stripe that preferentially attracts A (B) component is placed on the way of B(A) fluid stream, in the second set of patches, A-like and B-like stripes are reversed.

    We found that the system bifurcates between time-independent behavior and different types of regular, non-decaying oscillations in the structural characteristics that give rise to the periodic formation of B-in-A droplets near the front wall and, simultaneously, A-in-B droplets near the back wall. The surprisingly complex behavior is observed even in the absence of hydrodynamic interactions.

    Here are examples of two types of oscillations:
    Symmetric oscillations: Asymmetric oscillations:
    H=0.00028; time range t =55000 to t=73000 (60 snapshots) H=0.00032; time range t =55000 to t=73000 (60 snapshots)
    For details, see:

  • Case 2:

    Patches on the top and on the bottom substrates consist of two stripes only; A-like (B-like) stripe is places on the way of B(A) fluid stream.
    Complex structure, where A and B phase are intertwined, forms in the center of the channel and decays close to sidewalls. This structure is periodic in space (along the flow direction) and in time.
    In order to see the structure, we cut the channel by vertical plane near the center and made the front part of the channel transparent (movie on the left). Movie on the right shows the morphology at the outlet of the channel.

    For details, see:

    • Olga Kuksenok, David Jasnow, Anna C.Balazs. Diffusive Intertwining of Two Fluid Phases in Chemically Patterned Microchannels (Phys. Rev. E (2003), in press)
    • Olga Kuksenok and Anna C.Balazs. Harnessing Chemical Patterning to Direct the Flow of Binary Fluids in Microchannels (submitted).
    • Oscillatory Behavior in Binary Fluids Driven Through Patterned Microchannels (presentation; opens in a new window)

Binary Fluid within the Microchannels: Mixing and flow control.
We examine the behavior of two immiscible fluids, A and B, driven by a pressure gradient to flow through microchannels decorated with A- (B)-like patches (that are preferentially wetted by the A(B) fluid). We consider different arrangements of the A and B patches and study how these patches might be useful to promote mixing within patterned region or direct the fluids within the microchannels.
Related papers:
  • Olga Kuksenok and Anna C. Balazs. Simulating the dynamic behavior of immiscible binary fluids in three-dimensional chemically patterned microchannels. Phys. Rev. E 68, 011502 (2003).
    PDF file - 1,144 KB
  • Olga Kuksenok, J. M. Yeomans, and Anna C. Balazs. Using patterned substrates to promote mixing in microchannels. Phys. Rev. E 65 (3), 031502 (2002).
    PDF file - 7,852 KB
  • Olga Kuksenok, J.M. Yeomans and Anna C. Balazs. Creating localized mixing stations within microfluidic channels. Langmuir 17 (23), 7186-7190 (2001).
    PDF file - 1.17 MB

Modeling ternary fluids with reversible chemical reactions.

We developed two order parameter model to study dynamics of the ternary mixture where two components (A and B) may undergo reversible chemical reaction to form the third component (C). We examine the influence of the hydrodynamic interaction on the kinetics of the C-formation primarily in the limit were C acts as a compatibilizer.
Recent presentation:
Exploiting gradients in cross-link density to control the bending and self-propelled motion of active gels.
Oscillating polymer gels undergoing the Belousov.Zhabotinsky (BZ) reaction provide an ideal medium for probing the interplay between chemical energy and mechanical action. Inspired by recent experiments, we use computational modeling to determine how gradients in crosslink density across the width of a sample can drive long, thin BZ gels to both oscillate and bend, and thereby undergo concerted motion. Free in solution, these samples move forward (in the direction of lower cross-link density) through a rhythmic bending and unbending. Our simulations allow us to not only isolate optimal ranges of parameters for achieving this distinctive behavior but also provide insight into the dynamic coupling between chemical and mechanical energy that is needed to produce the self-sustained motion. We then model samples that are mechanically constrained by their attachment to a flat, rigid surface. By varying the concentration of the reagents in the solution, we show that the undulations of the sample's free end can be significantly modified, so that the overall motion can be directed either upwards or downwards. The findings from these studies provide guidelines for creating autonomously moving objects, which can be used for robotic or microfluidic applications.

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