Biomedical subjects

Olga Kuksenok

Publications and source records attributed to Olga Kuksenok.

6 recordsLinked to original sources

PubMed2005

Convection-driven pattern formation in phase-separating binary fluids.

Using a thermal-lattice Boltzmann model, we examine the rich phase behavior that develops when partially miscible fluids evolve in the presence of a vertical temperature gradient, which encompasses the critical temperature T(c) of the mixture. In particular, a binary AB fluid is confined between two plates in a gravitational field. The upper plate is fixed below T(c) and hence, the nearby fluid phase separates into A-rich and B-rich domains. The lower plate is fixed above the temperature T(c), and the surrounding fluid is in the homogeneous phase. A coupling between convection (driven by the temperature gradient) and phase separation gives rise to unique pattern formation. A number of regimes are identified: regularly spaced stripes, convective steady-state columns, the periodic disturbance of these columns, and finally, chaotic dripping from the upper surface. These results highlight dynamical behavior in partially miscible mixtures.

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PubMed2004

Effect of hydrodynamic interactions on the evolution of chemically reactive ternary mixtures.

We investigate the structural evolution of an A/B/C ternary mixture in which the A and B components can undergo a reversible chemical reaction to form C. We developed a lattice Boltzmann model for this ternary mixture that allows us to capture both the reaction kinetics and the hydrodynamic interactions within the system. We use this model to study a specific reactive mixture in which C acts as a surfactant, i.e., the formation of C at the A/B interface decreases the interfacial tension between the A and B domains. We found that the dynamics of the system is different for fluids in the diffusive and viscous regimes. In the diffusive regime, the formation of a layer of C at the interface leads to a freezing of the structural evolution in the fluid; the values of the reaction rate constants determine the characteristic domain size in the system. In the viscous regime, where hydrodynamic interactions are important, interfacial reactions cause a slowing down of the domain growth, but do not arrest the evolution of the mixture. The results provide guidelines for controlling the morphology of this complex ternary fluid.

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PubMed2003

Diffusive intertwining of two fluid phases in chemically patterned microchannels.

Via a coarse-grained model, we simulate the flow of a pressure driven binary AB fluid through a three-dimensional microchannel, which is decorated on both top and bottom with distinct A- and B-like patches. The advection is "frustrated" because A-like patches are placed in the path of the B stream and similarly, B-like patches are placed in the path of the A fluid. A competition between two factors, the advection caused by the imposed flow and the interactions between the confined fluids and the patterned substrates, introduces nonlinearity into the system. This nonlinear behavior gives rise to a temporally periodic state, where the A and B fluids are intertwined. In effect, the simple pattern of chemically distinct patches introduces positive feedback, which is responsible for the instability of the interface separating the injected fluids.

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PubMed2003

Periodic droplet formation in chemically patterned microchannels.

Simulations show that, when a phase-separated binary AB fluid is driven to flow past chemically patterned substrates in a microchannel, the fluid exhibits unique morphological instabilities. For the pattern studied, these instabilities give rise to the simultaneous, periodic formation of monodisperse droplets of A in B and B in A. The system bifurcates between time-independent behavior and different types of regular, nondecaying oscillations in the structural characteristics. The surprisingly complex behavior is observed even in the absence of hydrodynamic interactions and arises from the interplay between the fluid flow and patterned substrate, which introduces nonlinearity into the dynamical system.

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PubMed2003

Simulating the dynamic behavior of immiscible binary fluids in three-dimensional chemically patterned microchannels.

Using computer simulations, we investigate the behavior of an immiscible binary AB fluid that is driven to flow through a microchannel, which is decorated with a checkerboard pattern of chemically distinct A- and B-like patches on the top and bottom walls. We isolate conditions where the coupling between the imposed flow field and thermodynamic interactions yields a rich interfacial behavior between the A and B fluids and complex velocity patterns over the checkerboard domains. In effect, the A and B fluids undergo extensive mixing in specific regions of the channel, even for low Reynolds number flow. Decreasing the height-to-width ratio of the patterned microchannel enhances the extent of mixing between these two components. On the other hand, the length of the A/B interfaces is optimized in microchannels that have a square cross section. The results provide guidelines for designing microfluidic devices that can be used to effectively intermix multicomponent fluids.

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PubMed2002

Using patterned substrates to promote mixing in microchannels.

Using a lattice Boltzmann model for fluid dynamics, we investigate the flow and phase behavior of a binary fluid moving over a patterned substrate within a microchannel. The binary fluid consists of two immiscible components, A and B, and this liquid is subjected to a Poiseuille flow. The substrate is decorated with a checkerboard pattern of A- and B-like patches. Through a coupling of hydrodynamics and thermodynamics, each component is driven to flow from the nonwettable domains to wettable regions. As a consequence, the A and B fluids undergo extensive mixing within the microchannels. We investigate how the degree of mixing depends on the size of the patches, the velocity of the imposed flow field, and the characteristics of the fluid. The results provide guidelines for creating localized "mixing stations" within microfluidic devices. The findings also reveal how a combination of imposed flow fields and surface patterning can be exploited to control the phase behavior of complex fluids.

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