Biomedical subjects

David Jasnow

Publications and source records attributed to David Jasnow.

8 recordsLinked to original sources

PubMed2005

Local control of periodic pattern formation in binary fluids within microchannels.

Simulations show that a local perturbation (a "hot spot") at the inlet of a microchannel can be a source of traveling concentration waves in a binary fluid and can be exploited to create periodic, oscillatory patterns within the channel. We isolate two distinctly different types of traveling periodic patterns and estimate the wavelength of the structures. Our findings provide the first example of how a local perturbation can be used to create well-defined periodic patterns in two-phase flow within a confined geometry and can lead to new routes for creating gradient materials.

Journal Article↗

PubMed2005

Newtonian fluid meets an elastic solid: coupling lattice Boltzmann and lattice-spring models.

We integrate the lattice Boltzmann model (LBM) and lattice spring model (LSM) to capture the coupling between a compliant bounding surface and the hydrodynamic response of an enclosed fluid. We focus on an elastic, spherical shell filled with a Newtonian fluid where no-slip boundary conditions induce the interaction. We calculate the "breathing mode" oscillations for this system and find good agreement with analytical solutions. Furthermore, we simulate the impact of the fluid-filled, elastic shell on a hard wall and on an adhesive surface. Understanding the dynamics of fluid-filled shells, especially near adhesive surfaces, can be particularly important in the design of microcapsules for pharmaceutical and other technological applications. Our studies reveal that the binding of these capsules to specific surfaces can be sensitive to the physical properties of both the outer shell and the enclosed fluid. The integrated LBM-LSM methodology opens up the possibility of accurately and efficiently capturing the dynamic coupling between fluid flow and a compliant bounding surface in a broad variety of systems.

Journal Article↗

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.

Journal Article↗

PubMed2003

Cohesive energy, stability, and structural transitions in polyelectrolyte bundles.

A lattice of uniformly charged, infinitesimally thin rods decorated with an ordered array of counterions exhibits anomalous behavior as the spacing between the rods is varied. In particular, the counterion lattice undergoes a sequence of structural shearing or "tilting," phase transformations as the spacing between the rods decreases. The potential implications of this behavior with respect to the packaging of biologically relevant polyelectrolytic molecules are commented upon.

Biophysical Phenomena↗

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.

Journal Article↗

PubMed2003

Self-assembly of a binary mixture of particles and diblock copolymers.

Using theoretical models, we undertake the first investigation into the synergy and rich phase behavior that emerges when binary particle mixtures are blended with microphase-separating copolymers. We isolate an example of spontaneous hierarchical self-assembly in such hybrid materials, where the system exhibits both nanoscopic ordering of the particles and macroscopic phase transformation in the copolymer matrix. Furthermore, the self-assembly is driven by entropic effects involving all the different components. The results reveal that entropy can be exploited to create highly ordered nanocomposites with potentially unique electronic and photonic properties.

Journal Article↗

PubMed2002

Entropically driven formation of hierarchically ordered nanocomposites.

Using theoretical models, we undertake the first investigation into the rich behavior that emerges when binary particle mixtures are blended with microphase-separating copolymers. We isolate an example of coupled self-assembly in such materials, where the system undergoes a nanoscale ordering of the particles along with a phase transformation in the copolymer matrix. Furthermore, the self-assembly is driven by entropic effects involving all the different components. The results reveal that entropy can be exploited to create highly ordered nanocomposites with potentially unique electronic and photonic properties.

Journal Article↗

PubMed2002

Binary hard sphere mixtures in block copolymer melts.

We perform a self-consistent-field/density-functional-theory hybrid analysis for a system of diblock copolymers mixed with polydisperse, hard, spherical particles of various chemical species. We apply this theory to study the equilibrium morphologies of two different binary sphere/diblock melts. First, we examine the case where the particles have two different sizes, but both types are preferentially wetted by one of the copolymer blocks. We find that the single-particle distributions for the two species do not track one another and that the particles show a degree of entropically generated separation based on size, due to confinement within the diblock matrix. Second, we study the case where the particles are all the same size, but are of two different chemical species. We find that, as expected, the particle distributions reveal a degree of enthalpically driven separation, due to the spheres' preferential affinities for different blocks of the copolymer.

Journal Article↗