Biomedical subjects

D Jasnow

Publications and source records attributed to D Jasnow.

At least 19 recordsLinked to original sources

PubMed2000

Shear instabilities of freely standing thermotropic smectic- A films.

In this Letter we discuss theoretically the instabilities of thermotropic freely standing smectic- A films under shear flow [3]. We show that, in Couette geometry, the centrifugal force pushes the liquid crystal toward the outer boundary and induces smectic layer dilation close to the outer boundary. Under strong shear, this effect induces a layer buckling instability. The critical shear rate is proportional to 1/sqrt[d], where d is the thickness of the film.

Journal Article↗

PubMed2000

Interface and contact line motion in a two phase fluid under shear flow

We use a coarse grained description to study the steady state interfacial configuration of a two phase fluid under steady shear. Dissipative relaxation of the order parameter leads to interfacial slip at the contact line, even with no-slip boundary conditions on the fluid velocity. This relaxation occurs within a characteristic length scale l(0) = sqrt[xiD/V0], with xi the (microscopic) interfacial thickness, D an order parameter diffusivity, and V0 the boundary velocity. The steady state interfacial configuration is shown to satisfy a scaling form involving the ratio l(0)/L, where L is the width of the fluid layer, for a passive interface, and the capillary number as well for an active interface.

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PubMed2000

Forming supramolecular networks from nanoscale rods in binary, phase-separating mixtures

Simulations show that when low-volume fractions of nanoscale rods are immersed in a binary, phase-separating blend, the rods self-assemble into needle-like, percolating networks. The interconnected network arises through the dynamic interplay of phase-separation between the fluids, through preferential adsorption of the minority component onto the mobile rods, and through rod-rod repulsion. Such cooperative effects provide a means of manipulating the motion of nanoscopic objects and directing their association into supramolecular structures. Increasing the rod concentration beyond the effective percolation threshold drives the system to self-assemble into a lamellar morphology, with layers of wetted rods alternating with layers of the majority-component fluid. This approach can potentially yield organic/inorganic composites that are ordered on nanometer scales and exhibit electrical or structural integrity.

Journal Article↗

PubMed2000

Layer dynamics of freely standing smectic-A films

The dynamics of freely standing thermotropic smectic-A films are studied in the isothermal, incompressible limit via a continuous hydrodynamic description. The role of permeation in the films, the structure of the hydrodynamic normal modes, and the form of the autocorrelation functions for the smectic layer and order-parameter fluctuations are discussed. We find two characteristic lengths l(d)=sqrt[alphad/B] and l(c)=sqrt[eta(2)(3)d/8rhoalpha] associated with the dynamic behavior of the system, where alpha is the surface tension, d is the film thickness, B is the elastic constant for layer compression, eta(3) is the layer sliding viscosity, and rho is the density of the liquid crystal. The crossover from filmlike to bulklike behavior is controlled by l(d) alone; the crossover from overdamped to underdamped dynamics when the in-plane length scale is large compared to l(d) is controlled by l(c) alone.

Journal Article↗

PubMed1996