312 research outputs found
Corrugated interfaces in multiphase core-annular flow
Microfluidic devices can be used to produce highly controlled and
monodisperse double or multiple emulsions. The presence of inner drops inside a
jet of the middle phase introduces deformations in the jet, which leads to
breakup into monodisperse double emulsions. However, the ability to generate
double emulsions can be compromised when the interfacial tension between the
middle and outer phases is low, leading to flow with high capillary and Weber
numbers. In this case, the interface between the fluids is initially deformed
by the inner drops but the jet does not break into drops. Instead, the jet
becomes highly corrugated, which prevents formation of controlled double
emulsions. We show using numerical calculations that the corrugations are
caused by the inner drops perturbing the interface and the perturbations are
then advected by the flow into complex shapes
Dynamics of oppositely charged emulsion droplets
published_or_final_versio
Corrugated interfaces in multiphase core-annular flow
International audienceMicrofluidic devices can be used to produce highly controlled and monodisperse double or multiple emulsions. The presence of inner drops inside a jet of the middle phase introduces deformations in the jet, which leads to breakup into monodisperse double emulsions. However, the ability to generate double emulsions can be compromised when the interfacial tension between the middle and outer phases is low, leading to flow with high capillary and Weber numbers. In this case, the interface between the fluids is initially deformed by the inner drops but the jet does not break into drops. Instead, the jet becomes highly corrugated, which prevents formation of controlled double emulsions. We show using numerical calculations that the corrugations are caused by the inner drops perturbing the interface and the perturbations are then advected by the flow into complex shapes
Orientational correlations in active and passive nematic defects
We investigate the emergence of orientational order among +1/2 disclinations
in active nematic liquid crystals. Using a combination of theoretical and
experimental methods, we show that +1/2 disclinations have short-range
antiferromagnetic alignment, as a consequence of the elastic torques
originating from their polar structure. The presence of intermediate -1/2
disclinations, however, turns this interaction from anti-aligning to aligning
at scales that are smaller than the typical distance between like-sign defects.
No long-range orientational order is observed. Strikingly, these effects are
insensitive to material properties and qualitatively similar to what is found
for defects in passive nematic liquid crystals.Comment: 6 pages, 4 figure
Computer simulations of nematic drops: Coupling between drop shape and nematic order
We perform Monte Carlo computer simulations of nematic drops in equilibrium with their vapor
using a Gay-Berne interaction between the rod-like molecules. To generate the drops, we initially
perform NPT simulations close to the nematic-vapor coexistence region, allow the system to equilibrate
and subsequently induce a sudden volume expansion, followed with NVT simulations. The
resultant drops coexist with their vapor and are generally not spherical but elongated, have the rodlike
particles tangentially aligned at the surface and an overall nematic orientation along the main
axis of the drop. We find that the drop eccentricity increases with increasing molecular elongation,
κ. For small κ the nematic texture in the drop is bipolar with two surface defects, or boojums, maximizing
their distance along this same axis. For sufficiently high κ, the shape of the drop becomes
singular in the vicinity of the defects, and there is a crossover to an almost homogeneous texture; this
reflects a transition from a spheroidal to a spindle-like dro
Geometrical Control of Active Turbulence in Curved Topographies
We investigate the turbulent dynamics of a two-dimensional active nematic liquid crystal constrained to a curved surface. Using a combination of hydrodynamic and particle-based simulations, we demonstrate that the fundamental structural features of the fluid, such as the topological charge density, the defect number density, the nematic order parameter, and defect creation and annihilation rates, are approximately linear functions of the substrate Gaussian curvature, which then acts as a control parameter for the chaotic flow. Our theoretical predictions are then compared with experiments on microtubule-kinesin suspensions confined on toroidal droplets, finding excellent qualitative agreement.Theoretical Physic
Structural Properties of Thermoresponsive Poly(N-isopropylacrylamide)-poly(ethyleneglycol) Microgels
The application of RNA interference to treat disease is an important yet challenging concept in modern medicine. In particular, small interfering RNA (siRNA) have shown tremendous promise in the treatment of cancer. However, siRNA show poor pharmacological properties, which presents a major hurdle for effective disease treatment especially through intravenous delivery routes. In response to these shortcomings, a variety of nanoparticle carriers have emerged, which are designed to encapsulate, protect, and transport siRNA into diseased cells. To be effective as carrier vehicles, nanoparticles must overcome a series of biological hurdles throughout the course of delivery. As a result, one promising approach to siRNA carriers is dynamic versatile nanoparticles that can perform several in vivo functions.
Over the last several years, our research group has investigated hydrogel nanoparticles (nanogels) as candidate delivery vehicles for therapeutics, including siRNA. Throughout the course of our research, we have developed higher order architectures composed entirely of hydrogel components, where several different hydrogel chemistries may be isolated in unique compartments of a single construct. In this Account, we summarize a subset of our experiences in the design and application of nanogels in the context of drug delivery, summarizing the relevant characteristics for these materials as delivery vehicles for siRNA.
Through the layering of multiple, orthogonal chemistries in a nanogel structure, we can impart multiple functions to the materials. We consider nanogels as a platform technology, where each functional element of the particle may be independently tuned to optimize the particle for the desired application. For instance, we can modify the shell compartment of a vehicle for cell-specific targeting or evasion of the innate immune system, whereas other compartments may incorporate fluorescent probes or regulate the encapsulation and release of macromolecular therapeutics.
Proof-of-principle experiments have demonstrated the utility of multifunctional nanogels. For example, using a simple core/shell nanogel architecture, we have recently reported the delivery of siRNA to chemosensitize drug resistant ovarian cancer cells. Ongoing efforts have resulted in several advanced hydrogel structures, including biodegradable nanogels and multicompartment spheres. In parallel, our research group has studied other properties of the nanogels, including their behavior in confined environments and their ability to translocate through small pores
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