171 research outputs found
A microfluidic-multiwell platform for rapid phase mapping of surfactant solutions
Measurement of the phase behavior and (meta)stability of liquid formulations, including surfactant solutions, is required for the understanding of mixture thermodynamics, as well as their practical utilization. We report a microfluidic platform with a stepped temperature profile, imposed by a dual Peltier module, connected to an automated multiwell plate injector and optical setup, for rapid solution phase mapping. The measurement protocol is defined by the temperature step ĪT ā” T1 ā T2 (ā²100 āC), volumetric flow rate Q ā” ĪV/Īt (ā²50 Ī¼l/min), which implicitly set the thermal gradient ĪT/Īt (ā0.1ā50 āC/min), and measurement time (which must exceed the intrinsic timescale of the relevant phase transformation). Furthermore, U-shaped microchannels can assess the reversibility of such transformations, yielding a facile measurement of the metastable zone width of the phase diagram. By contrast with traditional approaches, the platform precisely controls the cooling and heating rates by tuning the flow rate, and the absolute temperature excursion by the hot and cold thermal profile, which remain stationary during operation, thus allowing the sequential and reproducible screening of large sample arrays. As a model system, we examined the transition from the micellar (L1) to the liquid crystalline lamellar phase (LĪ±), upon cooling, of aqueous solutions of sodium linear alkylbenzene sulfonate, a biodegradable anionic surfactant extensively employed in industry. Our findings are validated with quiescent optical microscopy and small angle neutron scattering data
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Dynamics of long gas bubbles rising in a vertical tube in a cocurrent liquid flow
Ā© 2019 American Physical Society. When a confined long gas bubble rises in a vertical tube in a cocurrent liquid flow, its translational velocity is the result of both buoyancy and mean motion of the liquid. A thin film of liquid is formed on the tube wall and its thickness is determined by the interplay of viscous, inertial, capillary and buoyancy effects, as defined by the values of the Bond number (Boā”ĻgR2/Ļ with Ļ being the liquid density, g the gravitational acceleration, R the tube radius, and Ļ the surface tension), capillary number (Cabā”Ī¼Ub/Ļ with Ub being the bubble velocity and Ī¼ the liquid dynamic viscosity), and Reynolds number (Rebā”2ĻUbR/Ī¼). We perform experiments and numerical simulations to investigate systematically the effect of buoyancy (Bo=0-5) on the shape and velocity of the bubble and on the thickness of the liquid film for Cab=10-3-10-1 and Reb=10-2-103. A theoretical model, based on an extension of Bretherton's lubrication theory, is developed and utilized for parametric analyses; its predictions compare well with the experimental and numerical data. This study shows that buoyancy effects on bubbles rising in a cocurrent liquid flow make the liquid film thicker and the bubble rise faster, when compared to the negligible gravity case. In particular, gravitational forces impact considerably the bubble dynamics already when B
Ultrahigh-Field Hole Cyclotron Resonance Absorption in InMnAs Films
We have carried out an ultrahigh-field cyclotron resonance study of p-type
In1-xMnxAs films, with Mn composition x ranging from 0% to 2.5%, grown on GaAs
by low-temperature molecular-beam epitaxy. Pulsed magnetic fields up to 500 T
were used to make cyclotron resonance observable in these low-mobility samples.
The clear observation of hole cyclotron resonance is direct evidence of the
existence of a large number of itinerant, effective-mass-type holes rather than
localized d-like holes. It further suggests that the p-d exchange mechanism is
more favorable than the double exchange mechanism in this narrow gap InAs-based
dilute magnetic semiconductor. In addition to the fundamental heavy-hole and
light-hole cyclotron resonance absorption appearing near the
high-magnetic-field quantum limit, we observed many inter-Landau-level
absorption bands whose transition probabilities are stronglydependent on the
sense of circular polarization of the incident light.Comment: 8 pages, 10 Postscript figure
Bacterial Biofilm Material Properties Enable Removal and Transfer by Capillary Peeling
Biofilms, surfaceāattached communities of bacterial cells, are a concern in health and in industrial operations because of persistent infections, clogging of flows, and surface fouling. Extracellular matrices provide mechanical protection to biofilmādwelling cells as well as protection from chemical insults, including antibiotics. Understanding how biofilm material properties arise from constituent matrix components and how these properties change in different environments is crucial for designing biofilm removal strategies. Here, using rheological characterization and surface analyses of Vibrio cholerae biofilms, it is discovered how extracellular polysaccharides, proteins, and cells function together to define biofilm mechanical and interfacial properties. Using insight gained from our measurements, a facile capillary peeling technology is developed to remove biofilms from surfaces or to transfer intact biofilms from one surface to another. It is shown that the findings are applicable to other biofilmāforming bacterial species and to multiple surfaces. Thus, the technology and the understanding that have been developed could potentially be employed to characterize and/or treat biofilmārelated infections and industrial biofouling problems
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