A Study of the Effective Interfacial Tension Between Miscible Fluids by Spinning Drop Tensiometer and Microfluidics

A miscible system is a system in which two fluids can completely dissolve in one another. A sharp concentration gradient can be observed in miscible systems. We studied the concentration gradient or miscible interface between IBA (isobutyric acid) and water, a miscible system near a consulate point (close to the system’s upper critical solution temperature [UCST]). The original hypothesis was that the sharp concentration gradient of IBA/water was due to barodiffusion, a diffusion effect driven by pressure. We tested this hypothesis by studying IBA/water at five different rotation rates and three different temperatures. At 20 oC, increasing rotation acceleration from 6000 to 15000 rpm resulted in increasing dissolution rate, thus demonstrating that barodiffusion did not cause the sharp concentration gradient. However, the rotation acceleration did not affect the dissolution rate at higher temperatures. Increasing the temperature from 20 oC to 27 oC caused EIT (effective interfacial tension) to decrease. Since surfactants generally lower the interfacial tension between immiscible fluids, we tested an anionic and cationic surfactant and evaluated how its concentration within cmc (critical micelle concentration) affected the EIT of a miscible system. With increasing surfactant concentration, the EITs generally decreased. At 20 oC, the ITs of IBA/water systems using surfactants were slightly higher than IBA/water systems without surfactant, which is unusual. At 30 oC, increasing and decreasing the rotation rate resulted in the averaged EIT and radii getting higher. We had some unusual behavior in the microfluidic device that we did not observe in the SDT (spinning drop tensiometer) because of mixing and the microsystem was done on a smaller scale so that larger effects from surface tension occurred, but some behaviors were the same, thus indicating that the behavior of the IBA/water system was not solely due to the instrument used

Studying diffusion of partially miscible and systems near their consolute point by laser line deflection

We propose that miscible systems can be divided into three types: miscible in all proportions, partially miscible but not near a consulate point, and a system with a consulate point. We studied two types of miscible systems by laser line deflection (LLD) in order to understand behavior observed in a spinning drop tensiometer; namely, that some miscible drops became diffuse over time while others maintained a sharp concentration profile as the drop dissolved. We previously studied a miscible system, dodecyl acrylate-poly(dodecyl acrylate) using LLD and found that the system relaxed as expected with a concentration-independent diffusion coefficient. We used LLD to study two other miscible systems: 1-butanol-water, and isobutyric acid-water above the latter\u27s upper critical solution temperature (UCST). The transition zone boundaries in the 1-butanol and water system propagated into the component that was not saturated with the other component. The boundaries propagated with a t0.09. When an equilibrated IBA-water system was heated above its UCST (26 °C), the transition zone propagated into the IBA-rich region. The propagation exhibited t0.06 behavior. The propagation of transition zone boundaries showed the same qualitative behavior under 1g acceleration in the LLD experiments as under the higher acceleration in the tensiometer so it is not necessary to invoke barodiffusion as the cause of the behavior although it may still affect the rate of diffusion. © 2008 Elsevier Ltd. All rights reserved

Instabilities of Diffuse Interfaces

Composition gradients in miscible liquids can create volume forces resulting in various interfacial phenomena. Experimental observations of these phenomena are related to some difficulties because they are transient, sufficiently weak and can be hidden by gravity driven flows. As a consequence, the question about their existence and about adequate mathematical models is not yet completely elucidated. In this work we present some experimental evidences of interfacial phenomena in miscible liquids and numerical simulations of miscible drops and diffuse interfaces

Effect of pseudo-gravitational acceleration on the dissolution rate of miscible drops

The effect of pseudo-gravitational acceleration on the dissolution process of two phase miscible systems has been investigated at high acceleration values using a spinning drop tensiometer with three systems: 1-butanol/water, isobutyric acid/water, and triethylamine/water. We concluded that the dissolution process involves at least three different transport phenomena: diffusion, barodiffusion, and gravitational (buoyancy-driven) convection. The last two phenomena are significantly affected by the centrifugal acceleration acting at the interface between the two fluids, and the coupling with the geometry of the dissolving drop leads to a change of the mass flux during the course of the dissolution process

Finding social dilemma: West of Babel, not east of Eden

Spontaneous order, Social dilemma, Social networks, Emergent theorizing, Gordon Tullock, James Buchanan, B4, D6, D7,