Osmotic Pressure and Phase Boundary Determination of Multiphase Systems by Analytical Ultracentrifugation

We present a novel method for measuring interbilayer forces in lamellar liquid crystals of amphiphilewater systems. In a centrifuge the gravitational effect is easily strong enough to produce clearly observable concentration gradients. During the experiment the concentration profile in the test-tube is monitored using NMR imaging of the deuterium quadrupole splitting in the lamellar phase, by temporarily transferring the sample into a NMR spectrometer. We also present a theoretical analysis of the experiment, where interactions dominate over entropy of mixing effects. For a system at sedimentation equilibrium one obtains a direct measurement of the interbilayer force, or equivalently chemical potential of the components over a substantial concentration range. It requires long times to obtain equilibrium in the centrifuge but very useful information about equilibrium and dynamic parameters is also obtained through an analysis of the sedimentation process. Experiments were performed on samples of a dilute lamellar phase of the non-ionic surfactant C 10 E 3 . After a few days of centrifugation a consistent concentration pattern was observed. At the bottom of the sample there appears a pure water-phase. The concentration profiles stabilize after a long centrifugation time. If they are related to the phase boundary the different profiles superimpose. This observation is consistent with the theory and the observation allows for a determination of how the chemical potentials vary with composition. The observed profiles are consistent with a dominating undulation force with a bilayer bending rigidity of 4.8-5.1 kT.

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“…An equivalent form of this equation was used in ref. 20. In analyzing the experiments one has the choice of using either eqn (4) or eqn (5).…”

Section: Equilibrium Centrifugation Of a Lamellar Phasementioning

confidence: 99%

Lamellar phase separation in a centrifugal field. A method for measuring interbilayer forces

et al. 2010

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“…Such development is crucial for the survival of this classical method, which even after more than 75 years of intense hydrodynamic research still offers room for the introduction of new experimental methods—multiphase osmotic pressure determination is just one recent example (Page et al 2008). A significant obstacle to innovation has been the dependence of the user community on a single ultracentrifuge platform, which requires feeding of light and electronics into the vacuum chamber of the ultracentrifuge.…”

Section: Discussionmentioning

confidence: 99%

The Open AUC Project

et al. 2009

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Progress in analytical ultracentrifugation (AUC) has been hindered by obstructions to hardware innovation and by software incompatibility. In this paper, we announce and outline the Open AUC Project. The goals of the Open AUC Project are to stimulate AUC innovation by improving instrumentation, detectors, acquisition and analysis software, and collaborative tools. These improvements are needed for the next generation of AUC-based research. The Open AUC Project combines on-going work from several different groups. A new base instrument is described, one that is designed from the ground up to be an analytical ultracentrifuge. This machine offers an open architecture, hardware standards, and application programming interfaces for detector developers. All software will use the GNU Public License to assure that intellectual property is available in open source format. The Open AUC strategy facilitates collaborations, encourages sharing, and eliminates the chronic impediments that have plagued AUC innovation for the last 20 years. This ultracentrifuge will be equipped with multiple and interchangeable optical tracks so that state-of-the-art electronics and improved detectors will be available for a variety of optical systems. The instrument will be complemented by a new rotor, enhanced data acquisition and analysis software, as well as collaboration software. Described here are the instrument, the modular software components, and a standardized database that will encourage and ease integration of data analysis and interpretation software.Electronic supplementary materialThe online version of this article (doi:10.1007/s00249-009-0438-9) contains supplementary material, which is available to authorized users.

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“…J can thus be converted to c by knowing the refractive index increment (∂n/∂c) of the sample. Page et al have used this technique to measure osmotic pressure in laponite-water binary mixtures [11]. This dispersion shows a transition between a dilute isotropic phase and a gel phase, the driving force of which is still under discussion [12][13][14][15].…”

Section: Osmotic Pressure Measurements In a Binary System By Analyticmentioning

confidence: 99%

Osmotic pressure in colloid science: clay dispersions, catanionics, polyelectrolyte complexes and polyelectrolyte multilayers

Carriere

Page

Dubois

et al. 2007

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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Osmotic pressure is a key parameter to understand the thermodynamics and the interactions in colloidal systems. We present here four examples to demonstrate the variety of information that can be extracted from it. The equation of state, i.e. the osmotic pressure versus concentration curve, could be established using analytical ultracentrifugation in binary clay-water mixtures. This method allows a quick and efficient determination of the phase boundaries, and the equation of state shows a good agreement with a Poisson-Boltzmann model. In ternary mixtures of water-anionic surfactant-cationic surfactant, phase separation with a different partitioning of the surfactant in both phases could be evidenced. In the monophasic domains, the surface charge density of the objects could be estimated from the equation of state. In mixtures of polyelectrolytes, different behaviours of the osmotic pressure with respect to the composition could be interpreted in terms of microphase separation, or homogeneous complexation, depending on the composition in polyelectrolyte. Finally, in a colloidal dispersion of spheres coated with polyelectrolytes, three different colloid-colloid interaction regimes could be identified, depending if the polyelectrolyte shells are collapsed onto the colloid, swollen, or non-overlapping. These examples illustrate the variety of information that osmotic pressure can give in a large variety of situations, making this technique an indispensable tool for the physico-chemist.

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Osmotic Pressure and Phase Boundary Determination of Multiphase Systems by Analytical Ultracentrifugation

Cited by 20 publications

References 66 publications

Lamellar phase separation in a centrifugal field. A method for measuring interbilayer forces

Lamellar phase separation in a centrifugal field. A method for measuring interbilayer forces

The Open AUC Project

Osmotic pressure in colloid science: clay dispersions, catanionics, polyelectrolyte complexes and polyelectrolyte multilayers

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