Search

Your search keyword '"Vagharchakian, Laurianne"' showing total 9 results
Start Over Author "Vagharchakian, Laurianne"
9 results on '"Vagharchakian, Laurianne"'

1. Capillary Bridge Formation and Breakage: A Test to Characterize Antiadhesive Surfaces

Author

Vagharchakian, Laurianne, Restagno, Frederic, and Leger, Liliane

Subjects
Condensed Matter - Soft Condensed Matter
Abstract

In order to characterize very weak adhesive surfaces, we have developed a quantitative test inspired by the Johnson, Kendall, and Roberts adhesion test for soft adhesives, which relies on the formation and then the rupture of a capillary bridge between the surface to be tested and a liquid bath. Both the shape and the kinetics of breakage of the capillary bridge for various coatings put into contact with liquids of various viscosities and surface tensions have been studied. Several pull off regimes can be distinguished. For low pull off velocities, a quasi-static regime is observed, well described by capillary equations and sensitive to the hysteresis of the contact angle of the fluid on the coating. Above a critical pull off velocity that depends on the fluid viscosity, a dynamic regime is observed, characterized by the formation of a flat pancake of fluid on the coating that recedes more slowly than the capillary bridge itself. After the breakage of the capillary bridge, a small drop can remain attached to the surface. The volume of this drop depends on the dynamical regime and is strongly affected by very small differences between the coatings. The aptitude of this test in characterizing very weakly adhesive surfaces is exemplified by a comparison between three different perfluorinated coatings.

Published
2009
Full Text
View/download PDF

2. Phase diagram for the adsorption of weak polyelectrolytes at a soft charged surface

Author

Vagharchakian, Laurianne, Desbat, Bernard, and Henon, Sylvie

Subjects
Adsorption -- Analysis, Thin films, Multilayered -- Structure, Thin films, Multilayered -- Chemical properties, Polyelectrolytes -- Chemical properties, Polyelectrolytes -- Structure, Chemicals, plastics and rubber industries
Abstract

The adsorption of polyelectrolytes at oppositely charged surfaces is experimentally studied. The polymer surface coverage, [Gamma], at equilibrium is measured by two reflectivity techniques, ellipsometry and polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS), as a function of the surface charge density [sigma], and of the polymer ionization degree, [alpha].

Published
2006

4. Adsorption de polyélectrolytes par une surface liquide chargée

Author

Vagharchakian, Laurianne, Laboratoire de Biorhéologie et Hydrodynamique Physico-chimique, Université Pierre et Marie Curie - Paris 6 (UPMC), Université Pierre et Marie Curie - Paris VI, Hénon Sylvie, and Hénon, Sylvie

Subjects
Ellipsometry, Poly(acide acrylique), Surface chargée, Spectrométrie Infrarouge, Ellipsométrie, Film de Langmuir, Charged Surface, Elasticity, Infrared Spectrometry, Langmuir Film, Polyélectrolyte faible, Weak Polyelectrolyte, Adsorption, [PHYS.PHYS.PHYS-DATA-AN] Physics [physics]/Physics [physics]/Data Analysis, Statistics and Probability [physics.data-an], Elasticité, [PHYS.PHYS.PHYS-DATA-AN]Physics [physics]/Physics [physics]/Data Analysis, Statistics and Probability [physics.data-an], Poly(acrylic acid)
Abstract

We have studied the adsorption of weak polyelectrolytes by a soft surface (Langmuir film) of opposite charge, as a function of the surface charge density Sigma and of the polymers charge fraction f. Different regimes have been evidenced (ellipsometry, IR spectroscopy). For small values of Sigma, the adsorbed polyelectrolytes neutralize the surface : Gamma=Sigma/f (number of adsorbed monomers per unit surface). For high values of Sigma, it costs less to continue the surface neutralization with counter-ions : Gamma~SigmaION/f with SigmaION~f^0.35. For weak f (~0.12), Gamma is significant and the mixed film properties (amphiphile+polyelectrolytes) are dominated by polymers. The surface pressure due to the polymers is proportional to Sigma^2. A regime change was observed in elasticity and overcompensation of the surface charge. It corresponds, according to recent theories, to a change in the polymer conformation, from flat to 3D. For higher f, the film properties are governed by the amphiphiles., L'étude porte sur l'adsorption de polyélectrolytes faibles par une surface liquide (film de Langmuir) de charge opposée. Nous avons quantifié l'adsorption des polyélectrolytes et étudié les propriétés de la couche adsorbée en fonction de f le taux charge des polyélectrolytes et de Sigma le nombre de charges portées par la surface par unité de surface. Différents régimes d'adsorption ont été mis en évidence (ellipsométrie, spectrométrie IR). Aux faibles densités surfaciques s

Published
2003

9. A Temporal Bottleneck in the Language Comprehension Network.

Author

Vagharchakian, Laurianne, Dehaene-Lambertz, Ghislaine, Pallier, Christophe, and Dehaene, Stanislas

Subjects
*COMPREHENSION, *NEUROPHYSIOLOGY, *BRAIN physiology, *ORAL communication, *WRITTEN communication, *FRONTAL lobe, *HUMAN information processing
Abstract

Humans can understand spoken or written sentences presented at extremely fast rates of∼400 wpm, far exceeding the normal speech rate (∼150 wpm). How does the brain cope with speeded language? And what processing bottlenecks eventually make language incomprehensible above a certain presentation rate?Weused time-resolved fMRI to probe the brain responses to spoken and written sentences presented at five compression rates, ranging from intelligible (60-100% of the natural duration) to challenging (40%) and unintelligible (20%). The results show that cortical areas differ sharply in their activation speed and amplitude. In modality-specific sensory areas, activation varies linearly with stimulus duration. However, a large modality-independent left-hemispheric language network, including the inferior frontal gyrus (pars orbitalis and triangularis) and the superior temporal sulcus, shows a remarkably time-invariant response, followed by a sudden collapse for unintelligible stimuli. Finally, linear and nonlinear responses, reflecting a greater effort as compression increases, are seen at various prefrontal and parietal sites. We show that these profiles fit with a simple model according to which the higher stages of language processing operate at a fixed speed and thus impose a temporal bottleneck on sentence comprehension. At presentation rates faster than this internal processing speed, incoming words must be buffered, and intelligibility vanishes when buffer storage and retrieval operations are saturated. Based on their temporal and amplitude profiles, buffer regions can be identified with the left inferior frontal/anterior insula, precentral cortex, and mesial frontal cortex. [ABSTRACT FROM AUTHOR]

Published
2012
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results