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DTSTAMP:20260414T205326
DTSTART:20150121T110000
SEQUENCE:0
TRANSP:OPAQUE
DTEND:20150121T123000
URL:https://murmitoyen.com/events/vanille/udem/detail/497256
LOCATION:Université de Montréal - Pavillon J.-Armand-Bombardier\, 5155\, 
 chemin de la rampe \, Montréal\, QC\, Canada\, H3T 2B2
SUMMARY:Conférence CRMAA avec le Professeur Joseph Zasadzinski *** ANNULÉ
 E
DESCRIPTION:*** Attention\, en raison d'une maladie\, le Professeur Zasadzi
 nski doit annuler sa visite au Département de chimie ce mercredi 21 janvi
 er. Sa conférence sera reportée à une date ultérieure\, encore indéte
 rminée. ***Titre : Surface Viscosity: What it Tells Us about Order and Or
 ganization in Lipid Monolayers.Endroit : Pavillon J.A.-Bombardier\, salle 
 1035 à 11 hHôte : William SkeneCette conférence sera prononcée par le
  professeur Joseph Zasadzinski du Département d'ingénierie chimique et s
 cience des matériaux au sein de l'University of Minnesota. Elle est comma
 nditée par le Centre de recherche sur les materiaux auto-assemblés (CRMA
 A) et sera donnée en anglais.Résumé : We use photolithography to micro
 fabricate ferromagnetic disks 1 micron in height and 20-100 microns in dia
 meter\, which contain a thin (100 nm) film of magnetic metal and a thin la
 yer of gold. We can float these disks on a Langmuir trough and apply known
  torques to oscillate the disks to evaluate the surface viscosity and elas
 ticity of lipid monolayers. As an alternative\, we rotate 5 micron long\, 
 300 nm diameter nickel wires in a magnetic field at the air-water interfac
 e. The small size of the disks and wires gives us sensitivity to small val
 ues of the surface viscosity that were impossible to access with macroscop
 ic probes.  We find that a surprising number of monolayers exhibit a Newt
 onian response with a constant surface viscosity over a range of surface p
 ressures.  We can identify second order phase transitions difficult to fi
 nd with isotherms or X-ray diffraction methods. The composition dependence
  of surface viscosity is also surprising. Adding small fractions of choles
 terol decreases the interfacial viscosity of dipalmitoylphosphatidylcholin
 e (DPPC) monolayers by an order of magnitude per wt%.  Grazing incidence 
 X-ray diffraction shows that cholesterol at these small fractions does not
  mix ideally with DPPC\, but rather induces nano-phase separated structure
 s of an ordered\, primarily DPPC phase bordered by a line-active\, disorde
 red\, mixed DPPC-cholesterol phase. We propose that the free area in the c
 lassic Cohen and Turnbull model of viscosity is inversely proportional to 
 the number of molecules in the coherence area\, or product of the two cohe
 rence lengths.  Cholesterol significantly reduces the coherence area of t
 he crystals as well as the interfacial viscosity. Using this free area col
 lapses the surface viscosity data for all surface pressures and cholestero
 l fractions to a universal logarithmic relation.  The extent of molecular
  coherence appears to be a fundamental factor in determining surface visco
 sity in ordered monolayers.Information supplémentaireAnnonce PDF de la co
 nférence 
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