Pierre Levitz du laboratoire Physique
 de 
la 
Matière
 Condensée présentera un séminaire le 9 février 2011 à 14h30 (1^er étage, bâtiment F, porte 113) intitulé :

Multiscale
 dynamics 
of 
confined 
fluid 
in 
colloidal 
and
 porous 
media


Résumé

Porous
 materials,
 concentrated
 colloidal
 suspensions
 are
 example
 of
 confining
 systems
 developing
 large
 specific
 surface,
 presenting
 a
 rich
 variety
 of
 shapes
 and
 exhibiting
 complex
 and
 irregular
 morphologies
 on
 a
 large
 length‐scale.
 Such
 a
 confinement
 strongly
 influences
 the
 molecular
 dynamics
 of
 embedded
 fluids.
 Two
 distinct
 and
 successive
 confined
 dynamics
 are 
generally 
considered 
in 
such 
systems : 
first, 
the 
fluid 
dynamics 
near 
the 
interface, 
second,
 the
 long 
range 
exploration 
of 
the 
pore 
network.

A
 coarse
 grain
 picture
 of
 the
 fluid
 dynamics
 near
 a
 surface
 can
 be
 considered
 as
 an
 intermittence
 of
 adsorption
 steps
 and
 bulk
 relocations
 from
 one
 point
 to
 another
 point
 of
 the
 interface.
 Adsorption
 statistics
 such
 as
 the
 adsorption
 time
 distribution
 and
 its
 first
 moment
 reflect
 the
 degree
 of
 interaction
 of
 the
 molecule
 with
 the
 colloidal
 interface.
 The
 relocation
 statistics
 strongly
 depends
 on
 the
 shape
 of
 the
 colloidal
 particle,
 the
 surface
 forces 
and 
the 
bulk 
confinement. 
In
 the 
first 
part 
of 
this 
talk, 
we 
analyze 
some 
properties 
of
 this
 intermittent
 dynamics
 (ID)
 for
 various
 colloidal
 interfacial
 geometries [1] [2].
 Direct
 comparisons 
with 
recent 
Molecular 
Dynamics 
simulations [3] 
are 
performed 
in 
relation
 with
 the
 nature
 of 
the 
geometrical 
confinement 
and 
the 
degree
 of 
interaction 
between 
the 
fluid 
and
 the
 interface.
 We
 also
 present
 an
 experimental
 study
 of
 the
 ID,
 using
 NMR
 relaxometry,
 for
 various
 porous
 solids
 or
 colloidal
 systems
 (Vycor
 glass [4],
 plaster
 pastes [5],
 flat
 colloidal
 clay
 particles [6], 
long 
and 
stiff 
nanometric 
strands [7]).



 Large
 iteration
 of 
the 
intermittent
 dynamics 
allows 
exploring
 the 
long 
range 
organization
 of
 the
 colloidal
 and/or
 porous
 matrix.
 However,
 most
 of
 natural
 or
 manufactured
 porous
 materials
 develop
 a
 complex
 hierarchical
 structure.
 It
 is
 then
 important
 to
 characterize
 in
 parallel
 the 
geometrical 
and 
the 
transport 
properties
 in 
the 
intermediate 
length 
scales, 
filling
 the
 gap
 from
 nano
 to
 micro
 scales.
 In
 this
 respect,
 we
 present
 some
 recent
 3D
 structural
 analysis
 using 
imaging 
techniques [8] 
such 
as 
X 
rays 
microtomography, 
or 
X 
rays 
microscopy
 and
 carried
 out
 on
 various
 hierarchical
 colloidal
 systems
 or
 pore
 network.
 We
 use
 these
 3D
 experimental
 configurations 
and 
a 
generalization
 of 
the 
intermittent 
dynamics 
to 
analyze
 the
 molecular
 exchange
 dynamics
 between
 different
 levels
 of
 pore
 organization.
 Comparison
 with
 experimental 
data 
from T₂‐T₂
 correlation
 spectroscopy 
is 
then 
provided.