1. No category

MICRO-RHEOLOGY BY NMR: Unveiling the non-Newtonian
properties of liquids by MGSE spectroscopy
Janez
1
Stepišnik ,
1 University
Aleš
1
Mohorič ,
Igor
1
Serša ,
Carlos
2
Mattea ,
2
Stapf
Siegfried
of Ljubljana, FMF, Institute „Jožef Stefan“, Ljubljana, Slovenia, and
2 Technical
Viscosity spectra of fluids
Passive micro-rheology
Micro-rheology is a technique used to measure the
rheological properties of a medium, such as microviscosity, via the measurement of the trajectory of a
flow tracer. Passive micro-rheology uses the thermal
energy (kT) to move the tracers, which trajectories
are measured optically either by microscopy or by
diffusing-wave spectroscopy in order to yield the
viscosity according to the generalized EinsteinSmoluchowsky relation1
and Franci
1,2
Bajd
University, Ilmenau, Germany
Measuring system-NMR mouse
VAS of a variety of liquids and their mixtures was
measured to get the viscosity spectra according to
formula h(w)=h0 D(0)/D(w), in which h0 is declared
fluid viscosity:
Glycerol
26oC
1
Re  (w ) =
D(w ),
kT
which links the mobility spectrum and the velocity
autocorrelation spectrum (VAS)

D(w ) =  v x (t )v x (0 ) cos(w t ) dt .
Newtonian
0
Modulated gradient spin-echo
Water
T= 24oC
echo2,3
The NMR method of modulated gradient spin
(MGSE) is a tool of magnetic resonance, which
provides VAS directly by modulating the phase of spin
bearing particles in the inhomogeneous magnetic
field. By taking into account Stokes law
Newtonian
50 v% glycerol/water mixture
T= 24oC
1
=
,
6p r h
the MGSE method provides also the viscosity
spectrum according to
1
D(w ) ~
.
h (w )
Toluene
T=24oC
Ethanol
T=24oC
CPMG train of p-radiofrequency (RF) pulses applied
together with the fixed gradient, G,
VAS of water/glycerol mixures measured by using two
different NMR devices
which periodically modulates the spin phases
discordance, is MGSE technique that gives the spin
echo decay,
References
3.5
Volume fraction
100 MHz NMR
G.t =const
Gmax=5.9 T/m
3.0
75
H2 0
33
H2 0
80
H2 0
50
H2 0
66
H2 0
2.0
1.5
D
x10 9 m2 s 1
2.5
0 H2 0
NMR mouse
18.7 MHz
G=21.7 T/m
1.0
0.5
0.0
in which the attenuation of N-th echo is
t
8 G
 (w m ) =
 D(w m ) 2 2 t ; t = Nt .
T2
p wm
2
www.PosterPresentations.com
2
4
6
8
kHz
2
Here, T2 is the spin relaxation, t is the spacing
between RF-pulses and wm=p/t is the modulation
frequency. By changing t we can obtain D(w) at
different modulation frequencies.
RESEARCH POSTER PRESENTATION DESIGN © 2012
0
Contact
Janez Stepišnik, University of Ljubljana, FMF,
Jadranska 19, 1000 Ljubljana, Slovenia,
[email protected]
10
[1] R. Kubo, The fluctuation-dissipation
theorem, Rep. Prog. Phys. 29, 1966, 25584.
[2] J. Stepišnik, Analysis of NMR selfdiffusion measurements by density matrix
calculation, Physica 104B (1981) 350- 361.
[3] P.T. Callaghan, J. Stepišnik,
Generalized analysis of motion using
magnetic field gradients, Advances in
Magnetic and Optical Resonance ed.
Waren S. Waren, Vol. 19, p. 324-397,
(1996), Academic Press.
[4] J. Stepišnik, S. Lasič, A. Mohorič, I.
Serša, A. Sepe, Spectral characterization
of diffusion in porous media by the
modulated gradient spin echo with CPMG
sequence, J. Magn. Reson., 182, 195-199
(2006).
[5] J. Stepišnik, A. Mohorič, C. Mattea, S.
Stapf, I. Serša, Velocity autocorrelation
spectra in molten polymer measured by
NMR modulated gradient spin-echo,
EuroPhysics Letters, 106 (2014) 27007.