Shear Elasticity and Surface Tension
The access to low-frequency shear elasticity is facilitated by minimizing any process
that alters the stress transmission. Degassed fluids and wetting protocol enable a
better stress transfer from the surface to the sample compared to conventional
measurements. It is however important to point out that the increased moduli values
are not due to interfacial surface tension (Johnston et al. 2013). The surface tension
(peripheral (air/fluid) or surface (fluid/substrate)) is supposed to not change during
the oscillatory motion. These conditions are fulfilled when the sample volume is kept
constant during the shear measurement [complete and homogeneous (without bubbles) filling of the gap, rigorous parallelism of the surfaces, and close equilibrium
conditions (low strain amplitudes)]. The simultaneous measurement of the normal
0,1
0
–0,1
0
10
3
10
2
10
1
10
0
10
–1
ω(rad/s)
ω(rad/s)
ω(rad/s)
Shear elastic plateau
Noisy signals
a
c
b
G ′
G ′′
G ′
G ′
G ′′
G ′′
G′,G′′(Pa)
G′,G′′(Pa)
G′,G′′(Pa)
time
10
0
10
3
10
2
10
1
10
0
10
3
10
2
10
1
10
0
10
–1
10
0
10
–1
10
0
10
20
30
40
t(s)
–0,05
0,05
Shear vs Normal forces
Normal force (volts)
Shear Strain Force (volts)
0
Fig. 9 (a) Photograph of the alumina fixtures (surface roughness <1 μm, parallelism <10
À3 rad
(zero-contact method via normal force and no-light transmission), diameter 40 mm). (b) Shear strain
force (red data points) and normal forces (green data points) are simultaneously measured during the
oscillatory shear strain motion using two multimeters connected to the shear strain and the normal
force transducers (ARES device, ω = 0.1 Hz, γ = 5%, e = 0.1 mm, liquid water at room
temperature). (c) Evolution of the viscoelastic signal with time: the liquid interaction with surface
is progressive (migration of bubbles, interaction with surface). Data points recorded on a polymer
melt at sub-millimeter thickness using alumina surface (total wetting conditions) - P. Kahl, PhD
thesis (https://www.theses.fr/2016LEMA1002.pdf).
262
L. Noirez
The access to low-frequency shear elasticity is facilitated by minimizing any process
that alters the stress transmission. Degassed fluids and wetting protocol enable a
better stress transfer from the surface to the sample compared to conventional
measurements. It is however important to point out that the increased moduli values
are not due to interfacial surface tension (Johnston et al. 2013). The surface tension
(peripheral (air/fluid) or surface (fluid/substrate)) is supposed to not change during
the oscillatory motion. These conditions are fulfilled when the sample volume is kept
constant during the shear measurement [complete and homogeneous (without bubbles) filling of the gap, rigorous parallelism of the surfaces, and close equilibrium
conditions (low strain amplitudes)]. The simultaneous measurement of the normal
0,1
0
–0,1
0
10
3
10
2
10
1
10
0
10
–1
ω(rad/s)
ω(rad/s)
ω(rad/s)
Shear elastic plateau
Noisy signals
a
c
b
G ′
G ′′
G ′
G ′
G ′′
G ′′
G′,G′′(Pa)
G′,G′′(Pa)
G′,G′′(Pa)
time
10
0
10
3
10
2
10
1
10
0
10
3
10
2
10
1
10
0
10
–1
10
0
10
–1
10
0
10
20
30
40
t(s)
–0,05
0,05
Shear vs Normal forces
Normal force (volts)
Shear Strain Force (volts)
0
Fig. 9 (a) Photograph of the alumina fixtures (surface roughness <1 μm, parallelism <10
À3 rad
(zero-contact method via normal force and no-light transmission), diameter 40 mm). (b) Shear strain
force (red data points) and normal forces (green data points) are simultaneously measured during the
oscillatory shear strain motion using two multimeters connected to the shear strain and the normal
force transducers (ARES device, ω = 0.1 Hz, γ = 5%, e = 0.1 mm, liquid water at room
temperature). (c) Evolution of the viscoelastic signal with time: the liquid interaction with surface
is progressive (migration of bubbles, interaction with surface). Data points recorded on a polymer
melt at sub-millimeter thickness using alumina surface (total wetting conditions) - P. Kahl, PhD
thesis (https://www.theses.fr/2016LEMA1002.pdf).
262
L. Noirez