Electronic Supplementary Material
1. Rheology of pure clay suspensions
Montmorillonite (MMT) suspensions with a range of clay and salt concentrations were
observed prior to any rheology experiments. Dilute and free flowing samples were
considered as sols and solid-like samples were regarded as gels. Only the viscous samples on
the boundary of the sol / gel transition were examined using oscillatory viscometry
experiments. The following criteria were used to identify a gel: (1) G’ is obviously higher
than G’’ and (2) G’ does not vary much over the whole frequency range. The oscillation
experiments gave the moduli over a range of frequencies. At low and medium salt
concentrations, 10-4 to 10-2 M NaCl, the repulsive gels have G’ values below 100 Pa, as
shown in Figure 1 (b-d). In the wide attractive gel region at high salt concentration, 10 -1 M
NaCl, samples possess relatively high G’ values: a 2 wt% gel has a G’ over 100 Pa (Figure 1
(a)). Comparing the 2.8 wt% samples at high (10-1 M NaCl) and medium (10-2 M NaCl) salt
concentrations, a liquid was transformed to a gel. The addition of salt decreased the double
layer repulsion and the van der Waals attraction became dominant, which yielded a
relatively strong gel.
105
104
Moduli (Pa)
103
102
101
100
G' MMT 2 wt%
G'' MMT 2 wt%
G' MMT 2.5 wt%
G'' MMT 2.5 wt%
G' MMT 6.7 wt%
G'' MMT 6.7 wt%
10-1
10-2
10-3
10-2
10-1
100
101
Frequency (Hz)
(a)
103
102
101
Modulus (Pa)
100
10-1
10-2
10-3
G' MMT 2.8 wt%
G'' MMT 2.8 wt%
G' MMT 3.5 wt%
G'' MMT 3.5 wt%
G' MMT 4 wt%
G'' MMT 4 wt%
10-4
10-5
10-6
10-2
(b)
10-1
100
Frequency (Hz)
101
103
102
Moduli (Pa)
101
100
10-1
10-2
G' MMT 3.4 wt%
G'' MMT 3.4 wt%
10-3
10-2
10-1
100
101
Frequency (Hz)
(c)
103
102
Modulus (Pa)
101
100
10-1
10-2
G' MMT 3.4 wt%
G'' MMT 3.4 wt%
10-3
10-2
(d)
10-1
100
101
Frequency (Hz)
Figure 1. Oscillation experiments: Moduli against frequency of MMT suspensions with (a)
0.1 M (b) 0.01 M (c) 0.001 M (d) 0.0001 M NaCl.
2. Rheology of surfactant treated clay
The effect of adsorption of the surfactant M1000 on G’ and G’’ is significant at medium and
low salt concentrations. MMT suspensions start to behave like a gel above 3 wt% clay at 10 -2
and 10-3 M NaCl without M1000. At a surface coverage equivalent to 0.4 CEC, M1000
transformed even 5.6 wt% clay samples to a liquid, with comparably low G’ and G’’,
increasing over frequency at both concentrations, as shown in Figure 2 (b) and (c). At very
low salt concentration (10-4 M NaCl), where repulsion between particles is strong, the effect
of M1000 is not obvious. A weak gel is formed at all clay concentrations tested, from 4 wt%
to 6.1 wt%. The values of G’ and G’’ increase with rising clay concentration but the increase
is small considering the increase in clay concentration. The G’ values of 5.5 wt% and 6.1 wt%
clay are similar to that of a 3.6 wt% MMT gel without M1000. Therefore, M1000 has an
effect to reduce the moduli of the gel, but not yet transform it to a liquid. At high salt
concentration, both the 4 and 6.7 wt % gels possess high moduli. The effect of M1000 on
the moduli and phase diagram is more pronounced at medium salt concentrations.
105
Modulus (Pa)
104
103
102
G' MMT 4 wt%
G'' MMT 4 wt%
G' MMT 6.7wt%
G'' MMT 6.7wt%
101
100
10-2
10-1
100
101
Frequency (Hz)
(a)
101
Modulus (Pa)
G' MMT 5.6 wt%
G'' MMT 5.6 wt%
100
10-1
10-2
(b)
10-1
100
Frequency (Hz)
101
102
G' MMT 5.6 wt%
G'' MMT 5.6 wt%
Modulus (Pa)
101
100
10-1
10-2
10-1
100
101
Frequency (Hz)
(c)
102
Modulus (Pa)
G' MMT 4 wt%
G'' MMT 4 wt%
G' MMT 5.6 wt%
G'' MMT 5.6 wt%
G' MMT 6.1 wt%
G'' MMT 6.1 wt%
101
100
10-2
(d)
10-1
100
101
Frequency (Hz)
Figure 2. Rheological measurements: Moduli against frequency of M1000 modified MMT
suspensions with (a) 0.1 M (b) 0.01 M (c) 0.001 M (d) 0.0001 M NaCl.
3. Polarising microscopy
Dried bare clay suspensions were observed by polarising microscopy. The string-like
structures in the bare clay sample are highly birefringent as shown in Figure 3 (a). A
polarising microscope image of the structure obtained after drying a clay sample treated
with M1000 (Figure 3 (b)) is also shown and no large scale structures are seen. However,
some bright specs are visible, indicating the presence of stacks of clay particles.
Figure 3. Polarising microscopy images of dried 1 wt% MMT aqueous suspensions at 0.0001
M NaCl and (a) no M1000; (b) 0.4 CEC M1000.