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form was found not to remain 100% complete, as observed in
1
2,20
previous reports.
Fig. 5 demonstrates that the viscosity is switch-
25
able. Although the Krafft point of C CNa is 71 1C, we also obtained
18
Scheme 2 The reversible reaction in the aqueous solution of sodium stearate
switchable viscosity with an aqueous solution of C CNa and tetra-
with CO
2
.
18
butylammonium bromide (TBAB) at 60 1C (Fig. S2, ESI†). The
addition of TBAB is known to decrease the Krafft point of sodium
but after a maximum, further increases in DMAE concentration carboxylate soaps and increase their solubility in aqueous solution.26
diminish the zero-shear viscosity, probably because of the formation
2
In summary, two kinds of CO -responsive solutions of
2
0
0
of branched micelles. Another additive, N,N,N ,N -tetramethyl-1,4- switchable viscosity have been investigated, consisting of either
1
9,20
butanediamine (TMDAB),
the aqueous solution with C18SNa. The viscosity was reversibly switchable water additive DMAE or TMDAB, or (b) a switchable
controlled by addition and removal of CO . The viscosity reaches a anionic surfactant C CNa with NaNO or TBAB. Addition or
maximum when the TMDAB : surfactant molar ratio is 1 : 2.
In order to achieve the opposite switchable viscosity (high and reversible changes in the viscosity.
was used for switching the viscosity of an aqueous solution of (a) normal surfactant C SNa and a
18
2
1
8
3
removal of CO2 into/from these solutions induced dramatic
when CO
which also can form worm-like micelles.
sodium salts also are CO
the absence of CO , such a surfactant is in its anionic form and support. P.G.J. also thanks the Killam Foundation/Canada
capable of forming micelles or stabilizing emulsions. Addition of Council of the Arts for a fellowship.
CO converts the fatty acid into its neutral form, which is
2
is absent), we tried fatty acid salts with long carbon tails
We thank the National Sciences and Engineering Research
3,23
In fact, fatty acid Council, the Ontario Research Chairs Program (Cunningham)
15,16
2
-triggered switchable surfactants.
In and the Canada Research Chairs Program (Jessop) for financial
2
2
incapable of stabilizing emulsions and has very poor aqueous
Notes and references
solubility. Removal of CO reverses the reaction (Scheme 2). We
2
1
2
C. A. Dreiss, Soft Matter, 2007, 3, 956.
Y. Han, Z. Chu, H. Sun, Z. Li and Y. Feng, RSC Adv., 2012, 2, 3396.
propose that an aqueous solution of sodium stearate (C18CNa)
and NaNO
3
should form switchable worm-like micelles, because
are efficient
3 Z. Chu and Y. Feng, Langmuir, 2012, 28, 1175.
Z. Chu and Y. Feng, Chem. Commun., 2011, 47, 7191.
5 Y. Han, Y. Feng, H. Sun, Z. Li, Y. Han and H. Wang, J. Phys. Chem. B,
011, 115, 6893.
4
the long carbon tail of C18CNa and addition of NaNO
in promoting micellar growth.
An aqueous solution of C18CNa (200 mM) and NaNO
3
5,24
2
3
(200 mM)
6 Z. Chu, Y. Feng, H. Sun, Z. Li, X. Song, Y. Han and H. Wang, Soft
Matter, 2011, 7, 4485.
at 80 1C had switchable viscosity (Fig. 5). Its zero-shear viscosity was
measured and is shown in Table S2 (ESI†). The highest zero-shear
viscosity measured is 12 400 mPa s without CO . After CO was
7
8
Z. Chu and Y. Feng, Soft Matter, 2010, 6, 6065.
(a) J. P. Rothstein, Strong flows of viscoelastic wormlike micelle
solutions, in Annual Rheology Reviews, ed. D. M. Binding and
K. Walters, The British Society of Rheology, Aberystwyth, Wales,
UK, 2009; (b) D. V. S. Gupta and B. Hughes, Unconventional
Fracturing Fluids in Proceedings of the Technical Workshops for
the Hydraulic Fracturing Study: Chemical & Analytical Methods, EPA
2
2
bubbled through the solution for 10 min at 80 1C, the mixture
became milky and had a much lower zero-shear viscosity of
2
.0 mPa s. In this stage, the aqueous solution became a suspension
of particles having an average particle size of 946 nm and a zeta-
potential of ꢀ23 mV. After N was sparged through the suspension
6
00/R-11/066, US, 2011.
9
H. Sakai, Y. Orihara, H. Kodashima, A. Matsumura, T. Ohkubo,
2
K. Tsuchiya and M. Abe, J. Am. Chem. Soc., 2005, 127, 13454.
for about 40 min at 80 1C, the viscosity increased back to 10 Z. Chu and Y. Feng, Chem. Commun., 2010, 46, 9028.
1
1
1
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1
2 360 mPa s. The reason why the maximum viscosity decreased
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1
1
4 J. R. Harjani, C. Liang and P. G. Jessop, J. Org. Chem., 2011, 76, 1683.
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Fig. 5 The switchable zero-shear viscosity of C18CNa (200 mM) and NaNO
200 mM) in water solution controlled by CO at 80 1C.
3
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(
2
This journal is c The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 2655--2657 2657