conference papers
Journal ofApplied
Crystallography
ISSN 0021-8898

Shear-induced structural transition in the lamellar
phase of the C16E7/D2O system. Time evolution ofsmall-angle neutron scattering at a constant shearrate

Received 16 August 2006
Accepted 21 March 2007

Kyoko Miyazaki, Yuriko Kosaka, Youhei Kawabata, Shigeyuki Komura and Tadashi
Kato*
Department of Chemistry, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachioji, Tokyo 192-0397, Japan.
Correspondence e-mail: kato-tadashi@c.metro-u.ac.jp# 2007 International Union of Crystallography
Printed in Singapore – all rights reservedThe time evolution of small-angle neutron scattering is measured for thelamellar phase of a nonionic surfactant C16H33(OC2H4)7OH (C16E7) in D2O at
48 wt% at 343 K under shear flow. At the shear rates of 0.3, 1 and 3 s1, a new
diffraction peak appears at higher q [where q = (4/)sin , and  and 2 are thewavelength of the neutron beam and the scattering angle, respectively] about 1–
2 h after applying shear flow and coexists with the initial diffraction peak. Thecoexistence of two peaks continues even after 5 h at 0.3 s1 whereas at 1 and3 s1 the peak at lower q disappears after about 3 h. These results indicate thatthe repeat distance decreases discontinuously and so suggest some sort oftransition. A plot of the repeat distance after 5 h versus shear rate shows aminimum at 1 s1, which is in good agreement with our previous results obtainedby increasing the shear rate stepwise.

1. Introduction
In recent years, the effects of shear flow on the structure of surfactant
self-assemblies have been studied extensively using microscopy,nuclear magnetic resonance (NMR), and scattering techniques suchas small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS) and small-angle light scattering (SALS). Among them,
the lamellar phase has become of interest because the shear-induced
state is sometimes not simply related to an existing equilibrium. Rouxand coworkers have found a transformation from the lamellar phaseto the ‘onion phase’ where multilamellar vesicles are close-packed(Diat et al., 1993, 1995; Sierro & Roux, 1997; Roux, 2000). Following
their pioneering study, various types of shear effects have beenreported (for example, see Richtreing, 2001).
In the previous study (Kato et al., 2004, 2005), we measured SANS
and SALS on the lamellar phase of a nonionic surfactant C16E7 [asurfactant having a chemical formula CnH2n+1(OC2H4)mOH isabbreviated as CnEm] in D2O at 40, 48 and 55 wt% at 340 K in therange of shear rate 103–10 s1, which is lower than in otherpublished studies. We have found a significant decrease in thelamellar repeat distance (d) at shear rates of 0.3–1 s1. The minimum
value of d is nearly equal to the thickness of the bilayers irrespectiveof the concentration, suggesting phase separation into concentrated
lamellar and water-rich regions, although macroscopic phaseseparation could not be observed by the naked eye (the outercylinder of the shear SANS cell is made of quartz). A reduction in therepeat distance by shear flow has been reported by several groups(Yamamoto & Tanaka, 1995; Idziak et al., 2001; Welch et al., 2002). In
these experiments, however, the amount of reduction is only a few
per cent of the initial repeat distance at rest. In our system, on theother hand, the repeat distance is decreased down to about 40% of
the initial one in the case of the 40 wt% sample. Such a large amounts332

Kyoko Miyazaki et al.  C16E7/D2O systemof decrease in the repeat distance has not been reported so far and so
it is important to elucidate the underlying mechanisms of thisphenomenon.
In the present study, the time evolution of SANS patterns has beenmeasured under a constant shear rate in the same system to pursue
the change in the lamellar repeat distance as a function of time.

2. Experimental
SANS measurements were carried out at the instrument SANS-U at
the Institute for Solid State Physics of the University of Tokyo inJRR-3M at Tokai with a Couette shear cell. The details of the shear
cell have been reported previously (Takahashi et al., 2000). Under aconstant shear rate (0.3, 1, 3, 10 and 30 s1), time-resolved twodimensional SANS patterns have been collected for about 6 h. The
exposure times were 3 and 10 min for the radial and tangential
configurations, respectively. Measurements have also been made forabout 2 h after stopping the shear.

3. Results and discussion
Fig. 1(a) shows the evolution of the two-dimensional SANS pattern
after applying shear flow with shear rate of 1 s1. The pattern in thetangential configuration at rest indicates strong orientation oflamellae to the gradient direction, which may be due to shear caused
by lowering the inner cylinder (stator) into the sample in the outercylinder (rotor). These two-dimensional patterns were reduced to
one-dimensional (1D) patterns in the neutral, flow and velocity
gradient directions by integrating the scattering intensity over asegment of width  = 10 , where  is the azimuthal angle. The 1Dpatterns for the neutral and velocity gradient directions are shown inJ. Appl. Cryst. (2007). 40, s332–s334

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Figure 1(a) Evolution of two-dimensional SANS patterns after applying shear flow at 1 s1for the sample containing 48 wt% C16E7 at 340 K for the radial (upper) andtangential (lower) configurations. The numbers indicate the strain. (b) Evolution ofdepolarized SALS patterns after applying shear flow at 1 s1 (upper) and 3 s1(lower) for the sample containing 48 wt% C16E7 at 340 K for the radialconfigurations. The numbers indicate the shear strain.

Fig. 2. This figure demonstrates that a new diffraction peak appears at
higher q [q is defined as (4/)sin , where  and 2 are the wavelength of the neutron beam and the scattering angle, respectively] andcoexists with the initial diffraction peak at a strain of 7680. At a strainof 17 160, the peak at lower q disappears and the peak intensity athigher q increases. These results indicate that the repeat distancedecreases discontinuously, suggesting some sort of transition.
Fig. 3 shows the evolution of the repeat distances (d) for the threeprincipal orientations of lamellae. The discontinuous decrease of d(see the dashed arrows) is observed at the shear rates of 0.3 and 3 s1
as well, although the coexistence of two peaks continues even after
330 min (a strain of about 6000) at 0.3 s1. At 30 s1, on the otherhand, the repeat distance decreases almost continuously and theamount of the decrease is small compared to the lower shear rates.
The discontinuous decrease begins to occur at strains of about 2000,
6000 and 10 000 for the shear rates of 0.3, 1 and 3 s1, respectively.
These results suggest that the strain plays an important role in thetransition but the critical strain increases with shear rate.
In Fig. 4, the repeat distance just before stopping shear (after about6 h) is plotted against the shear rate. This figure demonstrates that therepeat distance takes a minimum at around 1 s1. In our previousstudy (Kato et al., 2004), the shear rate increases stepwise (0.03 ! 0.1! 0.3 s1 and 0.3 ! 1 ! 3 ! 10 ! 30 s1 for first and second runs,
respectively, for the 48 wt% sample). The repeat distance takes aminimum also at around 1 s1. These results suggest that the shearrate dependence of the repeat distance in the steady state is almost
independent of the shear history.
Nettesheim et al. have investigated the effects of shear flow on thelamellar structures in the C10E3 and C12E4 systems. They suggest theformation of an intermediate structure oriented in the flow direction,corresponding to long multilamellar cylinders (or deformed onions)
before the formation of spherical onions (Nettesheim et al., 2003).
However, the repeat distance remains constant throughout thesetransition processes. Fig. 1(b) shows the evolution of depolarized
SALS patterns after applying shear flow at 1 and 3 s1. The four-Figure 2

Figure 3

Evolution of 1D SANS patterns after applying shear flow at 1 s1 for the sample
containing 48 wt% C16E7 at 340 K for the neutral (left) and velocity-gradient(right) directions. The numbers indicate the shear strain.

The repeat distance versus shear strain at 0.3, 1, 3 and 30 s1 for the sample
containing 48 wt% C16E7 at 340 K for the neutral (circles), flow (squares) andvelocity-gradient (triangles) directions.

J. Appl. Cryst. (2007). 40, s332–s334

Kyoko Miyazaki et al.  C16E7/D2O systems333

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system at rest, we have shown that bilayers in the lamellar phase havewater-filled defects below about 341 K and that the fraction of thedefects increases with decreasing temperature (Minewaki et al.,2001). Therefore, the time evolution of SANS and SALS patterns aswell as the shear stress at different temperatures may give some clue
as to the relations between the structural changes on the nanometre
and micrometre scales.
This research was partially supported by the Ministry of Education,
Science, Sports and Culture of Japan, Grant-in-Aid for Scientific
Research (B), 15340140, 2003–2005.

References
Figure 4
The repeat distance just before stopping shear (after about 6 h) versus shear rate
for the sample containing 48 wt% C16E7 at 340 K for the neutral (circles), flow(squares) and velocity-gradient (triangles) directions.

lobed pattern with a diffraction peak observed at 3 s1 indicates theexistence of onions. So the structural changes on the nanometre scale(reduction in the repeat distance) may be correlated with that on themicrometre scale (onion formation). However, detailed relations
between them are not still clear.
Recently, we have also found a change in spacing for a C12E5/D2O(35 wt%) system at 0.5–1 s1. Because the bilayer thickness of C12E5
is about 60% of that of C16E7, the bending constants () for these twosystems may be very different from each other. So the results forthese two systems suggest that the critical shear rate for the discontinuous change in spacing may depend on  only slightly. Before
drawing conclusions, however, we should perform more systematic
experiments for surfactants with different chain lengths, including
C10E3 and C12E4.
As has already been shown in the C10E3 system (Le et al., 2001;
Oliviero et al., 2003), the fraction of onions under shear flow strongly
depends on temperature. In our previous SAXS study on the C16E7s334

Kyoko Miyazaki et al.  C16E7/D2O system

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