A partially crosslinked bicontinuous cubic phase exhibiting a temperature range of more than 100°C

Article abstract of DOI:10.1039/c2cc16411f

A new methodology of partial crosslinking is presented for stabilizing the bicontinuous cubic phase without losing its dynamic nature. It was applied to a mixture of 1,2-bis[4′-(9′′-decenyloxy)benzoyl]hydrazine with a bi-functional linker, remarkably stab

Full text of DOI:10.1039/c2cc16411f

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2012, 48, 2225–2227
www.rsc.org/chemcomm
COMMUNICATION
A partially crosslinked bicontinuous cubic phase exhibiting a temperature
range of more than 100 8Cw
Suguru Miisako, Shoichi Kutsumizu* and Koichi Sakajiriz
Received 15th October 2011, Accepted 5th January 2012
DOI: 10.1039/c2cc16411f
A new methodology of partial crosslinking is presented for stabilizing
the bicontinuous cubic phase without losing its dynamic nature. It was
applied to a mixture of 1,2-bis[40-(90 0-decenyloxy)benzoyl]hydrazine
with a bi-functional linker, remarkably stabilizing the phase in
Q
comparison with the neat compound having no C C bond at the
Fig. 1 Molecular structures of BABH-10 and compound 1.
end of the alkyl tail.
Our research group has established the phase diagram of
a series of rod-like molecules, 1,2-bis(40-alkyloxybenzoyl)-
hydrazines [denoted as BABH-n, where n is the number of
carbon atoms in the alkyl tail].6 In contrast with the simplicity
of the molecular structure, the diagram is complicated; in
addition to a layered smectic C (SmC) phase region, regions
of two types of Cubbi LC phases with symmetries Ia3d and
Im3m are seen, the formation of which are dependent upon the
chain length n and temperature.6c–f In chemistry of Cubbi LC
phases, the majority of molecules exhibiting those phases
documented so far is rod-like,4a although Kato’s success was
accomplished for fan-shaped molecules. Considering the quite
high sensitivity of thermotropic Cubbi LC structures to the
molecular structure as mentioned above, preservation of
thermotropic Cubbi LC structures is still a challenging subject
to be continued. Thus, we have in this communication
introduced at the end of the alkyl tails of BABH-10 not a
1,3-diene as utilized by Kato but a CQC bond, as shown in
Fig. 1. Although it is known that the reactivity of the CQC
bond for photopolymerization is quite low, we have found
that UV irradiation of the mixture of this compound with a
diacrylate monomer and a photoinitiator profoundly stabilizes
the Ia3d-Cubbi LC structure in a remarkable wide temperature
range of more than 100 1C.
1,2-Bis[40-(90 0-decenyloxy)benzoyl]hydrazine (1) was synthe-
sized in two steps. The first step is Williamson etherification of
ethyl 4-hydroxybenzoic acid and 10-bromo-1-decene, to produce
4-(90-decenyloxy)benzoic acid (2). The second step is transfor-
mation of 2 into the acid chloride, followed by a reaction with
hydrazine monohydrate to give the final product 1. The crude
product was recrystallized, dried under vacuum, and the purity
was checked by TLC, 1H and 13C NMR, and elemental analysis.
Characterization data are included in ESI.w
Fig. 2 compares the phase behaviors of four systems, which are
BABH-10, compound 1, mixture of 1 with the bi-functional
linker and the photo-initiator, and the mixture after photo-
polymerization at B140 1C. BABH-10 exhibits two LC
phases, an Ia3d-Cubbi phase (143.5–153.9 1C) and a SmC
Liquid crystals (LCs) are one of the soft materials having self-
organized structures in dynamic state.1 Utilization of those
self-organized dynamic structures is a promising approach for
nano-structured functional materials.2 The LCs utilized so far are
one-dimensionally ordered smectic phases or two-dimensionally
ordered hexagonal phases, but recently, bi-continuous cubic
(Cubbi) LCs have attracted more attention.3–7
One of the features of Cubbi LCs is their three-dimensional
periodic structures with local liquid-like mobility preserved.
Several applications have been proposed for the Cubbi LCs
such as nano-porous templates,5a,b catalytic bases,3 separation
membranes,5c,d three-dimensional (ionic/electronic) conductors5e–i
and so on. In those cases, stabilization of the Cubbi LC structures
is crucial, but at present the structures are formed usually in
narrow ranges and at relatively high temperatures in thermotropic
systems. From this viewpoint, the in situ photopolymerization of
LC molecules with polymerizable moieties has been recognized as
a useful approach, and in fact, the preservation of lyotropic Cubbi
LC structures was already reported by Gin and his coworkers.5c,d,f
In thermotropic systems, however, there is another difficulty
encountered because the balance of size and shape of nano-
segregated parts within the molecule is so delicate that the
introduction of conventional polymerizable moieties such as
acrylate groups into LC molecules often destabilizes the original
Cubbi LC structures. Recently, Kato and co-workers have synthe-
sized fan-shaped molecules having three long aliphatic tails, into
two of which 1,3-diene end groups are incorporated, and success-
fully preserved the thermotropic Cubbi LC structures in a solid
polymer film.5h
Department of Chemistry, Faculty of Engineering, Gifu University,
1-1 Yanagido, Gifu 501-1193, Japan. E-mail: kutsu@gifu-u.ac.jp;
Fax: +81-58-293-2794; Tel: +81-58-293-2573
w Electronic supplementary information (ESI) available. See DOI:
10.1039/c2cc16411f
z Present address: Department of Organic and Polymeric Materials,
Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku,
Tokyo 152-8552, Japan.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 2225–2227 2225

View Article Online
This result, however, can be understood as follows: the
Cubbi structures are described by a TPMS dividing the space
into two separate sub-spaces. In the case of BABH-10, the
TPMS layers with a finite thickness are filled with molten alkyl
tails.6d By analogy with lyotropic Cubbi LC systems, Saito and
Sorai et al.8 pointed out that such alkyl tails serve as a solvent
(self-solvent), and in the binary mixtures with alkanes, the
alkyl tails can dissolve some amount of the second component
molecules with low dielectric constant, preserving or inducing
Cubbi phases identical with those formed in the corresponding
neat compounds.8a,c Therefore, in the present mixture, the
coexisting diacrylate monomer and the photo-initiator are also
considered such additional components soluble in the TPMS
regions.
Fig. 2 Comparison of phase behaviors of BABH-10, compound 1,
mixture of 1 with a bi-functional linker and a photo-initiator, and the
mixture after photopolymerization at B140 1C.
phase (153.9–166.4 1C) on heating.6a,b,e Compound 1 showed an
Ia3d-Cubbi phase (135.2–151.2 1C) but unlike BABH-10, not
followed by the formation of the SmC phase at the high
temperature side, directly transitioned to the isotropic liquid
(see Fig. S1–S3, ESIw). This can be explained in terms of change
in the average molecular shape previously discussed for
BABH-n.6e In the Cubbi phase, it is expected that the alkyl tails
are laterally expanded slightly compared to the central molecular
core. This is an origin of the Ia3d-Cubbi structure, which is
described in terms of the G type of a triply periodic minimal
surface (TPMS) framework.3 When going on to the high
temperature region, in BABH-10, weakening of the intermolecular
hydrogen bonding interactions effectively expands the central core
part, putting back the shape into a rod, in favor of a layered
structure of the SmC phase. In the case of compound 1, on the
other hand, the presence of CQC bond at the extremity of the
alkyl tail would reasonably lead to more lateral expansion than in
BABH-10. In fact, the lattice dimension of 1 was a = 6.95 nm at
150.1 1C, based on the X-ray diffraction (XRD) studies, which is
by 1.3% shorter than that of BABH-10 (a = 7.04 nm at
150.1 1C).6e This is consistent with the above-mentioned picture,
because the larger extent of deformation from a rod-shape would
result in a smaller size of the lattice dimension. The infrared
spectra (IR) for 1 revealed that the strength of the intermolecular
hydrogen bonding varies with temperature but no difference is
visible between 1 and BABH-10 (Fig. S4, ESIw). Finally, what to
note here is that the replacement of ethyl with vinyl (ethenyl)
headgroup is quite tiny but actually has a profound effect on the
phase behavior of the Cubbi phase-forming molecule. The
lowering of the clearing temperature by B10 1C is also consistent
with the results of Kelly’s extensive work on other LC materials.7
The photopolymerization of the mixture was carried out at
around 142 1C in the temperature region of the Cubbi LC
phase, and as the result of the polymerization, the Cubbi
structure was outstandingly stabilized: upon cooling from that
region, the structure was almost preserved down to room
temperature (Fig. 3b). The photograph taken at 50.0 1C
displays a completely black area (Fig. 3a). However, the
subsequent heating DSC curve (Fig. S7, ESIw) showed a tiny
endothermic peak at 120 1C, indicating the presence of a small
amount of region recrystallized, which is estimated as B18%
from the evaluation of the enthalpy change. A little bit
complicated result is that further heating showed a faint peak
at around 152 1C, suggesting a transition to the isotropic
liquid, although the XRD result (mentioned below) reveals
that the material is still in the Cubbi state. This suggests the
presence of some crosslinking inhomogeneity in the mixture.
The preservation of the Ia3d-Cubbi structure was also
confirmed by XRD as shown in Fig. 4. The radially-averaged
pattern at 45.0 1C shows two peaks at 2.19 and 2.52 nmꢀ1 with a
shoulder peak at 2.06 nmꢀ1. The reciprocal d-spacing ratio of the
former two peaks is O6:O8, which can be indexed to the (211)
and (220) reflections of an Ia3d-Cubbi lattice with a lattice
dimension a = 7.03 nm. The left-sided shoulder is probably
attributable to the crystalline state (see Fig. S2 and S5, ESIw).
The curve-fitting was applied to the pattern to extract the
crystalline peak, and from the peak area the percentage of the
crystalline state is evaluated as B20% (Fig. 4b). At temperatures
above 120 1C, the crystalline peak completely disappears,
indicating the formation of the Ia3d-Cubbi phase in the whole
area. The lattice dimension is a = 7.10 nm at 150.0 1C.
For photopolymerization, to compound
1 were added
1,6-hexanediol diacrylate as a bi-functional linker and 2,2-
dimethoxy-1,2-diphenylethan-1-one as a photo-initiator in a
molar ratio of 66.8 : 24.7 : 8.5. As shown in Fig. 2, the mixture
also showed an Ia3d-Cubbi phase, whose temperature range
(130.1–146.1 1C) shifted by B5 1C toward lower temperature
owing to the freezing-point depression in comparison with the neat
compound 1. The lattice dimension was a = 6.90 nm at 142.5 1C,
based on XRD (Fig. S5 and S6, ESIw), slightly shorter than that of
compound 1. However, one may be a little bit surprised at the
preservation of the Ia3d-Cubbi phase with a quite similar lattice
dimension in the mixture, if recalling both the substantial amount
of adducts in the mixture and the usual high sensitivity of Cubbi
LC phase formation to the molecular structure.
Fig. 3 Polarizing optical microphotographs of the mixture of
1/diacrylate/photo-initiator; (a) at 50 1C, where the whole area was
irradiated, and (b) at 49.3 1C, on cooling from the Cubbi phase
temperature region after polymerization. In (b), unlike in (a), the area
includes the region not irradiated in the left side, where the bright
image is seen; in the right side, a mosaic texture is barely visible,
suggesting partial crystallization.
c
2226 Chem. Commun., 2012, 48, 2225–2227
This journal is The Royal Society of Chemistry 2012

View Article Online
methodology when preserving the dynamic nature of the
self-organized structure characteristic of LCs.
Beam time at PF-KEK provided by Program 2010G533
is acknowledged. This work was supported in part by Grant-
in-Aid for Scientific Research (C) 18550121 from Japan
Society for the Promotion of Science (JSPS).
Notes and references
1 (a) I. W. Hamley, Introduction to Soft Matter; Polymer, Colloids,
Amphiphiles and Liquid Crystals, John-Wiley, Chichester, UK, 2000;
(b) C. Tschierske, Annu. Rep. Prog. Chem., Sect. C, 2001, 97,
191–267 and references therein; (c) Handbook of Liquid Crystals,
ed. D. Demus, J. W. Goodby, G. W. Gray, H.-W. Spiess and V. Vill,
Wiley-VCH, Weinheim, Germany, 1998.
2 (a) T. Kato, N. Mizoshita and K. Kishimoto, Angew. Chem., Int.
Ed., 2006, 45, 38–68; (b) Y. Sagara and T. Kato, Angew. Chem., Int.
Ed., 2008, 47, 5175–5178.
3 Bicontinuous Liquid Crystals; Surfactant Science Series Vol. 127, ed.
M. L. Lynch and P. T. Spicer, CRC Press, Taylor & Francis Group,
Boca Raton, 2005.
4 (a) S. Diele and P. Goring, Handbook of Liquid Crystals, vol. 2B,
¨
Fig. 4 (a) XRD patterns of the mixture of 1 with diacrylate and
photo-initiator at 45.0, 150.0, 180.1, 200.0, and 215.0 1C on the second
heating after photopolymerization at around 142 1C and subsequent
cooling down to room temperature. (b) Fraction of the Cubbi phase
evaluated from the XRD pattern as a function of temperature.
1998, pp. 887–900; (b) S. Diele, Curr. Opin. Colloid Interface Sci.,
2002, 7, 333–342; (c) S. Kutsumizu, Curr. Opin. Solid State Mater.
´
Sci., 2002, 6, 537–543; (d) M. Imperor-Clerc, Curr. Opin. Colloid
Interface Sci., 2005, 9, 370–376.
5 (a) C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and
J. S. Beck, Nature, 1992, 359, 710–712; (b) Y.-S. Lee, J.-Z. Yang,
T. M. Sisson, D. A. Frankel, J. T. Gleeson, E. Aksay, S. L. Keller,
S. M. Gruner and D. F. O’Brien, J. Am. Chem. Soc., 1995, 117,
5573–5578; (c) B. A. Pindzola, J. Jin and D. L. Gin, J. Am. Chem.
Soc., 2003, 125, 2940–2949; (d) M. Zhou, P. R. Nemade, X. Lu,
X. Zeng, E. S. Hatakeyama, R. D. Noble and D. L. Gin, J. Am.
Chem. Soc., 2007, 129, 9574–9575; (e) T. Ichikawa, M. Yoshio,
A. Hamasaki, T. Mukai, H. Ohno and T. Kato, J. Am. Chem. Soc.,
2007, 129, 10662–10663; (f) R. L. Kerr, S. A. Miller,
R. K. Shoemaker, B. J. Elliott and D. L. Gin, J. Am. Chem. Soc.,
2009, 131, 15972–15973; (g) M. Akhtarul Alam, J. Motoyanagi,
Y. Yamamoto, T. Fukushima, J. Kim, K. Kato, M. Takata,
A. Saeki, S. Seki, S. Tagawa and T. Aida, J. Am. Chem. Soc.,
2009, 131, 17722–17723; (h) T. Ichikawa, M. Yoshio, A. Hamasaki,
J. Kagimoto, H. Ohno and T. Kato, J. Am. Chem. Soc., 2011, 133,
2163–2169; (i) J.-M. Suisse, H. Mori, H. Monobe, S. Kutsumizu and
Y. Shimizu, Soft Matter, 2011, 7, 11086–11088.
6 (a) H. Schubert, J. Hauschild, D. Demus and S. Hoffmann, Z.
Chem., 2010, 18, 256; (b) D. Demus, A. Gloza, H. Hartung,
A. Hauser, I. Rapthel and A. Wiegeleben, Cryst. Res. Technol.,
1981, 16, 1445–1451; (c) H. Mori, S. Kutsumizu, T. Ito,
M. Fukatami, K. Saito, K. Sakajiri and K. Moriya, Chem. Lett.,
2006, 35, 362–363; (d) S. Kutsumizu, H. Mori, M. Fukatami and
K. Saito, J. Appl. Crystallogr., 2007, 40, s279–s282;
(e) S. Kutsumizu, H. Mori, M. Fukatami, S. Naito, K. Sakajiri
and K. Saito, Chem. Mater., 2008, 20, 3675–3687; (f) K. Ozawa,
Y. Yamamura, S. Yasuzuka, H. Mori, S. Kutsumizu and K. Saito,
J. Phys. Chem. B, 2008, 112, 12179–12181.
The relatively broad peaks clearly come from the crosslinking
inhomogeneity mentioned above. Increasing the temperature
further increases gradually the fraction of a broad halo at around
2.4 nmꢀ1, attributable to thermal fluctuation of the Cubbi
structure. The percentage of the halo increases beyond 160 1C,
suggesting partial melting of the Cubbi lattice, which corresponds
to the above-mentioned DSC peak. However, very surprisingly,
the (211) and (220) reflections of the Ia3d-Cubbi lattice still
remained at the highest temperature examined (215 1C), although
becoming quite weak.
An important point is that this stabilization of the Ia3d-Cubbi
LC structure is achieved in the presence of the terminal
CQC bond of compound 1, although it is known that the
reactivity of the CQC bond for photopolymerization is quite
low. The same type of photopolymerization was performed for
the mixture of BABH-10 with the similar molar ratios of
diacrylate and photo-initiator, but failed in preserving the Cubbi
structure, showing a macrophase-separation (Fig. S8, ESIw).
This demonstrates that the terminal CQC bond of compound
1 plays a crucial role in preventing macrophase-separation,
although the contribution to the network formation is partial
(estimated as B5%, see ESIw) and the network in the Ia3d-type
TPMS region is mainly produced from the bi-functional linkers.
In conclusion, in this communication, partial crosslinking of
the terminal alkyl tails of compound 1 with bi-functional linkers
has enabled the formation of the Cubbi LC phase in a very broad
range of temperature of more than 100 1C. This success demon-
strates that the concept of partial crosslinking can be a useful
7 S. M. Kelly, Liq. Cryst., 1996, 20, 493–515 and references therein.
8 (a) K. Saito, A. Sato and M. Sorai, Liq. Cryst., 1998, 25, 525–530;
(b) K. Saito, T. Shinhara and M. Sorai, Liq. Cryst., 2000, 27,
1555–1559; (c) S. Kutsumizu, K. Morita, S. Yano and S. Nojima,
Liq. Cryst., 2002, 29, 1459–1468; (d) K. Saito, T. Shinhara,
T. Nakamoto, S. Kutsumizu, S. Yano and M. Sorai, Phys. Rev.
E: Stat., Nonlinear, Soft Matter Phys., 2002, 65, 031719; (e) K. Saito
and M. Sorai, Chem. Phys. Lett., 2002, 366, 56–61; (f) M. Sorai and
K. Saito, Chem. Rec., 2003, 3, 29–39.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 2225–2227 2227