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materials is probably caused by higher volume of terminal
chains in comparison to the AuL2-1 having one and shortest
terminal chain per ligand.
Summarizing experimental facts: depending on temperature,
a different orientation of layers was induced by mechanical
shearing of samples; at low temperature transverse, while at high
temperature perpendicular orientation mode was observed. The
polarized IR spectroscopy proved that for most materials (with
one exception) mesogenic ligands in the whole temperature
range follow orientation of layers, they are oriented with their
long axes parallel to the planes made by gold nanoparticles.
Since the ligands in perpendicular and transverse alignment
modes can be either parallel or perpendicular to shearing
directions it is excluded that ligand molecule orientation drives
the sample (layers) alignment.
Noticeably, this is the first report on atypical alignment mode of
lamellar nanoparticle systems, apparently they respond to the
mechanical shear fundamentally differently than low weight LCs
and block copolymers; the parallel mode of alignment, typical for
low weight LCs and polymers, is never observed for NPs. Stability of
perpendicular layer alignment mode may be understood taking into
account that metal and organic sublayers are strongly coupled, as
ligands are covalently attached to metallic cores. Contrary to
parallel mode, the perpendicular one allows for lamellae deforma-
tion without strong distortion of the connection region between
Fig. 4 The polarized IR measurements performed for AuL2-2 samples
aligned at: (a) 40 1C, (b) 80 1C and for AuL2-1 samples aligned at: (c) 40 1C,
(d) 80 1C. For more details see the main text. f is the angle between
the shearing direction and polarization of IR light. Arrows show the
shearing direction.
low temperature the absorption for the phenyl rings was metal and organic sublayers.6 The stability of transverse alignment
strongest in the direction perpendicular to the shearing direc- mode is less clear. One can argue that it is favored by growing
tion (and thus perpendicular to the layer normal) while the material viscosity, as it was observed for samples sheared at lower
absorption for the alkyl groups under this condition was the temperatures. The presented results open up the way to prepare
weakest (Fig. 4a). For the sample sheared at high temperature hybrid NP materials in the form of large-area monodomains with
(80 1C) (Fig. 4b) the maximum of absorption for the phenyl controlled geometrical orientation, which can be important for
ring’s stretching was observed in the direction parallel to the application in advanced optoelectronics and photovoltaics.
shearing direction (which in this case was perpendicular to
The present study was supported by the Polish Ministry of
the layer normal) while absorption for alkyl chains was the Science and Higher Education grant Iuventus Plus nr IP2010
strongest in the direction perpendicular to the shearing direc- 047270.
tion (but parallel to the layer normal) (see also ESI†). It proves
that regardless of the temperature in which the sample was
aligned, the ligand molecules remain oriented with their long
axes parallel to the planes made by gold nanoparticles; the
structure resembles laminated smectic phases observed for
2 J. M. Lee, J. W. Choung, J. Yi, D. H. Lee, M. Samal, D. K. Yi, C.-H. Lee,
Notes and references
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drives the orientation of molecules in the organic sublayer. All
synthesized NP materials showed similar behavior with excep-
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chain and a long spacer unit. The sample of AuL2-1 sheared at
low temperature shows transverse mode of layer alignment with
ligands along the layers (Fig. 4c). However, for samples sheared
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observed perpendicular to the shearing direction, thus along
the layer normal, while the maximum of absorption for the
–CH2– groups’ stretching was observed in the direction parallel
to the shearing, thus perpendicular to the layer normal (Fig. 4d).
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long axes perpendicular to layers, as in conventional smectics.
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Chem. Commun., 2014, 50, 7975--7978 | 7977