10.1002/chem.201700723
Chemistry - A European Journal
FULL PAPER
method was used. In the first step the PMHS was dissolved in dried
toluene, then an appropriate amount of mesogenic ligand and a
platinum catalyst was added. The next step was cross-linking the
Experimental Section
Organic synthesis. Synthesis of used ligands, cross-linkers and
ligand for the functionalization of gold nanoparticles is described in
SI. Solvents and substrates were obtained from Sigma-Aldrich.
polysiloxane chains using the GNP@L2, L3 or L4 (Fig. 1), the
process was carried out at temperature of 75-80°C, constantly
maintaining the centrifugation of the reaction mixture. In the final
stage, the excess of unreacted ligand was removed by repeated
washings with dried toluene.
Before use, all solvents were dried over thermally
activated
molecular sieves. All reactions, except LCE and LCE-GNP
preparation and purification, were carried out under nitrogen
atmosphere in dried glassware. Purification of reaction products
was carried out by column chromatography using Sigma Aldrich
silica gel 60Å (230-400 mesh) at atmospheric pressure or by
crystallization if possible. Yields refer to chromatographically and
spectroscopically (1H NMR) homogeneous materials. The 1H NMR
and 13C NMR spectra were recorded at either 200 MHz or 500 MHz
NMR Varian Unity Plus.
Proton chemical shifts are reported in ppm (δ) relative to the internal
standard – tetramethylsilane (TMS δ=0.00 ppm). Detailed synthetic
procedures and analyses are given in the SI (Figures S1, S2, S3).
Nanoparticles synthesis. Gold NPs were synthesized according
to the modified Brust procedure.19 Briefly, AuCl3 in diluted HCl (1.7
XRD measurements. The small-angle X-ray diffraction (SAXRD)
studies have been carried out using Bruker Nanostar diffractometer
(CuKα radiation (wavelength 1.54 Å), parallel beam formed by cross-
coupled Goebel mirrors and three pinhole collimation system, MRI
TCPU-H heating stage, Vantec 2000 area detector). Samples of
GNP-L2 were prepared as thin films on a kapton tape and aligned by
mechanical shearing at elevated temperature. Samples of polymers
were measured in transmission, without substrates. The X-ray
diffraction patterns in wide angle range were collected using a Bruker
GADDS system (CuKα radiation, parallel beam formed by Goebel
mirror and two pinhole collimator, Vantec 2000 area detector,
equipped with modified Linkam heating stage).
Differential scanning calorimetry (DSC). Phase transition
temperatures and associated enthalpy changes for all organic
compounds and elastomers were determined with differential
scanning calorimeter, TA Q200. The samples of 2–5 mg were placed
into aluminum pans and kept in nitrogen atmosphere during
measurements. Cooling and heating rates of 10 K min-1 were
applied.
Transmission electron micrography. Transmission electron
micrography was performed using Zeiss Libra 120 microscope, with
LaB6 cathode, equipped with OMEGA internal columnar filters and
CCD camera. For TEM imaging materials were dropcasted onto TEM
carbon coated copper grids and thermally annealed at 90 oC.
Scanning electron micrography (with EDS). The samples were
analyzed using of a FE-SEM Merlin (Zeiss, Germany) instrument.
The chamber pressure was 1.10−5 Torr, and pictures were registered
for 3- and 15-kV electron beam. Before exposing the samples to the
electron beam, they were dried under vacuum for 24h.
Thermogravimetric analysis (TGA). Thermogravimetric analysis
were performed with a TA Q50 V20.13 analyzer. The measurements
were carried out in 100-600 °C range with 10 K min-1 heating rate in
air. Prior the measurement samples were conditioned at 100oC for
20 min.
mL of
a solution - 30% Au content, from Sigma-Aldrich), was
dissolved in 90 mL of distilled water and transferred into toluene
with tricaprylmethylammoniu chloride (5.0 g dissolved in 250 mL
of toluene). The resulting organic phase was then separated,
cooled down to 4oC and stirred with octane thiol (0.5 mL).
Reduction was performed using an excess of sodium borohydride
(1.2 g). After stirring at room temperature for 1h, the organic phase
was collected, washed with distilled water and concentrated to
ca. 5 mL. The resulting dark solution was suspended in 200 mL
of ethanol, cooled down to 4oC and centrifuged (5 min.; 1000RPM).
The black deposit was dissolved in a small amount of toluene (5 mL).
The washing procedure with ethanol was repeated twice. The
purification process and the refinement is based on the partial
precipitation of well dispersed nanoparticles utilizing mixtures of
ethanol and acetone. The dark brown precipitate obtained after
synthesis of nanoparticles was sonicated for 60 s and centrifuged (5
min, 13 000 rpm) in 15 mL of toluene. In the next step, the toluene
solution was precipitated with acetone-ethanol mixture (80 mL, 1:1)
and centrifuged (3 min, 8 000 RPM in 35oC). Again precipitate was
dissolved in a small amount of toluene (10 mL), precipitated with
acetone-ethanol (100 mL, 1:2) and centrifuged. The procedure was
repeated twice. The black precipitate was collected and used for
ligand exchange reaction.
Ligand exchange reaction on nanoparticles. Octyl thiol coated
NPs (GNP@C8) were used for the preparation of hybrid NPs
Acknowledgements
(
GNP@L2). To 25 mg of NPs dissolved in 15 ml of toluene 20 mg
of a mesogenic ligand (L2) was added. The reaction proceeded at
room temperature for 36 h. Then, NPs were precipitated with 20 ml
of acetone-ethanol mixture (1:2) and centrifuged. The supernatant
containing free thiol ligand molecules was collected and named as
MIX1. The precipitate was dissolved in 10 ml of toluene and
centrifuged (5 min, 13 000 rpm). This washing procedure was
repeated until no traces of free mesogenic ligand remained, as
determined by thin layer chromatography. The concentration of
nanoparticles was estimated via simple weight method. Gold
nanoparticles obtained in Brust method are relatively high
concentrated and can be easily purified in both cases: after the
synthesis or after ligand exchange in combination with complete
purification from the ligand excess. Briefly, a 0.25 mL toluene solution
of gold nanoparticles was placed in a carefully weighed weighing
vessel. After the solvent evaporation in 110oC the vessel was
weighted again on the precision scale and the concentration was
calculated and estimated as 4.6 mg/mL for GNP@C8and 2.3 mg/ml
for GNP@L2. Both solutions were sealed, stored in 4oC and used as
prepared for future experiments.
Supporting Information
Synthesis and characterization of materials, additional
experimental results: SEM, XRD, TGA, XPS, optical microscopy.
Structural properties obtained from MD simulations: Model
composition for modeling, radial density distribution, free volume
distribution, mean squared displacement.
Funding Sources
The work was supported by NCN (Poland) grants no: UMO-
2013/08/M/ST5/00781 (DP) and UMO-
2014/15/D/ST5/02570 (MW).
The work was supported by NRF (Korea) grants no:
2012R1A3A2048841 (MC).
Keywords: Liquid crystals • Nanoparticles • Liquid crystal
elastomers • Nanostructures • Surface chemistry
LCE preparation. In order to obtain the LCE's we applied a protocol
26
used
by
Finkelmann
and
other
authors.
The
poly(methylhydrosiloxane), cross-linker and mesogenic ligands were
used. The resulting material was partially oriented by means of
mechanical stress. The application of the mechanical stress is a
common method, the use of which has been initiated in the
aforementioned early works of Finkelmann. In the case of described
substances, the orientation was introduced analogously to modified
procedure described by Zentel and coworkers,27 where spin casting
[1] a) R. Eelkema, M. M. Pollard, J. Vicario, N. Katsonis, B. S. Ramon, C. W. M.
Bastiaansen, D. J. Broer, B. L. Feringa, Nature 2006, 440, 163; b) E. K.
Fleischmann, R. Zentel, Angew. Chem. Int. Ed. 2013, 52, 8810-8827; c) R. R.
Kohlmeyer, J. Chen, Angew. Chem. Int. Ed. 2013, 52, 9234-9237; d) S.
Iamsaard, S. J. Aßhoff, B. Matt, T. Kudernac, J. J. L. M. Cornelissen, S. P.
Fletcher, N. Katsonis, Nat. Chem. 2014, 6, 229-235, e) H. Jiang, S. Kelch, A.
Lendlein, Adv. Mater. 2006, 18, 1471-1475.
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