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M. Ordon et al. / Thermochimica Acta 643 (2016) 1–12
2.2. Samples preparation
sample. Additionally the measured spectra were corrected taking
into account scattering from the setup and empty cells, as well as
the background. The final small-angle neutron scattering curves
are presented in the absolute scale with background subtraction
[22]. The analysis of the SANS spectra was performed by the mod-
els proposed in the next sections using SasView software [23]. The
morphology of the samples at the macro-scale was monitored using
an optical microscope OLYMPUS SZX − ILLK 200 with max magnifi-
cation of 6.3 x (OLYMPUS OPTICAL CO (EUROPA) GMBH, Hamburg,
Germany).
For SANS experiment the gel samples were prepared
by dissolving white crystalline powder of 7OPhOLCA at
room temperature in deuterated DMSO-d6 with concen-
tration: “S1”—0.005 g/ml, “S2”—0.01 g/ml, “S3”—0.015 g/ml,
“S4”—0.02 g/ml and “S5”—0.025 g/ml. DMSO-d6, isotopic purity
solvent is used in order to enhance the neutron contrast and
therefore the sensitivity of the SANS technique. For better homog-
enization the solutions were mixed using a shaker at temperature
T = 60 ◦C and cooled to 20 ◦C. The samples for SANS experiments
were placed in quartz cells as shown in Fig. 3 and incubated at
room temperature for 12 h. A non-transparent, stable gel was
observed in the concentration above 0.015 g/ml. In this publication
we present the results of optical, spectroscopy and calorimetry
experiments for the samples in the concentrations of 0.015 g/ml
and 0.025 g/ml.
3. Result and discussion
For the organogelator samples with the concentration of
0.015 g/ml (mass 14.02 mg) two full cycles of heating and cooling
at a rate of 5◦/min were performed. The second cycle is shown in
Fig. 4. The phase transition between the Crystal and Gel phases
was observed during heating in the range of temperature: from
To = −5.25 ◦C to Te = 6.32 ◦C with a peak temperature Tp = 4.72 ◦C (To,
Te—onset and endset temperature) with a high value of enthalpy
amounting to ꢂH = 61.21J/g.
2.3. Experimental techniques
DSC measurements at the rate of 5deg/min were performed
using a DSC 822e Mettler Toledo Star System calorimeter. Calibra-
tion of the DSC822e Mettler Toledo Stare System was performed
using indium. The results of the indium check are within the toler-
ance limits defined by Mettler Toledo: Onset temperature: 156.6 ◦C
Additionally, we have observed transitions with small enthalpy
in the Gel phase. These transitions will be discussed in detail the
next section. Here, we indicate the physical parameters of the tran-
sitions Gel 1 (G1) → Gel 2 (G2) and Gel 2 (G2) → Gel 3 (G3) only.
The transition from G1 to G2 occurred at 28.42 ◦C (To)—34.92 ◦C
(Te), (ꢂH = 0.20J/g). The second transition from G2 to G3 was
observed above 39.82 ◦C (To) (ꢂH = 0.03J/g). The phase transition
to Sol was not observed. The substance did not decompose, while
heating up to 60 ◦C. The cooling cycle was performed immedi-
ately after the heating cycle. A minor change heat was observed at
18.58 ◦C (ꢂH = 0.21J/g). It was probably characterized by the transi-
tion from Sol to G3. This means that the sample was going to at least
Sol state during heating. However, the heat of this transition was
not high enough for its registration by DSC method. G3 appeared
in the range of about 7.50 ◦C. Then, at 14.99 ◦C the transition to
G2 (ꢂH = 0.08J/g) was observed. A suitable rate of measurement
made it possible to observe of the transition from G2 to G1 phase at
11.46 ◦C (ꢂH = 0.09J/g). Crystallization of the substance was iden-
tified due to an exothermic peak in the range from To = −5.37 ◦C to
Te = 7.53 ◦C (ꢂH = 81.90J/g).
In order to verify the effect of the concentration of the gel on the
phase transition temperatures shifts, the DSC experiment for a sam-
ple with the concentration of 0.025 g/ml (26.21 mg) was conducted
at a rate of 5deg/min. During heating an endothermic peak of melt-
ing Crystal phase to G1 phase at Tp = 4.37 ◦C (1 cycle, ꢂH = 52.99J/g),
4.62 ◦C (2 cycle, ꢂH = 56.74J/g) and 4.78 ◦C (3 cycle, ꢂH = 57.93J/g)
was observed. Unfortunately, the transitions G1 → G2 and G2 → G3
were not registered in DSC measurements for this sample. That is
the reason to make SANS experiment.
(
0.3 ◦C), our results 156.3 ◦C; Heat flow 28.45 J/g ( 0.6 J/g), our
results 27.89J/g, Our calibrations correspond to the requirements of
the Mettler Toledo Stare Thermal Analysis System (User Handbook,
Instruction of the Mettler Toledo).
IR spectra of the gel materials (concentration 0.015 g/ml) were
recorded using a FTIR Nicolet Magna 760 spectrometer. The mea-
surements were performed with a minimum of 64 co-added scans
surements the Linkam temperature controller was used, operating
at 2◦/min. The temperatures were stabilized and kept constant
while taking FTIR scans. Baseline correction was performed using
the PeakFit v4.12 [19]. The distribution of peaks on FTIR scans was
mathematically described by fitting Gauss functions to the data. The
number of peaks, peak centers and band shapes was assigned before
fitting. The heights, areas and widths (full-width at half-maximum,
FWHM) were allowed to vary during fitting. The sample of the gel at
room temperature was placed between the ZnSe windows. During
heating and cooling, the spectra were taken at 30 ◦C, 40 ◦C, 42 ◦C,
44 ◦C, 46 ◦C, 48 ◦C, 50 ◦C, 52 ◦C, 54 ◦C, 56 ◦C, 58 ◦C. The implemen-
tation of spectrum below room temperature was not possible for
reasons related to the apparatus.
Small Angle Neutron Scattering investigations were performed
at YuMO time-of-flight spectrometer at the IBR-2 pulsed reactor
(Dubna, Moscow region, Russia). The studied samples were placed
in 1 mm thick quartz cells (Hellma, Germany). During data collec-
tion the samples were kept in the temperature controlled holder
(
0.2 ◦C) connected to the liquid thermostat (Lauda, Germany).
Standard data acquisition time per sample was 30 min. Two ring
wire He3-detectors [20] at distances of 4 m and 13 m from the sam-
ple position were used in our experiment. The scattered intensity
(differential cross section per sample volume) was registered as a
function of the momentum transfer modulus q = (4/ꢁ) sin(/2),
where is the scattering angle and ꢁ is the incident neutron
wavelength. An incident neutron beam distribution provides an
available wavelength range of 0.5 ÷ 8 Å, which corresponds to
momentum transfer range q of 0.007 ÷ 0.5 Å−1. The raw data treat-
ment was done by the SAS program [21]. The measured SANS
spectra were converted to the absolute scale by normalization to
the incoherent scattering cross section of a standard vanadium
The greatest change in the phase transition temperature dur-
ing the heating cycle was observed for the phase transition
from Gel 3 to Sol phase. For a sample with the concentra-
tion of 0.015 g/ml the phase transition occurred in the range of
temperatures 39.82 ◦C–43.08 ◦C. A precise determination of this
temperature for sample “3” was not possible, which was due to the
fact that this transition was not observed using DSC method. For
sample “5” (concentration of 0.025 g/ml) the temperature of phase
transition from Gel 3 to Sol phase was characterized by an exother-
mic peak in a temperature range from To = 28.75 ◦C to Te = 35.27 ◦C
(ꢂH = 1.29J/g).