Solid State Phenomena Vol. 112 (2006) pp 89-92
Online available since 2006/May/15 at www.scientific.net
© (2006) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/SSP.112.89
Neutron Scattering in 3,3-dimethyl-2-butanol and 2,3 dimethyl-2-butanol
E. Juszyńska1,a, M. Massalska–Arodź1, J. Mayer 1 , I. Natkaniec1,2 J. Krawczyk1 , P.Tracz1
1/ The H. Niewodniczański Institute of Nuclear Physics PAN, ul. Radzikowskiego 152,
31 – 342 Kraków, Poland
2/ Frank Laboratory of Neutron Physics, Joint Institute of Nuclear Research, Dubna,
Russia.
a
[email protected],
Keywords: 3,3 dimethyl-2-butanol, 2,3 dimethyl-2-butanol, Neutron scattering, Glass
Abstract
Influence of the OH group position in the molecule on solid state polymorphism was found.
Dynamics in solid phases of two dimethyl butanols were studied by inelastic incoherent neutron
scattering. In glass of plastic crystal the boson peak was detected.
I. Introduction
Inelastic incoherent neutron scattering investigations of dynamics in two dimethyl butanols,
i.e., (CH3)3CCH2CH2OH (3,3DM-1B), (CH3)3CCH(OH)CH3 (3,3DM-2B) (CH3)2CHC(CH3)2OH
(2,3DM-2B), the isomers of neohexanol CH3CH2C(CH3)2CH2OH (2,2DM-1B) have been
undertaken as a part of the larger project concerning universal properties of organic glass formers
[1,2,3,]. These isomers have nearly globular molecules. One can expect that they reveal plastic
phase. In earlier calorimetric studies [4,5] significant differences in polymorphism between
subsequent isomers were found:
- for 3,3DM-1B crystallization was observed on heating while on cooling only glass of isotropic
liquid was found [4],
- for 3,3DM-2B and 2,3DM-2B crystallization was observed on cooling [5],
- for 3,3DM-2B additionally the anomaly pointing to a glass transition was identified at lower
temperature [5]. The aim of the present studies for 2,3 DM –2B and 3,3 DM-2B was to get insight
into influence of the position of the OH group in the molecule on the polymorphism of the
substances and on dynamics of their molecules.
II. Experimental
In order to check the sequence of thermodynamic phases differential scanning calorimetry
(DSC) was used on cooling and on heating the sample in the temperature range from 100 K to 300
K. Cooling and heating rate was changed from 1 K/min to 20 K/min. Mass of the sample was 5 mg15 mg.
Neutron scattering measurements were performed for several temperatures using the inverted
geometry spectrometer NERA at the high flux pulsed reactor IBR-2 at the JINR, Dubna, Russia [6].
IINS spectra were observed with help of 16 crystal detectors located at various angles from 20o to
160o in respect to the direction of incident beam. The spectra for different scattering angles were
added up, normalized to the monitor count and the background was subtracted. The corrections for
multiple scattering were not applied.
Measurements have been performed in various chosen temperatures down to 20 K on fast (10
K/min) and slow (1 K/min) cooling and on heating the sample. Sample was placed in the flat
hermetic aluminium vessel of a size of 16×7×0.1 cm3. Scattering intensity I (ω) was measured in
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Materials in Transition
the energy range up to 250meV. Density of states G(ω) was calculated according to the following
formula
d 2σ (κ ,ϖ )
khκ 2
exp(−2W )
G(ϖ )
(binc ) 2
=
dΩdϖ
k0 2Mϖ
1 − exp(−hϖ / k BT )
where: ko, k- are wave vectors of incident and scattered neutrons respectively and binc-stands for the
incoherent scattering length of hydrogen atom, κ is the momentum transfer of the neutrons. M
stands for molecular mass, exp (-2W) is the Debye- Waller factor. At NERA spectrometer the IINS
spectra are obtained simultaneously with the diffraction patterns.
III. Results
Fig.1 presents the scattering intensity vs. incoming neutron wavelength for 2,3 DM-2B at
various temperatures as the example of data obtained on the NERA spectrometer. In the range of
lattice vibrations one can see the intra molecular vibration. Such type of lattice spectra has been
observed for slow and rapid cooling of the sample. Always the spectra are typical for a proton glass.
20000
18000
16000
Intensity [a.u]
14000
12000
10000
8000
6000
4000
2000
0
1
2
3
4
5
6
7
W avelength [A]
Fig1. Scattering intensity vs. neutron wavelength for 2,3DM-2B at various temperatures from
bottom to top: 20 K, 100 K, 200 K, 255 K ( plastic crystal) and 265 K( isotropic liquid). At λ=4Å
the elastic peak is visible.
In Fig.2 the IINS results are presented in form of density of states G(ω) in frequencies for case of
rapid cooled sample of 2,3 DM-2B. No evidence of glass formation was obtained which is in
agreement with DSC results.
Solid State Phenomena Vol. 112
91
600
500
G(ω) [a.u]
400
300
200
100
0
0
100
200
300
400
500
600
700
800
-1
ω [cm ]
Fig. 2 Density of states vs. wavenumber for rapid cooling of 2,3 DM-2B. The measurements were
carried out at temperatures:20 K, 100 K, 150 K, 250 K, 265 K (from top to bottom). Background
was measured at 20 K only. No phase transition was detected and all spectra are measured in plastic
crystalline phase.
1400
1300
1200
1100
G(ω) [a.u]
1000
900
800
700
600
500
400
300
200
100
0
20
40
60
80
100
ω [m e V ]
Fig.3 Density of states at 20 K for a crystal of 2,3 DM-2B (lower curve) and for glass of the plastic
phase of 3,3 DM-2B (spectrum shifted along the vertical axis).
92
Materials in Transition
For 2,3 DM-2B at low energy transfer the parabolic frequency dependence of density of states was
received. The G(ω) ~ ω2 observed (Fig.3 lower curve) is consistent with the Debye theory for
dynamics of crystal lattice. Contrary to that, for 3,3 DM-2B the linear frequency dependence of
density of states G(ω) ~ ω (Fig.3 upper curve) was received . That confirms that at 20 K
investigations were performed for glass phase. This difference is related to harmonic localized
excitations observed in disordered glass [7,8,9] instead of phonons typical for long range ordered
crystal. Intensity of this so-called boson peak depends on details of molecular dynamics in liquid/
plastic glass-formers [10].
In case of diffraction investigations the patterns obtained for all substances were "quite poor”,
because incoherent scattering on hydrogen atoms. Only small and not very distinctive peaks
corresponding to a long range structural order in a crystal of 2,3 DM-2B are present at suitable
angles of detection. No peaks were detected for a glass of plastic phase of 3,3 DM-2B. Tendency to
creation of chains of hydrogen bonded molecules depends on location of OH group in the molecule
of examined isomers.
IV. Summary
In the isomers of neohexanol the various phase diagrams have been found. Influence of
location of the OH group in molecule on solid state polimorphism is shown. Glass of plastic phase
has been found for 3,3DM-2B with the most globular molecules. For 3,3 DM-1B of less globular
molecules formation of hydrogen bonded clusters in liquid phase can be the reason of easy
transition to glass of liquid [7]. No evidence of glass has been detected for 2,3DM-2B. In crystalline
phases of 3.3DM-1B and 2,3DM-2B the long range order of molecules is illustrated by parabolic
shape of density of states at low energy range at 20 K.
Acknowledgements
The paper is partially supported by Polish Ministry of Science and Information Society Technology
( grant no. 1PO3 060 28).
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Materials in Transition
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Neutron Scattering in 3,3-Dimethyl-2-Butanol and 2,3-Dimethyl-2-Butanol
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