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Thermal & Dielectric Spectroscopic Investigation on Orientationaly Disordered Crystal- Cyclobutanol
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ScienceDirect Materials Today: Proceedings 18 (2019) 1620–1626
www.materialstoday.com/proceedings
ICAM 18
Thermal & Dielectric Spectroscopic Investigation on Orientationaly Disordered Crystal- Cyclobutanol Nighil Nath M P1, Sulaiman M K 1,2, Mohamed Shahin Thayyil1* 1
Department of Physics, University of Calicut, Kerala, India 2 S.A.R.B.T.M Govt. College Koyilandy, Calicut, India
Abstract Orientationallydisordered crystals (plastic crystals) maintain translational order along their crystallographic axis while continue to have orientational degrees of freedom. Since freezing of orientational motion of molecule leads to glass transition, these rotationally disordered systems form glassy crystals below their glass transition temperature. Because of the presence of translational order, these kind of materials can easily treated in both mathematical and simulation approaches and are considered as the ideal or model system for studying glass transition phenomena. Here by using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS), thermal and dielectric behaviour of the orientation ally disordered phases of an organic plastic crystal cyclobutanol have been studied. During quench cooling of the sample below the melting point, three solid-solid phase transitions, one at 180K called phase I, other at 170K called phase II, and another one at 158 K and glass transition (133K) events were observed using the DSC. The dielectric spectra of the cyclobutanol were recorded in a wide frequency range of 10-2 Hz to 107Hz for different temperatures. The dielectric spectra revealed the presence of the three phases, of which phase I was observed below the melting point up to nearly 180 K, the phase II was observed up to nearly 170 K and phase III was observed further up to 158K. In these phases signatures of two structural α relaxations were observed. The secondary relaxation below the glass transition event was also seen, whose strength was found to be very small compared to those observed in other plastic crystals. The α relaxation showed non-Arrhenius temperature dependence depicted by Vogel-Fulcher-Tammann equation,while secondary relaxation mimicked Arrhenius temperature dependence
© 2019 Elsevier Ltd. All rights reserved. Peer-review under responsibility of the scientific committee of the International Conference on Advanced Materials for Technological Applications – ICAM 18. Keywords:Plastic crystal; glass transition; Solid-Solid Phase Transition; Phase change material; Broadband Dielectric Spectroscopy; DSC
2214-7853© 2019 Elsevier Ltd. All rights reserved. Peer-review under responsibility of the scientific committee of the International Conference on Advanced Materials for Technological Applications – ICAM 18.
Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
1621
1. Introduction Cooling a liquid by circumventing the crystallization results in an elongation of relaxation time and reaches in a metastable supercooled state and on further cooling it reaches to the glassy state. Any liquidif cooled fast enough, can bypass itscollapse to the crystalline phase, and is often called as structural or liquid-glass. However, in the case of liquid molecules with high symmetry the crystallization retains its rotational degrees of freedom due to the decoupling between the translational and rotational degrees of freedom leading to plastic crystalline phase, which on further cooling collapses to a normal crystalline phasewithout any translational or rotational degrees of freedom. Similar to liquid glasses, the plastic cyrstalline phase can also be supercooled to avoid its collapse to the NC phase, where the rotational disorder gets frozen kinetically and is generally referred to as orientational glass or glassy crystal.[1] The glassy crystals have many similarities with that of liquidglasses, but more simpler in mathematical and theoretical perspectives. Systematic study on PCs was done by Timmerman, who described the molecules which show orientational degrees of freedom in its rigid crystalline phase and such materials were named as ‘orientationally disordered crystals (ODIC)[2].They show long range order in translation, but the orientations remainindisordered manner. Due to their plasticity under mechanical stress, ODICs are also known as plastic crystals[2].The molecules forming such materials are usually more or less globular (or spherically symmetric around their crystallographic axis)in shape, providing little steric hindrance for rotationalfreedom [2, 3, 4].Globular molecules,thoseform plastic crystal obeyTimmerrmann’s criteria, entropy of melting (Sm) less than 21 J/Mol*K and satisfy the relation Tb/Tm ≤ 1.86. They are again classified in to three categories on the basis of entropy of melting. The molecules which belong to category I are almost spherical and octahedral, should have entropy of melting between 14 – 21 J/mol*K and have higher value of melting temperature. Higher melting temperatures of these molecules are due to their high symmetry along the crystallographic axis. Plastic crystals formed by these type of molecules show plastic phase over wide temperature range. Hexamethyl ethane and Admantane are typical examples of this category, whose melting temperatures are 220K and 335K respectively. Molecules belonging to category II are almost caged molecules or cyclic molecules in some way, and have entropy of melting between 7-14 J/Mol*K and have considerable melting temperature. In category III, molecules are least globular and hence entropy of melting is less than that for globular molecule i.e. ≤7 J/Mol*K. Compounds belonging to this category are identified by existence of plastic phase over a very narrow temperature range i.e. 45K for cyclohexeneoxide, 34K for cyclohexanol and 25K for cyclohexanone [5]. ODICis an intermediate crystalline state between the super cooled liquid and more ordered crystal [8] and it is the high temperature form of the solid. As the temperature decreases, the mutual orientations of molecules are expected to form short-range order similar to supercooled liquids while the molecular positions are essentially fixed due to long-range intermolecular interaction [2]. One of the most prominent feature of orientationally disordered crystal is that, it shows at least one solid-solid phase transition in their crystalline lattice and therefore it can be considered as a sold-solid phase change material (PCM)wherePCM is a substance with high heat of fusion which melts and solidifies at a certain temperature and is capable of storing large amount of energy i.e. heat of liberation during transition is very small. Hence it can be used as a thermal energy storage devices[7]. Physics of dynamically disordered system is considered as the one of the most prominent sub field of the condensed matter physics. Almost all orientationally disordered systems show the glass transition phenomena in their crystalline phases. Since these systems maintain translational periodicity, glass transition phenomena can be easily understood in both theoretical and mathematical simulation approaches and can be considered as a model system to understand the glass transition phenomena more accurately [4] The re-orientational motions of these molecules become frozen upon cooling, leads to an orientational glass and therefore exhibit glass transition phenomena that are equivalent to that of structural glass formers. Glassy crystal can be ascribed non-ergodic since after sufficiently long time the material is expected to arrive at both translational and orientatinal ordered crystalline state [5,6]. Here we studied the molecular mechanism responsible for the glass transition and verified the universal features of glass transition phenomenon in plastic phases of the ODICcyclobutanol using Broadband Dielectric Spectroscopy (BDS) and Differential Scanning Calorimetry (DSC).
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Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
2. Materials and Methods Cyclobutanol (purity >= 99%) was purchased from Sigma Aldrich and used without any further purification. Cyclobutanol at room temperature is a colorless liquid with no odor. Fig.1. shows the three dimensional view of the molecule.
Fig. 1Chemical Structure of cyclobutanol (C4H7OH)
2.1. Differential Scanning Calorimetry (DSC) DSC is one of the significant experimental technique to study the thermal properties of the materials. It provides different phases, transition temperatures and the enthalpy associated with different transitions.The sample cyclobutanol was loaded in to the liquid sample pan at room temperature. The sample was thermally scanned from 300K to 113K and then back to 300K from 113K at 10K/min. 2.2 Broadband Dielectric Spectroscopy (BDS) Dielectric measurements of ODIC cyclobutanol were carried out using Novocontrol GMBH Alpha dielectric spectrometer over the frequency range 10−2 Hz to 107 Hz in plastic and supercooled plastic phases. The sample was placed between two circular stainless steel electrodes (diameter 30 mm) separated with Teflon spacer 100 micron. The temperature of the sample was controlled by the Novocontrol Quattro system better than 0.1K, with the use of cryostat with nitrogen gas purge. 3. Results and Discussions 3.1 Differential Scanning Calorimetry Three solid-solid phase transitions and glass transition events were observed during thermal scanning using DSC as shown in Fig. 2. The melting point of the sample was obtained as 232K during the reheating of the quench cooled sample. During heating the sample, a small endotherm which occurs at 133K, and is identified as glass transition temperature (Tg), and a small exothermic peak occurs at 158K corresponding to third solid-solid phase transition and was identified as crystal III.A large exothermic peak was observed at 170K, just above the crystal III and is named as crystal II. Another small exothermic peak was observed at 180K, just above the crystal II and is named as crystal
Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
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I.Hence for cyclobutanol, Phase III exists between 158K and 170K, phase II extends from 170K to 180K and Phase Iextends from 180K up to melting temperature.
Fig. 2. DSC curve of cyclobutanol cycled from room temperature to 113K and back to room temperature
3.2 Broadband Dielectric Spectroscopy We measured the complex dielectric permittivity during super cooling the sample for different temperatures atthreefixed frequencies 100Hz, 1KHz and 10KHz. The dielectric loss spectra corresponding to three different frequencies are shown in Fig. 3.None of the crystallization event was observed during the cooling since sample does not have enough time to reach their stable crystalline state. Two kinds of dielectric relaxation processes were observed in the plastic and supercooled plastic phases of cyclobutanol, primary - relaxtion and secondary relaxtion. The more clear spectra showing were obtained during the heating scan (result not presented here)
10
1
100Hz 1KHz 10KHz
" 10
-1
10
-3
120
140
160
180
200
220
Temperature(K) Fig.3. The dielectric loss spectra corresponding to three different frequencies
Structural - relaxtion is observed near and above the glass transition temperature. Cooperative rearrangement of the molecule leads to structural relaxation whose strength increases with decreasing temperature which shifts towards lower frequency with decreasing temperature and finally freezes at Tg. The faster secondary –relaxtion is observed
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Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
below Tg. The strength of the secondary relaxation depends on the molecular mobility of side group (intra molecular) or rotation of the sub group. Secondary relaxation which involves the rotation of the entire molecule is known as Johari-Goldstein (JG) β relaxation which has intermolecular nature.Variation of dielectric permittivity with temperature for fixed frequencies is shown in Fig. 4.
Fig.4. Variation of dielectric permittivity with temperature for fixed frequencies
Temperature dependence of α relaxation processes of cyclobutanol shows non-Arrhenius behaviour and can be fitted using time honoured Vogel-Fluchers-Tammanns(VFT) equation f
,
=f
,
exp −B/(T − T0)
(1)
where T0 is the Vogel temperature at which relaxation time become infinity, f0,α is pre exponential factor, and = / where D and E are strength parameter and activation energy respectively. The parameters = obtained for the equation (1) are log (f , )=10.08,B=1033, T0=97K and strength parameter D=10.65.The glass transition tempetatureTg was as 133K, using VFT equation which is same as that obtained using DSC. Further fragility index m was calculated as 49 and hencecyclobutanolcan be classified as an intermediate fragile glass former according to Angell’s scheme of classification (Fig. 5). Even though most of the plastic crystals are strong in fragility, few of them are fragile e.g. Freon (m=68).
Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
4 2
1625
Cyclobutanol Cyclohexanol Cyclooctanol
Log()
0 -2
m=16
-4 -6
m=49
-8 -10
m=200 0.5
0.6
0.7
0.8
0.9
1.0
Tg/T
Figure 5 Angell plot of cyclobutanol.For comparison strong system (m=16) and fragile system (m=200) are used.
The secondary
–relaxtions show Arrhenius temperature dependence and were analysed using the equation f
= f exp (−Ea/RT)(2)
where Ea is the activation energy and R is the universal gas constant. The activation energy Ea was obtained as 60.24 kJ/mol. 4. Conclusion Relaxation dynamics of plastic and glassy phases of cyclobutanol were investigated using BDS and DSC. Different solid-solid phase transitions and glass transition events were identified with DSC results. Dielectric measurements showed non-Debye and non-Arrhenius character of the structural α relaxation. Cyclobutanol found to be an intermediate fragile glass former with fragility index m=49. Acknowledgements Authors gratefully acknowledge the financial assistance and research fellowship from KSCSTE, Govt. of Kerala, Indiaunder SRS. MST further acknowledgesresearch fundings of KSCSTE – SARD, UGC-MRP, Govt. of India, UGC-DAE, Govt. of India. References [1]. Madhusudan Tyagi and S S N Murthy Study of nature of glass transitions in the plastic crystalline phases of cyclooctanol,cycloheptanol,cyanoadamantane,cis-1,2-dimethylcyclohexane J Chem Phys. 2001;114(8):3640–3652 [2]. Professor J.Timmermanns-Plastic crystal- a historical review.J.Phys.chem.1961 vol-18 No 1.pp1-8 [3]. Ricardo Puertas, Maria A. Rute, JosepSalud, and David O. Lo´pezThermodynamic, crystallographic, and dielectric study of the natureOf glass transitions in cyclo-octanol Physical Review B 69, 224202 -2004 [4]. R. Brand, P. Lunkenheimer,a) and A. Loidl Relaxation dynamics in plastic crystals J Chem Phys. 2002;116(23):10386–1040 [5]. Calorimetric study on orientationally disordered crystals.Cyclohexene Oxide and Cyclohexanone— Nobuo Nakamuro ,Hiroshi suga and Syuzo Seki
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Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
[6]. The polymer–polymorphoid nature of glass aging process Victor S. Minaeva , Nikolai M. Parfenovb,n , Sergey P. Timoshenkova , Victor V. Kalugina , Ludmila P. Batyunyaa , DamirZh. Mukimov [7]. Thermodynamic investigation of a solid–solid phase change material2-Amino-2-methyl-1,3-propanediol by calorimetric methodsTong Bo a,c, Tan Zhi-Cheng b,c,*, Liu Rui-Bin a, Meng Chang-Gong a, Zhang Jing-Nan b [8]. Mayumi Mizukami, Hiroki Fujimori and MasaharuOguni- Possible emergence in plural sets of α and glass transitions in orientationally disordered crystal cyclohexanolSolid State Communications, Vol. 100, No. 2, pp. 83-88, 1996 [9]. Diandra L. Leslie-Pelecky and Norman O. Birge Dielectric measurements of model glass transitions in orientationally disordered crystal cyclooctanol Phys. Rev. B 50, 13250.
ScienceDirect Materials Today: Proceedings 18 (2019) 1620–1626
www.materialstoday.com/proceedings
ICAM 18
Thermal & Dielectric Spectroscopic Investigation on Orientationaly Disordered Crystal- Cyclobutanol Nighil Nath M P1, Sulaiman M K 1,2, Mohamed Shahin Thayyil1* 1
Department of Physics, University of Calicut, Kerala, India 2 S.A.R.B.T.M Govt. College Koyilandy, Calicut, India
Abstract Orientationallydisordered crystals (plastic crystals) maintain translational order along their crystallographic axis while continue to have orientational degrees of freedom. Since freezing of orientational motion of molecule leads to glass transition, these rotationally disordered systems form glassy crystals below their glass transition temperature. Because of the presence of translational order, these kind of materials can easily treated in both mathematical and simulation approaches and are considered as the ideal or model system for studying glass transition phenomena. Here by using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS), thermal and dielectric behaviour of the orientation ally disordered phases of an organic plastic crystal cyclobutanol have been studied. During quench cooling of the sample below the melting point, three solid-solid phase transitions, one at 180K called phase I, other at 170K called phase II, and another one at 158 K and glass transition (133K) events were observed using the DSC. The dielectric spectra of the cyclobutanol were recorded in a wide frequency range of 10-2 Hz to 107Hz for different temperatures. The dielectric spectra revealed the presence of the three phases, of which phase I was observed below the melting point up to nearly 180 K, the phase II was observed up to nearly 170 K and phase III was observed further up to 158K. In these phases signatures of two structural α relaxations were observed. The secondary relaxation below the glass transition event was also seen, whose strength was found to be very small compared to those observed in other plastic crystals. The α relaxation showed non-Arrhenius temperature dependence depicted by Vogel-Fulcher-Tammann equation,while secondary relaxation mimicked Arrhenius temperature dependence
© 2019 Elsevier Ltd. All rights reserved. Peer-review under responsibility of the scientific committee of the International Conference on Advanced Materials for Technological Applications – ICAM 18. Keywords:Plastic crystal; glass transition; Solid-Solid Phase Transition; Phase change material; Broadband Dielectric Spectroscopy; DSC
2214-7853© 2019 Elsevier Ltd. All rights reserved. Peer-review under responsibility of the scientific committee of the International Conference on Advanced Materials for Technological Applications – ICAM 18.
Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
1621
1. Introduction Cooling a liquid by circumventing the crystallization results in an elongation of relaxation time and reaches in a metastable supercooled state and on further cooling it reaches to the glassy state. Any liquidif cooled fast enough, can bypass itscollapse to the crystalline phase, and is often called as structural or liquid-glass. However, in the case of liquid molecules with high symmetry the crystallization retains its rotational degrees of freedom due to the decoupling between the translational and rotational degrees of freedom leading to plastic crystalline phase, which on further cooling collapses to a normal crystalline phasewithout any translational or rotational degrees of freedom. Similar to liquid glasses, the plastic cyrstalline phase can also be supercooled to avoid its collapse to the NC phase, where the rotational disorder gets frozen kinetically and is generally referred to as orientational glass or glassy crystal.[1] The glassy crystals have many similarities with that of liquidglasses, but more simpler in mathematical and theoretical perspectives. Systematic study on PCs was done by Timmerman, who described the molecules which show orientational degrees of freedom in its rigid crystalline phase and such materials were named as ‘orientationally disordered crystals (ODIC)[2].They show long range order in translation, but the orientations remainindisordered manner. Due to their plasticity under mechanical stress, ODICs are also known as plastic crystals[2].The molecules forming such materials are usually more or less globular (or spherically symmetric around their crystallographic axis)in shape, providing little steric hindrance for rotationalfreedom [2, 3, 4].Globular molecules,thoseform plastic crystal obeyTimmerrmann’s criteria, entropy of melting (Sm) less than 21 J/Mol*K and satisfy the relation Tb/Tm ≤ 1.86. They are again classified in to three categories on the basis of entropy of melting. The molecules which belong to category I are almost spherical and octahedral, should have entropy of melting between 14 – 21 J/mol*K and have higher value of melting temperature. Higher melting temperatures of these molecules are due to their high symmetry along the crystallographic axis. Plastic crystals formed by these type of molecules show plastic phase over wide temperature range. Hexamethyl ethane and Admantane are typical examples of this category, whose melting temperatures are 220K and 335K respectively. Molecules belonging to category II are almost caged molecules or cyclic molecules in some way, and have entropy of melting between 7-14 J/Mol*K and have considerable melting temperature. In category III, molecules are least globular and hence entropy of melting is less than that for globular molecule i.e. ≤7 J/Mol*K. Compounds belonging to this category are identified by existence of plastic phase over a very narrow temperature range i.e. 45K for cyclohexeneoxide, 34K for cyclohexanol and 25K for cyclohexanone [5]. ODICis an intermediate crystalline state between the super cooled liquid and more ordered crystal [8] and it is the high temperature form of the solid. As the temperature decreases, the mutual orientations of molecules are expected to form short-range order similar to supercooled liquids while the molecular positions are essentially fixed due to long-range intermolecular interaction [2]. One of the most prominent feature of orientationally disordered crystal is that, it shows at least one solid-solid phase transition in their crystalline lattice and therefore it can be considered as a sold-solid phase change material (PCM)wherePCM is a substance with high heat of fusion which melts and solidifies at a certain temperature and is capable of storing large amount of energy i.e. heat of liberation during transition is very small. Hence it can be used as a thermal energy storage devices[7]. Physics of dynamically disordered system is considered as the one of the most prominent sub field of the condensed matter physics. Almost all orientationally disordered systems show the glass transition phenomena in their crystalline phases. Since these systems maintain translational periodicity, glass transition phenomena can be easily understood in both theoretical and mathematical simulation approaches and can be considered as a model system to understand the glass transition phenomena more accurately [4] The re-orientational motions of these molecules become frozen upon cooling, leads to an orientational glass and therefore exhibit glass transition phenomena that are equivalent to that of structural glass formers. Glassy crystal can be ascribed non-ergodic since after sufficiently long time the material is expected to arrive at both translational and orientatinal ordered crystalline state [5,6]. Here we studied the molecular mechanism responsible for the glass transition and verified the universal features of glass transition phenomenon in plastic phases of the ODICcyclobutanol using Broadband Dielectric Spectroscopy (BDS) and Differential Scanning Calorimetry (DSC).
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Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
2. Materials and Methods Cyclobutanol (purity >= 99%) was purchased from Sigma Aldrich and used without any further purification. Cyclobutanol at room temperature is a colorless liquid with no odor. Fig.1. shows the three dimensional view of the molecule.
Fig. 1Chemical Structure of cyclobutanol (C4H7OH)
2.1. Differential Scanning Calorimetry (DSC) DSC is one of the significant experimental technique to study the thermal properties of the materials. It provides different phases, transition temperatures and the enthalpy associated with different transitions.The sample cyclobutanol was loaded in to the liquid sample pan at room temperature. The sample was thermally scanned from 300K to 113K and then back to 300K from 113K at 10K/min. 2.2 Broadband Dielectric Spectroscopy (BDS) Dielectric measurements of ODIC cyclobutanol were carried out using Novocontrol GMBH Alpha dielectric spectrometer over the frequency range 10−2 Hz to 107 Hz in plastic and supercooled plastic phases. The sample was placed between two circular stainless steel electrodes (diameter 30 mm) separated with Teflon spacer 100 micron. The temperature of the sample was controlled by the Novocontrol Quattro system better than 0.1K, with the use of cryostat with nitrogen gas purge. 3. Results and Discussions 3.1 Differential Scanning Calorimetry Three solid-solid phase transitions and glass transition events were observed during thermal scanning using DSC as shown in Fig. 2. The melting point of the sample was obtained as 232K during the reheating of the quench cooled sample. During heating the sample, a small endotherm which occurs at 133K, and is identified as glass transition temperature (Tg), and a small exothermic peak occurs at 158K corresponding to third solid-solid phase transition and was identified as crystal III.A large exothermic peak was observed at 170K, just above the crystal III and is named as crystal II. Another small exothermic peak was observed at 180K, just above the crystal II and is named as crystal
Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
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I.Hence for cyclobutanol, Phase III exists between 158K and 170K, phase II extends from 170K to 180K and Phase Iextends from 180K up to melting temperature.
Fig. 2. DSC curve of cyclobutanol cycled from room temperature to 113K and back to room temperature
3.2 Broadband Dielectric Spectroscopy We measured the complex dielectric permittivity during super cooling the sample for different temperatures atthreefixed frequencies 100Hz, 1KHz and 10KHz. The dielectric loss spectra corresponding to three different frequencies are shown in Fig. 3.None of the crystallization event was observed during the cooling since sample does not have enough time to reach their stable crystalline state. Two kinds of dielectric relaxation processes were observed in the plastic and supercooled plastic phases of cyclobutanol, primary - relaxtion and secondary relaxtion. The more clear spectra showing were obtained during the heating scan (result not presented here)
10
1
100Hz 1KHz 10KHz
" 10
-1
10
-3
120
140
160
180
200
220
Temperature(K) Fig.3. The dielectric loss spectra corresponding to three different frequencies
Structural - relaxtion is observed near and above the glass transition temperature. Cooperative rearrangement of the molecule leads to structural relaxation whose strength increases with decreasing temperature which shifts towards lower frequency with decreasing temperature and finally freezes at Tg. The faster secondary –relaxtion is observed
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Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
below Tg. The strength of the secondary relaxation depends on the molecular mobility of side group (intra molecular) or rotation of the sub group. Secondary relaxation which involves the rotation of the entire molecule is known as Johari-Goldstein (JG) β relaxation which has intermolecular nature.Variation of dielectric permittivity with temperature for fixed frequencies is shown in Fig. 4.
Fig.4. Variation of dielectric permittivity with temperature for fixed frequencies
Temperature dependence of α relaxation processes of cyclobutanol shows non-Arrhenius behaviour and can be fitted using time honoured Vogel-Fluchers-Tammanns(VFT) equation f
,
=f
,
exp −B/(T − T0)
(1)
where T0 is the Vogel temperature at which relaxation time become infinity, f0,α is pre exponential factor, and = / where D and E are strength parameter and activation energy respectively. The parameters = obtained for the equation (1) are log (f , )=10.08,B=1033, T0=97K and strength parameter D=10.65.The glass transition tempetatureTg was as 133K, using VFT equation which is same as that obtained using DSC. Further fragility index m was calculated as 49 and hencecyclobutanolcan be classified as an intermediate fragile glass former according to Angell’s scheme of classification (Fig. 5). Even though most of the plastic crystals are strong in fragility, few of them are fragile e.g. Freon (m=68).
Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
4 2
1625
Cyclobutanol Cyclohexanol Cyclooctanol
Log()
0 -2
m=16
-4 -6
m=49
-8 -10
m=200 0.5
0.6
0.7
0.8
0.9
1.0
Tg/T
Figure 5 Angell plot of cyclobutanol.For comparison strong system (m=16) and fragile system (m=200) are used.
The secondary
–relaxtions show Arrhenius temperature dependence and were analysed using the equation f
= f exp (−Ea/RT)(2)
where Ea is the activation energy and R is the universal gas constant. The activation energy Ea was obtained as 60.24 kJ/mol. 4. Conclusion Relaxation dynamics of plastic and glassy phases of cyclobutanol were investigated using BDS and DSC. Different solid-solid phase transitions and glass transition events were identified with DSC results. Dielectric measurements showed non-Debye and non-Arrhenius character of the structural α relaxation. Cyclobutanol found to be an intermediate fragile glass former with fragility index m=49. Acknowledgements Authors gratefully acknowledge the financial assistance and research fellowship from KSCSTE, Govt. of Kerala, Indiaunder SRS. MST further acknowledgesresearch fundings of KSCSTE – SARD, UGC-MRP, Govt. of India, UGC-DAE, Govt. of India. References [1]. Madhusudan Tyagi and S S N Murthy Study of nature of glass transitions in the plastic crystalline phases of cyclooctanol,cycloheptanol,cyanoadamantane,cis-1,2-dimethylcyclohexane J Chem Phys. 2001;114(8):3640–3652 [2]. Professor J.Timmermanns-Plastic crystal- a historical review.J.Phys.chem.1961 vol-18 No 1.pp1-8 [3]. Ricardo Puertas, Maria A. Rute, JosepSalud, and David O. Lo´pezThermodynamic, crystallographic, and dielectric study of the natureOf glass transitions in cyclo-octanol Physical Review B 69, 224202 -2004 [4]. R. Brand, P. Lunkenheimer,a) and A. Loidl Relaxation dynamics in plastic crystals J Chem Phys. 2002;116(23):10386–1040 [5]. Calorimetric study on orientationally disordered crystals.Cyclohexene Oxide and Cyclohexanone— Nobuo Nakamuro ,Hiroshi suga and Syuzo Seki
1626
Nighil et al. / Materials Today: Proceedings 18 (2019) 1620–1626
[6]. The polymer–polymorphoid nature of glass aging process Victor S. Minaeva , Nikolai M. Parfenovb,n , Sergey P. Timoshenkova , Victor V. Kalugina , Ludmila P. Batyunyaa , DamirZh. Mukimov [7]. Thermodynamic investigation of a solid–solid phase change material2-Amino-2-methyl-1,3-propanediol by calorimetric methodsTong Bo a,c, Tan Zhi-Cheng b,c,*, Liu Rui-Bin a, Meng Chang-Gong a, Zhang Jing-Nan b [8]. Mayumi Mizukami, Hiroki Fujimori and MasaharuOguni- Possible emergence in plural sets of α and glass transitions in orientationally disordered crystal cyclohexanolSolid State Communications, Vol. 100, No. 2, pp. 83-88, 1996 [9]. Diandra L. Leslie-Pelecky and Norman O. Birge Dielectric measurements of model glass transitions in orientationally disordered crystal cyclooctanol Phys. Rev. B 50, 13250.