146
M. Jasiurkowska-Delaporte
at high and low temperatures, respectively. A different crystallization behavior was
observed for 5P-Am*FLAm*P5: On heating from the glassy state, the metastable N*
phase transforms to an Is state which then undergoes crystallization to the Cr2 crystal.
The activation energy of non-isothermal crystallization in the Is phase (E a ≈ 54
kJ/mol) is significantly lower than for isothermal crystallization in the N* phase
(E a ≈ 114 kJ/mol). This can be attributed to the material having lower viscosity
in the isotropic state than in the N* phase, thus better facilitating molecular diffusion. It was found that both compounds displayed a correlation between molecular
dynamics and isothermal crystallization kinetics in the vicinity of the glass transition
temperature.
Complex crystallization was also observed for BBOA. During cooling, part
of the SmB cr phase crystallizes and the remainder vitrifies; the crystallization is
completed upon subsequent heating, when the glass softens. POM investigations
found that the degree of crystallinity increases upon heating, and that it follows
the same Avrami curve observed for crystallization upon cooling. DSC examination found the non-isothermal melt crystallization in the SmB cr phase is driven by
two factors depending on cooling rate: (i) thermodynamic forces at lower cooling
rates (3K/min ≤ φ ≤ 5K/min), with the energy barrier E a ≈ 175 kJ/mol, and (ii)
diffusion mechanism at higher cooling rates (5K/min > φ ≥ 30K/min), with E a
≈ 305 kJ/mol. The isothermal melt crystallization process in SmB cr , tested between
274 and 281 K, is restricted by the formation of nuclei. The isothermal and nonisothermal crystallization processes occurring at φ ≤ 5 K/min have similar activation
energy (E a ≈ 205 kJ/mol), which suggests that both processes are controlled by the
same mechanism. The Avrami and Ozawa parameters of crystal growth observed for
isothermal (2.3 ≤ n A ≤ 2.8) and non-isothermal (2.24 ≤ n o ≤ 2.67) experiments are
reduced in the smectic phase with respect to the three-dimensional process; this may
be due to the constraints placed on the SmB cr fractions by the surrounding crystalline
domains.
These findings may have considerable value in future research on LCs and their
applications; however, further studies are required on the relationship between the
structure of the mesophase and the kinetics of its crystallization.
Acknowledgements This work was financially supported by a National Science Centre (Grant
SONATA11: UMO-2016/21/D/ST3/01299). I thank all my co-workers, especially Dr. T. Rozwadowski for his valuable contribution to studies on crystallization and Dr. E. Juszy´ nska-Gał˛ azka for
DSC measurements and data discussion. I would also like to thank Prof. M. Massalska-Arod´ z for
stimulating discussions and critical reading of the chapter. The author acknowledges Prof. P. Kula
and M. Sc. E. Dmochowska for synthesizing the investigated materials.
References
1. Vallamkondu J, Corgiat E, Buchaiah G, Kandimalla R, Reddy P (2018) Cancers (Basel) 10:462
2. Woltman SJ, Jay GD, Crawford GP (2007) Nat Mater 6:929
M. Jasiurkowska-Delaporte
at high and low temperatures, respectively. A different crystallization behavior was
observed for 5P-Am*FLAm*P5: On heating from the glassy state, the metastable N*
phase transforms to an Is state which then undergoes crystallization to the Cr2 crystal.
The activation energy of non-isothermal crystallization in the Is phase (E a ≈ 54
kJ/mol) is significantly lower than for isothermal crystallization in the N* phase
(E a ≈ 114 kJ/mol). This can be attributed to the material having lower viscosity
in the isotropic state than in the N* phase, thus better facilitating molecular diffusion. It was found that both compounds displayed a correlation between molecular
dynamics and isothermal crystallization kinetics in the vicinity of the glass transition
temperature.
Complex crystallization was also observed for BBOA. During cooling, part
of the SmB cr phase crystallizes and the remainder vitrifies; the crystallization is
completed upon subsequent heating, when the glass softens. POM investigations
found that the degree of crystallinity increases upon heating, and that it follows
the same Avrami curve observed for crystallization upon cooling. DSC examination found the non-isothermal melt crystallization in the SmB cr phase is driven by
two factors depending on cooling rate: (i) thermodynamic forces at lower cooling
rates (3K/min ≤ φ ≤ 5K/min), with the energy barrier E a ≈ 175 kJ/mol, and (ii)
diffusion mechanism at higher cooling rates (5K/min > φ ≥ 30K/min), with E a
≈ 305 kJ/mol. The isothermal melt crystallization process in SmB cr , tested between
274 and 281 K, is restricted by the formation of nuclei. The isothermal and nonisothermal crystallization processes occurring at φ ≤ 5 K/min have similar activation
energy (E a ≈ 205 kJ/mol), which suggests that both processes are controlled by the
same mechanism. The Avrami and Ozawa parameters of crystal growth observed for
isothermal (2.3 ≤ n A ≤ 2.8) and non-isothermal (2.24 ≤ n o ≤ 2.67) experiments are
reduced in the smectic phase with respect to the three-dimensional process; this may
be due to the constraints placed on the SmB cr fractions by the surrounding crystalline
domains.
These findings may have considerable value in future research on LCs and their
applications; however, further studies are required on the relationship between the
structure of the mesophase and the kinetics of its crystallization.
Acknowledgements This work was financially supported by a National Science Centre (Grant
SONATA11: UMO-2016/21/D/ST3/01299). I thank all my co-workers, especially Dr. T. Rozwadowski for his valuable contribution to studies on crystallization and Dr. E. Juszy´ nska-Gał˛ azka for
DSC measurements and data discussion. I would also like to thank Prof. M. Massalska-Arod´ z for
stimulating discussions and critical reading of the chapter. The author acknowledges Prof. P. Kula
and M. Sc. E. Dmochowska for synthesizing the investigated materials.
References
1. Vallamkondu J, Corgiat E, Buchaiah G, Kandimalla R, Reddy P (2018) Cancers (Basel) 10:462
2. Woltman SJ, Jay GD, Crawford GP (2007) Nat Mater 6:929