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High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
Published on: October 31, 2019
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Nematic-like stable glasses without equilibrium liquid crystal phases.
Jaritza Gómez1, Ankit Gujral1, Chengbin Huang2
1Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
The Journal of Chemical Physics
|February 10, 2017
Summary
Physical vapor deposition (PVD) creates highly oriented posaconazole glasses, exhibiting nematic-like molecular alignment. These glasses demonstrate exceptional kinetic stability, surpassing even those of liquid crystal-forming itraconazole.
Area of Science:
- Materials Science
- Physical Chemistry
- Solid-State Physics
Background:
- Posaconazole, a rod-like molecule, was investigated for its thermal and structural properties in glassy states.
- Physical Vapor Deposition (PVD) is a technique used to prepare amorphous solid materials.
- Molecular orientation in glasses can significantly influence their properties and stability.
Purpose of the Study:
- To characterize the thermal and structural properties of posaconazole glasses prepared by PVD.
- To investigate the influence of substrate temperature on molecular orientation in PVD-prepared posaconazole glasses.
- To assess the kinetic stability of these highly oriented glasses.
Main Methods:
- Preparation of posaconazole glasses using physical vapor deposition (PVD) at varying substrate temperatures.
- Characterization of molecular orientation using ellipsometry and infrared (IR) spectroscopy.
- Assessment of kinetic stability through isothermal transformation studies.
Main Results:
- PVD glasses of posaconazole exhibit significant molecular orientation, particularly near the glass transition temperature (Tg).
- The orientation order parameter achieved is comparable to that of aligned nematic liquid crystals, with molecules parallel to each other and perpendicular to the interface.
- These posaconazole glasses display remarkable kinetic stability, with transformation to supercooled liquid occurring over extended timescales (∼105 τα).
- Compared to structurally similar itraconazole glasses, posaconazole glasses show higher kinetic stability despite potentially lower anisotropy.
Conclusions:
- PVD enables the preparation of highly anisotropic posaconazole glasses from a non-liquid crystalline molecule.
- The observed molecular orientation is consistent with a surface-mediated mechanism inherited from the equilibrium liquid's free surface.
- Posaconazole glasses possess exceptional kinetic stability, highlighting their potential for advanced material applications.
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