Nematic-like stable glasses without equilibrium liquid crystal phases
File(s)
Date
2017Author
Ediger, Mark
Lian, Yu
Bishop, Camille
Huang, Chengbin
Gujral, Ankit
Gomez, Jaritza
Publisher
American Institute of Physics
Metadata
Show full item recordAbstract
We report the thermal and structural properties of glasses of posaconazole, a rod-like molecule,
prepared using physical vapor deposition (PVD). PVD glasses of posaconazole can show substantial
molecular orientation depending upon the choice of substrate temperature, Tsubstrate, during deposition.
Ellipsometry and IR measurements indicate that glasses prepared at Tsubstrate very near the glass
transition temperature (Tg) are highly ordered. For these posaconazole glasses, the orientation order
parameter is similar to that observed in macroscopically aligned nematic liquid crystals, indicating that
the molecules are mostly parallel to one another and perpendicular to the interface. To our knowledge,
these are the most anisotropic glasses ever prepared by PVD from a molecule that does not form
equilibrium liquid crystal phases. These results are consistent with a previously proposed mechanism
in which molecular orientation in PVD glasses is inherited from the orientation present at the free
surface of the equilibrium liquid. This mechanism suggests that molecular orientation at the surface
of the equilibrium liquid of posaconazole is nematic-like. Posaconazole glasses can show very high
kinetic stability; the isothermal transformation of a 400 nm glass into the supercooled liquid occurs via
a propagating front that originates at the free surface and requires ∼105
times the structural relaxation
time of the liquid (τα). We also studied the kinetic stability of PVD glasses of itraconazole, which is
a structurally similar molecule with equilibrium liquid crystal phases. While itraconazole glasses can
be even more anisotropic than posaconazole glasses, they exhibit lower kinetic stability.
Subject
liquid crystals, vapor deposition, molecular orientation,
Permanent Link
http://digital.library.wisc.edu/1793/76434Description
The properties of vapor deposited Posaconazole glasses are studied.
Citation
Gómez, J., Gujral, A., Huang, C., Bishop, C., Yu, L. and Ediger, M.D., 2017. Nematic-like stable glasses without equilibrium liquid crystal phases. The Journal of Chemical Physics, 146(5), p.054503.