Nematic-like stable glasses without equilibrium liquid crystal phases.
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 Tsubstratevery 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 ∼105times 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.
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Jaritza
J
Gómez
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Ankit
0000000250652694
A
Gujral
School of Pharmacy, University of Wisconsin-Madison, 777 Highland Avenue, Madison, Wisconsin 53705-2222, USA.
Chengbin
C
Huang
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Camille
0000000228891752
C
Bishop
School of Pharmacy, University of Wisconsin-Madison, 777 Highland Avenue, Madison, Wisconsin 53705-2222, USA.
Lian
L
Yu
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
M D
0000000347158473
MD
Ediger