Vapor deposition of a nonmesogen prepares highly structured organic glasses

Abstract

We show that glasses with aligned smectic liquid crystal-like order can be produced by physical vapor deposition of a molecule without any equilibrium liquid crystal phases. Smectic-like order in vapor-deposited films was characterized by wide-angle X-ray scattering. A surface equilibration mechanism predicts the highly smectic-like vapor-deposited structure to be a result of significant vertical anchoring at the surface of the equilibrium liquid, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy orientation analysis confirms this prediction. Understanding of the mechanism enables informed engineering of different levels of smectic order in vapor-deposited glasses to suit various applications. The preparation of a glass with orientational and translational order from a nonliquid crystal opens up an exciting paradigm for accessing extreme anisotropy in glassy solids.

Orientationally ordered glasses via controlled deposition

“…By this measure, a short-range equilibrium correlation is converted into long-range order through the agency of the nonequilibrium fabrication process. This is the essence of the results of Bishop et al (5).…”

“…The immediate obstacle to this ambitious program is how to retain a microscopic structure, stabilized by virtue of being at a surface, once the material is no longer at a surface but incorporated into the bulk of the material. In PNAS, Bishop et al (5) report an experimental demonstration of just how this remarkable trick can be pulled off. An elongated organic molecule, posaconazole, was vapor deposited onto a silicon surface at a temperature of 324 K, just below the molecule's glass transition temperature T g , to produce an amorphous film.…”

“…An elongated organic molecule, posaconazole, was vapor deposited onto a silicon surface at a temperature of 324 K, just below the molecule's glass transition temperature T g , to produce an amorphous film. Using grazing-incidence wideangle X-ray scattering and optical birefringence (6), Bishop et al (5) establish that the posaconazole molecules were oriented with their long axes ∼33°from the substrate normal and were organized into layers parallel to the substrate surface. This structure resembles that found in smectic liquid crystal phases but posaconazole does not have any liquid crystal phases.…”

“…It does, however, exhibit a similar smectic-like structure at its equilibrium liquid surface, as established in ref. 5. While this ordering at the equilibrium surface is expected to extend a few molecular layers into the liquid (where a molecular layer is ∼3 nm), ordered films have been deposited up to 1 μm in thickness (5), i.e., macroscopic length scales.…”

Extreme Elasticity Anisotropy in Molecular Glasses

“…The substrate temperature T sub controls the structure of the vapor‐deposited glass through a surface equilibration mechanism that has been described elsewhere. [ 7,18,19 ] Figure 1b presents grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) data for itraconazole glasses deposited at the three substrate temperatures along with schematic illustrations of their structures. For the GIWAXS and BLS experiments, we utilize a coordinate system where the x 3 axis is along the substrate normal, as shown in Figure 1b, with orthogonal axes x 1 and x 2 lying in the plane of the sample.…”