Extreme Elasticity Anisotropy in Molecular Glasses

Abstract

Glasses are generally assumed to be isotropic and there are no literature reports of elastic anisotropy for molecular glasses. However, as glasses formed by physical vapor deposition can be structurally anisotropic, it is of interest to investigate the elastic anisotropy in these materials. Micro‐Brillouin light spectroscopy is used in several experimental geometries to determine the elastic stiffness tensors of three glass films of itraconazole vapor‐deposited at substrate temperatures (Tsub) of 330, 315, and 290 K, respectively. Significant elastic anisotropy is observed and, in these glasses, the elastic anisotropy shows a strong correlation with the molecular orientation. The out‐of‐plane and in‐plane Young's moduli of the high Tsub (330 K) sample, which features a predominantly vertical molecular orientation, exhibit a high anisotropy ratio of 2.2. The observed elastic anisotropy is much larger than those previously observed in liquid crystals and even many crystalline solids.

Orientation‐Engineered Small‐Molecule Semiconductors as Dopant‐Free Hole Transporting Materials for Efficient and Stable Perovskite Solar Cells

“…In fact, this temperature‐dependent molecular orientation has been observed in organic semiconducting glasses, in which the generic tendency of face‐on orientation at lower substrate temperatures is attributed to the lack of surface mobility. [ 41–42 ] It should be noted that glasses of organic semiconductors are naturally deposited as amorphous states in vacuum, unlike the crystallized DPh‐DNTT evaporated films we reported. Referring to the previous studies, [ 41–45 ] we proposed a plausible formation mechanism of the preferential face‐on orientation at lower substrate temperatures for our crystalline vapor‐deposited organic semiconductors.…”

“…[ 41–42 ] It should be noted that glasses of organic semiconductors are naturally deposited as amorphous states in vacuum, unlike the crystallized DPh‐DNTT evaporated films we reported. Referring to the previous studies, [ 41–45 ] we proposed a plausible formation mechanism of the preferential face‐on orientation at lower substrate temperatures for our crystalline vapor‐deposited organic semiconductors. We hypothesize that at low substrate temperature, organic molecules are inactive and lack of surface mobility, resulting in only a limited manner to locally reconfigure themselves.…”

Surface contacts strongly influence the elasticity and thermal conductivity of silica nanoparticle fibers

“…In fact, r a includes the contribution from r b at high W since K (~k n~ra ), the elastic response of a material to uniform compression, is no longer insensitive to stiffening caused by adhesion forces over a large area with radius r b . 47 Summing up this section, the enhanced elasticity in annealed fibers is favored by different processes, which include densification, cementation, and formation of covalent bonds, and their relative contribution depends on the annealing time. The rapid densification process is responsible for the elastic enhancements at short annealing (F-05).…”

On the origin of elasticity and heat conduction anisotropy of liquid crystal elastomers at gigahertz frequencies

“…Therefore, there remains a limited understanding of LCE mechanical anisotropy, especially on the microscopic scale. Here, we use Brillouin light spectroscopy (BLS), which offers a unique and the only not contact tool for evaluating the elasticity 39 of LCEs at GHz frequencies through the measurement of the sound velocities and attenuation of acoustic phonons at different wavelengths and polarizations (Fig. 1d ).…”