Organic Glasses with Exceptional Thermodynamic and Kinetic Stability

Abstract

Vapor deposition has been used to create glassy materials with extraordinary thermodynamic and kinetic stability and high density. For glasses prepared from indomethacin or 1,3-bis-(1-naphthyl)-5-(2-naphthyl)benzene, stability is optimized when deposition occurs on substrates at a temperature of 50 K below the conventional glass transition temperature. We attribute the substantial improvement in thermodynamic and kinetic properties to enhanced mobility within a few nanometers of the glass surface during deposition. This technique provides an efficient means of producing glassy materials that are low on the energy landscape and could affect technologies such as amorphous pharmaceuticals.

Supercooled liquids with enhanced orientational order

“…A successive annealing step locks the system into local free-energy minima, dictated by the precursor obtained by PVD. Similarly, PVD of organic glass formers below T g might yield ultradense glasses with highly efficient molecular packing, approaching the limit of the crystal 21,22 . Those new materials are characterized by an extremely low excess enthalpy and by a thermodynamic and kinetic stability neither achievable in ordinary glasses, nor by physical aging, hence the name 'ultrastable glasses'.…”

High Frequency Acoustics in Colloid-Based Meso- and Nanostructures by Spontaneous Brillouin Light Scattering

“…These two molecules are well-known glass-formers and their glasses have been previously prepared with physical vapor deposition. [31,174,175] During deposition, the temperature of the substrate T substrate and the deposition rate are the important control parameters. For this work, T substrate was held near 0.85 T g , i.e., 265 K for IMC and room temperature (≈295 K) for TNB.…”

“…[110,111,[171][172][173] Vapor deposition can build an efficiently packed amorphous material in a layer-by-layer fashion by taking advantage of the enhanced surface dynamics and thus is not limited by the slow relaxation dynamics of the bulk. [31] The mechanical properties of vapor-deposited films are determined using Brillouin light scattering spectroscopy (BLS). Because of the non-destructive nature of BLS, the moduli of the as-deposited glass, the supercooled liquid, and ordinary glass (created by cooling the liquid) can be determined from a single sample.…”

“…It has previously been shown that these deposition conditions produce glasses with low enthalpy, high density, and high kinetic stability. [31,[174][175][176][177] T substrate was controlled by attaching the SiO 2 substrates to a copper temperature stage (Fig. 6.1a).…”

“…The last chapter of this thesis shows how BLS can be used to investigate the mechanics and kinetics of so-called stable organic glasses, i.e., organic glasses that are created by very slow vapor deposition on a temperate substrate. [30,31] By doing so, the molecules have more time to rearrange in an energetically more favorable way, leading to elastic moduli comparable to normal glasses that are aged for at least several hundred years.…”