Large Mismatch in T_g Values Does Not Impede Formation of Stable Co-deposited Glasses

It has been well-established that the right combination of substrate temperature and deposition rate allows for the formation of a vapor-deposited glass with enhanced stability for a variety of materials. The stability of vapor-deposited glasses of more than one component, which are particularly important for technological applications such as OLED screens, is only just starting to be explored. In this work, we study the co-deposited glasses of methyl-m-toluate (MMT) and methyl acetate (MeAc), both small molecules that form stable glasses through vapor deposition. These particular molecules are very similar structurally, consisting of the same ester group with bonded to either a methyl group (MeAc) or a larger phenyl ring (MMT); however, their T_g values are different by ~50%, meaning that they have very different surface mobilities at the same substrate temperature. In this work, we observe the formation of stable vapor-deposited glasses of MMT/MeAc mixtures using dielectric spectroscopy, noting a similar dependence of the stability on the substrate temperature to the pure components relative to the T_g of the mixture. This result suggests that very large differences in T_g are not an impediment to the formation of stable co-deposited glasses.