title: Influence of Hydrogen Bonding on the Kinetic Stability of Vapor-Deposited Glasses of Triazine Derivatives.
abstract: It has recently been established that physical vapor deposition (PVD) can produce organic glasses with enhanced kinetic stability, high density, and anisotropic packing, with the substrate temperature during deposition (Tsubstrate) as the key control parameter. The influence of hydrogen bonding on the formation of PVD glasses has not been fully explored. Herein, we use a high-throughput preparation method to vapor-deposit three triazine derivatives over a wide range of Tsubstrate, from 0.69 to 1.08Tg, where Tgis the glass transition temperature. These model systems are structural analogues containing a functional group with different H-bonding capability at the 2-position of a triazine ring: (1) 2-methylamino-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (NHMe) (H-bond donor), (2) 2-methoxy-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (OMe) (H-bond acceptor), and (3) 2-ethyl-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (Et) (none). Using spectroscopic ellipsometry, we find that the Et and OMe compounds form PVD glasses with relatively high kinetic stability, with the transformation time (scaled by the α-relaxation time) on the order of 103, comparable to other highly stable glasses formed by PVD. In contrast, PVD glasses of NHMe are only slightly more stable than the corresponding liquid-cooled glass. Using IR spectroscopy, we find that both the supercooled liquid and the PVD glasses of the NHMe derivative show a higher average number of bonded NH per molecule than that in the other two compounds. These results suggest that H-bonds hinder the formation of stable glasses, perhaps by limiting the surface mobility. Interestingly, despite this difference in kinetic stability, all three compounds show properties typically observed in highly stable glasses prepared by PVD, including a higher density and anisotropic molecular packing (as characterized by IR and wide-angle X-ray scattering).
authors.affiliation: Département de chimie, Université de Montréal , C.P. 6128, Succ. Centre-Ville, Montréal, Québec H3C 3J7, Canada.
authors.forename: Audrey
authors.identifier: 0000-0002-0867-0231
authors.initials: A
authors.lastname: Laventure
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States.
authors.forename: Ankit
authors.identifier: 0000-0002-5065-2694
authors.initials: A
authors.lastname: Gujral
authors.affiliation: Department of Chemistry and Chemical Engineering, Royal Military College of Canada , Kingston, Ontario K7K 7B4, Canada.
authors.forename: Olivier
authors.identifier: 0000-0002-1737-6843
authors.initials: O
authors.lastname: Lebel
authors.affiliation: Département de chimie, Université de Montréal , C.P. 6128, Succ. Centre-Ville, Montréal, Québec H3C 3J7, Canada.
authors.forename: Christian
authors.identifier: 0000-0001-6144-1318
authors.initials: C
authors.lastname: Pellerin
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States.
authors.forename: M D
authors.identifier: 0000-0003-4715-8473
authors.initials: MD
authors.lastname: Ediger