Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Q05: Ultra-Stable GlassesFocus
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Sponsoring Units: DPOLY Chair: Gregory McKenna, North Carolina State University; Mark Ediger, University of Wisconsin - Madison Room: Room 128 |
Wednesday, March 8, 2023 3:00PM - 3:12PM |
Q05.00001: Two-step devitrification of ultrastable glasses Mark D Ediger, Camille Scalliet, Cecilia Herrero, Ludovic Berthier The discovery of ultrastable glasses has raised novel challenges about glassy systems. Recent experiments studied the macroscopic devitrification of ultrastable glasses into liquids upon heating but lacked microscopic resolution. We use molecular dynamics simulations to analyse the kinetics of this transformation. In the most stable systems, devitrification occurs after a very large time, but the liquid emerges in two steps. At short times, we observe the rare nucleation and slow growth of isolated droplets containing a liquid maintained under pressure by the rigidity of the surrounding glass. At large times, pressure is released after the droplets coalesce into large domains, which accelerates devitrification. This two-step process produces pronounced deviations from the classical Avrami kinetics and explains the emergence of a giant lengthscale characterizing the devitrification of bulk ultrastable glasses. Our study elucidates the nonequilibrium kinetics of glasses following a large temperature jump, which differs from both equilibrium relaxation and aging dynamics, and will guide future experimental studies. |
Wednesday, March 8, 2023 3:12PM - 3:24PM |
Q05.00002: Surface Mediated Formation of Stable Glasses Zahra Fakhraai, Peng Luo, Aixi Zhang, Alex R Moore, Sarah E Wolf, Shivajee Govind, Haoqiang Zhao, Patrick J Walsh, Robert A Riggleman It is undertowed that enhanced surface mobility mediates stable glass (SG) formation upon physical vapor deposition (PVD). The constraints imposed on the free surface also result in unique structures, such as the wetting of a chemical motif or the preferred orientation of elongated molecules. These structures can be immobilized throughout a PVD glass, which can be varied with substrate deposition temperature and rate. Here we investigate the thermodynamic and kinetic stability of SGs produced by two structurally similar molecules with different equilibrium shapes and molecular level flexibility. We demonstrate that molecular orientation is not necessary to produce SGs, and instead is an indication of reduced surface mobility and stability. Given sufficient equilibration time, with a thick enough mobile surface layer, PVD can generate isotropic SGs that resemble their extrapolated supercooled liquid state. As such, variation of orientational anisotropy can indirectly inform of the thickness of the mobile layer during deposition. Surprisingly, while more flexible molecules can produce kinetically improved stable glasses at high substrate temperatures, their improved packing is detrimental to maintaining enhanced mobility at low temperatures, which reduces their ability to form SGs. |
Wednesday, March 8, 2023 3:24PM - 3:36PM |
Q05.00003: Evidence of Sub-TK Fictive Temperatures Glasses: Vapor Deposited Amorphous Perfluoropolymer and a 50 Million-year-old Amber Gregory B McKenna, Dejie Kong, Amer El Banna, Yan Meng A major premise in glass-formers is the concept of an ideal, thermodynamic glass transition taking place at the Kauzmann temperature TK where the system entropy extrapolates to a zero value. This thermodynamically based TK is associated with the Vogel, Fulcher, Tammann temperature TVFT at which the dynamics extrapolate to divergence above zero Kelvin. At the same time, it is known that many non-crystallizable materials, especially polymers, form glasses. This suggests that the importance of the Kauzmann paradox to glass-formation may be problematic. Here we show results from two non-crystallizable ultra-stable glasses (evidenced by greatly reduced fictive temperatures) that give new insights into the conundrum of the Kauzmann paradox. In the first instance we use vapor deposition to make an ultra-stable amorphous perfluoropolymer (CYTOPTM) that shows a fictive temperature TF that is more than 60 K below the glass transition temperature Tg, and also approximately 11 K below TVFT. The second instance uses length change dilatometry measurements on a 50 million-year-old amber from Fushun, China. In this case direct measurements of the fictive temperature show that the material is not only ultra-stable, but also that the TF is as much as 196 K below the Tg, i.e., over 100 K below TVFT. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q05.00004: Stable film creation by swept swapping in simulations RICHARD B STEPHENS Random atom-pair swapping has been used in molecular dynamics simulations to accelerate the densification and stabilization of glass structures. Equilibrating them deeply below the glass transition requires very long simulations during which crystallization is a constant danger. Here we efficiently create films of size-dispersed, Lennard-Jones atoms which are stabilized down to 0.75 of the glass transition temperature (Tg), have density increased up to 3% and stability up to 500 times the as-deposited film. We achieve this using Metropolis rule Monte Carlo swap in a limited region that moves up through the film. This approach creates a large-atom-rich wave at the top of the swap region; the dis-/re-proportionation processes involved in creating this wave are possibly the source of our densification efficiency. Densification slows down at the highest densities below 0.75 Tg; we will discuss the change in dynamics occurring at this point. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q05.00005: Characterization of component segregation in co-deposited glasses of TCTA and Ir(ppy)3 Yejung Lee, Jianzhu Ju, Shinian Cheng, Junguang Yu, Lian Yu, Mark D Ediger Glasses of organic semiconductors produced by physical vapor deposition (PVD) have shown exceptional properties, such as high stability and control of molecular orientation. However, previous studies have focused on single component systems, and less is known about multi-component PVD glasses. In this work, we characterized co-deposited glasses of Ir(ppy)3 and TCTA by varying the mass ratio and deposition temperature. Grazing incidence wide angle X-ray scattering (GIWAXS) was performed to detect the component segregation. With 10% Ir(ppy)3, the molecules were well dispersed in the co-deposited glasses, while 30% Ir(ppy)3 glasses had large domains based on the analysis of the characteristic anisotropic peak that pure Ir(ppy)3 forms. Furthermore, differential scanning calorimetry (DSC) experiments showed that all co-deposited glasses have high kinetic stability compared to liquid-cooled glasses. |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q05.00006: Surface equilibrium mechanism controls the stability of co-deposited organic semiconductor glasses Shinian Cheng, Yejung Lee, Junguang Yu, Lian Yu, Mark D Ediger Highly stable glasses of organic semiconductors prepared by physical vapor deposition (PVD) are important materials as they inhibit chemical and physical degradation that leads to a loss of device performance. The highly enhanced stability of single-component PVD organic glasses can be understood with surface equilibrium mechanism. In this work, we investigate the effects of substrate temperature (Tsubstrate) on co-deposited glasses of m-MTDATA and TPD. Both spectroscopic ellipsometry and differential scanning calorimetry indicate that the stability is controlled by Tsubstrate/Tg, mixture (where Tg, mixture is the glass transition temperature of the mixture). An additional series of binary organic glasses have been prepared near Tsubstrate=0.85Tg, mixture. Interestingly, all co-deposited glasses show highly enhanced kinetic and thermal stability, comparable to the most stable single-component PVD glasses. These results indicate that the surface equilibrium mechanism can be extended to understand the stability of co-deposited organic glasses. |
Wednesday, March 8, 2023 4:12PM - 4:48PM |
Q05.00007: Relaxation dynamics of stable glassesJavier Rodriguez-Viejo Invited Speaker: Javier Rodriguez
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Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q05.00008: Molecular orientation of vapor-deposited organic glasses at buried heterointerfaces Thomas Ferron, Marie E Fiori, Mark D Ediger, Dean M DeLongchamp, Daniel Sunday Ultra-stable glasses prepared with physical vapor deposition can exhibit a preferred molecular orientation that leads to birefringence. This phenomenon has been extensively characterized in bulk glass, yet there is little information on how this orientation is influenced near buried heterointerfaces despite their importance to material properties. Here, we use polarized resonant soft X-ray reflectivity (P-RSOXR) to simultaneously depth-profile chemical composition and molecular orientation in bilayers of vapor-deposited organic semiconductors. P-RSOXR allows us to characterize a compositionally mixed interface morphology at the nanometer length scale and provide insight into ultra-stable glass assembly during vapor deposition. Our results reveal parallels between the molecular orientation near a buried heterointerface and the bulk structure of co-deposited mixed glasses, likely due to a change in mobility at the interface caused by the underlying material. This work provides potential strategies for realizing control over interfacial properties, a critical step in governing emergent behavior for applications involving ultra-stable glasses. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q05.00009: PVD Glasses: Beta Process Rejuvenation without Loss of Stability Megan Tracy, Benjamin J Kasting, Ranko Richert, Mark D Ediger Stable vapor-deposited films of organic glass-forming molecules transform to the supercooled liquid state in distinct ways compared to their liquid-cooled glass counterparts, featuring an elevated temperature for the onset of transformation upon heating the glass above Tg (Tonset) and a surface-initiated growth front mechanism. In this work, the beta relaxation process in stable glasses of methyl-m-toluate (MMT) is monitored with dielectric spectroscopy. For a glass deposited at 0.90Tg during annealing at 0.98Tg, the dielectric storage component increases significantly in the direction of the anticipated supercooled liquid. Surprisingly, this evolution occurs without any change in Tonset. This suggests that the beta process rejuvenates without any associated rejuvenation of the alpha (primary) relaxation, opening the possibility for new insights into the nature of the motions associated with the beta process and its relationship to the position of the glass in the potential energy landscape. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q05.00010: β-NMR studies of the depth and temperature dependence of dynamics in normal and ultrastable polystyrene glasses Iain D McKenzie, Derek Fujimoto, Victoria L Karner, Ruohong Li, W A MacFarlane, Ryan McFadden, Gerald Morris, Adam N Raegen, Monika Stachura, Michael F Thees, John O Ticknor, James A Forrest We have used β-detected nuclear magnetic resonance (β-NMR) with implanted spin-polarized 8Li+ to study the depth and temperature dependence of the γ-relaxation of polystyrene (PS), which involves motion of the phenyl side groups.1,2 Information about the dynamics is obtained by measuring the average spin-lattice relaxation rate, 1/T1avg of 8Li. Ultrastable glass (USG) films of highly monodisperse, low-molecular weight PS were prepared by physical vapor deposition. USG films exhibit properties similar to those of normal glass (NG) films that have been aged for several years. β-NMR measurements of USG and NG films indicate the bulk γ-relaxation is slower in the USG compared with the NG while the opposite is true near the free surface. We observe a change in the temperature dependence of 1/T1avg for 8Li implanted near the free surface that we associate with the glass transition. The near-surface Tg is lower in the USG film than in the NG film. These trends are more significant for samples with a larger apparent age, which is related to the fictive temperature. There is also a difference between the USG and NG films in the thickness of the near-surface region with enhanced dynamics. |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q05.00011: Formation of stable glasses on soft substrates Peng Luo, Sarah E Wolf, Shivajee Govind, RICHARD B STEPHENS, Donghyup Kim, Cindy Chen, Zahra Fakhraai Surface mediated stable glass (SG) formation upon physical vapor deposition allows access to near-ideal glassy states and tuning glass structures by adjusting the deposition substrate temperature and rate. Here, we demonstrate substrate rigidity as a new parameter to control glass stability and structure. We show that SGs of organic molecules (N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine) deposited on soft substrates (Polydimethylsiloxane) have higher refractive indices, more isotropic orientation, and dramatically suppressed layering structure compared to those deposited on Silicon. Measurements of the devitrification kinetics of these SGs show an additional moving transformation front initiated from the soft substrate, with faster initial velocity than the typically observed transformation front from the glass free surface. The fast transformation kinetics persist to a distance of ~80 - 100 nm from the soft interface, for SGs formed in the intermediate range of substrate temperatures. At lower substrate temperatures, SGs deposited on soft substrates exhibit higher kinetic stability than those deposited on rigid substrates. These results indicate increased range of mobility gradients on soft substrates which facilitates the glass kinetics, allowing access to lower energy states during vapor deposition. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q05.00012: Using Ultrafast Differential Scanning Calorimetry to Correlate Fragility to Ultrastability in Amorphous Chalcogenide Films Christopher N Madsen, Manel Molina-Ruiz, Donez J Horton-Bailey, Thomas J Dauer, Bengisu Yasar, Frances Hellman Amorphous materials, even of the same composition, can have highly variable material properties due to the local structure. This local structure also leads to the so-called "energy landscape" of a glass. An ultrastable glass is any that lies lower in this energy landscape than a traditional quenched glass. It has been hypothesized that fragility is a measure of surface to bulk diffusivity, and is therefore a controlling factor in allowing for vapor-deposited glasses to be grown as ultrastable films. By using ultrafast differential scanning calorimetry, we measure the glass transition temperature and thermodynamic properties of chalcogenide as-deposited films (including Ge-Te and Si-Te) to explore the dependence of ultrastability on fragility. |
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