Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session A43: Focus Session: Stable Glasses and Their Properties |
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Sponsoring Units: DPOLY Chair: Kenneth Kearns, Dow Chemicals Room: 214C |
Monday, March 2, 2015 8:00AM - 8:12AM |
A43.00001: Stable glasses from strong liquids Yeong Zen Chua, Mathias Ahrenberg, Michael Tylinski, Mark D. Ediger, Christoph Schick To date, only several materials have been observed to form ultra-stable glasses by vapor deposition. Some authors have suggested that fragility might be a controlling factor in the ability to form stable glasses by vapor deposition, with highly stable glasses only being possible for highly fragile liquids. Glasses of ethylcyclohexane, fragility index 56.5, and 1-pentene, a very small molecule, produced by physical vapor deposition have been characterized by \textit{in situ} AC chip nanocalorimetry. Since the fragility index of 1-pentene was not available, it was determined as 52 from the calorimetric glass transition temperatures measured in the frequency range from 0.2 Hz to 4 kHz. Ethylcyclohexane and 1-pentene are both strong glass formers, for which possibility of stable glass formation has been questioned. On the contrary, we observed formation of highly stable glasses of ethylcyclohexane and 1-pentene. The results on ethylcyclohexane and 1-pentene will be presented and compared with literature data of other known glass formers. [Preview Abstract] |
Monday, March 2, 2015 8:12AM - 8:24AM |
A43.00002: Stable Glasses of a Low Fragility Organic Liquid M. Tylinski, A. Sepulveda, A. Guiseppi-Elie, R. Richert, Y.Z. Chua, C. Schick, M.D. Ediger We have created stable glasses of the low fragility liquid methyl-$\textit{m}$-toluate (MMT, $\textit{m}$ = 60). The MMT stable glass films are prepared by physical vapor deposition and characterized $\textit{in situ}$ with AC nanocalorimetry and dielectric spectroscopy. Stable glasses of MMT have lower heat capacities and increased kinetic stability compared to the liquid-cooled glass. The films transform into the supercooled liquid via two mechanisms. A propagating front controls the transformation of thin films while a bulk mechanism dominates the transformation of thick films. This behavior is similar to other stable glass systems and shows that stable glasses can be prepared from liquids with a very wide range of fragilities (60 $<$ $\textit{m}$ $<$ 147). In one respect MMT stands out from previously studied systems. When a stable glass of MMT is annealed above T$_{g}$ the surface-initiated-front propagates 5 $\mu$m into the sample before the bulk mechanism dominates the transformation. This 5 $\mu$m length scale is significantly larger than what has been observed in other stable glass systems. [Preview Abstract] |
Monday, March 2, 2015 8:24AM - 8:36AM |
A43.00003: Synthesis and Characterization of Exceptionally Stable Glasses of 1,3-Bis(1-naphthyl),5-(2-aryl)benzene Tianyi Liu, Kevin Cheng, Elmira Salami, Feng Gao, Chen Li, Xiao Tong, Yue Zhang, Yi-Chih Lin, William Zhang, Ethan Glor, Patrick Walsh, Zahra Fakhraai Stable glasses can be prepared by physical vapor deposition (PVD). Compared to ordinary glasses, stable glasses have exceptional properties such as higher density and thermal stability. Deposition temperature is one of the most important parameters that controls the properties of PVD glasses. When scaled to the glass transition temperature (T$_{g})$, most stable glasses are usually obtained at deposition temperatures around 0.85 T$_{g}$. Chemical structure, entropy of super-cooled liquid, fragility and enhanced mobility may all affect the most stable structure obtained via PVD . To examine the effect of chemical structure, specifically the molecular weight effect on the stability of PVD glasses, we synthesized and characterized stable glasses of small organic molecule 1,3-bis(1-naphthyl),5-(2-naphthyl)benzene ($\alpha $,$\alpha $,$\beta $TNB) and its molecular analogues. With systematically changing its chemical structure, thermal expansion coefficients, fictive temperature and density of stable glasses all vary systematically. These results indicate the robust nature of stable glass formation and can elucidate the processes by which these glasses are formed. [Preview Abstract] |
Monday, March 2, 2015 8:36AM - 8:48AM |
A43.00004: Using deposition rate as a means to alter the properties of small molecule organic glasses for OLED applications Kenneth Kearns, Paige Krzyskowski, Zachary Devereaux Organic light emitting diode (OLED) devices rely on vapor-deposited, small molecule organic glasses. Recent work has shown that deposition condition plays a critical role in altering OLED device performance. Here it will be shown that the deposition rate alters the onset and fictive temperatures measured by differential scanning calorimetry (DSC) of the deposited glass. Glasses of the common hole transport materials NPD and TPD were prepared with onset temperatures 17 and 16 K higher, respectively, than the ordinary glass prepared by cooling the supercooled liquid. The thermal stability of glasses in functioning devices can be underestimated due to increases in onset temperature relative to Tg. The fictive temperatures for NPD and TPD were 32 and 27 K lower, respectively, than the Tg of the ordinary glass. These results are consistent with literature reports on other non-OLED glasses where enhanced surface mobility allowed for glasses with similar properties to be made. Ellipsometry studies on NPD showed that the fictive and onset temperatures were consistent with the DSC results. Additionally, the modeled birefringence of the as-deposited NPD glass was non-zero and quickly decreased upon heating above the onset temperature, which has implications for device performance. [Preview Abstract] |
Monday, March 2, 2015 8:48AM - 9:00AM |
A43.00005: Structural equivalence of equal-energy vapor deposited and liquid cooled films in two dimensions Daniel Reid, Ivan Lyubimov, Juan de Pablo Vapor deposition has been shown to provide a means of producing supercooled liquids with exceptional structural and kinetic stability compared to samples prepared by gradual cooling of a liquid. In this work, we study two-dimensional binary glassy films formed by vapor deposition and liquid cooling. We show that distinctive local structural regimes correspond directly to the structural energy of these films. We find the path towards equilibrium to be characterized by a transition in these structural regimes from medium sized square-ordered clusters to states with significant pentagonal local order. Tracking the degree of local order over a range of structural energies using both formation strategies, we find that the structure of vapor deposited and liquid cooled films are equivalent in films with equal inherent structural energies. Previous work has found that the substrate temperature that yields minimum energy for a vapor deposited film lies near 85\% of the material's glass transition temperature. Our simulations indicate that in two dimensions, the optimal substrate temperature for stable glass formation decreases with deposition rate. [Preview Abstract] |
Monday, March 2, 2015 9:00AM - 9:12AM |
A43.00006: Do Two-Level-Systems and Boson Peak persist or disappear in highly stable glasses? Miguel A. Ramos, Tomas Perez-Castaneda, Rafael Jimenez-Rioboo, Cristian Rodriguez-Tinoco, Javier Rodriguez-Viejo We have investigated how deep kinetic and thermodynamic stabilization in glasses can affect their universal properties at low temperatures. In particular, we have studied two different kinds of material which allow us to access highly-stable glassy states, as well as their corresponding conventional glasses: (i) ancient amber, which is a glass which has experienced an extremely long hyperaging process; and (ii) ultrastable thin-film glasses of indomethacin, prepared by physical vapor deposition at temperatures around 85{\%} of its glass-transition temperature. Specifically, we have studied 110-million-year-old$^{\mathrm{\thinspace }}$amber samples from El Soplao (Spain). Specific heat Cp measurements of pristine and rejuvenated samples were conducted in the temperature range 0.07K \textless T \textless 30K, as well as around its glass-transition temperature Tg $=$ 150\textordmasculine C. A modest increase of the boson-peak height (in Cp/T$^{\mathrm{3}})$ with increasing rejuvenation was observed. The amount of two-level systems (TLS) was however found to be exactly the same for the pristine hyperaged amber as for the subsequently rejuvenated samples. On the other hand, we have observed an unexpected suppression of the universal TLS in the ultrastable glass of indomethacin, whereas conventionally prepared thin films of the same material exhibit the usual linear term in Cp below 1 K ascribed to TLS in glasses. [Preview Abstract] |
Monday, March 2, 2015 9:12AM - 9:48AM |
A43.00007: Dielectric Relaxation of Materials that Form Ultra-Stable Glasses Invited Speaker: Ranko Richert Physical vapor deposition of glass forming materials onto substrates at temperatures around 0.8 Tg produces glasses of high density and low enthalpy. Using interdigitated electrode cells as substrates, such stable glasses can be studied by dielectric spectroscopy in situ. This technique is applied to monitor the dynamics of stable films upon their conversion to the ordinary supercooled liquid state. The dielectric loss during transformation indicates that the softening proceeds by a growth front mechanism and generates the ordinary liquid state without forming intermediates. The same technique is also used to assess the residual dynamics of the stable glassy state. We observe that processes such as the Johari-Goldstein beta relaxation are strongly suppressed in this stable state, consistent with the relatively low fictive temperature of these glassy states. \\[4pt] [1] Z. Chen, A. Sep\'{u}lveda, M. D. Ediger, R. Richert, J. Chem. Phys. 138, 12A519 (2013).\\[0pt] [2] A. Sep\'{u}lveda, M. Tylinski, A. Guiseppi-Elie, R. Richert, M. D. Ediger, Phys. Rev. Lett. 113, 045901 (2014). [Preview Abstract] |
Monday, March 2, 2015 9:48AM - 10:00AM |
A43.00008: Glasses with extreme anisotropy: vapor-deposition of liquid crystals Jaritza Gomez, Ankit Gujral, Mark D. Ediger Vapor-deposited glasses can exhibit considerable anisotropy even when prepared from molecules for which no liquid crystalline states are known. Here we use spectroscopic ellipsometry to characterize vapor-deposited glasses of itraconazole, a known liquid crystal former. We are able to prepare macroscopically homogenous birefringent glasses of itraconazole consistent with single liquid crystalline domains. Glasses prepared on substrates held between T$_{g}$ -- 10 K and the clearing temperature show a positive birefringence, indicating that itraconazole molecules orient perpendicular to the substrate. Results from wide angle x-ray scattering indicate that a smectic phase is prepared by vapor deposition at T$_{sub}$ $=$ T$_{g}$. Depositions onto low temperature substrates prepare glasses in which itraconazole molecules orient parallel to the substrate. These results confirm our ability to use liquid crystals to prepare glasses with extreme anisotropy through physical vapor deposition. [Preview Abstract] |
Monday, March 2, 2015 10:00AM - 10:12AM |
A43.00009: Controlling molecular orientational anisotropy in simulated vapor-deposited glasses Ivan Lyubimov, Lucas Antony, Juan de Pablo It has been shown that stable glasses can be formed via physical vapor deposition on a substrate with the properly tuned temperature. The kinetic stability of vapor deposited glasses has been well investigated, whereas some properties such as the anisotropy of molecular orientation is still not well characterized. We have performed molecular dynamics simulations mimicking the experimental vapor deposition process. The generic coarse-grained model for a small organic molecule reproduces the experimentally observed dependence of molecular orientation on the substrate temperature. The molecular orientation in the glasses changes with the substrate temperature from isotropic at the glass transition temperature, T$_{\mathrm{g}}$, to slightly normal to the substrate at temperatures just below T$_{\mathrm{g}}$. For very low substrate temperatures the molecular orientation becomes predominantly parallel to the substrate, as expected. We investigate the mechanism of this behavior and explain the tendency to orient perpendicularly to the substrate in terms of equilibrium liquid properties at a free interface. Our results provide insight into the emergence and role of anisotropic packing in the stability of vapor deposited glasses. [Preview Abstract] |
Monday, March 2, 2015 10:12AM - 10:24AM |
A43.00010: The stability of a simulated model-glass created by cooling at a constant rate Hannah Staley, Elijah Flenner, Grzegorz Szamel Vapor deposition is used to create glasses that are much more stable than those obtained by cooling. To understand properties of stable glasses, computer simulations of vapor deposition and of random pinning have been used to create and examine properties of simulated stable glasses. However, little is known about the stability of simulated glasses that are created by cooling at a constant rate. We create simulated glasses by cooling a model glass-former at different rates. We examine the glass's stability by measuring the average potential energy, the average inherent structure energy, the dynamics upon reheating, and the shear modulus. When possible, we compare these results to those obtained from simulations of vapor deposited glasses and from simulated glasses created by random pinning. [Preview Abstract] |
Monday, March 2, 2015 10:24AM - 10:36AM |
A43.00011: Beating the bulk: Bypassing the bulk glass transition by fast heating Marta Gonzalez-Silveira, Cristian Rodriguez-Tinoco, Joan Rafols-Ribe, Aitor F. Lopeandia, Maria Teresa Clavaguera-Mora, Javier Rodriguez-Viejo Transformation into the supercooled liquid via propagating fronts has been thoroughly studied in several ultrastable thin film glasses. In this work we show that the transformation mechanism in vapor deposited films of IMC has profound implications in the analysis of the specific heat curves [1]. We propose an ad-hoc surface normalization of the heat capacity data that yields curves which collapse into a single one irrespective of their thickness. The surface-normalized specific heat curves are fitted with a heterogeneous transformation model to evaluate the velocity of the growth front over a much wider temperature interval than previously reported. In addition, we evaluate the transformation rate in films with lower stability. Interestingly, the transformation via parallel fronts is not an exclusive characteristic of ultrastable glasses. We observe how fast heating rates can induce this type of transformation in glassy films whose stabilities are close to the conventional glass. Although the absolute velocity of the growth front depends on stability, no change is observed in the relation between velocity and relaxation time as a function of stability. \\[4pt] [1] C. Rodriguez-Tinoco, et al. J. Phys. Chem. B, 2014, 118, 10795 [Preview Abstract] |
Monday, March 2, 2015 10:36AM - 10:48AM |
A43.00012: How much time is needed to form a stable glass? AC calorimetric study of vapor-deposited glasses of ethylcyclohexane Christoph Schick, Yeong Zen Chua, Mathias Ahrenberg, Michael Tylinski, Mark D. Ediger Consistent with previous work on other organic molecules, we observe that highly stable glasses are formed at substrate temperatures around 0.85 Tg, where Tg is the conventional glass transition temperature. Ethylcyclohexane is the least fragile organic glass-former for which stable glass formation has been established. The isothermal transformation of the vapor-deposited glasses into the supercooled liquid state was also measured. At eight substrate temperatures, the transformation time was measured for glasses prepared with deposition rates across a range of four orders of magnitude. At low substrate temperatures the transformation time is strongly dependent upon deposition rate, while the dependence weakens as Tg is approached from below. These data provide an estimate for the surface equilibration time required to maximize kinetic stability at each substrate temperature. This surface equilibration time is much smaller than the bulk alpha-relaxation time and within two orders of magnitude of the beta-relaxation time of the ordinary glass. Stable glasses are formed even for substrate temperatures below the Vogel and the Kauzmann temperatures. Surprisingly, glasses formed in the limit of slow deposition at the lowest substrate temperatures are not as stable as those formed near 0.85 Tg. [Preview Abstract] |
Monday, March 2, 2015 10:48AM - 11:00AM |
A43.00013: Controling thickness dependent elastic moduli of organic glass films using deposition temperature Bryan Vogt The elastic moduli of vapor-deposited small molecule glasses, commonly utilized for OLEDs, are examined using surface wrinkling. It is known that the deposition temperature can strongly influence the dynamics of vapor deposited glasses and this can be used to tune the modulus of bulk-like glasses. Here, examination of ultrathin ($<$30 nm) films provides a route to further test hypotheses about mobile surface layers near Tg. We find that the proximity of the mechanical testing temperature to bulk Tg controls if the modulus is increased or decreased in ultrathin films for materials deposited at low temperatures. Moreover, the thin film behavior of these small molecule glasses are altered by the deposition temperature to generate films with moduli nearly twice that obtained for analogous films fabricated under normal vapor deposition conditions. For N,N$'$-Di-[(1-Naphthyl)-(N,N$'$-diphenyl]-1,1$'$-biphenyl)-4-4$'$-diamine (NPD) with a bulk Tg of $\sim$90$^{\circ}$C, the modulus of the material is optimized if deposited at 70 C (0.94Tg). The stable glass deposition temperature of 0.85Tg reported originally by Ediger and coworkers results in more than 20\% decrease in the elastic modulus. This suggests that the optimum deposition temperature depends on property of interest. [Preview Abstract] |
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