Glasses, Optical Materials, and Devices: Current Issues in Science & Technology: Advances in Understanding Glassy State and Glass Transition
Program Organizers: Jincheng Du, University of North Texas; S. Sundaram, Alfred University

Wednesday 2:00 PM
October 2, 2019
Room: A106
Location: Oregon Convention Center

Session Chair: John Mauro, Pennsylvania State University; Pierre Lucas, University of Arizona

2:00 PM  Invited
Fluctuations in Glass-forming Systems: John Mauro1; 1The Pennsylvania State University
    All glasses are topologically disordered materials, yet the degree of disorder can vary as a result of internal fluctuations in structure and topology. These fluctuations depend on both the composition and temperature of the system. Most prior work has considered the mean values of liquid or glass properties, such as the average number of topological degrees of freedom per atom; however, the localized fluctuations in properties also play a key role in governing the macroscopic characteristics. In this presentation, I review recent progress in understanding the role of fluctuations in glass-forming systems.

2:30 PM  Invited
Fragile-to-Strong Transitions in Glass Forming Liquids: Pierre Lucas1; 1University of Arizona
    Since they were first reported almost two decades ago, fragile-to-strong (FTS) transitions have been observed in all categories of glass-forming systems including metallic, covalent, ionic and molecular liquids. In these systems, a transition from Arrhenius to non-Arrhenius viscosity behavior is observed in conjunction with anomalies in multiple thermodynamic variables including the heat capacity, the thermal expansion coefficient and the isothermal compressibility. FTS are therefore associated with a liquid-liquid phase transition which is directly related to the observation of polyamorphism. This presentation will review the experimental evidences supporting the existence of FTS transitions. In particular FTS transitions are found to be concomitant with a peak in heat-capacity as well as density extrema associated with a negative expansion coefficient in the region of the transition. Moreover, spectroscopic analyses also show distinct structural changes across these liquid-liquid transitions. Reports of FTS transitions and polyamorphism in each category of liquid will also be reviewed.

3:00 PM  
Rheological Characterization of Calcium- and Iron-rich Silicate Slags during Solidification: Christopher Giehl1; Mario Kleindienst1; Daniela Ehgartner1; 1Anton Paar
    High temperature rheometry is a sensitive technique to monitor changes in visco-elasticity of molten materials like slags, silicate and glass melts. This may involve subliquidus formation or dissolution of crystals, crystal ripening, bubble coalescence, ascent and degassing processes. Multicomponent silicate melts are, in contrast to e.g. single oxide melts, usually characterized by a crystallization temperature interval, within which the system can be termed a suspension. Concentric cylinder oscillatory rheometry are a means to discriminate viscous and elastic components of the visco-elastic behaviour of partially molten systems. Here, we present rotational and oscillatory concentric cylinder measurements on a calcium- and iron-rich silicate slag with shear-rate dependent behaviour at different super-liquidus to sub-liquidus temperatures. Shear-thinning becomes more pronounced with decreasing temperatures, likely as a result of the increasing solid fraction.

3:20 PM Break

3:40 PM  Invited
Rheology of Glass-forming Liquids as a Probe of the Energy Landscape: Sabyasachi Sen1; 1University of California, Davis
    Atomistic understanding of the dynamical slowdown and strong vs. fragile behavior of supercooled liquids near glass transition remain one of the most intriguing and unsolved problem in condensed matter physics. Although several theoretical models have been proposed in the literature over the last decades to explain these phenomena, direct experimental tests of the validity and the relative merits of these models have remained rather scant. In this talk I will discuss the ongoing studies in our laboratory of the linear and non-linear rheological behavior of a variety of chalcogenide liquids under oscillatory and steady shear. Experiments in the linear regime provide important clues into the nature of the free energy landscape that controls the equilibrium dynamic properties of highly viscous liquids near glass transition, while those in the nonlinear regime will shed light on the modification of this landscape, that gives rise to phenomena such as shear thinning.

4:10 PM  Invited
Accessing New Glassy States via Pressure Processing: Liping Huang1; 1Rensselaer Polytechnic Institute
    Glass has been primarily made by cooling high temperature liquid fast enough to avoid crystallization. This limits the composition range that can form glasses and the resulting structure and properties, as only a small portion of the glassy states can be accessed. Studies by ourselves and others have found that pressure processing provides a means of accessing unique glassy states that can’t reached by melt quenching, resulting in novel properties such as high elastic modulus, high hardness, high thermal-mechanical stability and reduced optical loss/dispersion. Pressure can also be used to consolidate glassy nanoparticles to form nanoglass with composition/structure variation on a much longer length scale than in bulk samples. Our study shows that room temperature consolidation of glassy nanoparticles may provide a universal method for synthesizing oxide glasses with enhanced ductility. Structure-property relations in pressure processed glasses will be discussed in detail, comparing to those from melt quenching.

4:40 PM  Invited
Ultrafast Glass Science – Fundamentals and Applications: S. K. Sundaram1; 1Alfred University
    Understanding ultrashort laser pulses-glass interactions is critical for pushing the frontier of ultrafast glass science and produce novel states and structures in glasses, ceramics, and glass-ceramics. First, an overview of generation and control of ultrashort pulses covering nano-, pico-, femto-, and attosecond timescales will be presented. Chirped pulse amplification (CPA) that led to advancement of ultrashort laser pulses will be introduced, followed by details on how these pulses interact with glasses. Linear and nonlinear optical processes induced by the laser pulses will be discussed. Feasibility of high-harmonic generation (HHG) in quartz crystal and fused silica reported in the literature will be presented. Femtosecond laser based processing e.g., writing of wave guides, gratings, band gap structures, and strengthening, will be described. Several ideas on study of fundamental glass science will be outlined. The presentation will conclude with the promise of extreme light sources in study of materials including glasses.

5:10 PM  
Is λ-transition in Liquid Sulfur a Fragile-to-Strong Transition?: Bing Yuan1; Bruce Aitken2; Sabyasachi Sen1; 1University of California, Davis; 2Corning Inc.
    The abrupt and large increase in the viscosity of liquid sulfur above the -transition temperature Tl corresponds to a structural transformation in the form of ring-to-chain polymerization reaction. The mechanistic connection between this structural transformation and viscosity is investigated by studying the composition dependence of the shear relaxation behavior of supercooled SxSe100-x liquids as their structural evolution mimics that of liquid sulfur across the -transition. The results of parallel-plate rheometry, when taken together, indicate that the viscosity of these liquids is controlled by the S/Se – S/Se bond scission/renewal dynamics and the timescale of this dynamics rapidly increases as the relative concentrations of rings and chains in the structure become comparable. The coexistence of these two types of topological elements in these liquids lowers the conformational entropy of the chain elements due to steric hindrance from the ring elements, resulting in a rapid drop in the fragility as S is added to Se. The same topological effect, resulting from the ring-to-chain transformation in liquid S, renders the highly fragile molecular liquid below Tl to a strong polymerized liquid above Tl.