Showing papers by "Sylwester J. Rzoska published in 2017"

Discovery of Ultra-Crack-Resistant Oxide Glasses with Adaptive Networks

Abstract: Despite their transformative role in our society, oxide glasses remain brittle. Although extrinsic postprocessing techniques can partially mitigate this drawback, they come with undesirable side effects. Alternatively, topological engineering offers an attractive option to enhance the intrinsic strength and damage resistance of glass. On the basis of this approach, we report here the discovery of a novel melt-quenched lithium aluminoborate glass featuring the highest crack resistance ever reported for a bulk oxide glass. Relying on combined mechanical and structural characterizations, we demonstrate that this unusual damage resistance originates from a significant self-adaptivity of the local atomic topology under stress, which, based on a selection of various oxide glasses, is shown to control crack resistance. This renders the lithium aluminoborate glass a promising candidate for engineering applications, such as ultrathin, yet ultrastrong, protective screens.

Structural origin of high crack resistance in sodium aluminoborate glasses

Abstract: Sodium aluminoborate glasses are found to exhibit favorable mechanical properties, especially high crack resistance, due to their relatively low resistance to network compaction during sharp-contact loading. We here reveal the origin of the high crack resistance by investigating changes in structure and mechanical properties in compositions ranging from peralkaline to peraluminous and by varying the pressure history through an isostatic N 2 -mediated pressure treatment at elevated temperature. This approach allows us to study the composition dependence of the ease of the glassy network compaction and the accompanying changes in structure and properties, which shed light on the processes occurring during indentation. Through solid state NMR measurements, we show that the network densification involves an increase in the average coordination number of both boron and aluminum and a shortening of the sodium-oxygen bond length. These changes in the short-range order of the glassy networks manifest themselves as an increase in, e.g., density and indentation hardness. We also demonstrate that the glasses most prone to network compaction exhibit the highest damage resistance, but surprisingly the crack resistance scales better with the relative density increase achieved by the hot compression treatment rather than with the extent of densification induced by indentation. This suggests that tuning the network structure may lead to the development of more damage resistant glasses, thus addressing the main drawback of this class of materials.

Modifier field strength effects on densification behavior and mechanical properties of alkali aluminoborate glasses

Abstract: The constituents of oxide glasses are typically classified as network formers, which form the rigid backbone of glasses, and network modifiers, which tend to either charge stabilize tetrahedral network formers or depolymerize the network. Although it is well known that the properties of glasses depend on their degree of polymerization, little is known about the role of the type of elements used as network modifiers. Here, based on a series of aluminoborate glasses comprising varying alkali oxide modifiers, we show that the glasses' structural and mechanical properties are controlled by the field strength (ratio of charge to size) of the modifiers. Namely, we show that the stiffness, hardness, and toughness depend on a fine balance between the atomic bonding energy, the packing efficiency of the atoms, and the ability of the network to densify reversibly or irreversibly, with each of these features showing a different dependence on the modifier field strength. This opens a new degree of freedom in the optimization of glass properties.

Dissolution Kinetics of Hot Compressed Oxide Glasses.

Abstract: The chemical durability of oxide glasses is an important property for a wide range of applications and can in some cases be tuned through composition optimization. However, these possibilities are relatively limited because around 3/5 of the atoms in most oxide glasses are oxygens. An alternative approach involves post-treatment of the glass. In this work, we focus on the effect of hot compression on dissolution kinetics because it is known to improve, for example, elastic moduli and hardness, whereas its effect on chemical durability is poorly understood. Specifically, we study the bulk glass dissolution rate of phosphate, silicophosphate, borophosphate, borosilicate, and aluminoborosilicate glasses, which have been compressed at 0.5, 1.0, and 2.0 GPa at the glass transition temperature (Tg). We perform weight loss and supplementary modifier leaching measurements of bulk samples immersed in acid (pH 2) and neutral (pH 7) solutions. Compression generally improves the chemical durability as measured from w...

Impact of ferroelectric and superparaelectric nanoparticles on phase transitions and dynamics in nematic liquid crystals

Abstract: Results of broadband dielectric spectroscopy (BDS) studies of pure liquid crystalline (4-pentyloxy-4-biphenylcarbonitryle) 5OCB and its nanocolloids with BaTiO_{3} nanoparticles (NPs) under varying pressure and temperature are presented. The notable impact of NPs on phase transitions and dynamics was found. Particularly strong impact on pretransitional behavior was observed for relatively low concentrations of NPs, which can be related to the NPs-induced disorder. There are also notable differences between pressure and temperature paths of studies for nanocomposites, absent for the pure LC compound. For instance, tests focused on the translational orientational decoupling via the fractional Debye-Stokes-Einstein relation yielded S=0.71 and S=0.3 for the temperature and pressure paths, respectively: S=1 is for the complete coupling. The possible theoretical frame of observed phenomena is also proposed.

Network Glasses Under Pressure: Permanent Densification in Modifier-Free Al2O3−B2O3−P2O5−SiO2 Systems

Abstract: Is your phone's screen cracked, or your car's windshield? Making tougher glass is an important challenge for applications It is known that modifying the structure of an amorphous solid at high pressure and temperature yields properties unattainable under normal conditions, but deeper physical insight is crucial for designing damage-resistant glasses In studying modifier-free quaternary glasses, the authors establish a unified picture of the role of atomic structure in opposing densification, demonstrating that crack resistance can be controlled at the atomic scale

Evaluation of quality changes of beetroot juice after high hydrostatic pressure processing

Abstract: Freshly squeezed commercially available beetroot juice, a popular beverage in Poland, is a good source of betalains, but as a root vegetable can contain undesirable microflora from the soil. The objective of this study was to investigate the effect of new preservation technique, high hydrostatic pressure, on the beetroot juice quality. Samples of beetroot juice were treated with pressure 300, 400 and 500 MPa/20°C/up to 10 min. Reduction in the total count of spoilage microorganisms reached 3.8, 4.1 and 4.5 log cfu/mL, depending on the pressure. After this treatment beetroot juice showed a 11.3–12.2% decrease in betacyanins content and 7.7–8.9% in betaxanthins content. A significant reduction of the number of spoilage microorganisms with a slight degradation of pigments indicates the possibility of industrial application of high pressure to the preservation of beetroot juice.

Dissolution Kinetics of Hot Compressed Oxide Glasses

Abstract: The chemical durability of oxide glasses is an important property for a wide range of applications and can in some cases be tuned through composition optimization. However, these possibilities are relatively limited because around 3/5 of the atoms in most oxide glasses are oxygens. An alternative approach involves post-treatment of the glass. In this work, we focus on the effect of hot compression on dissolution kinetics because it is known to improve, for example, elastic moduli and hardness, whereas its effect on chemical durability is poorly understood. Specifically, we study the bulk glass dissolution rate of phosphate, silicophosphate, borophosphate, borosilicate, and aluminoborosilicate glasses, which have been compressed at 0.5, 1.0, and 2.0 GPa at the glass transition temperature (Tg). We perform weight loss and supplementary modifier leaching measurements of bulk samples immersed in acid (pH 2) and neutral (pH 7) solutions. Compression generally improves the chemical durability as measured from weight loss, but the effect is highly composition- and pressure-dependent. As such, we show that the dissolution mechanisms depend on the topological changes induced by permanent densification, which in turn are a function of the changes in the number of nonbridging oxygens and the network cross-linking. We also demonstrate a direct relationship between the chemical durability and the number of chemical topological constraints per atom (nc) acting within the molecular network.

Pressure-driven structural depolymerization of zinc phosphate glass

Abstract: Understanding pressure-induced structural transformation in glasses is important for designing more damage resistant compositions, since the contact damage that leads to fracture induces high stress levels. However, although phosphorus oxide is an important component in various glasses of industrial interest, knowledge of the structural response of phosphate-based glasses to high pressure remains very limited. In this study, we investigate the influence of hot isostatic compression on the structure, volume densification, and mechanical properties (hardness, crack resistance, and brittleness) of a zinc phosphate glass with O/P ratio = 3.25. Bulk glasses are compressed up to 2 GPa at the glass transition temperature, enabling permanent densification, in turn leading to an increase in hardness and brittleness and decrease in crack resistance. Using Raman and 31P NMR spectroscopy we find that hot compression results in a non-monotonic change in the phosphate network polymerization degree, which is further accompanied by changes in the bond angles and extent of network disorder. We also show that densification during indentation and hot compression is associated with similar structural changes, suggesting that part of the mechanically applied energy during contact damage will be consumed by the pressure-driven structural changes.

Accessing Forbidden Glass Regimes through High-Pressure Sub-Tg Annealing.

Abstract: Density and hardness of glasses are known to increase upon both compression at the glass transition temperature (Tg) and ambient pressure sub-Tg annealing. However, a serial combination of the two methods does not result in higher density and hardness, since the effect of compression is countered by subsequent annealing and vice versa. In this study, we circumvent this by introducing a novel treatment protocol that enables the preparation of high-density, high-hardness bulk aluminosilicate glasses. This is done by first compressing a sodium-magnesium aluminosilicate glass at 1 GPa at Tg, followed by sub-Tg annealing in-situ at 1 GPa. Through density, hardness, and heat capacity measurements, we demonstrate that the effects of hot compression and sub-Tg annealing can be combined to access a “forbidden glass” regime that is inaccessible through thermal history or pressure history variation alone. We also study the relaxation behavior of the densified samples during subsequent ambient pressure sub-Tg annealing. Density and hardness are found to relax and approach their ambient condition values upon annealing, but the difference in relaxation time of density and hardness, which is usually observed for hot compressed glasses, vanishes for samples previously subjected to high-pressure sub-Tg annealing. This confirms the unique configurational state of these glasses.

New dynamics in poly(propylene glycol) based glass-forming nanocomposites

Abstract: Results of broadband dielectric spectroscopy and rheological studies of poly(propylene glycol) + SiO 2 nanocomposites are presented They show that the dynamics in high-concentrated composites is dominated by confinement and adsorption effects The most notable finding is the impact of nanoparticles on fragility, the fractional translational – orientational decoupling and the shift of dynamics towards the pure Vogel-Fulcher-Tammann pattern, associated with the lack of local symmetry preferences

Dynamics in poly(propylene glycol) and silica oxide nanoparticles composite glassforming system

Abstract: Results of broadband dielectric spectroscopy and rheological studies of poly(propylene glycol) + SiO${_2}$ nanocomposites are presented. They show that the dynamics in high-concentrated composite is determined by confinement and adsorption effects, resulting from interactions of confined polymers correspond with the host system at the interface between PPG and solid nanoparticles. The evolution of relaxation times follows the clear Vogel-Fulcher-Tammann pattern, what is proved by the supplementary activation energy temperature index analysis. The strong influence of nanoparticles on the transitional dynamics and the fragility in the ultraviscous domain was noted.