Atomic scale foundation of temperature-dependent bonding constraints in network glasses and liquids

Bauchy, Mathieu; Micoulaut, Matthieu

doi:10.1016/j.jnoncrysol.2011.03.017

Cited by 134 publications

(185 citation statements)

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“…To derive angular (BB) constraints, we follow the angular motion around each individual atom k (k ¼ O, Si) defined by a set of two neighbours. Over the time MD trajectory, the corresponding bond-angle distribution P k (y) allows defining a mean (the first moment of P k (y)) and a standard deviation s k (the second moment) that shows a bimodal distribution f(s k ) for various thermodynamic conditions 15,19 . Atoms subject to a rigid bending interaction contribute to the part of f(s k ) with low s k (typically, s k o10°), have a corresponding angle that acts as a rigid BB constraint, and induce network stiffening.…”

Section: Glass Transition Cyclementioning

confidence: 99%

Densified network glasses and liquids with thermodynamically reversible and structurally adaptive behaviour

2015

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If crystallization can be avoided during cooling, a liquid will display a substantial increase of its viscosity, and will form a glass that behaves as a solid with a relaxation time that grows exponentially with decreasing temperature. Given this 'off-equilibrium' nature, a hysteresis loop appears when a cooling/heating cycle is performed across the glass transition. Here we report on molecular dynamics simulations of densified glass-forming liquids that follow this kind of cycle. Over a finite pressure interval, minuscule thermal changes are found, revealing glasses of 'thermally reversible' character with optimal volumetric or enthalpic recovery. By analysing the topology of the atomic network structure, we find that corresponding liquids adapt under the pressure-induced increasing stress by experiencing larger bond-angle excursions. The analysis of the dynamic behaviour reveals that the structural relaxation time is substantially reduced in these adaptive liquids, and also drives the reversible character of the glass transition. Ultimately, the results substantiate the notion of stress-free (Maxwell isostatic) rigidity in disordered molecular systems, while also revealing new implications for the topological engineering of complex materials.

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Section: Glass Transition Cyclementioning

confidence: 99%

Densified network glasses and liquids with thermodynamically reversible and structurally adaptive behaviour

2015

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“…Following the methodology reported in Ref. [21], we analyzed each MD trajectory to enumerate BS and BB constraints using a method already well established for chalcogenide and oxide glasses [35][36][37][38][39]. To count the number of BS constraints that apply to a central atom, we compute the radial excursion σ r of each neighbor.…”

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“…We perform the same kind of analysis to enumerate the BB constraints applying to a central atom 0 by computing the angular excursion σ θ of each angleî0j formed with the i, j first neighbors. Following this method, the distinction between active and inactive constraints can be clearly established at the atomic scale [21,38]. Note that free water molecules are excluded from this enumeration, as they do not belong to the network and, thus, do not contribute to its global rigidity.…”

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“…This can be explained by the fact that Mauro's model assumes an equivalent contribution of each constraint to the macroscopic hardness. However, the energy of BB constraints is typically lower than that of BS constraints [38,41], so that both should not necessarily contribute with the same weight to hardness. Moreover, angular and radial constraints should have a different contribution to resist different kinds of deformations like bulk isostatic compression or shearing.…”

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Rigidity Transition in Materials: Hardness is Driven by Weak Atomic Constraints

et al. 2015

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Understanding the composition dependence of the hardness in materials is of primary importance for infrastructures and handled devices. Stimulated by the need for stronger protective screens, topological constraint theory has recently been used to predict the hardness in glasses. Herein, we report that the concept of rigidity transition can be extended to a broader range of materials than just glass. We show that hardness depends linearly on the number of angular constraints, which, compared to radial interactions, constitute the weaker ones acting between the atoms. This leads to a predictive model for hardness, generally applicable to any crystalline or glassy material. DOI: 10.1103/PhysRevLett.114.125502 PACS numbers: 62.20.Qp, 31.15.xv, 61.43.−j Rigidity theory [1-4], or topological constraint theory, is a powerful tool for capturing the atomic topology of glasses by reducing their network to mechanical trusses [5]. Following this mechanical analogy, a glass can be flexible, stressed-rigid, or isostatic, if the number of constraints per atom n c , comprising radial bond stretching (BS) and angular bond bending (BB), is lower, higher, or equal to three, the number of degrees of freedom per atom, respectively. Flexible networks show internal degrees of freedom, the floppy modes [6], which allow for local deformations; whereas stressed-rigid ones are completely locked by their high connectivity. In between, by being rigid but free of eigenstress [7], compositions exhibiting an isostatic behavior show some remarkable properties, such as a space-filling tendency [8], very weak aging [9], and anomalous behaviors, such as maximal fracture toughness [10].One of the major successes of this approach is the design of the Gorilla© Glass 3 by Corning©, which was created by atomic-scale modeling before anything had been melted in the lab [11,12]. Indeed, by capturing the chemical details of glasses that are relevant to macroscopic properties while filtering out those that are not, rigidity theory [13][14][15] has been used to predict the composition dependence of hardness, H, which characterizes resistance to permanent deformations under a load. Hence, topological constraint theory is a promising tool for designing stronger materials, which has recently been identified as a "grand challenge" for the future [16][17][18]. Topological constraint theory has also been applied to studying the folding of proteins [19,20]. However, it is still unknown whether it could be applied to a larger range of materials and, consequently, used to predict mechanical properties like hardness from the mere knowledge of composition.Recently, relying on molecular dynamics (MD) simulations, we showed that rigidity concepts could be applied to calcium-silicate-hydrate, ðCaOÞ x ðSiO 2 Þ 1−x−y ðH 2 OÞ y , or C-S-H, the binding phase of concrete [21]. From a topological point of view, C-S-H is a complex material as (1) it contains several chemical components, (2) its structure is anisotropic, inhomogeneous, and partially crystalline [22][23][24][...

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“…The glass transition manifested with a change in the slope of V (T ), as typically observed in silicate glasses. 25 The glass transition temperature T g can be determined from the cross-point of the high-and low-temperature extrapolation of V (T ). We found T g = 1098 K with a cooling rate of 20 K/ps.…”

Section: Glass Transitionmentioning

confidence: 99%

Order and disorder in calcium–silicate–hydrate

Bauchy

Qomi

Ulm

et al. 2014

The Journal of Chemical Physics

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Quasielastic and inelastic neutron scattering on hydrated calcium silicate pastes J. Chem. Phys. 121, 3212 (2004) Despite advances in the characterization and modeling of cement hydrates, the atomic order in Calcium-Silicate-Hydrate (C-S-H), the binding phase of cement, remains an open question. Indeed, in contrast to the former crystalline model, recent molecular models suggest that the nanoscale structure of C-S-H is amorphous. To elucidate this issue, we analyzed the structure of a realistic simulated model of C-S-H, and compared the latter to crystalline tobermorite, a natural analogue of C-S-H, and to an artificial ideal glass. The results clearly indicate that C-S-H appears as amorphous, when averaged on all atoms. However, an analysis of the order around each atomic species reveals that its structure shows an intermediate degree of order, retaining some characteristics of the crystal while acquiring an overall glass-like disorder. Thanks to a detailed quantification of order and disorder, we show that, while C-S-H retains some signatures of a tobermoritelike layered structure, hydrated species are completely amorphous. © 2014 AIP Publishing LLC.

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Atomic scale foundation of temperature-dependent bonding constraints in network glasses and liquids

Cited by 134 publications

References 64 publications

Densified network glasses and liquids with thermodynamically reversible and structurally adaptive behaviour

Densified network glasses and liquids with thermodynamically reversible and structurally adaptive behaviour

Rigidity Transition in Materials: Hardness is Driven by Weak Atomic Constraints

Order and disorder in calcium–silicate–hydrate

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