The calcium silicate hydrates

Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments / Albert Rimola;Dominique Costa;Mariona Sodupe;Jean-François Lambert;Piero Ugliengo. In: CHEMICAL REVIEWS. ISSN 0009-2665. STAMPA. 113:6(2013), pp. 4216-4313. Original Citation: Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments

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Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments

There has been substantial renewed interest in negative thermal expansion following the discovery that cubic ZrW2O8 contracts over a temperature range in excess of 1000 K. Substances of many different kinds show negative thermal expansion, especially at low temperatures. In this article we review the underlying thermodynamics, emphasizing the roles of thermal stress and elasticity. We also discuss vibrational and non-vibrational mechanisms operating on the atomic scale that are responsible for negative expansion, both isotropic and anisotropic, in a wide range of materials.

https://iopscience.iop.org/article/10.1088/0953-8984/17/4/R03/pdf

Negative thermal expansion

Interatomic potential for Si–O systems using Tersoff parameterization

Silica nanostructures find applications in drug delivery, catalysis, and composites, however, understanding of the surface chemistry, aqueous interfaces, and biomolecule recognition remain difficult using current imaging techniques and spectroscopy. A silica force field is introduced that resolves numerous shortcomings of prior silica force fields over the last 30 years and reduces uncertainties in computed interfacial properties relative to experiment from several 100% to less than 5%. In addition, a silica surface model database is introduced for the full range of variable surface chemistry and pH (Q2, Q3, Q4 environments with adjustable degree of ionization) that have shown to determine selective molecular recognition. The force field enables accurate computational predictions of aqueous interfacial properties of all types of silica, which is substantiated by extensive comparisons to experimental measurements. The parameters are integrated into multiple force fields for broad applicability to biomolecu...

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Force Field and a Surface Model Database for Silica to Simulate Interfacial Properties in Atomic Resolution

An X-ray study of the temperature dependence of the quartz structure

The temperature dependence of atomic positions, mean-square displacements and probability density functions in a synthetic specimen of berlinite was analyzed using X-ray single crystal data measured at fourteen values of temperature. The characteristic features and the temperature dependence of the structure of berlinite were found to be quite similar to those of quartz, in detail. With increasing temperature, the equilibrium position of an atom, if expressed in fractional coordinates, appears to move steadily toward its β-position along a straight line, and finally attain the β-phase positions after abrupt displacements in a narrow temperature range around 583 °C. The temperature dependence of the displacements of atoms from the corresponding high-symmetry β-positions, in α-berlinite, is well fitted with a classical Landau type expression of first-order phase transitions.

The temperature dependence of the crystal structure of berlinite, a quartz-type form of AlPO4

The refinement of the crystal structure of cuspidine

The crystal structure of the low temperature form of natural melanophlogite, 46SiO 2 · 6M 14 · 2M 12 (M 14 = N 2 , CO 2 ; M 12 = CH 4 , N 2 ), was determined using single-crystal X-ray diffraction data at room temperature. The structure is tetragonal with space group P 4 2 / nbc and unit cell a = 26.818(2) and c = 13.365(1) A, which is the (2 ×2 × 1) superstructure of high-temperature cubic melanophlogite and includes four formula units. The structure with 335 variable parameters including anisotropic temperature factors (or atomic displacement factors) was refined to R = 0.0288 for 2706 observed reflections. The main silica framework consists of nearly regular SiO 4 tetrahedra forming large internal voids represented by distorted tetrakaidecahedra and pentagondodecahedra, which accommodate CO 2 or N 2 and CH 4 or N 2 guest molecules, respectively. This low temperature form is a displacive variant of the cubic high-temperature form. The mean bond length is 1.588(4) A for Si-O, and the bond angles for Si-O-Si are distributed over a large range from about 145 to 171° with a mean value of 159.4(3)°. The thermal vibrations of Si are nearly isotropic with amplitudes approximately equal to the average mean square displacement of 0.0119(4) A 2 . The thermal vibrations of the O atoms are highly anisotropic with a wide range of mean square displacements. There is a positive correlation between the Si-O-Si bond angles and the mean-square displacements of the O atoms.

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The crystal structure of low melanophlogite

Unit-cell parameters, Raman scattering profiles and DTA curves were measured on monoclinic tridymite from fired silica brick. Ten peaks appear in the Raman measurements from 100 to 1250 cm at 25°C, and their positions and widths show no significant change up to 110°C. The monoclinic unit-cell parameters, a, b, c and , slightly increase or remain nearly constant with increasing temperatures up to 110°C. Both the Raman spectra and the unit-cell parameters undergo significant changes in the range from 110 to 115°C. Only two endothermic peaks, at 117 and 166°C, appear in the DTA curve measured on a powdered sample of nearly pure monoclinic phase in a heating run from 25 to 300°C. In X-ray single-crystal refinements, the structural parameters including anisotropic temperature factors of atoms were fully determined for the monoclinic phase at 25, 80, 90 and 100°C, and the orthorhombic phase at 140°C. The difference between the temperature factors on both sides of the transition point is the most remarkable: 0.0286 A in average for all O atoms at 100°C in the monoclinic phase and 0.0713 A at 140°C, both for Beq. The averaged Si-O distances calculated for the atomic mean positions decrease with increasing temperatures: 1.599 A at 25°C, 1.595 A at 100°C and 1.576 A at 140°C, whereas the values corrected for the thermal displacement parameters remain unchanged at 1.61 A through all the temperatures studied.

Kuniaki Kihara

Papers

An X-ray study of the temperature dependence of the quartz structure

The temperature dependence of the crystal structure of berlinite, a quartz-type form of AlPO4

The refinement of the crystal structure of cuspidine

The crystal structure of low melanophlogite

X-ray, DTA and Raman studies of monoclinic tridymite and its higher temperature orthorhombic modification with varying temperature