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

The clinical success of modern dental ceramics depends on an array of factors, ranging from initial physical properties of the material itself, to the fabrication and clinical procedures that inevitably damage these brittle materials, and the oral environment. Understanding the influence of these factors on clinical performance has engaged the dental, ceramics, and engineering communities alike. The objective of this review is to first summarize clinical, experimental, and analytic results reported in the recent literature. Additionally, it seeks to address how this new information adds insight into predictive test procedures and reveals challenges for future improvements.

Performance of Dental Ceramics Challenges for Improvements

A refined and generalized version of a previously suggested model of the silica surface, in which geminal silanols are situated on surface segments similar to (100)-type faces of the β-cristobalite structure and single silanols are situated on surface segments similar to corresponding (111)-type faces, is supported by extensive spectroscopic data In this model single silanols on the same (111)-type surface segment cannot form hydrogen bonds with each other Whether or not adjacent geminal silanols on the same (100)-type surface segment can form hydrogen bonds with each other depends on the relative orientation of their hydroxyl groups When two surface segments of either (100)- or (111)-type intersect convexly, hydroxyl groups cannot participate in hydrogen bonding across the intersection; but when two surface segments intersect concavely, those silanols situated at the intersection can form hydrogen bonds with their counterparts across the intersection All the hydrogen-bonding silanols in this generali

A Detailed Model of Local Structure and Silanol Hydrogen Bonding of Silica Gel Surfaces

A pronounced increase of interface energy of room temperature bonded hydrophilic Si/Si, Si/SiO/sub 2/, and SiO/sub 2//SiO/sub 2/ wafers after storage in air at room temperature, 150/spl deg/C for 10-400 h has been observed. The increased number of OH groups due to a reaction between water and the strained oxide and/or silicon at the interface at temperatures below 110/spl deg/C and the formation of stronger siloxane bonds above 110/spl deg/C appear to be the main mechanisms responsible for the increase in the interface energy. After prolonged storage, interface bubbles are detectable by an infrared camera at the Si/Si bonding seam. Desorbed hydrocarbons as well as hydrogen generated by a reaction of water with silicon appear to be the major contents in the bubbles. Design guidelines for low temperature wafer direct bonding technology are proposed. >

Low temperature wafer direct bonding

Solid state 29 Si magic angle sample spinning nuclear magnetic resonance spectroscopy and Raman spectroscopy were used to investigate the local silicon environment and siloxane ring vibrations in amorphous silica gels. Our results unambiguously relate the 608 cm −1 Raman “defect” in a-SiO 2 with reduced SiOSi bond angles indicative of strained 3-membered rings of silicate tetrahedra.

NMR confirmation of strained “defects” in amorphous silica

Slow crack growth data, molecular‐orbital calculations, and vibrational spectroscopy results are used to develop an atomistic model for environmentally controlled fracture of silica glass. The model is based on chemically active bond defects generated by the strain field of the crack tip. Molecular‐orbital results suggest that bond angle deformations are most effective in increasing the chemical activity of the Si–O–Si bond. Vibrational spectra identify silica polymorphs containing highly strained bonding configurations. A comparison of strained bond reactivity with crack growth results shows that strained silica polymorphs can be used to model the crack tip chemical reactions controlling slow fracture. Based on model complexes, a two‐dimensional fracture model involving kink site nucleation and motion is developed. The model shows that the stress intensity dependence of the crack growth rate is controlled by the energy required to form chemically active defects in the silica structure. The absolute rate of fracture depends on the combined rates of active bond formation and chemical attack at strain induced defects. Crack growth data suggest that for silica, strain activation occurs prior to the adsorption of environmental chemicals.

T. A. Michalske

Papers

Slow fracture model based on strained silicate structures