Nanoporous Glass Research Articles

The Effect of the Nanoscale Structure of Nanobioceramics on Their In Vitro Bioactivity and Cell Differentiation Properties

The effect of the nanoscale structure of bioceramics on their in vitro bioactivity and capacity to osteogenically differentiate stem cell is studied. Nanoparticles of hydroxyapatite (nHA), bioactive glass (nBG), nanoporous bioactive glass (MBG), and nanoporous bioactive glass nanospheres (nMBG) are investigated. The nanometric particle size of bioceramics seems to be more determining in controlling the ability to induce bone‐like apatite as compared to the nanoporous structure. At short incubation time, nBG also produces a bioactive extracellular medium capable of upregulating key osteogenic markers involved in the development of a mineralizing phenotype in DPSCs. The bioactive properties of nBG are promissory for accelerating the bone regeneration process in tissue engineering applications.

Radiation-induced change of OH content in Yb-doped silica glass

Yb-doped silica glasses containing low, medium, and high content of OH are prepared through nanoporous glass sintering technology. High-OH sample exhibits better X-ray irradiation resistivity than low- and medium-OH samples. After irradiation, OH content of low- and medium-OH samples increases 37.5% and 11%, respectively; in contrast, OH content of high-OH sample decreases dramatically. The different OH content changes among the samples are discussed regarding the proposed inter-conversion reactions involving Si-H and Si-OH during the irradiation.

Synthesis and study of bismuth-containing high-silica glass by the IR spectroscopy method

Bismuth-containing high-silica glasses (BCHSGs) based on the matrices of high-silica nanoporous glasses have been synthesized. The structure of BCHSG plates has been investigated by means of the IR spectroscopy method in the frequency range 4000–400 cm−1. The bands corresponding to vibrations of the Bi-O bonds in structural units [BiO3] and [BiO6] were found on the spectral transmission curves of the synthesized BCHSGs. Besides, peaks corresponding to the presence of the α-Bi2O3 phase in the glass were revealed. It has been established that, depending on the BCHSG thermal treatment and the bismuth concentration in glass, changes of the glass structure and formation of Bi-O-Si bonds take place.

Enhanced green upconversion luminescence in Yb–Tb co-doped sintered silica nanoporous glass

We report on a new kind of green-emitting (543 nm) high-silica luminous glass, which is fabricated by sintering of Yb3+–Tb3+ co-doped nanoporous glass. The fluorescence spectra show that there is an energy transfer between Yb3+ and Tb3+. The energy transfer process can be enhanced by addition of Al3+ into the Yb3+–Tb3+ co-doped nanoporous glass, and the energy transfer rate can be enhanced more than three times than that of Yb3+–Tb3+ co-doped porous glass. The role of Al3+ has been discussed, and the fluorescence decay curve reveals that the Al3+ play an important role in the energy transfer process.

Hierarchical nanoporous glass with antireflectivity and superhydrophilicity by one-pot etching.

We have developed a hierarchical nanoporous layer (HNL) on silicate glass by a simple one-pot etching method. The HNL has a three-dimensionally continuous spongelike structure with a pore size of a few tens of nanometers on its apparent surface. The pore size gradually decreases from the apparent surface to the HNL-bulk interface. This HNL bestows significant properties to glass: low optical reflectivity that reflects 7% less visible light than nontreated glass and long-persistence superhydrophilicity that keeps its water contact angle at about 5° for more than 1 year. The superhydrophilicity also realizes antifogging and antifouling functionalities.

Unexpected sorption-induced deformation of nanoporous glass: evidence for spatial rearrangement of adsorbed argon.

Sorption of substances in pores generally results in a deformation of the porous matrix. The clarification of this effect is of particular importance for the recovery of methane and the geological storage of CO2. As a model system, we study the macroscopic deformation of nanoporous Vycor glass during the sorption of argon using capacitative measurements of the length change of the sample. Upon desorption we observe an unpredicted sharp contraction and re-expansion peak, which contains information on the draining mechanism of the porous sample. We have modified the theoretical model by Gor and Neimark1 to predict the sorption-induced deformation of (partly) filled porous samples. In this analysis, the contraction is attributed to a metastable or nonequilibrium configuration where a thin surface layer on the pore walls coexists with capillary bridges. Alternatively, pore blocking and cavitation during the draining of the polydisperse pore network can be at the origin of the deformation peak. The results are a substantial step toward a correlation between the spatial configuration of adsorbate, its interaction with the host material, and the resulting deformation.

Light-controlled tuning of the optical properties of nanoporous glass.

Materials having tunable optical properties are of great interest for photonic applications. Promising candidates in that context are transparent nanoporous media whose optical properties change after infiltration of a liquid into the pores. Herein we present an all-optical method to tune the light scattering properties of a nanoporous glass based on the light-induced phase change of the fluid filling the pores. The thermodynamic state of the gas inside the nanopores determines the light scattering, thereby the light transmission. The extent of capillary condensation inside the nanoscale pores is controlled by heat generated from light absorption inside the medium. The material can be configured in such a way that a laser beam of sufficient intensity either opens up or shuts down its own light path on a time scale of a few seconds. The scattering events inside the medium change the beam profile from Gaussian to super-Gaussian with a more homogeneous intensity distribution close to the beam axis. Our results demonstrate a new way of tuning the light transmission properties of nanoporous materials that could find various applications in integrated optical systems and optofluidic devices.

Influence of Protein Adsorption onto Titanium Surfaces on Osteoblasts Cell Activity

Protein adsorption occurs immediately following implantation of a biomaterial, and it is widely assumed that this will have an influence on the subsequent cellular response.1 Despite numerous studies, there are still questions on the degree of influence that this process has on initial cellular events, particularly when the surface exhibits topography.2 To investigate this question, we have compared the osteoblastic cell growth onto polished and nanoporous titanium and glass as control by modulating the exposure to serum proteins during the initial phase of cell culture.

Synthesis and characterization of silver nanoparticles in a nanoporous glass

We obtained a metal-dielectric composite by thermal restoration of silver atoms from an alcohol solution of a precursor in nanoporous glass with pores with a radius of 2 nm. The concentration, size, and asphericity degree of metal nanoparticles formed in the pores are characterized according to the measured extinction spectra of the material.

Light-Driven Hydrogen Production by Hydrogenases and a Ru-Complex inside a Nanoporous Glass Plate under Aerobic External Conditions.

Hydrogenases are powerful catalysts for light-driven H2 production using a combination of photosensitizers. However, except oxygen-tolerant hydrogenases, they are immediately deactivated under aerobic conditions. We report a light-driven H2 evolution system that works stably even under aerobic conditions. A [NiFe]-hydrogenase from Desulfovibrio vulgaris Miyazaki F was immobilized inside nanoporous glass plates (PGPs) with a pore diameter of 50 nm together with a ruthenium complex and methyl viologen as a photosensitizer and an electron mediator, respectively. After immersion of PGP into the medium containing the catalytic components, an anaerobic environment automatically established inside the nanopores even under aerobic external conditions upon irradiation with solar-simulated light; this system constantly evolved H2 with an efficiency of 3.7 μmol H2 m(-2) s(-1). The PGP system proposed in this work represents a promising first step toward the development of an O2-tolerant solar energy conversion system.

Freezing and melting of hydrogen confined in nanoporous silica

Thermodynamic properties of condensed hydrogen in geometric confinement remain poorly understood. Here, we use relaxation calorimetry to study solidification and melting of H2 in a series of Vycor-type nanoporous silica glasses with interconnected pores with average diameters in a wide range of ∼100–3000 Å. We find that the depression of freezing and melting temperatures for this quantum system follows the classical Gibbs–Thomson-like behavior, scaling inversely with the pore size when correlated to pore diameters measured directly by electron microscopy, rather than conventional gas sorption techniques. The shapes of pore size distributions derived from hydrogen thermoporometry are, however, more complex than those measured by gas sorption. The ratio between temperatures of the depression of freezing and melting suggests that the actual pore geometry in Vycor-type nanoporous glasses deviates from cylindrical.

Effect of water uptake on the fracture behavior of low-k organosilicate glass

Water uptake in porous low-k dielectrics has become a significant challenge for both back-end-of-the-line integration and circuit reliability. This work examines the effects of water uptake on the fracture behavior of nanoporous low-k organosilicate glass. By using annealing dehydration and humidity conditioning, the roles of different water types and their concentrations are analyzed in detail. For as-deposited SiCOH films, annealing dehydration can enhance the resistance to crack occurrence, and these enhancements can be offset by higher humidity conditioning. It was found that the film-cracking threshold can be lowered by in-diffused water in the film as well as by water at the SiCOH/subtract interface. This occurs because the water decreases the film fracture energy and adhesion energy, respectively. By conditioning at high humidity, the variation of the film cracking threshold agrees well with the behavior of the film hardness and modulus of elasticity as a function of relative humidity. The crack morphologies of low-k porous films are also implicitly related to water uptake in the materials. Film cracking thresholds and crack morphologies of UV-cured low-k materials exhibit a weaker dependence on the water uptake, indicating a low degree of hydrophilicity of the SiCOH film after UV curing, which corroborates the previous results. Furthermore, by measuring the surface crack length, the material–fracture toughness can be found. The results demonstrate that neither annealing dehydration nor water uptake have significant effects on fracture toughness of as-deposited SiCOH, while for UV-cured SiCOH, annealing enhances the film-fracture toughness.

Ytterbium-doped silica photonic crystal fiber laser fabricated by the nanoporous glass sintering technique

Based on the sintering of ytterbium-doped nanoporous glass, a nonchemical vapor deposition process aimed at fabricating a large-mode area of photonic crystal fibers has been proposed for the preparation of active silica glass. With the relatively low doping concentration and boron in the silica glass as benefits, a close refractive index between the core and the cladding was obtained. The refractive index variation indicated good homogeneity of the doped fiber core. Up to 34.8 W laser output was demonstrated with the PCF laser and the slope efficiency was 71.3%. The output laser beam quality had slightly multimode behavior, with a mean M2 of 2.42.

Salt Bridges Contained in Nanoporous Glasses or Polymers: Improved Alternatives to Vycor

Nanoporous glass plugs are widely used to contain the electrolyte solution that forms a salt bridge between the sample and the reference electrode. Even though reference electrodes with plugs made of nanoporous glass (such as Vycor or CoralPor glass) are commercially available and are frequently used, the limits of their use were not explored until very recently [1]. It will be shown in this presentation that at ionic strengths lower than 100 mM, the half-cell potentials of reference electrodes with nanoporous glass plugs are not sample independent, as it would be desirable, but they depend on the ionic sample composition. Sample dependent shifts of more than 50 mV in the half cell potential were encountered. Reference potentials were found to be affected in aqueous solutions by HCl, NaCl, KCl, and CaCl2, and in acetonitrile by trifluoroacetic acid and the supporting electrolyte tetrabutylammonium perchlorate. These observations cannot be explained by the liquid junction potential between two mutually miscible electrolyte solutions, as commonly described with the Henderson equation. Instead, they result from the surface charge density on the glass surface and the resulting electrostatic screening of ion transfer into the glass pores when the latter have dimensions comparable to or smaller than the Debye length. Users of reference electrodes with nanoporous plugs at the junction to the sample need to be aware of these limitations to avoid substantial measurement errors.This presentation will also address how problems at the junction to nanoporous plugs can be avoided using novel plug materials and selecting electrolyte conditions judiciously.

Bioactive Glass: Hierarchically Nanoporous Bioactive Glasses for High Efficiency Immobilization of Enzymes (Adv. Funct. Mater. 15/2014)

Bioactive Glass: Hierarchically Nanoporous Bioactive Glasses for High Efficiency Immobilization of Enzymes (Adv. Funct. Mater. 15/2014)

Optical response of alkali metal atoms confined in nanoporous glass*

We study the influence of optical radiation on adsorption and desorption processes of alkali metal atoms confined in nanoporous glass matrices. Exposure of the sample to near-IR or visible light changes the atomic distribution inside the glass nanopores, forcing the entire system to evolve towards a different state. This effect, due to both atomic photodesorption and confinement, causes the growth and evaporation of metastable nanoparticles. It is shown that, by a proper choice of light characteristics and pore size, these processes can be controlled and tailored, thus opening new perspectives for fabrication of nanostructured surfaces.

Proton conduction in nanopores of sol–gel-derived porous glasses and thin films

Nanoporous glasses and nanoporous thin films were prepared using sol–gel method, and proton conductivities in nanopores of sol–gel-derived porous glasses and thin films are overviewed in this paper. Proton motions inside nanopores were monitored by impedance and nuclear magnetic resonance (NMR) spectroscopies. The impedance data is correlated with the proton motion in bulk scale, whereas NMR data is correlated with that in nanometer scale, respectively. From the comparison of the activation energies obtained from impedance and NMR spectroscopies, percolation of proton conducting path and its relation to the amount of absorbed water molecules are shown. In the case of nanoporous thin films, directions of pores can be controlled by using cationic and non-ionic surfactants. Relationship between direction of pores and proton conductivity is discussed based on impedance test results.

Vibrational spectra of carbon dioxide adsorbed on nanopore walls at supermonolayer and submonolayer coverage

Coherent anti‐Stokes Raman scattering (CARS) spectroscopy is applied to probe the microstructure of CO2 adsorbed in nanoporous glass Vycor with a mean pore radius of 2 nm. CARS spectra of the Q‐branch (1388 cm‐1) were measured at 22 °C at pressures decreasing in a range providing the transition from the condensed phase in the whole volume of the pores to submonolayer coverage on their walls. The spectral behavior demonstrates sequential changes in the fluid state inside the nanopores. The analysis of the experimental results allowed us to characterize and compare the spectral properties of gas‐like, liquid‐like, and surface adsorbed carbon dioxide. The results provide clear evidence that as the surface coverage is decreased, the vibrational frequency shifts down. Copyright © 2014 John Wiley & Sons, Ltd.

Structure and spectral properties of the photochromic quartz-like glasses activated by silver halides

Photochromic quartz-like glasses (PCQGs) were successfully synthesized by an impregnation of silica nanoporous glasses (SNPGs) with photosensitive phases (AgCl, AgBr, AgI) in or without the presence of CuO as a sensitizer followed by sintering of the samples. Characterization of PCQGs was carried out using the transmission electron microscopy (TEM), X-ray powder diffraction (XRPD) and UV–VIS–NIR spectroscopy methods. According to TEM, images revealed that the size of the individual isolated particles and agglomerates, which are contained silver-phases inside a silica matrix, is from 10 to 100nm. It was shown that PCQGs preferably contain the crystalline phase of AgBr. In the spectral curves of optical density of the PCQG subjected to UV laser irradiation, the plasmon resonance peaks of the quasi-metallic silver nanoparticles were found.

THERMAL CONDUCTIVITY OF NANOPOROUS GLASS ALUMINA FILM AND COMPOSITES

In this paper, cross-plane thermal conductivities of the nanoporous glass alumina film (NGAF) and its composites ( Ag /NGAF, with Ag nanowires embedded in) were measured. And a model was setup to predict the thermal conductivity of the nanoporous material. Results show that the thermal conductivity of the NGAF is about 50 times smaller than that of the ceramic alumina. It is about 0.5 W ⋅ m -1⋅ K -1 and depends on both the pore radius and the porosity. The thermal conductivity of the Ag /NGAF is not larger than that of the NGAF. The contact resistance and the unfilled space between Ag nanowires and the matrix are responsible for that.