Disordered Pore Structure Research Articles

Comparative Studies of Ultra Low-κ Porous Silica Films with 2-D Hexagonal and Disordered Pore Structures

AbstractPeriodic 2-dimensional (2-D) hexagonal and the disordered pore structure silica films have been developed using nonionic surfactants as the templates. The pore structure was controlled by the static electrical interaction between the micelle of the surfactant and the silica oligomer. No X-ray diffraction peaks were observed for the disordered mesoporous silica films, while the pore diameters of 2.0-4.0 nm could be measured by small angle X-ray scattering spectroscopy. By comparing the properties of the 2-D hexagonal and the disordered porous silica films which have the same porosity, it is found that the disordered porous silica film has advantages in terms of the dielectric constant and Young's modulus as well as the hardness. The disordered porous silica film is more suitable for the interlayer dielectrics for ULSI.

Effects of water content and sol viscosity on morphology of porous silica thermal insulating layer

Amorphous porous silica thin films as a thermal insulating layer in pyroelectric infrared (IR) detector were prepared by a modified sol–gel method. These silica films possessed sponge-like disordered pore structure. The effects of water content and sol viscosity on morphology of the films were investigated. The results shown: with decreasing water content and increasing sol viscosity, the pore size, root-mean-square surface roughness (RMSSR), and thickness of the films increased obviously. However, the porosity did not change greatly. While the values of the water content and the sol viscosity changed from 91.69 to 79.58 wt.% and 5.59 to 59.37 cP, respectively, the thickness of single layer film increased from 0.34 to 1.50 μm, and the values of porosity just fluctuated between 45 and 50%. A crack-free, uniform porous silica films with porosity of 45% and thickness of 15 μm also could be obtained by repeating coating procedure easily.

Probing the Diffusion of a Dilute Dye Solution in Mesoporous Glass with Fluorescence Correlation Spectroscopy

The translational motion of rhodamine 6g dye molecules near the surface of a mesoporous glass with a disordered pore structure and a nominal pore diameter of 130 A is measured by the application of fluorescence correlation spectroscopy (FCS) to fluorescence burst data as dye molecules diffuse through the laser excitation volume. FCS analysis indicates that the motion of the rhodamine 6g molecules in the mesoporous glass deviates from simple Brownian motion with a single diffusion constant. Two models, including two-component diffusion and diffusion plus adsorption, are utilized to fit the correlation data. The multicomponent diffusion model comprised of free diffusion (with a diffusion coefficient of 4.89 × 10-7 cm2/s) and transient adsorption/desorption (desorption time of 67 ms) provides the best fit and the most plausible explanation of the correlation data. Possible explanations for the shift to multicomponent diffusion, such as restriction of the dye molecules within the pores of the glass, as well a...

Synthesis of mesoporous titanium dioxide materials by using a mixture of organic compounds as a non-surfactant template

Mesoporous titanium dioxide materials have been successfully prepared at ambient temperature via HCl-catalyzed hydrolysis and polycondensation reactions of titanium(IV) n-butoxide by employing a mixture of β-cyclodextrin (CD) and urea (U) as a non-surfactant template, followed by removal of the mixture with water extraction. FT-IR analysis demonstrates the complete removal of the template molecules after extraction with water. The characterization results of nitrogen adsorption–desorption measurements show that the obtained materials have type IV isotherms with H2 hysteresis loops. The BJH pore size distribution plots indicate that the pore sizes show no obvious changes with the decrease in weight ratio of CD/U (3.7–4.1 nm) or increase in template content (3.9–3.6 nm). The interactions induced by hydrogen bonding between these two molecules and inorganic species play important roles in the above results. Small- and large-angle powder X-ray diffraction patterns and transmission electron microscopy reveal that the afforded titanium dioxide materials have anatase structures as well as disordered pore structures.

Wetting stability of Si-MCM-41 mesoporous material in neutral, acidic and basic aqueous solutions

The wetting stability of three calcined Si-MCM-41 materials synthesized at room temperature and under hydrothermal conditions with and without pH adjustment and salt addition was studied by SAXS, SEM, HR-TEM, BET-BJH, FTIR and NMR techniques. The stability was investigated after wetting with neutral, basic and acidic aqueous solutions and further recalcination. Calcined Si-MCM-41 materials synthesized at room temperature fully degraded under wetting with neutral water. Crystallization under hydrothermal conditions improved their wetting stability. pH adjustment and NaCl addition during hydrothermal crystallization led to a further improvement. It was proposed, based on spectroscopic data, that the structure degradation during wetting is caused by hydration of the siloxane structure at the wetting stage followed by siloxane hydrolysis-hydroxylation of strained Si(OSi) 4 units and their rearrangement-redehydroxylation during recalcination. This leads to intergrowth of curved hexagonal crystal rods, reduction of the surface area and pore volume of the material forming a disordered pore structure with increased pore walls thickness. The water-stable Si-MCM-41 synthesized with pH adjustment and salt addition was also insensitive to wetting with acidic aqueous solution. However, treatment of this non-strained material with a basic solution at pH 7.8–8.9 resulted in silica leaching and a reduction in crystallinity, the mean pore diameter and the pore volume. The rod shape and surface area remained relatively unchanged after wetting at pH 7.8.