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The microporosity of the heat-treated single-wall carbon nanohorn (SWNH) particles is characterized by nitrogen adsorption at 77 K and the molecular potential calculation using the function, which is based on the Lennard-Jones pair potential. The depth difference of the molecular potential for N 2 between the SWNH intraparticle pore and the interparticle space is close to 1000 K. Although the SWNH without the heattreatment has no open intra-nanohorn space, the intraparticle pores open with the high-temperature treatment in O 2 . The heat-treatment at 693 K opens almost perfectly the intraparticle pores, leading to 0.47 mL g -1 of the micropore volume and 1010 m 2 g -1 of the specific surface area. The subtraction of the N 2 adsorption isotherm of the SWNH from that of the SWNH treated at 693 K gave the N 2 adsorption isotherm only in the intraparticle pore spaces. The adsorption sites derived from the difference adsorption isotherm are assigned to the pores having different interaction potentials.

We report a method for fabricating optical quality silica and silica-titania glasses by additive manufacturing, or 3D printing. Key to this success was the combination of sol-gel derived silica and silica-titania colloidal feedstocks, 3D direct ink writing (DIW) technology, and conventional glass thermal processing methods. Printable silica and silica-titania sol inks were prepared directly from molecular precursors by a simple one-pot method, which was optimized to yield viscous, shear-thinning colloidal suspensions with tuned rheology ideal for DIW. After printing, the parts were dried and sintered under optimized thermal conditions to ensure complete organic removal and uniform densification without crystallization.Characterizations of the 3D-printed pure silica and silica-titania glasses show that they are This article is protected by copyright. All rights reserved. 2 equivalent to commercial optical fused silica (Corning ® 7980) and silica-titania glasses (Corning ULE ® 7972). More specifically, they exhibit comparable chemical composition, SiO 2 network structure, refractive index, dispersion, optical transmission, and coefficient of thermal expansion. 3D printed silica and silica-titania glasses also exhibited comparable polished surface roughness and meet refractive index homogeneity standards within range of commercial optical grade glasses. This method establishes 3D printing as a viable tool to create optical glasses with compositional and geometric configurations that are inaccessible by conventional optical fabrication methods. † denotes value determined by LA-ICP-MS; a-SiO 2 used to represent amorphous SiO 2

The experimental evidence that the surface of pure vitreous silica can be hydrophobic imposes strong limitations on possible atomic configurations at that surface. This is due primarily to the fact that the electric field of the partially ionic SiO2 can have very strong interactions with adsorbed polar molecules and with water in particular. The simulations reported here indicate that a surface structure consisting of a random net of almost regular corner-sharing SiO4 tetrahedra with a low concentration of defects such as nonbridging oxygen atoms is capable of producing hydrophobicity. It is shown that the defects as well as distortion of the SiO4 tetrahedra as measured by their dipole and quadrupole moments give rise to hydrophilic adsorption sites on the surface. Computer simulation of such a random net at a surface runs into a general problem typical of computer simulations of amorphous solids: at temperatures near to but above the glass transition temperature, the time scale of the molecular dynamics is many orders of magnitude less than the experimental structural relaxation times of the material. A solution to this problem was obtained here by imposing a constraint on the molecular dynamics simulation that directs the chain of simulated configurations toward one without nonbridging oxygens. This is demonstrated by showing that the binding energies of a water molecule over the surface of this solid are smaller than the energy liquefaction, which is taken here as the criterion for hydrophobicity.

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