Porous vycor glass: The microstructure as probed by electron microscopy, direct energy transfer, small-angle scattering, and molecular adsorption

Abstract

We provide a comprehensive analysis of the microstructure of the porous glass, vycor. Using transmission electron microscopy, small-angle x-ray scattering, molecular adsorption, and the dynamic process of direct energy transfer, a consistent picture of the mass, pore, and interfacial features of this material is presented. From a transmission-electron-microscopy image of an ultrathin section of vycor the material appears to have a homogeneous distribution of mass with no hierarchical organization. The pore interface exhibits a roughness which is probed by both small-angle x-ray scattering and molecular adsorption. The roughness has an upper cutoff of <20 Å which is not resolved in the transmission-electron-microscopy image and is shown to be unimportant to the dynamics of the direct energy transfer process. The dimensionality probed by direct energy transfer is shown to be related to interfacial geometrical crossover from two dimensional to three dimensional, which is characterized by a persistent length of the interface of 45 Å.

Superfluidity of DenseHe4in Vycor

“…The interaction between the helium atoms and the Vycor particles is determined by demanding that a complete layer of the particles give the same LJ (3-9)potential. Experiments [11] show that the roughness in Vycor is on the scale of 0.8nm, not very different from what we have assumed. Figure 1 shows the wall potential and the surface roughness.…”

Equilibrium phase transitions in a porous medium

“…We do not include symmetry-breaking interactions between the porous medium and the mixture inside it. We have chosen to focus on Vycorlike media made via spinodal decomposition, 12,13 rather than on aerogels, which are made by poorly understood aggregation processes. Using a recently developed algorithm 14 we are able to efficiently simulate spinodal decomposition, and so to construct porous media that should have a geometry very similar to that of Vycor glass.…”

“…12 The simplest models for this phase-separation process are dynamical Ising models with locally conserved magnetization. 13 In this section we describe the simulation of the production of Vycor, using phase separation in a threedimensional Ising model.…”

Внутренняя Структура Магнитных Пористых Стекол И Сегнетоэлектрических Нанокомпозитов На Их Основе

“…Ранее было показа-но, что в обычных пористых щелочно-боросиликатных стеклах типа Vycor [32,33] существует " модулированная структура" на характерном масштабе L ∼ 2π/Q max с L порядка 30−45 nm, причем эта величина не зависит от среднего диаметра пор, т. е. является исключитель-но типичной характеристикой пористых матриц. Для наших образцов роль величины L играет параметр d. Отметим, что после второго цикла травления (стекла Fe20MАP) положение максимума сдвигается в сторону меньших Q, параметр d увеличивается, а сам пик ста-новится (pис.…”