Contribution of Pore-Connectivity to Permeation Performance of Silicalite-1 Membrane; Part I, Pore Volume and Effective Pore Size

The micropore volumes and effective pore sizes of two types of silicalite-1 membranes were compared with those of a typical silicalite-1 powder. The silicalite-1 membrane with fewer grain boundaries in the membrane layer showed similar micropore volume and effective pores size to those of the silicalite-1 powder. In contrast, when the silicalite-1 membrane contained many grain boundaries, relatively small micropore volume and effective pore size were observed, suggesting that narrowing and obstruction of the micropore would occur along grain boundaries due to the disconnection of the zeolite pore. The silicalite-1 membrane with fewer grain boundaries exhibited relatively high permeation properties for C6-C8 hydrocarbons. There was an over 50-fold difference in benzene permeance between these two types of membranes. We concluded that it is important to reduce grain boundaries and improve pore-connectivity to develop an effective preparation method for obtaining a highly permeable membrane.

Acoustical Properties of Fiberglass Blankets Impregnated with Silica Aerogel

It is known that aerogel impregnated fibrous blankets offer high acoustic absorption and thermal insulation performance. These materials are becoming very popular in various industrial and building applications. Although the reasons for the high thermal insulation performance of these materials are well understood, it is still largely unclear what controls their acoustic performance. Additionally, only a small number of publications to date report on the acoustical properties of fibrous blankets impregnated with powder aerogels. There is a lack of studies that attempt to explain the measured absorption properties with a valid mathematical model. This paper contributes to this knowledge gap through a simulation that predicts the measured complex acoustic reflection coefficient of aerogel blankets with different filling ratios. It is shown that the acoustic performance of a fibrous blanket impregnated with aerogel is generally controlled by the effective pore size and porosity of the composite structure. It is shown that there is a need for refinement of a classical Biot-type model to take into account the sorption and pressure diffusion effects, which become important with the increased filling ratio.

Two sides of the same inverse problem, in identifying the pore size distribution based on experiments with non-Newtonian fluids

<p>Following the capillary bundle concept, i.e. idealizing the flow in a saturated porous media in a given direction as the Hagen-Poiseuille flow through a number of tubular capillaries, one can very easily solve what we would call the <em>forward problem</em>: Given the number and geometry of the capillaries (in particular, given the pore size distribution), the rheology of the fluid and the hydraulic gradient, to determine the resulting flux. With a Newtonian fluid, the flux would follow the linear Darcy law and the porous media would then be represented by one constant only (the permeability), while materials with very different pore size distributions can have identical permeability. With a non-Newtonian fluid, however, the flux resulting from the forward problem (while still easy to solve) depends in a more complicated nonlinear way upon the pore sizes. This has allowed researchers to try to solve the much more complicated <em>inverse problem</em>: Given the fluxes corresponding to a set of non-Newtonian rheologies and/or hydraulic gradients, to identify the geometry of the capillaries (say, the effective pore size distribution).</p><p>The potential applications are many. However, the inverse problem is, as they usually are, much more complicated. We will try to comment on some of the challenges that hinder our way forward. Some sets of experimental data may not reveal any information about the pore sizes. Some data may lead to numerically ill-posed problems. Different effective pore size distributions correspond to the same data set. Some resulting pore sizes may be misleading. We do not know how the measurement error affects the inverse problem results. How to plan an optimal set of experiments? Not speaking about the important question, how are the observed effective pore sizes related to other notions of pore size distribution.</p><p>All of the above issues can be addressed (at least initially) with artificial data, obtained e.g. by solving the forward problem numerically or by computing the flow through other idealized pore geometries. Apart from illustrating the above issues, we focus on <em>two distinct aspects of the inverse problem</em>, that should be regarded separately. First: given the forward problem with <em>N</em> distinct pore sizes, how do different algorithms and/or different sets of experiments perform in identifying them? Second: given the forward problem with a smooth continuous pore size distribution (or, with the number of pore sizes greater than <em>N</em>), how should an optimal representation by <em>N</em> effective pore sizes be defined, regardless of the method necessary to find them?</p>

Reducing the Pore Size of Covalent Organic Frameworks in Thin-Film Composite Membranes Enhances Solute Rejection

Three imine-linked covalent organic framework (COF) films are incorporated as active layers into separate thin-film composite (TFC) membranes and tested for their ability to reject an organic pollutant surrogate and salt from water. The synthesized membranes consist of a polyacrylonitrile (PAN) membrane supporting a <b>TAPB-PDA-H</b>, <b>TAPB-PDA-Me</b>, or <b>TAPB-PDA-Et</b> COF thin film. The latter two COFs direct six methyl and ethyl substituents per tiled hexagon into the pores, respectively, while maintaining the same topology across the series. These substituents decrease the effective pore size of the COF compared to the parent <b>TAPB-PDA-H</b> COF. The <b>TAPB-PDA-Me</b> membrane rejects Rhodamine-WT (R-WT) dye and NaCl better than the <b>TAPB-PDA-H</b> membrane, and the <b>TAPB-PDA-Et</b> membrane exhibits the best rejection overall. The solution-diffusion model used to analyze this permeation behavior indicates that there is a systematic difference in rejection as subsequent pendant groups are added to the interior of the COF pore. These findings demonstrate the concept of tuning the selectivity of COF membranes by systematically reducing the effective pore size within a given topology.<br>