Transport through permselective membranes

Asymmetric Mass Transport through Dense Heterogeneous Polymer Membranes: Fundamental Principles, Lessons from Nature, and Artificial Systems

“…symmetric. [25] By contrast, heterogeneous polymer membranes, which feature multiple phases and spatial inhomogeneities in their structure, exhibit a much more complicated transport profile. In this case, the permeability not only depends on the penetrant concentration and the temperature, but is also varies with the position.…”

“…In this case, the permeability not only depends on the penetrant concentration and the temperature, but is also varies with the position. [25] These structural and compositional inhomogeneities may be created by the same building block, e.g., in phase segregated copolymers, semi-crystalline polymers, or polymers with inhomogeneously distributed cross-links or micropores and/or by combining several constituents, e.g., in polymer blends, composites, or interpenetrating networks. [25,26] Thus, the options to tailor the type and degree of structural heterogeneity in polymer membranes are essentially limitless.…”

“…[25] These structural and compositional inhomogeneities may be created by the same building block, e.g., in phase segregated copolymers, semi-crystalline polymers, or polymers with inhomogeneously distributed cross-links or micropores and/or by combining several constituents, e.g., in polymer blends, composites, or interpenetrating networks. [25,26] Thus, the options to tailor the type and degree of structural heterogeneity in polymer membranes are essentially limitless. In these systems, transport is considerably affected by the nature of the polymer components and phases, their interaction with the permeating species, the spatial distribution and volume of the phases, interfacial phenomena, and other parameters.…”

“…In these systems, transport is considerably affected by the nature of the polymer components and phases, their interaction with the permeating species, the spatial distribution and volume of the phases, interfacial phenomena, and other parameters. [25,27,28] According to membrane theory, compositional and/or structural gradients in the transversal direction of the membrane may result in asymmetric permeation properties. [11][12][13][14][15][16]29,30] Such gradients of inhomogeneity may be structural and/or compositional and are commonly found in many living organisms, [17][18][19][31][32][33][34][35] including plants and insects.…”

“…Similarly to layered designs, the volume fraction and the distribution of the phases affect the anisotropy and the transport properties in the case of compositionally graded heterogeneous membranes. [11,25,36] Therefore, a prerequisite of asymmetric mass transport is the presence of structural and/or compositional gradients leading to a spatial-dependency of the permeability coefficient of the membrane. Based on the pioneering work of Rogers, Stannett, and Szwarc, and later studies, the direction and magnitude of transport asymmetry in polymer-based artificial dense membranes is dictated by the component with superior deviation from "ideality", i.e., pressure-sensitive permeability caused by a non-ideal diffusion and/or sorption.…”