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Apr 9, 2020

ACS Spring 2020 National Meeting & Expo

HRMAS NMR diffusometry of multicomponent mixtures in porous materials

NMR

diffusion

porous

PFG NMR

Abstract

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Abstract

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Keywords

NMR

diffusion

porous

PFG NMR

Abstract

Directly measuring the individual molecular diffusion for different chemical species in complex mixtures that are absorbed into porous materials is critical for the development and optimization of applications including separation membranes, conductive layers in battery and fuel cells, along with porous coatings and barriers. For multi-component mixtures (MCM) the relative impact of the different factors controlling porous diffusion is of interest. These variables include i) pore size, ii) surface adsorption energies, and iii) molecular-molecular interactions within the mixture. The role of these different variables may be different for each species in the MCM depending on the pore chemistry, the composition of the mixture, and the degree of accessible pore volume loading. The development of new characterization methods that allow for the measurement of individual diffusion rates for each species in complex mixtures is therefore crucial for understanding the diffusional process in pores. In this presentation, the implementation of high-resolution magic angle spinning (HRMAS) NMR diffusometry techniques to probe diffusion of MCM for different porous material are discussed. The use of MAS greatly reduces the magnetic susceptibility heterogeneity within the materials leading to significant improvements in chemical shift resolution, thus allowing the diffusion rates for individual chemical species in MCM to be realized (see Figure). This example demonstrates diffusion measurements for a highly heterogeneous material, composed of a rigid porous aluminum oxide support, containing an absorbed polymer (PDMS) swollen with a chemical penetrant (octane). Additional experimental examples along with a discussion of the benefits and limitations of HRMAS NMR diffusometry in porous materials will be presented.

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All rights reserved.