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A novel dual mode X-band EPR resonator for rapid in situ microwave heating

Folli, Andrea, Choi, Heungjae, Barter, Michael, Harari, Jaafar, Richards, Emma, Slocombe, Daniel, Porch, Adrian and Murphy, Damien M. 2020. A novel dual mode X-band EPR resonator for rapid in situ microwave heating. Journal of Magnetic Resonance 310 , 106644. 10.1016/j.jmr.2019.106644

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Abstract

A unique dual mode X-band CW EPR resonator designed for simultaneous EPR measurement and rapid MW induced sample heating is described. Chemical reactions subjected to a flow of energy and matter can be perturbed away from the thermodynamic equilibrium by imposing a rapid shock or physical change to the system. Depending on the magnitude of the perturbation, these changes can dictate the subsequent evolution of the entire system, allowing for instance to populate non-equilibrium reactive intermediate states. Temperature jump (T-jump) experiments are a common method to achieve such perturbations. Most T-jump experiments are based on Joule Heating methods or IR lasers. Here we demonstrate the principle of rapid sample heating based on microwaves. The benefits of MW heating include i) rapid and efficient heating (i.e. using a tuned resonant cavity, 99% efficient power transfer to the sample can be achieved), and ii) volumetric heating (i.e. the entire sample volume rises in temperature at once, since heat is generated in the sample instead of being transferred to it). Accordingly, the key concept of the design is the use of a cavity resonator allowing EPR detection (at 9.5 GHz) and sample heating (at 6.1 GHz). Temperature enhancements of 50 °C within a few seconds are possible. This is evidenced and illustrated here by probing the temperature-induced variation of the rotational dynamics of 16-doxyl stearic acid methyl ester (16-DSE) spin probe grafted on the surface of sodium dodecyl sulphate (SDS) micelles in water, as well as copper (II) acetylacetonate in chloroform. Rapid changes in the rotational dynamics of the paramagnetic centres provide direct evidence for the in situ and simultaneous EPR measurement-heating capabilities of the resonator. Improvements afforded by the use of pulsed MW sources, will enable faster heating time scales to be achieved. In the longer term, this current study demonstrates the simple and direct possibilities for using MW heating as a means of performing T-jump experiments.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Engineering
Publisher: Elsevier
ISSN: 1090-7807
Funders: EPSRC
Date of First Compliant Deposit: 11 November 2019
Date of Acceptance: 8 November 2019
Last Modified: 13 Dec 2019 14:11
URI: http://orca.cf.ac.uk/id/eprint/126721

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