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This study is seeking a better understanding of polyethylene glycol (PEG) as a solvent to promote its use in chemical synthesis. The effect of adding two solutes of interest, 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) and 5-tert-butylisophthalic acid (5-TBIPA) to PEG200 (average molar weight of 200 g·mol−1) on the solution density, viscosity, and selfdiffusion coefficients is monitored in a temperature range of 298.15–358.15 K to deduce how these solutes interact with the PEG200 solvent. The effect of water, the most common impurity in PEGs, is also monitored and found to be nearly negligibly small. Addition of (5-TBIPA) increases solution density and viscosity. Combined with the observation that 5-TBIPA consistently self-diffuses at about half the rate as PEG200 at all investigated experimental conditions, this suggests strong attractive solute–solvent interactions likely through hydrogen bonding interactions. In contrast, addition of TEMPO causes lower solution densities and viscosities suggesting that the solute–solvent interactions of TEMPO lead to an overall weakening of the intermolecular interactions present compared to neat PEG200. Inspection of the viscosity and self-diffusion temperature dependence reveals slight deviations from the Arrhenius equation. Interestingly, the activation energies obtained from the viscosity and the self-diffusion data are essentially identical in values suggesting that the same dynamic processes and thus the same activation barriers govern translational motion and momentum transfer in these PEG200 solutions.
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Laser Induced Temperature Perturbation on Ultramicroelectrodes: Unsupported Solutions in Nonaqueous Methanol
Temperature dependence studies of electrochemical parameters provide insight into electron transfer processes. In cases where adding excess electrolyte causes experimental complications, e.g., colloidal systems, organic or biological samples, it is preferable to deal with the high resistivity of the medium. We validate the use of unsupported and weakly-supported solutions in thermoelectrochemical experiments. The temperature dependence of the diffusion coefficient allows calibration of the steady-state current to measure changes when a continuous-wave (CW) ultraviolet laser,λ= 325 nm, illuminates an ultramicroelectrode (UME) from the front. Calibrating the steady-state current ratios, before and after heating with a thermostatic bath, allows temperature measurements within an accuracy of 0.6 K. The solutions are without supporting electrolytes in methanol, a volatile solvent, and we use a model that accurately describes the viscosity and temperature dependence of the solvent. We calculated the temperature and derived an equation to estimate the error in the temperature measurement. A numeric method yields satisfactory results, considering the changes for both diffusion coefficients and viscosity explicitly, and predicts the thermostatic temperature bath, agreeing with the theoretical model’s error. In unsupported solutions, the ferrocene diffusion coefficient and the iodide apparent diffusion coefficient follow the expected increase with temperature. Under CW laser illumination, the UME temperature increase is: ΔT = 4 ± 1 K.
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- Award ID(s):
- 1905312
- PAR ID:
- 10361739
- Publisher / Repository:
- The Electrochemical Society
- Date Published:
- Journal Name:
- Journal of The Electrochemical Society
- Volume:
- 169
- Issue:
- 1
- ISSN:
- 0013-4651
- Page Range / eLocation ID:
- Article No. 016509
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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