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Dynamics and Structure of a Bitumen Emulsion as Studied by 1H NMR Diffusometry
Andrei Filippov1, Hilde Soenen2, Johan Blom3
1Chemistry of Interfaces, Department of Civil and Environmental Engineering, Luleå University of Technology, Luleå SE-97187, Sweden.
ACS Omega
|October 9, 2023
Summary
This study reveals bitumen emulsions behave as complex water/oil/water (WOW) multiple emulsions. Confined water diffusion within bitumen droplets differs significantly from the continuous aqueous phase.
Area of Science:
- Physical Chemistry
- Colloid Science
- Materials Science
Background:
- Bitumen emulsions are complex multiphase systems.
- Understanding water diffusion dynamics is crucial for emulsion stability and applications.
- Previous studies lacked detailed insights into the distinct diffusion behaviors within different emulsion phases.
Purpose of the Study:
- To investigate the self-diffusion of water in a bitumen emulsion using Nuclear Magnetic Resonance (NMR).
- To characterize the diffusion dynamics in both the continuous aqueous phase and the dispersed bitumen droplets.
- To establish a structural model for the bitumen emulsion based on diffusion data.
Main Methods:
- Proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy and diffusometry were employed.
- Paramagnetic doping with manganese sulfate (MnSO₄(aq)) was used to enhance NMR signal contrast.
- Emulsion structure was analyzed under conditions of compromised stability, including freezing at 253 K.
Main Results:
- The continuous aqueous phase exhibits water diffusion with an activation energy similar to bulk water but a diffusivity reduced by a factor of two.
- The dispersed bitumen phase contains confined water within droplets, exhibiting a fully restricted diffusion regime.
- The characteristic cavity size for confined water in bitumen droplets was determined to be approximately 0.11 μm.
Conclusions:
- The bitumen emulsion can be accurately modeled as a complex water/oil/water (WOW) multiple emulsion.
- The ¹H NMR and diffusometry data support the proposed WOW emulsion model.
- The findings provide a detailed understanding of water diffusion at the nanoscale within bitumen emulsions.
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