This annual report summarizes progress during the current reporting period (Year 3, 2024-2025) on the development of low-power acoustic excitation as a non-thermal method to accelerate aging in wet dispersions and nanoemulsions while preserving natural destabilization pathways. In other words, the central premise is that aging can be made faster without changing how it occurs. Acoustic perturbations are intended to increase the frequency of microscopic rearrangement and barrier-crossing events that already govern real-time aging, rather than introducing new degradation mechanisms. The biggest goal that the team wanted to accomplish this past year was to increase the rate of acceleration and to obtain correlations between the destabilization rate with material parameters. We are pleased to report that this goal was indeed met, with many promising routes that the project can take in Phase II.
The acoustic acceleration concept was tested across three systems of increasing complexity: a model depletion-induced colloidal gel, a commercial solid particulate agrochemical formulation, and oil-in-water nanoemulsions. Across all systems studied, low-power acoustic excitation produced statistically significant acceleration of aging, with acceleration factors ranging from approximately 1.5× in weak colloidal gels to roughly 4-5× in nanoemulsions and complex formulations. Importantly, the sequence of destabilization events appeared to remain unchanged. We found that acoustic exposure reduced the macroscopic phase separation time and increased the sedimentation rate while preserving particle morphology and microstructural signatures consistent with natural aging.
Direct comparison with thermal aging underscores the importance of mechanism fidelity. Although heating produced faster macroscopic failure, it also led to dense plug formation, particle fusion, and other irreversible changes that were absent during natural aging. Acoustic aging, by contrast, accelerated failure while maintaining representative pathways. Overall, the results demonstrate that low-power acoustics can substantially reduce aging times while preserving the physical mechanisms that control real-time stability, supporting its potential as a predictive accelerated aging method for industrial dispersions.
Two Ph.D. students were partly supported by this project. Each of them was assigned a different dispersion class to investigate and we were able to come up with an acoustic acceleration setup that is compatible with the lab's confocal laser scanning microscope. In the future, we will focus on the mechanisms through which low power acoustic energy enhances phase separation, and consider designs that are compatible with rheology measurement tools in the group. Scalability of the technique will also be considered after additional validation measurements are successful. These future research thrusts are described more fully in the renewal proposal submitted for consideration at the 2026 IFPRI Winter Meeting.