This study assesses the use of acoustic waves as a non-destructive accelerated aging method to be tested on multiple formulations including particle dispersions and emulsions. Two Ph.D. students in the PI's group, who are partially supported by this IFPRI grant, are working on the project. The method serves as an alternative to conventional techniques such as centrifugation and thermal aging, which either fail to capture essential destabilization mechanisms or may harm sensitive components. The project was initiated based on feedback from our industry liaison panel, which expressed interest in developing methods to expedite particle aggregation and subsequent sedimentation in colloidal dispersions. Selected samples from IFPRI members were tested as part of the project.
To address specific industry needs on stability testing, we examined model poly(methyl methacrylate) colloidal gels and commercially available agricultural dispersions provided by the panel, in addition to a model oil-in-water nanoemulsion system used in our group. We initially compared samples that were naturally aged, heat aged, and exposed to high and low powered ultrasound waves. Heating induced chemical degradation, solute particle melting, and solvent evaporation—each of which deviated mechanistically from the original natural aging pathway. High powered ultrasound waves caused irreversible yielding of the samples. Based on these initial results, a decision was made to focus solely on comparing natural and low-power acoustic aging methods.
A major technical goal in Y1 is the design of acoustic transducers compatible with confocal microscopy and rheometry, enabling detailed imaging and precise measurement of particle dynamics during acoustic treatment. We have achieved this goal for ex situ testing of small volume samples (<20 mL). Temperature measurements showed that the low-power acoustic transducers generated little dissipative heat and that the samples could be kept at ±3°C of room temperature without a need for cooling devices.
This custom experimental setup produced finely tuned acoustic waves at much lower power (<2 W) and pressures (<200 kPa) and allowed for controlled, efficient aging acceleration without compromising system integrity. While initial results on the IFPRI agricultural dispersion were mixed, accelerated phase separation was induced reproducibly for PMMA colloidal gels. For nanoemulsion samples, dynamic light scattering measurements suggest that a moderate acoustic pressure hastened both Ostwald ripening and coalescence processes. Additional tests are underway to determine the reproducibility and viability of these results through a more careful analysis of the intensity and number-weighted particle size distributions. Another set of IFPRI samples that are analogous to these emulsion systems have been obtained and will be tested.
Efforts in Y1 were primarily targeted at establishing method viability. In Y2, we plan to systematically check the macroscopic and microscopic effects of acoustic aging on both classes of materials, and to begin identifying the destabilization mechanisms that acoustic aging targets. We plan to continue providing regular updates to our IFPRI industry partner as well as to the IFPRI liaison meetings scheduled every 2 months.