(463c) Accelerating Aging in Colloidal Dispersions Using Acoustics

The aging behavior of colloidal dispersions, often accompanied by microstructural changes and phase separation, is important across many industries in extending the shelf life of products exposed to various environmental conditions. This study investigates the use of low power ultrasound to accelerate aging without significant changes in the temperature. Acoustic waves are applied to a commercial dispersion composed of fluorescently dyed colloidal solids (30 – 50 wt.%) suspended in an aqueous media in the presence of surfactants (1 – 3 wt.%), dispersant (< 10 wt.%) and stabilizers. Rheological and microstructural studies are conducted on samples that have been naturally aged, and acoustically aged (20 kHz, 10W) over a 30-day period. Steady shear experiments (σ = 0.1 to 10 Pa) and oscillatory amplitude sweeps (σ = 0.1 to 10 Pa, f = 0.5 Hz) are conducted using a stress-controlled rheometer with a parallel plate geometry, while a confocal laser scanning microscope is used to image the microstructure when the sample is subjected to different accelerated aging techniques. Our results indicate that natural aging results in a ~25% increase in the particle size, over a 30 day period. Comparison of the acoustic aging data with that obtained from natural and heat aging suggests that low power sound waves induce flocculation at rates that are nearly 15´ higher, without chemical degradation and melting effects caused by elevated temperatures. Application of acoustic powers of different magnitudes will test the idea that the introduction of external energy enhances the thermal motion of the system, thus potentially enabling the acceleration of microstructural rearrangements through particle collisions without causing catastrophic yielding.