Colloidal gels age differently under shallow, deep quenches

Colloidal gels are assembled from nano to micro sized particles that glue themselves together. They are ubiquitous in biology, foods, and consumer products such as ceramics, asphalt, and cement.

Understanding the relationships between structure and properties in colloidal gels is crucial for their various applications. For example, water filtration requires a porous structure, while some other instances such as ceramic turbine blades might instead necessitate an ultra-high strength material without cracks or pores to weaken it.

Suman and Wagner examined the aging of a model, thermoreversible colloidal gel with rheology measurements.

“Aging is the gel slowly evolving over time to some final state,” said author Norman Wagner. “Such aging proceeds by local particle rearrangements that usually allow the gel to strengthen when it is homogenous.”

The researchers explored the aging process after quenching the gel, or taking it from a liquid suspension to a gel state via temperature cooling. As expected, shallow quenches left the gel homogenous and allowed it to strengthen slowly with time.

“However, a deep quench takes the gel below the phase separation temperature where nucleation and growth, or even spinodal decomposition, can occur,” said Wagner. “Phase separation then fights with gel formation to create an inherently nonequilibrium system. The aging behavior becomes rather interesting and exciting as large changes in mechanical strength occur suddenly.”

Even deeper quenching reaches into the realm of glass formation, trapping the nonequilibrium gel and greatly inhibiting further aging.

This knowledge on the competition between gelation, phase behavior, and glass formation can be used to inform the design and engineering of materials with specific structures and properties.

Source: “Anomalous rheological aging of a model thermoreversible colloidal gel following a thermal quench,” by Khushboo Suman and Norman J. Wagner, Journal of Chemical Physics (2022). The article can be accessed at https://doi.org/10.1063/5.0094237 .

This paper is part of the Slow Dynamics Collection, learn more here .