Mesogels control volume to explore the glass transition

While liquids flow freely and crystalline solids remain in fixed positions with time, glasses are unique because they lie somewhere between these states. In a single snapshot, glass looks as disordered as a liquid, but it has the mechanical properties of a solid.

This makes the glass transition simultaneously interesting and difficult to study. It is often explored with colloidal particles that are easier to see in experiments than single atoms. These constituent particles are suspended in solution.

Temperature controls the glass transition of molecular glass formers. For colloids, by contrast, glassiness is ruled by the fraction of the volume occupied by the particles. However, changing suspension volume fraction accurately is challenging and involves preparing a new sample for each target state. Instead, thermoresponsive microgels, which absorb and expel water according to temperature, are frequently used as a tunable method to change volume fractions.

Behra et al. took a different approach by adding poly(N-isopropylacrylamide) mesogels to a suspension of silica colloidal particles. These mesogels control the volume fraction of the colloidal silica particles in a reproducible manner while avoiding problems with previous microgels where particle interactions changed with temperature.

“The ratio between the size of these chunks of gels and the silica colloidal particles is ten times the size ratio between the sun and the moon,” said author Luca Cipelletti. “We call them mesogels because they are pieces of gels between the microscopic size of the particles and the macroscopic size of our sample container.”

The authors plan to explore the glass transition in these samples with fast and slow changes in temperature and under repeated cycles of temperature change.

Source: “Controlling the volume fraction of glass-forming colloidal suspensions using thermosensitive host ‘mesogels’,” by Juliette Behra, Ambre Thiriez, Domenico Truzzolillo, Laurence Ramos, and Luca Cipelletti, Journal of Chemical Physics (2022). The article can be accessed at https://doi.org/10.1063/5.0086822 .

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