Controlling the volume fraction of glass-forming colloidal suspensions using thermosensitive host mesogels

The key parameter controlling the glass transition of colloidal suspensions is phi, the fraction of the sample volume occupied by the particles. Unfortunately, changing phi by varying an external parameter, e.g., temperature T as in molecular glass formers, is not possible, unless one uses thermosensitive colloidal particles, such as the popular poly(N-isopropylacrylamide) (PNiPAM) microgels. These, however, have several drawbacks, including high deformability, osmotic deswelling, and interpenetration, which complicate their use as a model system to study the colloidal glass transition. Here, we propose a new system consisting of a colloidal suspension of non-deformable spherical silica nanoparticles, in which PNiPAM hydrogel spheres of similar to 100-200 mu m size are suspended. These non-colloidal mesogels allow for controlling the sample volume effectively available to the silica nanoparticles and hence their phi, thanks to the T-induced change in mesogels' volume. Using optical microscopy, we first show that the mesogels retain their ability to change size with T when suspended in Ludox suspensions, similarly as in water. We then show that their size is independent of the sample thermal history such that a well-defined, reversible relationship between T and phi may be established. Finally, we use space-resolved dynamic light scattering to demonstrate that, upon varying T, our system exhibits a broad range of dynamical behaviors across the glass transition and beyond, comparable with those exhibited by a series of distinct silica nanoparticle suspensions of various phi. Published under an exclusive license by AIP Publishing.

Automated summary

This paper proposes a new system to effectively control the proportion of particles in a colloidal suspension by changing the volume of hydrogel spheres. The study shows that the system exhibits similar glass transition and dynamic behavior as silica nanoparticle suspensions with different particle ratios.