Research on linking molecules in colloidal gels helps improve their tunability

Colloidal gels are a promising subject for self-assembling materials due to their tunable optical and mechanical properties. However, factors regarding the fabrication and control over their physical properties are still far from being well understood.

Howard et al. looked at a way to manipulate the nanoscale structure of gels formed connecting inorganic nanocrystals via tunable linkers. The authors investigated the flexibility of the linker molecules that mediate bonding between distinct nanocrystals. By using computational models to simulate different linkers – some which were highly flexible and others that were rigid, the authors found a range of resultant properties.

“The main point that comes from the work is if you can control the linker in the solution, then you can switch the material properties pretty dramatically without affecting the building blocks at all,” said author Thomas Truskett.

They found that both the highly flexible and the highly rigid linkers increased nanocrystal adhesiveness, creating a more solid-like material with improved mechanical integrity. However, semi-flexible linkers were found to disperse the nanocrystals in the solvent, making for a thinner liquid.

“I think the linkers’ impact on the behavior of materials is greater than we anticipated originally,” Truskett said.

The group’s results show that this behavior exhibited by the semi-flexible linkers is due to a self-looping behavior. Semi-flexible linkers are the perfect length to loop back on themselves and stick to the same nanocrystal they originated on, instead of bridging to other nanocrystals. These findings will help design gels to avoid this property or perhaps even exploit it for use in switchable applications.

Source: “Effects of linker flexibility on phase behavior and structure of linked colloidal gels,” by Michael P. Howard, Zachary M. Sherman, Adithya N. Sreenivasan, Stephanie A. Valenzuela, Eric V. Anslyn, Delia J. Milliron, and Thomas M. Truskett, Journal of Chemical Physics (2021). The article can be accessed at https://doi.org/10.1063/5.0038672 .