EventDr. Martin Gerard

Atomic analogues in colloidal crystals

Colloidal crystal are assemblies of nanoparticles that one wants to tailor for specific applications, for instance catalysis in proteins crystals or optical responses. Crystalline properties are dictated by the lattice, spacing and crystal habits of the assemblies. These colloidal crystals are often understood by analogy with atomic counterparts and described as such in the literature, i.e CsCl as a means of describing body-centered systems. In this picture, individual particles are often analogized with atoms and their chemical interactions with electron-based bonds. However, these models are generally simple, and unexpected behavior often arises when systems are slightly outside of tested grounds. In this talk, I will address some of the discrepancies and challenges when using atomic orbitals to rationalize colloidal crystal engineering with DNA molecules.

First, I will talk about systems comprised of anisotropic particles, where the particle shape is expected to assume the role of atomic orbitals. As the DNA shell length is increased, one would expect an anisotropic to spherical transition. Unexpectedly, for ligand shells with lengths comparable with particle size, the shell deforms and new phases with broken symmetries appear. I will show and discuss a variety of puzzling phases obtained from anisotropic particles.

Second, I will discuss lattices comprised of a mixture of small (1.5 nm) and large (10 nm) particles. In such systems, the smaller particles are delocalized and roam the crystal akin to electrons in a classical metal. The stochiometric ratio between small and big particles takes the role of valency and can be continuously varied unlike regular assemblies. Finally, I will show that by tuning DNA properties or temperature, these particles undergo a localization transition, an analogue to metalinsulator transitions of atomic systems.


About The Speaker


Dr. Martin Girard obtained his bachelor degree in engineering physics from Polytechnique Montréal Canada in 2012, followed by his Master studies on waveguides and metamaterials in terahertz domain. In 2018, he completed his PhD studies at Northwestern University on self-assembled crystal structures composed of DNA coated nanoparticles. Dr. Girard has recently joined the Max-Planck-Institute for polymer research in Mainz to continue his studies on phase transitions in phospholipid membranes.