DrSean Collins

I lead a research group specialising in nanoscale structural and spectroscopic studies of molecular materials with a focus on applications for sustainability. Research in the group spans advanced electron microscopy approaches for understanding the materials microstructure and its connection to functional properties in materials from organic semiconductors to metal–organic frameworks (MOFs) and polymeric supports for single-atom catalysis. Application areas encompass membranes for fuel cells, and optoelectronic devices to probing fundamentals of leaf waxes and polymer nanoparticles for and agrochemical and pharmaceutical formulations. 

Organic and hybrid semiconductors: Organic and hybrid semiconductors (including halide perovskites) continue to set new records for efficiency, but the detailed features that limit performance often remain obscured. We apply advanced low-dose electron microscopy methods for diffraction and spectroscopy (linking chemistry, structure, and changes in optical properties), most notably four-dimensional scanning transmission electron microscopy (4D-STEM) and electron energy loss spectroscopy (EELS), to gain new insight into the structures, interfaces, and dynamic changes during device ageing that are needed to disentangle intrinsic and extrinsic limitations and develop targeted interventions to improve efficiency and durability. 

Metal–organic frameworks (MOFs): MOFs have been recognised for their high surface area, but technological demands - whether in carbon capture, water harvesting, membrane technologies for chemical separations or fuel cells, or in catalysis - increasingly prioritise their controlled, solid state functional group chemistry and crystal structure defined pore-size selectivity. The emergence of glassy MOFs has created a lot of new approaches for composite formation to control and modify these properties. We explore the crystalline as well as the disordered and amorphous phases (using pair distribution function analysis and total scattering approaches in electron microscopy) and interfaces of MOFs to identify the active fraction, especially in composites where interfacial interactions modify the performance of the materials as a whole.

Pharmaceuticals and agrochemicals: Many pharmaceutical and agrochemical formulations (or their targets) are made from molecular crystals and polymers. Understanding solubility and bioavailability, polymorphism (different molecular packing arrangements), and shelf life (hydration/dehydration) as well as new drug delivery modalities like polymer nanoparticles require new tools for probing the surface and internal structure of molecular solids. We advance 4D-STEM and electron microscopy based spectroscopies, including using cryogenic electron microscopy methods, to develop quantitative descriptions of materials systems and processes like how polymer nanoparticles fuse and how composition modifies domain structure in multi-component leaf waxes.

Cutting across these application areas, we are interested in fundamental questions:

Defects and grain microstructure - Molecular materials are highly anisotropic and comprise both weak intermolecular interactions and strong intramolecular bonds. They are also very sensitive to electron beam irradiation needed to probe the characteristic length scales of interfaces, grain boundaries, and defects (e.g. stacking faults, dislocations). We seek to learn the distinct rules (in comparison to inorganic solids) for materials microstructure in organic materials.

Phase transitions and dynamics - We are interested in documenting the sequence of events at the smallest length scales to understand how materials change with time (semiconductor device degradation, polymer nanoparticle fusion) or with exposure to heat (dehydration, melting).