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Hanna Hulkkonen: Harnessing the power of molecular self-assembly – new approach to building optical nanomaterials

Hanna Hulkkonen.
What if in the future we could have functional materials that build themselves? New advancements in block copolymer technology enable us to design and build nanopatterned photonic materials using molecular self-assembly.

Nature is excellent at self-assembly. Many living organisms can build micro- or nanostructured materials that have intriguing optical properties. Butterfly wings are iridescent because the wings are textured with light-reflecting nanostructures. A moth’s eye is structured to be non-reflective for better vision and stealth. Similar structures can be nowadays re-created in the lab using synthetic molecules called block copolymers.

Block copolymers are molecules that can organize themselves into periodic 2D or 3D nanostructures. M.Sc. (Tech.) Hanna Hulkkonen has investigated how these self-assembling polymers can be utilized to fabricate light-manipulating materials. These structured nanomaterials can be used to enhance light-harvesting in solar cells or reduce screen glare in optical displays.

The challenge of self-assembly is figuring out how to guide the polymers into the desired structure. The process is called annealing.

“One of the difficulties of annealing is that the process isn’t easy to control and the self-organization usually takes several days,” Hulkkonen explains.

In her research, Hanna Hulkkonen treated block copolymers with a solvent vapor to partially dissolve the molecules and boost their mobility resulting in rapid self-assembly.

“I developed an extremely precise method to control the amount of solvent in the polymer during the annealing. It’s all computer-controlled now, so we can exactly repeat the treatment protocol. The results show that highly ordered nanostructures could be self-assembled in minutes,” Hulkkonen says.

“What intrigues me is that these polymers are so versatile. We use them as blueprints for building functional materials,” she continues.

By designing the placement and shape of the nanostructures carefully, the way that light interacts with the material can be changed. The dissertation shows that near-perfect absorption of visible light could be achieved in a dome-patterned material.  The material shows promise for high-sensitivity optical sensors.

Hanna Hulkkonen has carried out her research in the Nanophotonics research group at Tampere University.

The doctoral dissertation of M.Sc. (Tech.) Hanna Hulkkonen in the field of photonics titled Nanophotonic Materials by Block Copolymer Self-Assembly will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University in the Auditorium TB109 of the Tietotalo building on Friday 12 March 2021 at 12 o’clock. The Opponent will be Assistant Professor Pawel Majewski from the University of Warsaw, Poland. The Custos will be Associate Professor Tapio Niemi from the Faculty of Engineering and Natural Sciences at Tampere University.

The event is streamed live via Zoom

The dissertation is available online at: http://urn.fi/URN:ISBN:978-952-03-1882-6

Photo: Heidi Tuorila

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