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XX5.06 - Responsive Surface Topographies Formed by Liquid Crystal Networks 
April 23, 2014   9:45am - 10:00am

Throughout the course of evolution, living creatures have developed a wide range of motions and survival strategies based on the unique topologic patterns on their surfaces. Gecko lizards climb on tilted, vertical and inverted surfaces yet can still easily detach by adapting the microstructures on their feet. Thanks to the complex and fine architectures on their surface, lotus flower leaves are highly water repellent and self-cleaning by rolling water droplets. And even our human respiratory system makes use of little moving protrusions and cilia to protect the nasal passageways and other parts of the respiratory tract, filtering out dust and other particles that enter nose with breathed air.Inspired by nature, we developed responsive surface topographies that can be switched on and off in a pre-designed manner. Here we provide a general method to generate surface topographies. It is based on the change of molecule organization in ordered liquid crystal polymer networks. A local change in the degree of molecular orderresults in a local expansion of the film leading to the desired protrusions.Previously, we published the formation of dynamic protrusions in liquid crystal networks modified with azobenzene moieties as crosslinks. The protrusions can be actuated by either uniform light exposure or by localized exposure. Here, we investigated the changes in density upon reduction of LC order in the polymer networks. In general, this topic remained underexposed in photo-triggered LC networks until now. But here it proves one of the leading mechanisms for protrusion formation leading to expansions of the order of 10 % of the initial thickness of the film. This is supported further by density measurements. The combination density effects with director-driven expansion even could increase protrusion formation up to 20 % of the initial thickness.In the presentation new strategies will be elucidated that lead to lateral dimensions of the dynamic protrusions down to micrometer level while further improving the height of the structures to values exceeding 20% of the initial film thickness. We will also demonstrate some properties of the films leading to applications in robotics and self-cleaning.

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Keynote Address
Panel Discussion - Different Approaches to Commercializing Materials Research
Business Challenges to Starting a Materials-Based Company
Fred Kavli Distinguished Lectureship in Nanoscience
Application of In-situ X-ray Absorption, Emission and Powder Diffraction Studies in Nanomaterials Research - From the Design of an In-situ Experiment to Data Analysis