Azobenzene polymer networks have drawn interests in the area of adaptive materials and structures due to their novel photo-responsive material coupling. These materials undergo a complex light driven molecular conformation change of the azobenzene chromophore when the material is exposed to ultraviolet (UV) or blue-green light. This photoisomerization process is characterized by a molecular conformation change from a rod shaped molecule to a strongly kinked molecule, also known as trans-cis photoisomerization under UV light exposure. Exposure to blue-green light can lead to a trans-cis-trans photoisomerization or a relaxation from the kinked cis state back to the trans rod state. The latter process is of strong interests for adaptive structure applications because the relaxation back to the trans state can be controlled by the orientation of polarized light. When these azobenzene molecules undergo this process in a polymer network, bending and twisting deformation can be controlled by the polarization orientation of the blue-green light. To better understand the distribution of the molecular conformation changes that influences macroscopic polymer deformation, we have conducted solid state Nuclear Magnetic Resonance (ss-NMR) tests on fluorine doped azobenzene polymer networks. Here, we illustrate measurable chemical shifts due to blue light exposure near the 450 nm wavelength using a static ss-NMR probe. The results are compared to ss-NMR at different temperatures using Magic Angle Spinning (MAS) NMR to understand any potential influences of heat relative to photoisomerization.
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NMR Characteristics of Photomechanics and Thermomechanics of Azobenzene Polymer Networks
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Worden, M, Wang, H, Paravastu, A, & Oates, WS. "NMR Characteristics of Photomechanics and Thermomechanics of Azobenzene Polymer Networks." Proceedings of the ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. Volume 2: Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Bio-Inspired Materials and Systems; Energy Harvesting. Stone Mountain, Georgia, USA. September 19–21, 2012. pp. 175-179. ASME. https://doi.org/10.1115/SMASIS2012-8076
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