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Publication Surface anchoring energy of cholesteric liquid crystals(2019-01-01) Guo, Tianyi; Zheng, Xiaoyu; Palffy-Muhoray, PeterIn this paper, we propose a suitable surface energy expression for cholesteric liquid crystals. We show that there exists a symmetry allowed term for chiral nematics that doesn’t appear in the traditional Rapini-Papoular surface energy form. We discuss some consequences of this new surface anchoring term.Publication Photoinduced Deadhesion of a Polymer Film Using a Photochromic Donor–Acceptor Stenhouse Adduct(2019-01-01) Mostafavi, Seyed Hossein; Li, Wangxiang; Clark, Kyle D.; Stricker, Friedrich; de Alaniz, Javier Read; Bardeen, Christopher J.Photoisomerization of molecules dissolved in a polymer film can modulate its properties. In a previous paper (Mostafavi, S. H.; Macromolecules 2018, 51, 2388−2394), it was found that the ultraviolet light-induced photoisomerization of spiropyran dopants could substantially increase adhesion to a glass surface. In this work, a different photochromic reaction, the visible-light-induced cyclization of a donor–acceptor Stenhouse adduct (DASA), leads to the opposite effect: the deadhesion of a polystyrene film from a clean glass surface. Measurements of the shear and pull-off adhesion strengths before and after visible irradiation show a light-induced decrease of 20–30%. The time required for delamination in water shows an even more dramatic decrease of 90%. Changes in the water contact angle and other measurements suggest that molecular-level noncovalent interactions between the polymer and glass are weakened after photoisomerization, possibly due to the molecular contraction of the DASA that disrupts the interaction between its amine groups and the surface silanols. The ability to reduce polymer adhesion using visible light enables the controlled release of dye molecules from a glass container, where these have been stored as a dry powder, into an aqueous solution. Embedding photochromic molecules in a polymer can lead to new effects that may have practical applications in stimuli-responsive materials.Publication Norbornadienes: Robust and Scalable Building Blocks for Cascade “Click” Coupling of High Molecular Weight Polymers(2019-01-01) St. Amant, Andre H.; Discekici, Emre H.; Bailey, Sophia J.; Zayas, Manuel S.; Song, Jung-Ah; Shankel, Shelby L.; Nguyen, Shay N.; Bates, Morgan W.; Anastasaki, Athina; Hawker, Craig J.; de Alaniz, Javier ReadHerein, we report the development of a scalable and synthetically robust building block based on norbornadiene (NBD) that can be broadly incorporated into a variety of macromolecular architectures using traditional living polymerization techniques. By taking advantage of a selective and rapid deprotection with tetrazine, highly reactive “masked” cyclopentadiene (Cp) functionalities can be introduced into synthetic polymers as chain-end groups in a quantitative and efficient manner. The orthogonality of this platform further enables a cascade “click” process where the “unmasked” Cp can rapidly react with dienophiles, such as maleimides, through a conventional Diels–Alder reaction. Coupling proceeds with quantitative conversions allowing high molecular weight star and dendritic block copolymers to be prepared in a single step under ambient conditions.Publication Light intensity as mechanical potential: a symmetry-based approach(2019-01-01) Guo, Tianyi; Zheng, Xiaoyu; Palffy-Muhoray, PeterLight-induced motion is of increasing importance in materials development. In many situations, modelling the detailed dynamics of light-induced phenomena is not practical, yet a description of the behaviour is needed. We attempt to show here that in some such situations, symmetry arguments can prove useful. We outline a simple scheme where symmetry arguments can be useful in modelling the dynamics, and show, in three examples, that in some instances, light intensity may be regarded as a mechanical potential. Such an approach may help in understanding photoactuations in situations where more detailed analyses are impractical.Publication Performance of Composite Glass–Diarylethene Crystal Photomechanical Actuator Membranes(2022-01-01) Dong, Xinning; Guo, Tianyi; Kitagawa, Daichi; Kobatake, Seiya; Palffy-Muhoray, Peter; Bardeen, Christopher JHybrid organic–inorganic composites based on organic photochromic crystals embedded in inorganic templates provide a new approach to photomechanical materials. Diarylethene (DAE) nanowire crystals grown in Al2O3 membranes have exhibited reversible photoinduced bending and lifting [Dong, X., Chem. Mater. 2019, 31, 1016−1022]. In this paper, the hybrid approach is extended to porous SiO2 membranes. Despite the different template material (SiO2 instead of Al2O3) and much larger channels (5 μm diameter instead of 0.2 μm diameter), similar photomechanical behavior is observed for this new class of organic–inorganic hybrid actuators. The ability to reuse individual glass templates across different DAE filling cycles allows us to show that the DAE filling step is crucial for determining the mechanical work done by the bending template. The bending curvature also depends quadratically on the template thickness, in good agreement with theory. The light-induced bending can be repeated for up to 150 cycles without loss of performance, suggesting good fatigue resistance. The results in this paper demonstrate that the hybrid organic–inorganic approach can be extended to other host materials and template geometries. They also suggest that optimizing the organic filling and template thickness could improve the work output by an order of magnitude.