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1. Nonlinear chiral rheology of phospholipid monolayers

   https://doi.org/10.1039/c8sm00184g  

   Kim, KyuHan; Choi, Siyoung Q.; Zasadzinski, Joseph A.; Squires, Todd M. (January 2018, Soft Matter)

   Microbutton rheometry reveals that the chiral morphology of dipalmitoylphosphatidylcholine (DPPC) monolayers imparts a chiral nonlinear rheological response. The nonlinear elastic modulus and yield stress of DPPC monolayers are greater when sheared clockwise (C), against the natural winding direction of DPPC domains, than counter-clockwise (CC). Under strong CC shear strains, domains deform plastically; by contrast, domains appear to fracture under strong C shearing. After CC shearing, extended LC domains develop regular patterns of new invaginations as they recoil, which we hypothesize reflect the nucleation and growth of new defect lines across which the tilt direction undergoes a step change in orientation. The regular spacing of these twist-gradient defects is likely set by a competition between the molecular chirality and the correlation length of the DPPC lattice. The macroscopic mechanical consequences of DPPC's underlying molecular chirality are remarkable, given the single-component, non-cross-linked nature of the monolayers they form. 

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2. Actuating superparamagnetic nanoparticle monolayers

   https://doi.org/10.1073/pnas.2424073122  

   Esposito, Edward_P; Lopez_Rios, Hector_Manuel; Olvera_de_la_Cruz, Monica; Jaeger, Heinrich_M (March 2025, Proceedings of the National Academy of Sciences)

   Magnetically responsive, mechanically flexible microstructures are desirable for applications ranging from smart sensors to remote-controlled actuation for surgery or robotics. Embedding magnetic nanoparticles into a thin matrix of elastic material enables high flexibility while exploiting the magnetic response of the individual particles. However, in the ultrathin limit of such nanocomposite materials, the particles become too small to sustain a permanent dipole moment. This implies that now large magnetic field gradients are required for actuation, which are difficult to achieve with externally applied fields. Here, we demonstrate through experiment and simulation that monolayer sheets of close-packed paramagnetic nanoparticles in a uniform applied field can generate large local field gradients through particle interactions. As a result, a strong collective magnetization is obtained that leads to large deflections of freestanding sheets already in moderate applied fields. Exploiting the vector nature of the applied field, we furthermore find that it is possible to induce more complex curvature and twist the sheets. Finally, we show that paramagnetic nanoparticle monolayers applied as coatings can generate sufficient force to deflect strips of nonmagnetic material that is several orders of magnitude thicker. 

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3. Dynamic Reconfiguration of Compressed 2D Nanoparticle Monolayers

   https://doi.org/10.1021/acsnano.1c09853  

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4. Structural Order and Plasmonic Response of Nanoparticle Monolayers

   https://doi.org/10.1021/acsphotonics.3c01813  

   Green, Allison M.; Chang, Woo Je; Sherman, Zachary M.; Sakotic, Zarko; Kim, Kihoon; Wasserman, Daniel; Milliron, Delia J.; Truskett, Thomas M. (March 2024, ACS Photonics)
5. Structural Effects of Cation Binding to DPPC Monolayers

   https://doi.org/10.1021/acs.langmuir.0c02555  

   Javanainen, Matti; Hua, Wei; Tichacek, Ondrej; Delcroix, Pauline; Cwiklik, Lukasz; Allen, Heather C. (December 2020, Langmuir)

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