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1. Diffusion of Anisotropic Colloidal Microparticles Fabricated Using Two‐Photon Lithography

   https://doi.org/10.1002/ppsc.202100033  

   Doan, David; Kulikowski, John; Gu, X. Wendy (July 2021, Particle & Particle Systems Characterization)

   Abstract Polymeric particles with complex shapes are required for biomedical therapies, colloidal self‐assembly, and micro‐robotics. It has been challenging to synthesize particles beyond simple shapes (e.g., spheres, cubes) with high structural accuracy using existing methods. Here, a method for fabricating polymeric microparticles of complex 3D shapes is reported using two‐photon lithography, and dispersing the particles in an aqueous solution on a glass substrate. The fabrication of polyhedrons (e.g., tetrahedron, pyramid), polypods (e.g., tetrapod, hexapod), and other shapes of 5–10 µm in size is demonstrated. Confocal microscopy is used to track the motion of the sphere, tetrahedron, tetrapod, and screw‐shaped particles near the substrate, and determine their translational diffusion coefficients. HYDRO++ is used to simulate the motion of the particles far from the substrate. The influence of particle size and substrate effects on diffusion in the spherical particles is determined and finds that the non‐spherical particles have increased hindrance at the substrate compared to the spherical particles. 

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2. Controlling morphology in electrosprayed methylcellulose nanowires via nanoparticle addition: coarse-grained modeling and experiments

   https://doi.org/10.1039/D2NR04177D  

   Blisko, Jonathan M.; Grzenda, Michael J.; Vladimirsky, Rachel M.; Shuck, Christopher E.; Singer, Jonathan P.; Yong, Xin (December 2022, Nanoscale)

   Electrospray deposition (ESD) has shown great promise for manufacturing micro- and nanostructured coatings at scale on versatile substrates with complex geometries. ESD exhibits a broad spectrum of morphologies depending upon the properties of spray fluids. Among them are nanowire forests or foams obtained via the in-air gelation of electrospray droplets formed from methylcellulose (MC) solutions. In this study, we explored MC ESD loaded with nanoparticles of various shapes and uncovered the effects of particle fillers on morphology evolution using coarse-grained simulations and physical experiments. Utilizing electrostatic dissipative particle dynamics, we modeled the electrohydrodynamic deformation of particle-laden MC droplets undergoing in-flight evaporation. The simulations quantitatively predict the suppression of droplet deformation as the size or concentration of spherical nanoparticles increases. While small particles can be readily encapsulated into the nanowire body, large particles can arrest nanowire formation. The model was extended to nanoparticles with complex topologies, showing MC nanowires emerging from particle edges and vertices due to curvature-enhanced electric stress. In all cases, strong agreements were found between simulation and experimental results. These results demonstrate the efficacy of the coarse-grained model in predicting the morphology evolution of electrosprayed droplets and lay the groundwork for employing MC nanowires for developing nanostructured composites. 

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3. Size-Based Filtration of Poly-Disperse Micro-Particle by Dipping

   https://doi.org/10.1115/MSEC2022-85680  

   Khalil, Md Ibrahim; Khoda, Bashir (June 2022, Proceedings of the ASME 2022 17th International Manufacturing Science and Engineering Conference)

   Abstract In manufacturing industries, spherical micro-particles are commonly used as (e.g., brazing powder, metal filler, and 3D printing powder) which are produced with droplet-based particle fabrication techniques. Such processes create spherical morphology but introduce polydispersity and follow a continuous exponential pattern commonly expressed with Rosin-Rammler expression. Sorting those micro-particles in a narrower size range is an important but difficult, costly, and challenging process. Here we demonstrate the successful separation of the particles from a poly-disperse mixture with a particle volume fraction of 10% by dipping process. Nickel-based micro-particles (avg. dia. 5.69 μm) are added in a binder-based liquid carrier system. To encounter the gravitational force, external kinetic energy in the form of agitation is applied to ensure the uniform dispersion of the particles. The cylindrical substrate is prepared and dipped in the ‘pseudo suspension’ to separate the particles by adhering to it. The substrate is dried, and images are taken to characterize the separated particles using image J software. A clear size distribution can be observed which is also plotted. Additionally, a relationship between the process parameter and sorted particles has been established. The proposed method is quick, controllable, and easy to implement, which can be a useful tool for sorting wide-range poly-disperse particles. 

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4. Breaking Parallel Orientation of Rods via a Dendritic Architecture toward Diverse Supramolecular Structures

   https://doi.org/10.1002/anie.201904749  

   Zhang, Ruimeng; Feng, Xueyan; Zhang, Rui; Shan, Wenpeng; Su, Zebin; Mao, Jialin; Wesdemiotis, Chrys; Huang, Jiahao; Yan, Xiao‐Yun; Liu, Tong; et al (July 2019, Angewandte Chemie International Edition)

   Abstract Self‐assembled nanostructures of rod‐like molecules are commonly limited to nematic or layered smectic structures dominated by the parallel arrangement of the rod‐like components. Distinct self‐assembly behavior of four categories of dendritic rods constructed by placing a tri(hydroxy) group at the apex of dendritic oligo‐fluorenes is observed. Designed hydrogen bonding and dendritic architecture break the parallel arrangement of the rods, resulting in molecules with specific (fan‐like or cone‐like) shapes. While the fan‐shaped molecules tend to form hexagonal packing cylindrical phases, the cone‐shaped molecules could form spherical motifs to pack into various ordered structures, including the Frank–Kasper A15 phase and dodecagonal quasicrystal. This study provides a model system to engineer diverse supramolecular structures by rod‐like molecules and sheds new light into the mechanisms of the formation of unconventional spherical packing structures in soft matter. 

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5. Facile Process for Fabrication of Silicon Micro–Nanostructures of Different Shapes as Molds for Fabricating Flexible Micro–Nanostructures and Wearable Sensors

   https://doi.org/10.1021/acsami.2c22285  

   Ding, Xiaoke; Rubby, Md Fazlay; Que, Suya; Uchayash, Sajid; Que, Long (March 2023, ACS Applied Materials & Interfaces)

   We report a method to fabricate silicon micro–nanostructures of different shapes by tuning the number of layers and the sizes of self-assembled polystyrene beads, which serve as the mask, and by tuning the reactive ion etching (RIE) time. This process is simple, scalable, and inexpensive without using any sophisticated nanomanufacturing equipment. Specifically, in this work, we demonstrate the proposed process by fabricating silicon micro- or nanoflowers, micro- or nanobells, nanopyramids, and nanotriangles using a self-assembled monolayer or bilayer of polystyrene beads as the mask. We also fabricate flexible micro–nanostructures by using silicon molds with micro–nanostructures. Finally, we demonstrate the fabrication of bandage-type electrochemical sensors with micro–nanostructured working electrodes for detecting dopamine, a neurotransmitter related to stress and neurodegenerative diseases in artificial sweat. All these demonstrations indicate that the proposed process provides a low-cost, easy-to-use approach for fabricating silicon micro–nanostructures and flexible micro–nanostructures, thus paving a way for developing wearable micro–nanostructures enabled sensors for a variety of applications in an efficient manner. 

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