This letter reports optical properties of spherical dielectric particles with alternating layers of high and low refractive indices. The authors “predesigned” and synthesized polymer microspheres with alternating polystyrene and poly(trifluoroethyl methacrylate) layers of various thicknesses. Extinction of the microspheres was examined in a broad spectral range. A multipole expansion of electromagnetic field was applied for calculating the extinction efficiency of the particles. Excellent agreement was obtained between experimental and theoretical extinction curves.
Chemically and topographically patterned nanoparticles (NPs) with dimensions on the order of tens of nanometers have a diverse range of applications and are a valuable system for fundamental research. Recently, thermodynamically controlled segregation of a smooth layer of polymer ligands into pinned micelles (patches) offered an approach to nanopatterning of polymer-functionalized NPs. Control of the patch number, size, and spatial distribution on the surface of spherical NPs has been achieved, however, the role of NP shape remained elusive. In the present work, we report the role of NP shape, namely, the effect of the local surface curvature, on polymer segregation into surface patches. For polymer-functionalized metal nanocubes, we show experimentally and theoretically that the patches form preferentially on the high-curvature regions such as vertices and edges. An in situ transformation of the nanocubes into nanospheres leads to the change in the number and distribution of patches; a process that is dominated by the balance between the surface energy and the stretching energy of the polymer ligands. The experimental and theoretical results presented in this work are applicable to surface patterning of polymer-capped NPs with different shapes, thus enabling the exploration of patch-directed self-assembly, as colloidal surfactants, and as templates for the synthesis of hybrid nanomaterials.
This Letter describes the generation of 2D colloidal lattices in microchannels by coupling the laminar flow of dispersions of spherical colloids and geometrical confinement. We describe a nonequilibrium, convective, mechanism leading to formation of ordered 2D structures of both closed-packed hexagonal and non-closed-packed rhombic symmetries. The number and types of possible lattices is determined by the ratio of the width of the channel to the diameter of the particle. The structures tend to return to a regular lattice after a defect is introduced; that is, for example, they tend to self-repair disorder induced by particle polydispersity, contaminants, and flow instabilities. The stability of different lattices is analyzed numerically for particles with different polydispersity.
Generation of nanostructures containing from several to thousands of inorganic nanorods (NRs) organized in a highly ordered manner paves the way for applications that exploit directional properties of NR arrays. Self-assembly of NRs provides a simple and cost-efficient strategy for producing NR ensembles. This tutorial review highlights recent advances in the field of NR synthesis, summarizes the types of ligands used for NR synthesis and stabilization, reviews experimental and theoretical work on NR self-assembly that is driven by interactions between the ligands and describes current properties and applications of self-assembled NR structures.
Miniaturisierte Technik: Eine neue Strategie für die größen-, form- und zusammensetzungsspezifische Herstellung monodisperser Kolloidpartikel wird vorgestellt. Hoch monodisperse Flüssigkeitstropfen werden mithilfe einer Mikrofluidikvorrichtung gebildet. Die Tropfen werden in einem Mikrokanal in Form gebracht (Kugeln, Scheiben und Stäbe; siehe Bilder) und in situ entweder durch Polymerisation oder durch Thermofixierung verfestigt.
Over the past decade, droplet microfluidics has attracted growing interest in biology, medicine, and engineering. In this feature article, we review the advances in droplet microfluidics, primarily focusing on the research conducted by our group. Starting from the introduction to the mechanisms of microfluidic droplet formation and the strategies for cell encapsulation in droplets, we then focus on droplet transformation into microgels. Furthermore, we review three biomedical applications of droplet microfluidics, that is, 3D cell culture, single-cell analysis, and in vitro organ and disease modeling. We conclude with our perspective on future directions in the development of droplet microfluidics for biomedical applications.
Composite films of proteins and polysaccharides have a broad range of biomedical and food packaging applications, in which they are frequently exposed to fluid environments with varying ionic strengths. In the present work, we report the behavior of biopolymer films derived from chitosan (Ch), gelatin (GEL), and Ch/GEL mixture in salt solutions with varying concentrations and ion charges. The swelling and dissolution of the Ch films reduced with increasing salt concentration due to the polyelectrolyte behavior of this biopolymer, while the GEL films displayed a polyampholyte behavior, in which film swelling and dissolution were enhanced in salt solutions. Composite Ch/GEL films followed the behavior of GEL. The release of small ionic and zwitter-ionic molecules from the films was enhanced in ionic solutions due to the screened attraction between these molecules and the polymer matrix. These results provide insight into the behavior of protein/polysaccharide films in varying ionic environments, thus enabling enhanced design of biomaterials for a broad range of applications.
Temperature-responsive self-assembly (TRSA) of polymer-stabilized nanoparticles is a promising method that is useful for many applications. Currently, polymers ligands with a lower critical solution temperature are used for TRSA, which requires the use of specific polymer–solvent couples. We report a comprehensive study of TRSA of nanoparticles grafted with polymer ligands with an upper critical solution temperature (UCST). Upon cooling the nanoparticle solution below the transition temperature, the nanoparticles assembled in clusters, while upon heating these clusters dissociated into individual nanoparticles. The TRSA was reversible and reproducible. In the heating and cooling steps, the dimensions of nanoparticle clusters were controlled by the superposition of temperature and incubation time. The transition to TRSA was governed by the solvent quality for the polymer ligands and was tuned by varying solvent composition. The utilization of UCST polymer ligands offers an effective method for the preparation of assemblies of polymer-tethered nanoparticles, broadens the range of polymers used for TRSA, and enables control of the degree and temperature of nanoparticle assembly.
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