Freeze‐Drying of Soft Nanoparticles with Projection Coronas Forms Three‐Dimensional Microconstructs

Abstract

The self-assembly of organic [1,2] and inorganic [3±6] particles can lead to various constructs with unique morphologies. Velev et al. reported the dielectrophoretic assembly of gold nanoparticle wires, [3] and Caruso et al. produced thin films of gold nanoparticles and hierarchically ordered monoliths of zeolite nanoparticles. [4,5] On the other hand, the three-dimensional (3D) assembly of organic particles can be manipulated by various organochemical modifications and can be controlled to give a wide-range of sizes. These features are important in the study of biomedical materials that use nanoparticles with immobilizing bioactive molecules on their surfaces, as well as in photonic devices prepared by colloidal crystallization [7] of nanoparticles, comparable in size to the wavelength of visible light (about 200±800 nm). Three-dimensional microconstructs with spherical morphology have been formed by the organization of nanoparticles on a spherical solid template, i.e., hetero-assembly, [8,9] which creates constructs based on nanoparticle±template interactions, and the construct morphology is controlled by the template shape. The organization of only one species of nanoparticles (homoassembly) can also lead to 3D microconstructs, some of which have been prepared by interparticle accumulation on a droplet template in a liquid±liquid [10±12] or an air±liquid system. [13] As the morphology is determined by the droplet shape, the constructs were always spherical or hemispherical. Homoassembly may represent a simple bottom±up technique using interparticle interactions and may be a basic step leading to the development of more complex organization methods, such as hetero-assembly. However, to the best of our knowledge, there have been no studies on 3D-microconstruct formation using simple polymeric-particle homo-assembly without a solid or liquid-droplet template. We have demonstrated an efficient one-step method for controlling the shape of a nanoparticle. [14,15] Here we report that freeze-drying results in the successful formation of 3D microconstructs by the simple homo-assembly of shape-controlled polymeric nanoparticles, by using physical interactions such as the exclusion force from freezing water.We recently prepared uniform nanoparticles of poly(styrene-co-acrylonitrile-co-poly(ethylene glycol) monomethoxy methacrylate, poly(St-co-AN-co-PEGm)s, with projection coronas (Fig. 1a) by the dispersion radical polymerization of monomers in an ethanol±water mixture. [14,15] The projection size increased with increasing polymerization period, whereas the polymer composition did not change.[15] Polymerization for 1 h yielded nanospheres without projections (Fig. 1c). The projections began to appear at 2 h, and after 3 h the projections gradually began to grow (transmission electron microscopy (TEM) images inset in Figs. 1d,e). However, we previously showed that the number of projections per nanosphere remained at 26 ± 2, regardless of the polymerization period after 2 h.[15]Figures 1c±e show scanning electron microsc...

Soil organic matter in nano-scale structures of a cultivated Black Chernozem

“…1 and 2 confirmed those made by Chenu and Plante (2006), who reported that SOM in soil particle fractions b2 μm consist of nm to μm size aggregates in which OM is strongly associated with minerals. Also, our observations are consistent with findings by Kaneko et al (2005) who showed that freeze-drying and resuspension in water of nano-size constructs preserve the physical conditions of the original nanoparticles and do not induce collapse of their structures. Thus, the analytical approach used in our study helped to retain most of the architectural arrangements of SOM and of colloidal organo-mineral complexes found at the nano-scale in soils.…”

“…In addition, these humic substances interacting with clay colloids appear to prevent total dispersion of individual inorganic particles at the nanoscale under the mild sonication step we used. We consider that the TEM micrographs represent most nanostructures as found in-situ and are consistent with reports by Kaneko et al (2005) that the architecture of nanostructures are preserved when they are freeze-dried and resuspended in water.…”

Re‐Dispersible 1D and 2D Nanoparticle Solid Powders without any Surfactant

“…The aqueous suspensions of the above mentioned nanoparticles can form a hydrogel by increasing nanoparticles concentration and changing the pH values and ionic concentration . In the gel state, nanoparticles form a loose percolated network in which most of the rod‐like nanoparticles adopt a head‐to‐tail packing mode, and the plate‐like nanoparticles assume face‐to‐edge and edge‐to‐edge modes to form a “house‐of‐cards” structure . If these 3D loose structures formed in the gelation process can be maintained, the original good dispersibility of nanoparticles will be awakened.…”

Nano Grape Formation by isotactic‐Poly(methacrylic acid)‐block‐Poly(butyl acrylate)

“…The development of nanostructures has received much attention, such as core-corona nanospheres, [1][2][3] micelles, [4][5][6] vesicles, [7] and networks. [8] This is significant because unique nanostructures provide functional materials such as drug-delivery systems and vaccines.…”