Nanoparticle-shelled hollow structures

Interfacial Stabilization and Other Approaches to the Assembly of Nanoparticle-Shelled Hollow Structures as Emulsions and Foams... 

Chemical vapor condensation (CVC) was applied by Lee for the production of Ti02 nanoparticles by decomposition of Ti(0)(acac)2. In the temperature range of 800-1000 °C hollow-shell nanoparticles (10-40 nm diameter, 4-5 nm thick) of anatase-rutile mixed phases were obtained. The formation of the hollow structure is a result of the competition... 

Fig. 19 Schematic diagram showing the self-assembly of gold and silica nanoparticles into hollow spheres with a two-layer shell structure. Reprinted with permission from [49], copyright (2002) American Chemical Society...

With regard to the preparation of multicompartment polymer capsules based on this SIP method, a successful approach was demonstrated by Kang et al. [17] who used a two-step distillation/precipitation polymerization of methacrylic acid (MAA) and A-isopropylacrylamide (NIPAM), respectively, onto silica nanoparticles as templates. More interestingly, due to the PMAA inner shell and PNIPAM outer shell, the hollow structure can respond independently to changes in pH and temperature. After loading DOX into the capsules, temperature- and pH-controlled release of anticancer drug behavior was demonstrated. 

Laser ablation of the layered structure under inert atmosphere has been used to prepare IF-M0S2 and WS2 with metal encapsulated and hollow onionlike structures at 450, 650, 850, and 1050°C [66]. The nanoparticles of WS2 grown at 450 and 650°C contain three concentric WS2 outer layers with metals encapsulated within. Laser ablation at higher temperature (1050°C) yields WS2 nanoparticles with hollow closed-cage polyhedral nanotubes these have diameters ranging from 10 to 15 nm and contain 4-8 concentric WS2 shells. Similar results have been obtained for M0S2 at 1050°C. 

Khanal, A., Inoue, Y., Yada, M., and Nakashima, K. (2007) Synthesis of silica hollow nanoparticles templated by polymeric micelle with core-shell-corona structure. /. Am. Chem. Soc., 129, 1534-1535. 

The advances in nanotechnology and synthesis methods have enabled nanomaterials to be produced in various shapes and structures. Coating of a luminescent layer activated by lanthanide ions on nanoparticles such as SiC>2 or AI2O3 is one of such approaches to develop new nanophosphors. In section 6, we review recent work on interesting spectroscopic features and luminescence dynamics of lanthanide ions in other novel low-dimensional nanostructures including core-shell, one-dimensional (ID) nanowires and nanotubes, two-dimensional (2D) nanofilms, hollow nanospheres, 2D nanosheet and nanodisk which have also attracted extensive attention. 

Inorganic nanoparticles themselves can be assembled into mesoscopic structures. Dinsmore et al. proposed an approach for the fabrication of solid capsules from colloidal particles with precise control of size, permeability, mechanical strength, and compatibility (Fig. 2.9).44 This unusual mesoscopic structure is called colloidosome and is prepared through emulsion droplets at a water-oil interface. Following the locking together of the particles to form elastic shells, the emulsion droplets were transferred to a fresh continuous-phase fluid identical to that contained inside the droplets. The resultant structures are hollow, elastic shells whose permeability and elasticity can be precisely controlled. 

Abstract Nanoparticles (NPs, diameter range of 1-100 nm) can have size-dependent physical and electronic properties that are useful in a variety of applications. Arranging them into hollow shells introduces the additional functionalities of encapsulation, storage, and controlled release that the constituent NPs do not have.This chapter examines recent developments in the synthesis routes and properties of hollow spheres formed out of NPs. Synthesis approaches reviewed here are recent developments in the electrostatics-based tandem assembly and interfacial stabilization routes to the formation of NP-shelled structures. Distinct from the well-established layer-by-layer (LBL) synthesis approach, the former route leads to NP/polymer composite hollow spheres that are potentially useful in medical therapy, catalysis, and encapsulation applications. The latter route is based on interfacial activity and stabilization by NPs with amphiphilic properties, to generate materials like colloidosomes, Pickering emulsions, and foams. The varied types of NP shells can have unique materials properties that are not found in the NP building blocks, or in polymer-based, surfactant-based, or LBL-assembled capsules. 

The other type of nanoparticulate structure and fabrication morphology is the core-shell and associated hollow spheres. In this instance, a spherical nanostructure is established by polymerization onto a preformed nanoparticle. Different template materials have been used for fabrication. For chemical-sensing applications, the two most widely used have been silica and polystyrene, as highly monodisperse nanoparticles of these materials can be reliably synthesized. In addition, their surface chemistry can be modified to achieve different monomer interactions. Core-shell structures could be formed from the... 

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